BULLETIN OF THE BRITISH MUSEUM (NATURAL HISTORY) GEOLOGY VOL. XVI 1968 TRUSTEES OF THE BRITISH MUSEUM (NATURAL HISTORY) LONDON: 1970 DATES OF PUBLICATION OF THE PARTS No. i. gth February ..... 1968 No. 2. 6th February ..... 1968 No. 3. 2oth February . . . . 1968 No. 4. igth April . . . . . . 1968 No. 5. i4th June 1968 No. 6. 2nd July 1968 No. 7. 1 3th August ..... 1968 PRINTED IN GREAT BRITAIN BY ALDEN & MOWBRAY LTD AT THE ALDEN PRESS, OXFORD CONTENTS GEOLOGY VOLUME XVI No. i. Silicified Brachiopods from the Visean of County Fermanagh (II). C. H. C. BRUNTON i No. 2. A Revision of the Foraminiferal genus Austrotrillina Parr. C. G. ADAMS 71 No. 3. British Neocomian Rhynchonelloid Brachiopods. E. F. OWEN AND R. G. THURRELL 99 No. 4. The Lower Palaeozoic Brachiopod and Trilobite faunas of Anglesey. D. E. B. BATES 125 No. 5. The Caudal Skeleton in Lower Liassic Pholidophorid Fishes. C. PATTERSON 201 No. 6. The Subphylum Calcichordata (Jefferies 1967) Primitive fossil Chordates with Echinoderm affinities. R. P. S. JEFFERIES 241 No. 7. Palaeoniscoidea-Schuppen aus dem Unterdevon Australiens und Kanadas und aus dem Mitteldevon Spitzbergens. H.-P. SCHULTZE 341 Index to volume XVI 369 SILICIFIED BRACHIOPODS FROMV EB mt THE VISEAN OF COUNTY FERMANAGH (II) C. H. C. BRUNTON BULLETIN OF THE BRITISH MUSEUM (NATURAL HISTORY) GEOLOGY Vol. 16 No. i LONDON: 1968 SILICIFIED BRACHIOPODS FROM THE VISEAN OF COUNTY FERMANAGH (II) BY C. H. C. BRUNTON Pp. 1-70 ; 9 Plates ; 52 Text-figures BULLETIN OF THE BRITISH MUSEUM (NATURAL HISTORY) GEOLOGY Vol. 16, No. i LONDON: 1968 THE BULLETIN OF THE BRITISH MUSEUM (NATURAL HISTORY), instituted in 1949, is issued in five series corresponding to the Departments of the Museum, and an Historical series. Parts will appear at irregular intervals as they become ready. Volumes will contain about three or four hundred Pages, and will not necessarily be completed within one calendar year. In 1965 a separate supplementary series of longer papers was instituted, numbered serially for each Department. This paper is Vol. 16, No. i of the Geological (Palaeontological] series. The abbreviated titles of the periodicals cited follow those of the World List of Scientific Periodicals. World List abbreviation : Butt. Br. Mus. nat. Hist. (Geol.). Trustees of the British Museum (Natural History) 1968 TRUSTEES OF THE BRITISH MUSEUM (NATURAL HISTORY) Issued 9 February, 1968 Price 2 ic SILICIFIED BRACHIOPODS FROM I THE VISEAN OF COUNTY i FERMANAGH (II) By C. H. C. BRUNTON MS accepted May gth 1967 CONTENTS Page I. INTRODUCTION AND ACKNOWLEDGMENTS ..... 4 II. SYSTEMATIC DESCRIPTIONS ....... 4 Superfamily Craniacea Menke ...... 4 Family Craniidae Menke ....... 4 Crania quadrata (M'Coy) ...... 5 Acanthocrania cf. laevis (Keyes) ..... 7 Philhedra trigonalis (M'Coy) ...... 8 Superfamily Enteletacea Waagen . . . . . . 10 Family Enteletidae Waagen . . . . . . 10 Schizophoria resupinata dorsosinuata Demanet . . n Family Rhipidomellidae Schuchert . . . . . 17 Rhipidomella michelini (L'Eveilte) . . . . . 17 Superfamily Strophomenacea King . . . . . 21 Family Leptaenidae Hall & Clarke . . . . . 21 Leptagonia analoga (Phillips) ...... 29 Superfamily Davidsoniacea King . . . . . . 31 Family Orthotetidae Waagen . . . . . . 31 Brochocarina wexfordensis (Symth) . . . . . 34 Orthotetinid gen. et sp. indet. ..... 39 Family Schuchertellidae Williams ..... 39 Serratocrista fistulosa, gen. et. sp. n. . . . . . 40 Family Meekellidae Stehli ....... 42 Schellwienella radialis (Phillips) ..... 42 Superfamily Chonetacea Bronn ...... 46 Family Chonetidae Bronn ...... 48 Globosochonetes parseptus gen. et. sp. n. 49 Rugosochonetes silleesi sp. n. . . . . . . 55 Rugosochonetes delicatus sp. n. ..... 62 Rugosochonetes transversalis sp. n. ..... 65 Plicochonetes buchianus (de Koninck) .... 67 III. REFERENCES ......... 68 SYNOPSIS This paper, the second of a series describing the Vis6an brachiopods from near Derrygonelly in county Fermanagh, deals with the Inarticulata, Enteletacea, Strophomenacea, David- soniacea and Chonetacea. Brochocarina and Serratocrista are new Davidsoniacean genera and Globosochonetes a new chonetid genus; four new species are described. Additional evidence is presented for the separation of Leptagonia from Leptaena and the relationship of the Chonetacea to the Productacea is discussed. GEOL. 1 6, i. i 4 SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH I. INTRODUCTION AND ACKNOWLEDGMENTS THIS study follows that of the Productacea (Brunton 1966) as part of a series dealing with the brachiopods etched out with acid from Visean limestones at the Sillees river near Bunnahone Lough, or on the southern shore of the nearby Carrick Lough, about 2 miles N.W. of Derrygonnelly in county Fermanagh, Northern Ireland. All the material is from these localities unless otherwise stated in the text, and is of a Low D zone age. A locality map was given in the previous part (Brunton 1966 ; 178, fig. 2) . I take pleasure in thanking Professor A. Williams for his help and encouragement while engaged upon much of the work in his department during the tenure of a D.S.I. R. studentship. I am grateful to Dr. H. M. Muir-Wood, late of the British Museum (Natural History); Dr. I. Rolfe, Hunterian Museum, Glasgow; the late Professor R. G. S. Hudson, Trinity College, Dublin; Dr. G. A. Cooper, Smithsonian Institution, Washington; Dr. K. E. Caster, University of Cincinnati; Mr. J. M. Edmonds, University Museum, Oxford and Mr. M. Mitchell, Institute of Geological Sciences, London for the loan of specimens in their care and for advice. Some of the photographs were taken by members of the Photographic Department of the British Museum (Natural History) ; to them and many other helpers I extend my thanks. I am grateful for having had my attention drawn to the fact that in my previous publication upon the Productacea (1966) I did not make clear from which locality new taxa were collected. The information is given below: Dasyalosia panicula Brunton : Carrick Lough. D. lamnula Brunton: Bunnahone. Krotovia lamellosa Brunton: Bunnahone. Eomarginifera (Eomarginiferina) trispina Brunton: Bunnahone. II. SYSTEMATIC DESCRIPTIONS Unless otherwise stated the majority of the specimens here described were collected from the Sillees River locality (Irish Grid Reference 2105 : 3550) : other specimens are from the Carrick Lough locality (Irish Grid Reference 2092 : 3538). The fauna from these localities (separated by a distance of I mile) are considered to be of the same age (low D Zone). All specimens prefixed by B or BB are in the collection of the British Museum (Natural History). The depository of other specimens is given in the text. Class INARTICULATA Suborder CRANIIDINA Waagen 1885 Superfamily GRANIACEA Menke 1828 Family CRANIIDAE Menke 1828 Genus CRANIA Retzius 1781 TYPE SPECIES. Anomia craniolaris Linne, by subsequent designation of Schmidt (1818 : 71). Williams (1943 : 70) erected the subgenus Lissocrania for " Cranias with dorsal valves devoid of radial costae or spines. Ornamentation, if any, consists of con- SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH 5 centric growth lines or of fine radiating striae or both." The type species, Crania dodgei Rowley is poorly known and its interior was not described by Rowley (1908), Weller (1914) or Williams (1943). The type species of Crania s.s., from the Creta- ceous, and the modern C. anomala (Miiller) are devoid of radial ribbing and may have slightly larger dorsal posterior adductor scars than anterior scars. Thus, with our present knowledge, the retention of Lissocrania is unjustified, and in the recently published Brachiopoda Treatise (1965) it is tentatively placed in synonymy with Crania. Other non-ribbed craniid genera are Petrocrania Raymond 1911 (= Craniella Oehlert 1888) and the poorly known genus Philhedrella Kozlowski 1929, originally erected as a subgenus of Philedra. Distinction between these two genera may lie in the presence of well defined dorsal mantle canal traces in Petrocrania and in its dorsal posterior adductor scars being larger than the anterior scars, apparently unlike Philhedrella. In his revision of craniids von Huene (1899) included C. quadrata (M'Coy) and C. kirkbyi Davidson in Craniella (now Petrocrania) , but as this group is not known to possess sigmoidal mantle canal traces in the dorsal valve they should probably be removed from Petrocrania. Conceivably they could be assigned to Philhedrella or Crania. Species at present within Philhedrella range from the Ordovician to Upper Silurian, while Crania species are described from the Carboni- ferous times up to the Recent. As the former genus is inadequately known Crania is perhaps the more appropriate genus within which to place C. quadrata, the species to which the smooth-shelled Fermanagh craniids are assigned. There are marked differences in the morphology of Carboniferous and Cretaceous Crania. The Mesozoic forms are thick shelled with deeply impressed muscle scars, particularly those of the pedicle valve which are cavernous in form, and a limbus is common. Palaeozoic shells are thin and the muscle scars are commonly raised areas in both valves; the brachial valve is without the internal radial ridges seen between the muscle scars of the Mesozoic forms. Such differences may result from a greater ability of Mesozoic shells to deposit skeletal material and it may prove more realistic to distinguish the Palaeozoic species as a group. A clear understanding of Philhedrella may reveal that this genus would be suitable for some non-ribbed Palaeozoic species presently assigned to Crania. Crania quadrata (M'Coy) (PI. i, figs. 1-9) 1844 Orbicula quadrata M'Coy: 104, pi. 20, fig. i. 1861 Crania quadrata (M'Coy) Davidson: 194, (1863) pi. 48, figs. 1-13. 1899 Craniella quadrata (M'Coy) Huene: 148. DESCRIPTION. Outline irregular, rounded to subquadrate when undeformed, with gently folded margin, posteriorly flattened to gently sulcate ; ventral valve entirely fixed; dorsal valve subconical with beak directed posteriorly and closer to posterior margin; ornamentation of concentric growth lines and scattered short spine-like protuberances, valve margins may be slightly thickened; dorsal anterior adductor 6 SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH scars close to apex, separated by distance equal to width of scar and from less distinct, widely spaced posterior scars situated close to valve margin ; slight radial ridge from beak to valve edge between the muscle scars; shell substance punctate. MEASUREMENTS (in mm.) : length width Incomplete brachial valve (66.55599) c - T ^'5 c - 2 ' Complete brachial valve (66.55600) 7-5 8-6 Complete brachial valve (66.55601) 3-7 3-9 Complete brachial valve (66.55602) 2-2 2-3 Complete brachial valve (66.55603) 2-1 2-4 Incomplete brachial valve (66.55616) 2-1 1-2 DISCUSSION. The fauna from Fermanagh includes a wide range of sizes, from about i-o mm. to an incomplete brachial valve about 20-0 mm. wide. Pedicle valves are absent from the collections. Among the juvenile valves are some small shells of up to 5 mm. long which are almost as high as long and which have well defined narrow posterior trigonal areas. Together with these highly conical valves are more typically proportioned specimens looking more like the larger specimens. It may be that different habitats induced differing juvenile forms or that we have in the collection a different species, only represented by these small shells. An example of these conical forms is figured (PI. i, figs. 6, 7). Normally the larger valves are about one-half as high as long. Valve outline is variable, depending upon the shell's site of attachment and pro- bably upon its degree of crowding, but one well formed specimen, with a high degree of bilateral symmetry may be taken as being typical of undeformed specimens (PL i, figs. 4, 5). The posterior trigonal area is differentiated by a pair of shallow sulci extending from the beak to the valve margin. Anteriorly the margin is slightly bilobed as a result of a third antero-median shallow groove. These features, to- gether with the more posteriorly placed beak, give the valves a distinct orientation. Although appearing smooth externally, save for a few growth-lines, these valves are also ornamented by sparcely scattered more or less concentrically arranged spine- like protuberances. The possibility that these structures are an artifact of the sili- cification process has been recognized, but rejected on account of their regular de- velopment upon the specimens available. Rarely these " spines " can be seen to project at a high angle from the surface, but only for about o-i mm., and they are spaced about 0-4 mm. apart. This is considerably more widely scattered than are the " spines " of Acanthocrania. Internally the anterior muscle scars are situated towards the top of the trigonal posterior region, on the slight infolds of the valve, and extend for nearly one-half of the distance towards the margin. The smaller, more rounded posterior scars are not radially aligned with the anterior scars and are only slightly more widely spaced. Dividing the trigonal area is a slight median thickening which is most clearly de- veloped near the somewhat thickened valve margin. SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH 7 In 1858 Davidson erected the species Crania kirkbyi, from the Permian of N.E. England, which he described as being "... sub-quadrate, with rounded angles, and is sometimes a little indented at its anterior margin ". Davidson continued by saying that the external surface was closely covered by a multitude of minute, short, hollow, spinose tubercles, which produce a granulated aspect." (1858 : 49). The interior was poorly described. In 1863 Davidson added a note upon the species saying that he thought the granulation was unnatural and that his species may be the same as C. quadrata (M'Coy) from the Carboniferous. He figured the two species on plate 54 (1863) and the two appear identical If Davidson's first impressions regarding the granulated looking surface of C. kirkbyi were correct it would seem even more likely that the two are conspecific. Genus ACANTHOCRANIA Williams 1943 TYPE SPECIES. Crania spiculata Rowley (1908), by original designation of Williams (1943 : 71). Acanthocrania cf. laevis (Keyes) (PI. i, figs. 10-14) 1894 Crania laevis Keyes: 40. 1914 Crania laevis Keyes; Weller: 47, pi. i, fig. 33. DESCRIPTION. Outline transversely elliptical with flattened posterior margin; ventral valve unknown; dorsal valve deep, lateral profile asymmetric, anteriorly evenly convex, posteriorly steep to concave ; beak posteriorly directed and may be below valve apex; ornamentation of sporadic sublamellose growth-lines and closely spaced radially directed spines at low angle to valve surface, arranged more or less concentrically and quincuncially ; adductor scars divided, anterior pair just posterior of valve apex, near beak, similarly sized posterior scars close to valve margin and widely separated; shell substance punctate. MEASUREMENTS (in mm.) length width Complete brachial valve (66.55604) 4-6 5-7 DISCUSSION. Wright (1963 : 249) discusses the genus mentioning its range from the Ordovician to the Carboniferous. The first record of the genus from the British Isles is that of Wright for Ashgillian specimens from the Portrane Limestone of Co. Dublin. The type species is a North American Visean form and this Fermanagh record is the first from the upper Palaeozoic of the British Isles. The specific description of A . laevis given by Keyes is inadequate and the species not illustrated. However, Weller (1914) gave a full description, with a figure, of the specimen from "... the Burlington Limestone . . . used by Keyes ", and from 8 SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH this it is clear that it is closely comparable to the Fermanagh material. The specific name given by Keyes (1894) is inapt but possibly results from the lectotype being silicified and the papillose surface being thought to result from this process. Keyes noted that the surface was " marked by concentric lines of growth ", but it was Weller who described the papillose or spinose nature of the surface. This external ornamentation is well preserved on the few valves available from Fermanagh and near the margins, where the " spines " are longest, they are up to 0-4 mm. long. These papillae or spines may be morphologically associated with the shell punctua- tion, which is only clearly visible on the internal surfaces of the Fermanagh speci- mens. The spines arise from the shell in positions corresponding to the internal positions of punctation and both have similar numbers per unit area, although there are commonly rather more spines. This may result from the coalescence of several juvenile punctae into a single larger puncta within younger parts of the shell. This has been described previously in Crania (e.g. Joubin, Blockman) and recently re- figured by Rowell (in Williams et al. 1965, fig. 77). Weller's description (1914 : 48) of the brachial valve interior of the American material is accurate for the present specimens and the widely spaced posterior adductor scars are slightly larger than the closely and apically placed anterior scars. The posterior scars are less well defined and it is likely that with age they would have grown more prominent and proportionately still larger than the anterior scars. The margins of the valve are not greatly thickened although slight lamellae were de- veloped. As there is only one complete specimen, together with fragments, it is impossible to present variation studies on this species. Rarely the brachial valve may have grown in a distorted fashion and may show signs of the skeletal material against which it grew. Genus PHILHEDRA Koken 1889 TYPE SPECIES. Philhedra baltica Koken by original designation of Koken (1889 : 465). Philhedra trigonalis (M'Coy) (PI. i, figs. 15-29) 1844 Orbiculata trigonalis M'Coy: 401, pi. 20, fig. 2. 1899 Philhedra trigonalis (M'Coy) Huene: 147. DESCRIPTION. Outline subrounded to longitudinally subelliptical ; profiles asym- metrical and variable with beak posterior of mid-length and at apex of valve; margins of brachial valve irregularly shaped through contact with substrate ; growth- lines distinct and commonly interrupting radial ribs which extend from near apex to valve margins, ribs increase in width and added by branching and rare intercala- tion; brachial valve interior with anterior adductor scars slightly raised, oval, closely placed near beak and divergent towards less distinct ovoid posterior scars SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH 9 which extend close to valve margin; pedicle valve thin and poorly known, with growth-lines and distorted to conform to object of attachment; shell substance punctate. MEASUREMENTS (in mm.) length width Complete brachial valve (66.55608) n-o 8-4 Incomplete brachial valve (66.55609) 11-4 c. 7-5 Complete shell attached to rugosochonetid (66.55607) 8-5 7-5 Complete brachial valve (66.55610) 8-0 6-7 Distorted brachial valve (66.55611) 6-9 7-4 Incomplete shell (66.55612) 5-7 5-6 Complete brachial valve ( (66.55613) 4-0 4-2 Complete brachial valve (66.55614) 2-7 2-5 DISCUSSION. The Fermanagh sample is varied in size (having a range of from 2-0 mm. to 12-0 mm. long) and outline. The beak is asymmetrically placed and the height of the shells differs from just under one-half to less than one-quarter of the shell length. Ventral valves are rarely preserved and their interiors have not been observed. However, it is clear that these valves were much effected by the sub- strate; they commonly show growth-lines and are punctate. The dorsal valve is rounded to subelliptical in outline with little or no posterior flattening, as is common in Acanthocrania and Philhedrella. The posterior slope is less steep than in these genera although the beak is posterior of mid-length. The larger shells are more elongate than the smaller ones and in profile they retain their height for a short distance before dropping to the anterior margin (PL i, fig. 17). The costae arose within about I mm. of the beak and costellae were added by unequal branching or intercalation. The rib crests are somewhat serrated and commonly interrupted by the growth-lines; their width increases slightly towards the valve margins. Some shells became distorted from growth against foreign objects, such as fenestellid colonies, (PI. i, fig. 25) and the substrate upon which the shells grew had a marked effect upon the shape of the commissure. Apart from the adductor scars and punctae the brachial valve interior is devoid of structures. In the present silicified material the punctae are most clearly developed and largest close to the valve margins. One valve has a tent-like ridge anterior of the beak and oblique to the mid-line (PL i, fig. 29). The antero-lateral end of this ridge appears to be broken and there is nothing to suggest that there was another ridge on the opposite side of the shell or that damage to the shell resulted in its formation. The distinction between Crania and Philhedra rests principally upon the relative sizes of the muscle scars in the dorsal valve and external ornamentation ; Philhedra being distinguished as having larger anterior scars than posterior scars and better defined costellate ribbing. io SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH Class ARTICULATA Order ORTHIDA Schuchert & Cooper 1932 Superfamily ENTELETACEA Waagen 1884 Family ENTELETIDAE Waagen 1884 Subfamily SCHIZOPHORIINAE Schuchert & Le Vene 1929 Genus SCHIZOPHORIA King 1850 TYPE SPECIES. Anomites resupinatus Martin 1809, by original designation of King (1850 : 106). George & Ponsford (1938 : 228) selected a neotype for S. resupinata (Martin) and this specimen (BM(NH) 66.2420) was later figured by Bond (1942, pi. 21). The specimen is large; 55-5 mm. long, 72 mm. wide and 32-5 mm. thick, and as Bond said " would approach Demanet's variety gigantea " (PI. 2, figs. 1-3). The Fermanagh shells range in length from i mm. to 13-5 mm. and never display the resupination of the pedicle valve commonly seen in large specimens, such as the neotype. In his study of Carboniferous Schizophoria Bond (1942, for 1941) divided the British and Belgium species into those with coarse ornamentation, i.e. with 3 or 4 ribs per mm. about io mm. from the umbo, and those species with fine ribbing, i.e. 6-9 ribs per mm., io mm. from the umbo. Into the former group he placed 5. resupinata and its varieties gigantea Demanet, dorsosinuata Demanet, lata Demanet, pinguis Demanet, rotundata Demanet, and elboltonensis George & Ponsford, (which are further united by having dental plates at about 70 from one another) together with the species 5. nuda George & Ponsford, S. hudsoni George and 5. connivens (Phillips). The type specimen of Phillips' species is lost and his figure (1836, pi. n, fig. 2) is inconclusive. However, Bond selected a neotype from among specimens in the Gilbertson Collection in the British Museum (Nat. Hist.) (6.387, re-registered as 66.54902) which is distinguished from 5. resupinata by its more globose profile, near sulciplicate anterior commissure, short hinge line, narrowly divergent dental plates (30) and small size (16 mm. long) . However, Bond admits that only one specimen with such a commissure was seen in his study and that its shape variants grade into some of the more rounded and globular variants of 5. resupinata. The dental plates are said to be a valid distinction. This being so the Fermanagh shells can not be attributed to S. connivens as their dental plates diverge at about 70, like 5. resupinata s.s. George & Ponsford (1938) spoke of S. dorsosinuata Demanet as a distinct species and illustrated sections of three specimens that they attributed to Demanet's variety. Two of these illustrations (1938, figs. 11, 14) are of interest in that the brachiophore bases are at an angle to the brachiophores, as are those of the Fer- managh shells. Serial sectioning has confirmed this feature in a topotype specimen of Demanet's var. dorsosinuata from Tournai, 6elgium (kindly presented by Dr. P. Sartenaer) and has led me to assign the Fermanagh specimens to what I consider SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH n the subspecies 5. resupinata dorsosinuata Demanet. The brachial valve of the neo- type is sulcate for approximately the first 50 mm. of its length. This dorsal sulcation is not a common feature but when present most probably produced a unisulcate anterior commissure, similar to that of the present material, before the onset of resupination of their pedicle valves. Schizophoria resupinata (Martin) dorsosinuata Demanet (PL 2, figs. 7-37; Text-figs. 1-4) 1861 Orthis resupinata (Martin) Davidson (pars.): 130, pi. 30, fig. i, non figs. 2-5. 1934 Schizophoria resupinata var. dorsosinuata Demanet: 53, pi. 3, fig. 14, 15. 1938 Schizophoria cf. dorsosinuata Demanet; George & Pensford, figs n, 14. 1942 Schizophoria resupinata var. dorsosinuata Demanet; Bond: 289. DIAGNOSIS. Small, biconvex dorsally sulcate Schizophoria with unisulcate anterior commissure; brachiophores subparallel but brachiophore bases diverging to valve floor. DESCRIPTION. Outline rounded subrectangular, length about four-fifths maxi- mum width, hinge-line straight, about one-half width, cardinal extremities rounded, anterior margin gently rounded to emarginate and commissure slightly unisulcate; profile biconvex, depth about one-half length, increasing with age; gentle dorsal sulcation; radial ornament of low rounded and delicate ribs, about 14 in 2-5 mm. at 5 mm. antero-medianly from dorsal umbo, about 10 costae and first order costellae commonly remaining prominent ; branching by intercalation and rib apertures well developed; concentric ornament sporadic but distinct; ventral interarea concave, apsacline, delthyrium triangular, open; dorsal interarea about one-half length of ventral interarea, curved anacline, with open notothyrium, chilidium obsolete; teeth strong, triangular in outline and diverging at about 45 from mid-line, supported by receding divergent plates fused posteriorly to inner surfaces of umbonal slopes; notch below teeth articulating with apophyses on brachiophores; base of dental plates extending anteriorly as ridges laterally enclosing oval muscle scars about two- fifths valve length ; muscle field width about three quarters its length and medianly divided by strong anteriorly widening ridge on antero-lateral faces of which are narrow lanceolate adductor scars; mantle canal traces obscure, but pair of strong vascula media extend anteriorly from anterior ends of each diductor scar; cardinal process developed as ridges across floor of notothyrial cavity, between brachiophore bases, with distally expanded and incised myophore, trilobed in adults; brachio- phores strong, diverging at about 40 from mid-line, median faces vertically disposed and fulcral plates well developed; brachiophore bases diverging to valve floor, continued anteriorly as indistinct ridges surrounding adductor field but interrupted by traces of three mantle canals ; adductor field about four-ninths valve length and about as long as wide, divided medianly and into posterior and anterior scars; marginal follicular embayments may persist posteriorly. 12 SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH MEASUREMENTS (in mm.) length width Complete shell (66.52701) 13-8 16-0 Complete shell (66.52702) 13-0 Pedicle valve (66.52703) 11-3 14-5 Incomplete brachial valve (66.52705) 12-5 Complete brachial valve (66.52707) 3-1 3-7 Complete brachial valve (66.52708) 3-8 4-6 Complete brachial valve (66.52709) 5*5 6-7 Incomplete brachial valve (66.52711) c. 16-0 Complete pedicle valve (66.52713) 2-0 2-6 Complete pedicle valve (66.52714) 7-0 8-5 Incomplete brachial valve (66.52715) c. 11-5 Complete shell (66.52716) 2-9 3-6 Complete shell (66.52717) 1-3 1-6 DISCUSSION. The present Fermanagh Schizophoria specimens accord most closely with Demanet's variety from the Tournaisian of 6elgium. Similar specimens were described by Sanders (1958 : 43) from rocks of Kinderhook age in Mexico under the new name 5. sulcata. This silicified material shows interiors comparable to those from Fermanagh although the Mexican shells are about 10 mm. longer and relatively thicker. The cardinal process's of both faunas are comparable in having a bifid central lobe and a pair of lateral lobes within the notothyrial cavity (Sanders 1958, pi. 3, fig. 19, cf. PI. 2, fig. 17). Sanders characterizes his species by " the sulcus on each valve ", (p. 44) but only that on the dorsal valve is clear from his figures. The external radial ornamentation arose from the initial 10 or 12 costae by the apparent intercalation of costellae, mostly posteriorly. The costae arose within 0-3 mm. of the umbones of each valve. The brachial valve commonly had a median costa for about the first 3 mm. of growth which subsequently was usually diverted to one side of the median sulcus. First order costellae were added at about 0-5 mm. and second order costellae may show at a length of 1-5-2-0 mm. These additions appear as intercalations, but on close study it is usually possible to determine from which parent rib the costella had arisen, and in this way it can be seen that there is a tendency towards median branching across the sulcus and lateral branching on the dorsal flanks. On pedicle valves lateral branching is more common in a manner similar to that illustrated by Williams & Wright (1963 : 23). 6iernat (1959 : 61) records 12 ventral and 13 dorsal costae on 5. striatula from the mid-Devonian of Poland. These arose at a length of about 0-45 mm. and with a further 0-5 mm. of growth both first and second order costellae arose. On young specimens a few mm. long, only the apical tips of the beaks are free of costae and these areas represent the brephic valves and protegulal nodes. On Fermanagh shells the ribs are low and rounded and increase in size only slightly towards the anterior margins so that 2, 6, 8, 3 and I specimens have respectively 12, 13, 14, 15 and 16 ribs in 2-5 mm. at a distance of 5 mm. from the dorsal umbo. Along the costae and primary costellae, SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH 13 which commonly remain rather larger than the intervening ribs, rib apertures (" hollow costellae " of Schuchert & Cooper, 1932 : 143) occur 3 or 4 times per 10 mm. length. This frequency appears to be less than illustrated by Davidson (1861, pi. 30, fig. id) or Sanders (1958, pi. 3, fig. 22) but is probably the result of their in- creased occurrence with age and size of the shell. These apertures have been inter- preted as small spine bases viz. Davidson (1861 : 130), Dunbar & Condra (1932 : 54 and Cvancara (1958 : 857). Demanet figures what he describes as an external im- pression of a brachial valve (1934, pi. 3, fig. 13) of 5. resupinata var. rotundata Demanet showing minute needle-like rods of iron oxide extending away from the mould into what must have been shell substance. Demanet (1934 : 52) is un- doubtedly correct in interpreting these minute rods as being infillings of the shell punctae. There is no clear evidence yet available indicating the significance of the rib aperatures. If, however, their open nature at the valve margins, prior to second- ary shell deposition, indicates a functional origin at the mantle margins, it seems likely that the apertures may have assisted in the sensory apparatus of the shell in a way comparable to the "sensory" spines described by Rudwick (1965 : 610). The development of the ventral interior can be traced readily from valves of less than 2 mm. long, by which stage the bilobate muscle field was well developed (PI. 2, fig. 32). The teeth were not differentiated from the interarea until the valve was about 6 mm. long, but the dental plates were already strongly formed and fused with the inner surfaces of the valve posteriorly. Only along their anterior margins did the dental plates remain discrete from the valve. The ridges enclosing the lateral margins of the muscle field were developed by this stage, as was the strong median ridge, but differentiation within the muscle field is impossible to distinguish. In- deed, it is commonly impossible to see the narrow adductor scars on the median ridge or the narrow lateral lobes of the diductor scars even on the largest shells available. The ventral adjuster scars are rounded trigonal markings upon the inner surfaces of the dental plates. The coefficients of correlation for all measured parameters are high (see Tables i, 3) indicating a regular proportional growth. The increased curvature anteriorly of the brachial valve results in an allometric effect for length relative to width (p < o-oi), but is not apparent in the sample for other paired parameters. In his studies of S. resupinata s.l. from the Lower Carboniferous reefal limestones of northern England, Parkinson (1954) illustrates a possible allometric change in the growth ratios of plots of thickness against length or width at a shell width of about 20 mm. As has been pointed out by Veevers (1959), allometry cannot be clearly indicated without tests of significance having been applied to differing sectors of the growth axis, and this Parkinson did not do. The shallow dorsal sulcus became distinguishable in valves about 3 mm. long, but became prominently developed between 5 and 10 mm. from the umbo and persisted to the anterior margin. Internally the dorsal muscle field is discernible in shells about 2 mm. long, as is the small knob-like cardinal process and, rarely, the two median mantle canal traces. When the valve was about 3 mm. long a small ridge started to develop on the postero-lateral surfaces of the brachiophores, within the sockets, which grew anteriorly to form fulcral plates. These were not sufficiently I 4 SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH developed to arch the crural pits until the valve was about 5 mm. long. At this stage the brachiophore tips were about 2 mm. apart, and although the median ridge had not yet developed between the adductor scars, they were divided into anterior and posterior scars by a laterally directed pair of mantle canals (PL 2, fig. 30). The growth of the cardinal process took place from the apex of the notothyrial chamber as a longitudinally disposed ridge, to the ventral surface of which were attached the diductor muscles. The ridge was not divided distally into myophore lobes, as is commonly found in adult dalmanellids, and the muscle bases presumably extended along its length and onto its flanks. (Text-fig, i). Shell thickening at the FIGS. 1-4. Illustrations of the ontogeny of the cardinalia of Schizophoria resupinata dorsosinuata Demanet showing the development of the trilobed cardinal process from the notothyrial platform ; br, brachiophore ; br.b, brachiophore base ; car.p, cardinal process (juvenile primary lobe); c.p, crural pit; f.p, fulcral plate (in Fig. 3 the brachiophore tip is not drawn so as to reveal the fulcral plate) ; n.p, notothyrial platform; r.f.p, rudimen- tary fulcral plate on juvenile specimen; s, socket. base of the cardinal process built a notothyrial platform, distinguishable in valves about 6 mm. long. This platform remained sunk below the dorsal interarea and even in adult Fermanagh shells was no more than I mm. long. During growth the diductor muscle bases must have spread laterally onto a pair of ridges (Text-figs. 2, 3) which developed from the notothyrial platform with deeply crenulated crests, like that of the median cardinal process itself (PI. 2, fig. 20). In valves over 10 mm. long a variable degree of fusion occurred between these lateral ridges and the main median myophore so that the antero-ventral face of the cardinal process and noto- thyrial platform became trilobed with the notothyrium almost filled by the three myophore ridges (Text-fig. 4). Additional shell deposition antero-laterally on the median lobe may have resulted in it having become bifid and in its covering the two SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH 15 lateral lobes. The adult cardinal process is, therefore, a composite trilobed structure, as reported by Demanet (1934 : 47), built principally of the median primary lobe, but accompanied by secondary lateral lobes added during growth. In discussing the cardinal process of British Avonian Schizophoria George & Pons- ford (1938 : 233) illustrate serial sections of several specimens and conclude that, while it is variable in form, the cardinal process commonly consists simply of a median serrated " node ". Section 40, of 5. nuda George & Ponsford, would be like that of the Fermanagh specimens if the " accessory processes " flanked the median ridge rather than both being on one side. It is possible that less widely spaced sections would have revealed the secondary lateral lobes and the more ridge-like nature of the cardinal process across the notothyrial floor. A comparison of type material of 5. nuda, preserved as internal moulds in the British Museum (Natural History) (66.2407-2411), with brachial valve interiors reasonably assigned to 5. resupinata s.s. (PL 2, figs. 5, 6) shows that the two are probably comparable within the limits of specific variation. Bond retained 5. nuda principally because of its unusual state of preservation, but this hardly seems a worthy reason for specific distinction. In her study of Mid-Devonian orthoids from Poland, 6iernat (1959 : 57) describes and figures the variation to be seen in the cardinal process of adult Schizophoria striatula (Schlotheim) . She writes that the cardinal process "may be single or bifid ", although it would seem from her figures (1959, text-fig. 20, and pi. 9, figs, i, 2) that the cardinal process of her material probably grew in a similar way to that of the Fermanagh specimens, viz. the variation being around a basically trilobed structure. The difference would seem to be one of terminology, for in her discussion of the ontogeny of the cardinal process, 6iernat describes how " 2 or 3 elevations appear in the notothyrial cavity on each side of the cardinal process " and continues by TABLE i I mm. (var.) = 6-76 (14-613) w mm. (var.) = 8-42 (22-280) r = 0-996 a (var.) = 1-235 (o-ooin) w mm. (var.) = 8-42 (22-280) x mm. (var.) = 4-79 (8-355) r = 0-987 a (var.) = 0-612 (0-00089) I mm. (var.) = 6-76 (14-613) tE mm. (var.) = 2-01 (1-189) r = 0-990 a (var.) = 0-285 (0-00015) T mm. (var.) = 6-76 (14-613) 31 mm. (var.) = 2-72 (2-838) r = 0-992 a (var.) = 0-441 (0-00028) cTI mm. (var.) = 2-72 (2-838) Hi mm. (var.) = 1-95 (0-866) r = 0-974 a (var.) = 0-552 (0-00142) TABLE i. Statistics of length (1), maximum width (w), width of hingeline (x), thickness (th), and length (dl) and width (di) of the diductor muscle scars of 13 pedicle valves of Schizophoria resupinata dorsosinuata Demanet. i6 SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH TABLE 2 No. of ribs. 12 13 14 15 16 No. of specimens 2 6 8 3 i TABLE 2. The number of ribs counted in a width of 2-5 mm., 5 mm. antero-medianly from the umbo of 20 pedicle valves of Schizophoria resupinate dorsosinuata Demanet. J mm. (var.) = 5-14 (7'39 8 ) w mm. (var.) = 6-42 (11-899) r = 0-998 loge l_ (var. loge 1) = 1-514 (0-2469) loge w (var. log e w) = 1-552 (0-2791) r e = 0-997 a (var.) = 1-063 (0-00045) w mm. (var.) = 6-42 (11-899) x mm. (var.) = 3-01 (2-714) r = 0-998 a (var.) = 0-478 (0-00006) s mm. (var.) = 1-18 (0-206) t mm. (var.) = 1-92 (0-503) r = 0-963 a (var.) = 1-563 (0-0119) TABLE 3 I mm. (var.) = 5-14 (7-398) tE mm. (var.) =1-31 (0-441) r = 0-926 a (var.) = 0-244 (0-00053) _T mm. (var.) = 5-14 (7-398) aH mm. (var.) = 2-31 (1-446) r = 0-987 a (var.) = 0-442 (0-00034) ad mm. (var.) = 2-31 (1-446) v mm. (var.) = 2-18 (0-773) r = 0-949 a (var.) = 0-731 (0-00213) I mm. (var.) = 5-14 (7-398) s mm. (var.) = 1-18 (0-206) r = 0-976 a (var.) = 0-167 (0-00020) TABLE 3. Statistics of length (1), maximum width (w), thickness (th), width of hinge-line (x), length of adductor scars (ad), width of adductor scars (v), length of the extent of the brachiophores (s) and the width at the brachiophore tips (t) of 17 brachial valves of Schizophoria resupinata dorsosinuata Demanet. saying that the adult anterior aspect may be " multifid " while the lateral elevations became thicker and " together with the cardinal process fill all width of the noto- thyrial cavity ". It seems, therefore, that she retains the term cardinal process only for the central " single or bifid " ridge within the notothyrial cavity and looks upon the lateral " elevations " as being separate structures. She does not indicate a function other than that of diductor muscle attachment, nor does she differentiate the " cardinal process " from lateral elevations in text-fig. 20 (1959 : 57) and it would seem more reasonable to include all outgrowths of the notothyrial platform as con- stituents of the cardinal process. The intimacy and degree of fusion between the lateral ridges and the median ridge preclude the possibility that the lateral ridges bore the dorsal adjuster muscles. SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH 17 The internal surfaces of the valves are variably thickened, specimens from Carrick Lough commonly being thinner than those from Bunnahone. In these thinner shelled specimens traces of the radial mantle canals are more prominent, being marked by low bordering ridges, and are represented externally by slightly accen- tuated radial ribs. A deepening of these canal traces is usually terminated anteriorly by a rib aperture (PL 2, fig. 37) which only retained a broad connection to the outer surface while still close to the valve margin. In some young thin-shelled forms up to 7 or 8 mm. long, the traces of each follicular embayment can be followed back to the muscle field, but more commonly secondary shell obscured these, except over the last i mm. towards the valve margin. All these traces probably mark the positions of small mantle canals that led to each setal follicle at the mantle edges. Accentuated " growth-lines " tend to be more crowded anteriorly, indicating re- tradations of late growth, and it may be that these specimens were living in con- ditions marginal to their optimum habitat so never reaching a size more typical for the species. Family RHIPIDOMELLIDAE Schuchert 1913 Genus RHIPIDOMELLA Oehlert 1890 TYPE SPECIES. Terebratula michelini L'Eveille, by original designation of Oehlert (1890 : 39). Rhipidomella michelini (L'Eveille) 1835 (PL 3, ngs. 1-25, Text- fig. 5) DIAGNOSIS. Gently dorsibiconvex Rhipidomella with prominent, trifid cardinal process and well developed posteriorly convex chilidial plates; ventral diductor scars subrhombiodal in outline, about three-fifths valve length and without strong postero-laterally enclosing ridges. DESCRIPTION. Outline subrounded to rounded trigonal, hinge-line about two- fifths maximum width which is anterior of mid-length, length slightly less than width, adult anterior margin only gently curved; profile biconvex with depth slightly less than one-half length ; slight median sulcation of brachial valve and an- tero-median flattening of pedicale valve; multi-costellate with 9 or 10 ribs in 2-5 mm., 5 mm. antero-medianly from dorsal umbo, costellae added by bifurcation; growth-lines sporadic and prominent; ventral interarea concave, apsacline, dethy- rium open with apical angle of about 80; dorsal interarea shorter, orthocline to anacline, notothyrium more or less closed by chilidial plates ; teeth strong, diverging antero-dorsally at about 40 from mid-line, dental plates vertically disposed but slightly divergent to valve floor ; pedicle callist developed apically, dental plates with anteriorly directed notches to receive postero- ventral apophyses of brachiophores ; adductor field small, oval to rectangular and anteriorly raised; diductor scars variably impressed, adult scars lobate to subflabellate, surrounding adductor scars, anteriorly ridged and surrounded by slight thickening from bases of dental plates; valve margins strongly crenulated; cardinal process prominent, distally trifid with GEOL. 1 6, I. 2 i8 SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH median ridge extending beyond lateral ridges, postero-laterally enclosed by chilidial plates from below which strong brachiophores extend at 35 to 40 from mid-line; inner faces of brachiophores curved, and bases recurved to floor of valve to enclose deep sockets; adductor field quadrate to trigonal, extending about one-half valve length and separated by low wide ridge which may accommodate dorsal adjuster muscle scars posteriorly, adductor scars possibly divided with more prominent rounded-quadrate anterior scars. MEASUREMENTS (in mm.) length width Complete shell (33.52718) 10-9 117 Pedicle valve (66.52719) 8-8 Complete pedicle valve (66.52720) 9-2 9-9 Incomplete pedicle valve (66.52721) c. 15-0 Complete brachial valve (66.52722) 7-6 8-5 6rachial valve (66.52723) 7-0 7-3 Complete shell (66.52724) 4-6 5-0 Young pedicle valve (66.52725) 3-4 3-6 Young brachial valve (66.52726) 3-4 3-6 DISCUSSION. Unlike many species of Rhipidomella, which are dorsibiconvex, the present material is almost equibiconvex. While both valves are approximately equal in depth, the convexity of the pedicle valve is greatest posteriorly, close to the umbo, and that of the brachial valve near to its mid-length. These differences are associated with the anterior flattening of the pedicle valve and the median to antero- median slight sulcation of the brachial valve ; features which led to a faintly bilobed body cavity. The form of the valve profile is also associated with the radial orna- ment. It can be demonstrated that there is a distinct tendency for branching of costae and costellae to occur downslope, i.e. over the medianly sulcate region of the brachial valve branching took place more commonly from the median sides ("in- ternal " of 6ancroft (1928 : 60)), whereas on the flanks, branches commonly arose laterally ("externally" 6ancroft) (Williams & Wright 1963 122). The relation- ship between the mantle edge and the shell margins of dalmanellids has been dis- cussed by Williams & Wright (1963 : 19), and it seems likely that the radial ornament of such shells is intimately associated with the mantle canal system. The grooves seen at certain growth stages on some of the follicular eminences, the shell pro- tuberances between each setal follicle, can be related to external rib branchings. These grooves soon reached the dimensions of the previously formed follicular em- bayments and became buried in secondary shell deposits posteriorly, so that it is only rarely possible to see the positions of the branchings internally. However, ex- ternally they are commonly clear and probably accurately mark the positions of canal and follicular proliferations. The follicular eminences and embayments form a prominent marginal crenula- tion in rhipidomellids. The use of these crenulations for supra-specific taxonomic discrimination raises difficulties. Crenulations vary in detail according to both the SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH 19 age of the brachiopod and their distance from the margin of the shell. Certainly the Fermanagh specimens, believed to be conspecific with the type species of Rhipido- mella, show variation in the cross-section of their crenulations (Text-fig. 5) at different distances from the margin. It is important, therefore, to define closely any such variation used as taxonomic criteria. A comparision of a small collection of R. henryhousensis Amsden, recently placed in Dalejina by Boucot et al. (1963 : 337), with the Fermanagh specimens shows that differences in their marginal crenulations exist, but other differences may be noted; the absence of chilidial plates and more equally branching ribs in the American species. These differences are, at the best, merely observations, as the American mid-point FIG. 5. Three transverse sections parallel to the hinge-line of Rhipidomella michelini (L'Eveille) showing the anterior internal marginal crenulations. The mid-point of the shell is indicated on the sections which are 0-4 mm., (a), 0-6 mm.; (b), and 0-8 mm.; (c) from the anterior edge of the shell. material at hand appears to be slightly abraded. A more equal rib branching, i.e. one in which the branching approaches dichotomy, in R. henryhousensis could ex- plain the more regular grooves on the follicular eminences at the valve margins. This seems to be fairly persistent throughout ontogeny, whilst in the Fermanagh speci- mens a closely comparable style of branching was usually restricted to the first few mm. of growth. The rib apertures (or hollow ribs) of Rhipidomella are well known and have, been assumed to be the bases of spinose extensions of the shell (Davidson 1861 : 133, pi. 30, figs 6, 7). The frequency of these apertures is not constant in R. michelini , but is commonly 3 in 5 mm. length of rib. The apertures face anteriorly and away from the valve surface at a low angle, their openings being hooded by the rib poster- iorly. Anteriorly the rib is suppressed for a short distance leaving a slight de- pression. At no time has any sign of spine-like prolongations been seen attached to the valves, either from the Fermanagh fauna or from specimens from Clattering Dykes, possibly figured by Davidson (1861, pi. 30, fig. 6). The openings lead posteriorly along the rib and into the shell substance at a narrow angle. However, only marginally do they open internally on to the floor of one of the follicular embayments. Because of the rapid infilling of these embayments by secondary 20 SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH shell, the openings do not persist over the internal surfaces and, therefore, could not have contained living tissue unless connected by thin strands, such as those joining to the caecae. It is conceivable that the apertures were analogous to the hollow spines of productoids (also commonly marginal) in providing some sort of sensory receptors. In all known aspects other than the prominence of the muscle scars, in particular the ventral diductor scars, the shells of the Fermanagh fauna agree with the type species R. michelini (L'Eveille), as described by Demanet (1934 : 37, pi. 2). Al- though the longest valves reach about 12 mm. the muscle scars are all faintly im- pressed and it seems clear that differential shell deposition alone was responsible for the prominence of the scars found in larger specimens of R. michelini. Campbell (1957 : 51) casts doubt upon the assumption that the dorsal adductor scars were divided into two pairs in the Lower Carboniferous species. Judging from the present material and topotypic material from Belgium (PI. 3, fig. 5) his doubts seem valid, and no posterior scars have been distinguished with certainty. Demanet (1934 : 39), Dresser (1954 : 22), and Campbell (1957) believe the pedicle callist (Schuchert & Cooper 1932 : 9) to be the seat of the ventral pedicle adjuster muscles. However, it is more likely that it developed because of the anterior retreat of the junction between the pedicle and outer epithelium (Williams 1956 : 255, who termed it the " pedicle collar "). The umbonal cavity, between the dental plates, probably accommodated the base of the pedicle, to which were attached adjuster muscles ex- tending antero-laterally across the cavity floor onto the bases of the dental plates. The dorsal adjuster muscles probably passed between and anterior to the dorsal ends of the diductor muscles and were attached posteriorly between the dorso- median bases of the brachiophores, close to the base of the cardinal process. TABLE 4 I mm. (var.) = 4-69 (8-340) w mm. (var.) = 5-01 (8-836) r = 0-997 a (var.) = 1-029 (0-000213) wmm. (var.) = 5-01 (8-836) Ejj mm. (var.) = 1-64 (0-523) r = 0-941 a (var.) = 0-245 (0'0045) I mm. (var.) = 4-69 (8-340) x mm. (var.) = 2-34 (1-709) r = 0-995 a (var.) = 0-452 (0-00014) x mm. (var.) = 2-34 (1-709) y mm. (var.) = 2-20 (1-488) r = 0-992 a (var.) = 0-936 (0-00046) bi mm. (var.) = 0-74 (0-138) EJ mm. (var.) = 1-64 (0-523) r = 0-939 a (var.) = 1-947 (0-0298) TABLE 4. Statistics of length (1), maximum width (w), length to which the adductor scar extends (x), width of adductor scars (y), and the widths of the brachiophores at their junctions to the interarea (bi) and at their anterior tips (b%) in 17 brachial valves of Rhipidomella michelini (L'Eveille). SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH TABLE 5 Delthyrial angle 65 70 75 80 85 No. of specimens i 3 3 8 2 TABLE 5. The total angle of divergence of the teeth and margins of the delthyrium, in 17 pedicle valves of Rhipidomella michelini (L'Eveill6). TABLE 6 I mm. (var.) = 4-39 (6-200) w mm. (var.) = 4-70 (6-859) r = 0-995 a (var.) = 1-052 (0-00031) I mm. (var.) = 4-39 (6-200) mm. (var.) = 2-06 (0-915) r == 0-989 a (var.) = 0-384 (0-00009) TABLE 6. Statistics of length (1), width (w), and thickness (th) of 20 shells of Rhipidomella michelini (L'Eveille). TABLE 7 No. of ribs 8 9 10 No. of specimens 4 7 6 TABLE 7. The number of ribs in a width of 2-5 mm., 5 mm. antero-medianly of either umbo on Rhipidomella michelini (L' Eveille). Order STROPHOMENIDA Opik 1934 Superfamily STROPHOMENACEA King 1846 Family LEPTAENIDAE Hall & Clarke 1894 nom transl. Cooper 1956 Subfamily LEPTAENINAE Hall & Clarke 1894 Genus LEPTAGONIA M'Coy 1844 1844 Leptagonia M'Coy: 116 (pars). 1846 Leptaena King: 28 (pars). 1852 Leptaena (Leptagonia) M'Coy: 223 (pars). 1861 Strophomena Davidson: 119 (pars). 1929 Leptagonia Schuchert & LeVene: 74. 1947 Pseudoleptaena Miloradovich : 96. 1952 Leptaenella Sokolskaja: 35, non Leptaenella Fredericks 1917. 1958 Leptagonia M'Coy; Cvancara: 859. DIAGNOSIS, (emended) Biconvex, strongly geniculate and rugose Leptaenidea; ventral and dorsal muscle scars situated upon prominent pseudospondylium and complex muscle platforms respectively. 22 SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH DESCRIPTION. Outline irregularly quadrate, profile of adult disc biconvex, dorsally directed trail variably developed, commonly affected by opposite folding; rugae regularly and concentrically developed on disc; costae fine, even, rarely branching dichotomously ; ventral interarea apsacline, delthyrium wide, covered apically by pseudodeltidium in various stages of resorption, foramen supra-apical, commonly sealed in adult shells; dorsal interarea short anacline, chili dium large; teeth strong, widely divergent, crenulated; dental lamellae continuous with sub- circular pseudospondylium, elevated anteriorly ; lanceolate adductor scars on broad median ridge; antero-lateral areas of ventral disc rarely raised as low mounds; cardinal process lobes strongly projecting from beneath chilidium with posteriorly directed myophores and strongly curved bases defining subcircular hollow; dorsal adductor field borne on complex platform with elevated subquadrate posterior scars, highly arched in young valves, flanking raised triangular to rectangular anterior scars separated posteriorly by low ridge of secondary shell and anteriorly by deep groove from which median septum extends anteriorly; adult disc enclosed anteriorly by secondary ridge; mantle canal system pinnate to lemniscate; shell substance pseudopunctate. TYPE SPECIES. Producta analoga Phillips by subsequent designation of Schuchert & LeVene (1929 : 74). DISCUSSION. The genus Leptagonia was originally established by M'Coy in 1844, and was later defined by him as including shells with " both valves abruptly bent at right angles towards the entering " (brachial) " valve and the rostral portion con- centrically wrinkled" (1852 : 233). This was done in the belief that Leptaena Dalman was typified by Leptaena transversalis Dalman (now Plectodonta transversalis, and thereby restricted to plectambonitacean-like shells). Six species were described by M'Coy and assigned to Leptagonia, the first being Producta analoga Phillips, a poorly defined species from the Lower Carboniferous of Bolland, Yorkshire, and Redesdale, Northumberland, but at that time believed to be closely related to Leptaena depressa J. de C. Sowerby and L. rugosa Dalman from the Upper Silurian and Upper Ordovician respectively, and also to Productus plicatilis J. de C. Sowerby (now type species of Plicatifera Chao. from the Carboni- ferous). In 1855 he included Leptaena distorta J. de C. Sowerby within Leptagonia, a species also from the Lower Carboniferous. Davidson (1861 : 119-122) concluded that L. depressa, L. analoga and L. distorta were synonymous and did not merit more than varietal rank of Strophomena rhom- boidalis (Wahlemberg) . In describing Leptaena as a species of Strophomena, Davidson was exercising the conservatism that pervaded his approach to brachiopod systematics, because King (1846) had already named a rugate, geniculate species of Dalman, viz. Leptaena rugosa (see Spjeldnaes 1957 : 172) as type species of Leptaena. Until recently most palaeontologists have accepted the Carboniferous form as a true Leptaena, differing only specifically from L. rugosa, L. rhomboidalis , L. depressa, etc. although Hall & Clarke (1891 : 280) did observe that " the extreme differentia- tion of the muscular area as described is even more distinctly exhibited in the forms SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH 23 of the early Carboniferous than in those of the Silurian and Devonian ". During the early part of this century L. analoga continued to be thought of as a true Leptaena; admittedly Schuchert & LeVene (1929) designated the species as the type of Lep- tagonia, but then promptly described M' Coy's genus as a subjective synonym of Leptaena. In 1947, Miloradovich proposed the genus Pseudoleptaena for leptaenids with a pseudospondylium and a cruralium and cited L. distorta Sowerby as the type; and in 1952 Sokolskaja erected the genus Leptaenella for leptaenids with a ventral pseudo- spondylium, naming P. analoga Phillips as type species. In so doing she was evi- dently unaware that not only had P. analoga been already designated as the type species of Leptagonia by Schuchert & LeVene, but also that Leptaenella had already been proposed by Fredericks (1918 : 89) for certain Devonian leptaenids that appear to be congeneric with Leptaena s.s. Thus, in effect, Russian palaeontologists are recognising the generic validity of Leptagonia and the problem becomes one of deciding firstly, if Leptagonia is sufficiently distinct from Leptaena to warrant resusci- tation; and secondly whether Pseudoleptaena, as typified by L. distorta, is also different enough to be retained. Some of the more pertinent features that differentiate Leptagonia from Leptaena are as follows. In Leptaena geniculation is like an exaggeration of the anterior ruga so that both valves bend in the same direction, whereas Leptagonia is dominantly biconvex as a result of valve growth towards the commissural plane, prior to the strong geniculation. Although the ventral interiors do not greatly differ in general arrangement, the pseudospondylium of Leptagonia is an expression of anterior growth of the confining rim of the ventral muscle field away from the floor of the valve and as such is developed more fully than in Leptaena (PI. 3, fig. 28 ; Text-fig. 7). Anteriorly it is so elevated as to simulate a true spondylium simplex (Text-fig. 8). The superficial pattern of the dorsal muscle fields for L. depressa and Leptagonia are similar, but it originates in different ways. In Leptaena the dorsal adductors were attached directly to the floor of the brachial valve and were surrounded or slightly elevated by normal processes of shell accretion during growth of the shell. The ontogenetic development of the dorsal muscle field of Leptagonia, as seen in a series of dorsal interiors varying in width from 3-7 mm. to 60 mm., on the other hand, was intimately connected with two pairs of muscle plates. In the smallest specimens these plates arise from the floor of the valve, a median pair from below the cardinal process extending anteriorly and separated by a deep groove ; and a lateral pair arising from the anterior edges of the socket plates and extending anterolaterally to flank the median pair. These plates are only fused to the floor of the valve posteriorly and at their lateral margins (Text-fig. 10) so as to form anteriorly and antero-laterally direc- ted cavities, all of which must have contained folds of the dorsal mantle epithelium during early life. Each pair of plates respectively accommodated the bases of the anterior and posterior adductor muscles. At the same stage of growth, a pair of ridges extended anteriorly from the points of coalescence of the posterior and anterior adductor plates with each other and with the floor of the valve, which continue parallel to the median septum, at a distance of 0-7 mm. on either side of it and for approximately one-half of its length (PI. 4, fig. 7) ; they are thought to have defined 24 SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH the vascula myaria which probably continued posteriorly along the depression between the anterior and posterior adductor plates. It is also possible that the body wall, separating the visceral and brachial cavities, may have been supported at these ridges. In brachial valves with the median septum extending anteriorly for a distance of about 9 mm., a considerable amount of shell thickening has taken place. The lobes of the cardinal process had grown ventrally and are separated distally by a notch of variable dimension, containing the median indentation of the chilidium. The rounded pit below the cardinal process is encased in secondary shell obliterating the posterior ends of the adductor plates. (Text-fig, n). These progressively lost 1mm. 1mm 8 FIGS. 6-8. Illustrations of transverse sections of Leptagonia analoga (Phillips) at 2-0 mm., Fig. 6; 3-0 mm., Fig. 7; and 4.5 mm., Fig. 8. from the ventral umbo of a specimen about 30 mm. wide across the visceral disc, a.a.p, anterior adductor platform; a.r, ad- ductor ridge in pedicle valve; c, cavity below dorsal adductor platform; c.p, cardinal process; p.a.p, posterior adductor platform; p.f, pedicle foramen; pss, pseudospondy- lium. SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH their tent-like shape through infilling of the underlying chambers ; presumably dur- ing the anterior withdrawal of the mantle epithelium and through secondary shell deposition by the epithelium associated with the muscle bases. Concurrently, the ridges lateral to the median septum became increasingly prominent and thickening 10 FIGS. 9-14. Illustrations of the ontogeny of the brachial valve interior of Leptagonia analoga (Phillips) (Figs. 9-13), and details of the adult cardinal process (Fig. 14). All viewed dorsally except fig. 10, viewed postero-dorsally. ar, " alveolus ", the subcircular hollow between the bases of the cardinal process; ch, chilidium; c.p, cardinal process; m.c, traces of the mantle canals; s.p, socket plates; sr.r, ridge surrounding the sub- rhomboidal region. 26 SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH occurred between them and the anterior part of the median septum to produce a subrhomboidal structure enclosing the septum anterior to the adductor plates (cf. Leptaena rhomboidalis] . From the lateral corners of this area small subsidiary ridges extend forward which probably denned the outer edges of the vascula my aria trunks. At this stage, the lateral and anterior borders of the adductor plates remain discrete from the valve floor, but the degree of arching seldom exceeds i mm. In specimens whose median septum extends n mm. from the base of the cardinal process, the posterior adductor plates are generally raised above those associated with the anterior adductor scars (Text-fig. 12). However, this is a temporary feature, as large specimens, with a median septum of 16-5 mm. have both adductor scars at much the same level. In the largest specimens, the infilling of the chambers below the adductor plates is almost complete, only the lateral margins of the posterior plates showing slight arching. The anterior and posterior scars are less well differentiated, only being separated by a low ridge (Text-fig. 13). The posterior and median borders of the muscle fields are well defined by the continued deposition of secondary shell so as to form a short median ridge extending from the pit between the cradinal process lobes and termininating in the groove between the anterior scars. The subrhomboidal area is well developed and the shell especially thickened round the anterior region of the median septum. The small subsidiary ridges, marking the vascula myaria can now be traced anteriorly to where they branch towards the anterior margin of the brachial cavity. By this stage the cardinal process lobes are well separated ventrally and their flat ends are slightly striated for the reception of the dorsal diductor bases. The chilidium had grown ventrally to enclose the posterior faces of the lobes in such a way as to form two cavities from which the diductor muscles extended (Text-fig. 14). The point of articulation of the valves was always anterior to the interareas, so that during growth the chilidium extended antero-laterally to infill the redundant posterior regions of the sockets. This complicated development contrasts strongly with the simple accretionary processes that were responsible for the differentiation of the dorsal adductor scars of Leptaena. From a provisional investigation of Devonian Leptaena in collections from Germany and North America it would seem that internal morphology is intermediate between Silurian Leptaena and Carboniferous Leptagonia. The Devonian muscle fields are more elevated, especially anteriorly, than those of Silurian specimens, and the cardinal process, with its supporting ridges is comparable to Leptagonia in that the myophore bases diverge antero-ventrally to enclose a deep rounded alveolus. The socket ridges are characteristic in Leptagonia as they curve smoothly onto the cardinal process rather than being sharply distinct as in L. depressa and L. rhom- boidalis. In his original description of L. distorta, the type species of Pseudoleptaena, J. de C. Sowerby (1840 : 10) referred to it as having " A thicker shell than L. analoga; well distinguished by its projecting beak, very convex valves, which are not com- pressed near the beak, and its smaller size." The specimens were collected by Gilbertson from the Isle of Man. This description would be adequate for shells at a SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH 27 stage of development as illustrated in Text-figs. II and 12, which are essentially the same as text-fig. 27 of Pseudoleptaena distorta in Sarycheva & Sokolskaja (1952 : 37). Thus, the cruralium and pseudospondylium of Miloradovich's genus are developmental stages in the growth of the adult Leptagonia and invalidate the retention of Pseudoleptaena as a distinct genus. The mantle canal system of Leptagonia differs somewhat from that illustrated for Leptaena by Williams (1956 : 274). His illustration shows saccate gonocoels sur- rounded by major sinus trunks from which are given off numerous peripheral sinuses. In Leptagonia it appears that the gonocoels themselves were lemniscate, giving off the periferal sinuses (PI. 3, fig. 30), with the vascula media and my aria retained medianly (Text-fig. 15). However, it might be that this condition is only apparent, and could have developed from the pattern illustrated by Williams by the enlarge- ment of the gonocoels so as to have ruptured some of the more peripheral mantle sinuses and their main connecting trunks. Fragments of traces of the mantle 1 cm. FIG. 15. Illustration of an internal mould of the pedicle valve of Leptagonia analoga (Phillips), showing the impressions of the pseudospondylium and mantle canals; a.s, scars of adductor muscles; d.s, scar of diductor muscles; g, gonocoel, with traces of peripheral canals; v.m, vasculum medium canal traces. canals can be seen throughout most of the thickness of the shell substance and always seem to arise from the edges of the gonocoel, rather than from main vascula trunks, so that it seems unlikely that overgrowth of the gonadial regions has oblitered a former pattern of the mantle canal system. Cvancara (1958 : 861) speaks of " two suboval areas " on either side of the dorsal and ventral muscle fields which he says " appear " to be the only areas of pseudopunctation in Leptagonia. It seems likely that the regions to which he refers are the finely papillose areas, here considered as gonocoels (PI. 4, fig. 2) and that he is incorrect in thinking the teleolae to be confined to those regions. Admittedly, there is a concentration of taleolae in the shell substance antero-lateral of the muscle fields, but they also occur within the shell substance of the muscle platforms and are scattered throughout the rest of the shell. From internal moulds it seems probable that the taleolae were also concen- trated more strongly at the base of the trail. The pseudopunctae of Leptagonia are inwardly directed flexures of the shell fibres surrounding narrow non-fibrous taleolae so as to produce a closely fitting series of sharp cones, marked internally 28 SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH by small tubercles. They were probably formed at the points of attachment of small muscle strands within the mantle, which may have assisted in the circulation or explusion of the gonadial products from the mantle canal system, and in the movement of the mantle edges. Such an interpretation might explain the concentra- tion of taleolae in the gonadial regions, and at the base of the trail. An unusual feature seen rarely in pedicle valves is the development of two slight conical thickenings of the shell symmetrically placed between the pseudospondylium and the anterior margin of the disc. Similar, though more papillose humps are to be seen in some Silurian leptaenids, and may indicate that the spirolophe was slightly conical and directed towards the dorsal valve. Longitudinal sections of young shells, of hinge-width approximately 2-5 cm. show an open supra-apical pedicle foramen. A study of the shell texture shows the canal through the shell to be lined with fibres disposed parallel to the canal surface and more or less normal to the ventral, external, surface of the valve, an area which FIG. 1 6. Illustration of a median longitudinal section through a young shell of Leptagonia analoga (Phillips) showing the cavity below the dorsal adductor platform, thickening anterior to the cardinal process and the pedicle aperture with its lining of secondary fibrous calcite; a.p, adductor platform; c.p, cardinal process; p.a, pedicle aperture. must have been covered by chitin (Text-fig. 16). In describing his Australian specimens of cf. L. analoga Cvancara (1958 : 860) apparently noted the same feature for he states that " The foramen appears to be lined with a tubular sheath ". The disposition of these fibres and their inferred relationship to the epithelium which secreted them is obscure, but it would seem likely that they were deposited during the withdrawal of the outer epithelium following the development and redundancy of the nepionic pedicle sheath (Arber 1939 : 84). Outer epithelium must have extended through the nepionic shell to have formed the pedicle sheath. During subsequent growth the withdrawal of the outer epithelium resulted in the deposition of fibres parallel to the pedicle canal and also drew its junction with the pedicle epithelium inwards, so lining the canal with chitin. Spaces within the shell substance, parallel to these fibres, suggest that there might have been periodic advance and retraction of the outer epithelium to pedicle epithelium boundary. In 1958 Cvancara came to the same conclusions about the reintroduction of Leptagonia as the correct generic name for the distinctive Carboniferous leptaenids. He bases his reasoning upon a study of the ventral valves in which he observed the muscle field to be supported upon a " well-developed spondylium ", in contrast to SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH 29 the flat muscle field of Leptaena. Cvancara did not examine the type specimen of L. analoga, but there can be little doubt that the upper Tournasian specimens from New South Wales which he describes are closely comparable with Phillips' species. Leptagonia analoga (Phillips) (PL 3, figs. 26-31. PL 4, figs. 1-9. Text-figs. 6-17) 1836 Producta analoga Phillips: 116, pi. 7, fig. 10. 1844 Leptagonia analoga (Phillips) M'Coy: 117. 1861 Strophomena rhomboidalis var. analoga (Phillips) Davidson: 119, pi. 28, figs. 1-6, 9-13. 1958 Leptagonia cf. L. analoga (Phillips); Cvancara: 860, pi. 100, figs 6-13. DIAGNOSIS. Subquadrate to semicircular Leptagonia with adult disc about one- half as long as wide, outline commonly modified by emargination medianly and less commonly laterally; immature shells plano-convex, adult shells biconvex, about one- half as deep as long, commonly uniplicate, rarely parasulcate ; dorsally directed trail variably developed; visceral region with 14-18 regular rugae having mean wave- lengths of i-o mm. and 1-4 mm. for the fifth and tenth rugae; rounded costae, commonly 5 or 6 in 2 mm., 10 mm. antero-medianly of umbones; pseudospondylium subcircular, seven-tenths as long as wide and about one-third as long as length of disc; dorsal muscle field one-half as long as wide, median septum extending forward for about two-fifths length of disc. MEASUREMENTS (in mm.) length width LECTOTYPE. Complete eroded specimen (6.8963) c. 20 c. 44 Incomplete pedicle valve (L. 3817/1) 32 c. 50 Incomplete brachial valve (68.52731) c. 54 Complete brachial valve (66.52730) 6-0 c. 6-9 Internal mould (66.55777) 3 c - 45 Complete shell (66.52729) c. 5-0 5-5 LOCALITIES AND HORIZONS: Lectotype from 6olland, Yorkshire. 6.8936 (PL 3, figs. 26, 27). L. 3817/1 from the Caldwell Collection, Hunterian Museum, Glasgow, collected from the Lower Carboniferous of Carrick-on-Shannon, Counties Leitrim and Ros- common, Ireland. B6.55777 Gilbertson Collection, probably from the Lower Carboniferous of the Isle of Man. 66.52729-30. The subreefal limestones and shales of 6unnahone, 2 miles N.W. of Derrygonnelly, Co. Fermanagh. Low. D. zone. 6.. 52731. The 6allyshannon limestone of Streadagh Point, Co. Sligo, Ireland S 2 . DISCUSSION. There is considerable variation of outline and in the length of visceral disc at which geniculation took place, so that the number of rugae on the 30 SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH ventral discs of nineteen specimens from Carrick-on-Shannon ranges from 13 to 23. The wave-lengths of the fifth and tenth rugae from the umbo varies from 0-8 mm. to i-i mm. (mean i-o mm.) and from i-i mm. to i-6mm. (mean 1-4 mm.), on 15 specimens. Costation was little affected by the point at which geniculation occurred and remains with 3, 6, 4 and 3 specimens having respectively 4, 5, 6 and 7 costae per 2 mm. width at 10 mm. antero-medianly from the ventral umbo. Almost invariably FIG. 17. Illustration of the anterior region of a median longitudinal section through the shell of Leptagonia analoga (Phillips) showing the secondary marginal ridge around the visceral region of the brachial valve, developed at the point of geniculation. The brachial cavity is to the right on the illustration. the trail is depressed medianly, commonly also affecting the anterior margin of the disc to form a uniplicate commissure. Those shells which geniculated before the more usual disc length of about 27 mm. may be slightly depressed laterally as well as antero-medianly (cf. Davidson 1861, pi. 28, fig. 7). Such shells have been separated as L. distorta, but within large samples no satisfactory separation from L. analoga can be established. All contain the same internal structures at various stages of development, and the length at which the trail developed ranges from typical L. distorta, about 15 mm. long, to full sized specimens of L. analoga. It is necessary SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH 31 to discover whether valid stratigraphic or fades differences occur within these forms before being at all sure of their taxonomic positions. Irregularly concentric fine growth lines are continued on the trail, while the traces of the mantle canal system can also commonly be seen within the shell sub- stance below every second or third rib. The rugae are not continued on to the trail. The ridge around the adult dorsal visceral disc is of secondary shell material and becomes increasingly prominent through adulthood. (Text-fig. 17). Only a few specimens of L. analoga were found among the etched material from Co. Fermanagh, but the author has made use of specimens in the Caldwell Collection from Carrick-on-Shannon, about 36 miles S.S.W. of Derrygonnelly, kindly lent by the Hunterian Museum, Glasgow. Measurements on 10 brachial valve interiors from this collection shows that the length of the median septum, measured from the posterior margin of the adductor field, is consistently similar to the total width of the socket ridges (r = 0-924). Superfamily DAVIDSONIAGEA King 1850 Family ORTHOTETIDAE Waagen 1884 Subfamily ORTHOTETINAE Waagen 1884 ' [= Derbyoidinae Thomas 1958] Genus BROCHOCARINA nov. 1855 Leptaena (Strophomena) M'Coy: 450 (pars). 1861 Streptorhynchus King 1850: Davidson: 123 (pars) pi. 26, figs. 5 (?2 and 6) non Figs, i, 3 and 4. 1910 Schuchertella Girty 1904; Thomas: 126. 1930 Schuchertella Smyth: 555, pi. 15, figs. 5-9. DIAGNOSIS. Thin plano-convex Orthotitinae with entire chilidium; dental ridges deep, fusing posteriorly in ventral apex with trifid ridges enclosing lanceolate adductor scars. DESCRIPTION. Outline subsemicircular, profile more or less plano-convex with narrow body cavity; ventral interarea long, apsacline, with arched pseudodeltidium, perideltidium variably defined; dorsal interarea and chilidium reduced; radial ornament parvicostellate with costellae regularly intercalated; teeth strong, con- tinued at delthyrial margins as obliquely disposed posteriorly prominent dental ridges; ventral muscle field defined only in adult shells, adductor scars lanceolate, inserted posteriorly between low trifid ridges, diductor scars flanking and spreading anteriorly ; cardinal process low, lobes well separated by sulcus with median chilidial ridge; socket plates at about 20 to hinge-line, slightly recurved; adductor field obscurely impressed, apparently flabellate to subcircular and separated by slight median ridge in adult shells ; shell substance irregularly pseudopunctate. TYPE SPECIES. Schuchertella wexfordensis Smyth 1930. DISCUSSION. The new genus Brochocarina conforms to the requirements of the family Orthotetidae Waagen 1884, in having a low cardinal process and ventral 32 SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH interior with a low median septum continuous with the inside of the pseudodeltidium and fused to the dental ridges. At subfamilial level the distinction between Ortho- tetinae Waagen, and Derbyiinae Stehli, is based upon the form of the socket plates; those genera with widely divergent socket plates, which tend to recurve towards the posterior margin as they fuse to the dorsal valve floor, being placed in the Ortho- tetinae, while those genera with less widely divergent socket plates, fusing to the floor without curvature, being assigned to the Derbyiinae. The genus possesses somewhat recurved socket plates, an ill-defined dorsal adductor field, greatly re- duced dorsal interarea and small chilidium and is therefore assigned to the Ortho- tetinae. The genera comprising the Orthotetinae are distinguished by differences in their ventral interiors, the form of the cardinal process lobes and the shell profile. Bro- chocarina differs from Orthotetes Fischer de Waldheim (? Werriea Campbell 1957) in having a less highly developed ventral median septum which has never been ob- served to have fused with the dental ridges posteriorly to such an extent as to have formed a delthyrial chamber (The " spondylium " of early authors and " secondary spondylium " of Thomas 1958 : 9). Hipparionyx Vanuxem is clearly distinguished by its subcircular outline, strongly impressed ventral interior and high, strongly divergent cardinal process lobes. A comparison of the original descriptions of Derbyoides Dunbar & Condra (1932 : 114) and Tapajotia Dresser (1954 : 33) suggests that these genera are less distinctive than was thought by Thomas (1958 : 21) or by Dresser himself. While admitting " that Tapajotia is closely related to Derbyoides " Dresser separates the two largely on his mistaken belief that Derbyoides possesses a strong ventral median septum. In fact Dunbar & Condra (1932 : 115) state that " A median septum is present but rather weak and low, extending not over one-third the distance to the front of the valve ", and inspection of their pi. 9, fig. 13 confirms this statement. For the above reasons Campbell (1957 : 46) states that Tapajotia " is probably a synonym of Derbyoides ". This conclusion was arrived at by Mendes (1958 : 317, 319) in his re- view of the Tapajos River fauna of the Amazon Valley, and is supported by Cooper (personal communication). However, having studied topotypic material of Derby- oides and Tapajotia the writer is of the opinion that the two genera are distinctive and worthy of separation from Brochocarina gen. nov., while all three were probably closely related and derived from a schuchertellid stock. The distinction between Derbyoides (PI. 4, figs. 10-14) an d Tapajotia (PI. 4, figs. 15-23) include the following features. The brachial valve of Derbyoides is " strongly and rather evenly convex, with the highest point near the mid-length ", (Dunbar & Condra 1932 : 115) and the valves are commonly faintly medianly sulcate in con- trast to the plane, posteriorly flattened valves of both Tapajotia and Brochocarina. Dresser is mistaken in describing the widest part of Tapajotia as being " anterior " to the transverse mid-line. His illustrations, and the material at hand, show the greatest width to be at one-third the shell length, and the hinge-line width to be nine-tenths of this width. The greatest width of Derbyoides is at mid-length and the hinge-line is only three-quarters this width. The dorsal interiors differ in that a short median septum is developed between and anterior to the clearly impressed SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH 33 adductor scars of Derby oides, neither of which are seen in Tapajotia, and its cardinalia are more massive, extending for one-third of the hinge-line width as compared to one-quarter the width in Tapajotia. The ventral adductor scars are similar, but differ in being more elongately lozenge-shaped in Derby oides, those of Tapajotia having more or less parallel lateral margins bordered by slight ridges. The delthyrial angle is about 20 greater in Derby oides than in Tapajotia or Brochocarina, and its shell substance is much thicker and led to the development of marginal ridges around the edges of both valves. FIGS. 18-20. Illustrations comparing the cardinalia of Derby oides Dunbar & Condra (Fig. 18), Tapajotia Dresser (Fig. 19), and Brochocarina gen. n. (Fig. 20) in posterior (on the left) and internal (on the right) views. Brochocarina is distinguished from both Derbyoides and Tapajotia primarily by reason of its ventral interior. The teeth of the American genera are traced along the edges of the delthyrium as low ridges which do not fuse at the beak of the valve to form a ventral median septum. The teeth of Brochocarina are supported by distinct dental ridges, strongly differentiated from the inner surface of the interarea. In adulthood these ridges reached almost to the valve floor and throughout life they fused posteriorly and gave rise to the tripartite median septum that separated and enclosed the lanceolate adductor scars (pi. 5, figs. 8, 13). The dorsal cardinalia is similar to that of Tapajotia, but differs in that the socket plates diverge at 20 to 25 from the hinge-line instead of at about 35 in the Brazilian and Nebraskan genera (Text-figs. 18-20). The outline of Brochocarina tends to be more semicircular than that of the other genera, as its maximum width is commonly GEOL. 1 6, I 3 34 SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH at the hinge-line. The plano-convex profile is like that of Tapajotia but different from the dorsi-biconvex profile of Derbyoides. The external radial ornament, with about ii ribs in 5 mm. at 10 mm. antero-medianly of the dorsal umbo, is of much the same frequency as that of the American genera. However, the form of the ribbing does vary. Brochocarina is parvicostellate with narrow, rather angular ribs which only attain their full dimensions after about 5 mm. (First order costellae attain full size after 3 or 4 mm. while second and third order costellae only attain full size after about 10 mm., if at all.) This led to the development of relatively wide inter- spaces, especially posteriorly, and this contrasts with the more regular, rounded radial ornament of the other two genera. Thus, Brochocarina may be distinguished principally by its ventral interior and narrowly divergent socket plates. Derbyoides differs in its convex and heavily thickened brachial valve and in having a medianly developed dorsal septum. The Fermanagh shells are older than the other genera of the subfamily, except for Hipparionyx, and yet show a stage of development of the ventral interior apparently intermediate to that of Tapajotia and Orthotetes. Of the presently described genera Brochocarina could have been ancestral to Derbyoides and Tapajotia by the reduction of the dental ridges in these later genera, and to Orthotetes by the increased deposition of secondary shell in this region. Brochocarina wexfordensis (Smyth) (PL 4, figs. 24-26, PL 5, figs. 1-23. Text-figs. 18-26) 1855 ILeptaena (Stromphomena) crenistria (Phillips); M'Coy: 450. 1861 Streptorhynchus crenistria (Phillips) Davidson (pars) : 124, pi. 26, fig. 5, (?2 and 6) non figs, i, 3 and 4. 1930 Schuchertella wexfordensis Smyth: 555, pi. 20, figs. 5-9. 1931 Derbyia ambigua Muir-Wood (pars) : 144, fig. 3, non pi. 10, figs. 4, 5. DIAGNOSIS (emended). Outline subsemicircular, with length about two- thirds maximum width; radial ornament unequi-parvicostellate with about 6 ribs in 2-5 mm. width, 5 mm. antero-medianly from dorsal umbo, interrupted by occasional growth lamellae, growth-lines numerous; pseudodeltidium arched with apical angle about 65, flanked by wide perideltidium with apical angle about 130, teeth pro- minent, adult dental ridges deep, almost reaching floor of valve; socket plates low, about one-quarter hinge width, recurving posteriorly to floor of valve. MEASUREMENTS (in mm.) : length width HOLOTYPE. Complete brachial valve (T.C.D.i96/io86) 36-3 c. 49-6 PARATYPE. Incomplete pedicle valve (T.C.D. 199/1086) 63-5 Incomplete pedicle valve (66.52732) 67-9 Incomplete pedicle valve (66.52734) c. ii-o Incomplete brachial valve (66.52735) c. 9-5 Complete brachial valve (66.52736) 32-3 c. 53-0 Complete crushed shell (66.52738) c. 64-0 c. 90-0 SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH 35 LOCALITIES AND HORIZONS: Holotype and paratype: Smyth Collection Nos. 196/1086, 199/1086 at Trinity College, Dublin, collected from Lower Carboni- ferous rocks on the west side of Hook Head, Co. Wexford. ?Ci. 66.52732-52736 : Subreefal limestones and shales of Bunnahone and Carrick Loughs, 2 miles N.W. of Derrygonnelly, Co. Fermanagh. D x . 66.52738: Bundoran shales, Bundoran, Co. Donegal. S 2 . DISCUSSION. In all known respects the present Fermanagh material agrees with the type specimens of Schuchertella wexfordensis Smyth, 1930, from upper Tournaisian and lower Visean beds of Hook Head, Co. Wexford. Although a statistical com- parison of the growth axes " a " for the Hook Head and Fermanagh specimens in- dicates that there is a slight significant difference (0-02 < p < 0-05), the ventral interiors are identical (cf. PI. 4, fig. 24 with PI. 5, fig. 13) and no differences can be distinguished between the external ornamentation. The two are, therefore, con- sidered to be conspecific. In 1931 Muir-Wood (in Garwood) described a new species of davidsoniacean, Derbyia ambigua, from C 2 beds in Roxburghshire. Five of the original specimens are in the British Museum (Nat. Hist.), but they are not all conspecific and two (6.56425, 6.56410) are thought to be conspecific with Smyth's species while a third fragment (6.56415) is probably conspecific. The holotype of D. ambigu (6.56411) and the pedicle valve interior (6.56416) figured (1931, pi. 10, fig. 5) are distinctive. Without brachial valve interiors it is difficult to be certain about the generic designation, but the high ventral median septum and small delthyrial cavity are more reminiscent of Orthotetes than Derbyia. The description of Leptaena (Strophomena) crenistria (Phillips), given by M'Coy in 1855 (: 450) is in agreement with the present species in all recorded features. However, it is not conspecific with Spirifera crenistria Phillips (1836 : 216) which has a convex brachial valve (pi. 9, fig. 6) and is assigned correctly by Thomas to Schellwie- nella (1910 : 126). The illustration of Streptorhynchus crenistria (Phillips) by David- son (1861, pi. 26, fig. 5) has been variously ascribed; to Schuchertella by Thomas (1910) and Smyth (1930 : 555), and to Tapajotia by Dresser (1954 : 37). Dresser considered Davidson's specimens to be " specifically distinct from T. tapajotensis because they possess a much deeper impression of the muscle scars in both valves ". This observation could be used to separate the present species from that illustrated by Davidson. It should be remembered, however, that his specimen illustrated in fig. 5 is from Hook Head, the type locality, and that several of Davidson's illustrations are somewhat stylized. It may be that Davidson's figs. 2 and 6 (cf. pi. 26) are also conspecific. The species differs from Schuchertella pseudoseptata Campbell (1957 ' 46), des- cribed by him as closely resembling 5. wexfordensis, by not having socket plates which are parallel to the hinge-line. Campbell's species apparently never reached the dimensions of S. wexfordensis, and from the description is only comparable in its ventral muscle field and septation. Growth of the shell was almost equally radial to give a high coefficient of correla- tion between length and width (r = 0-998). The greatest width is almost invariably at the hinge-line, so that the cardinal extremities remain at 90 or less. Costellation 36 SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH is probably a reflection of setal growth at the mantle margin, and as such remains constant throughout several genera of the davidsoniaceans. As in other genera, the costae number sixteen to eighteen on each valve, one to four orders of costellae being regularly and symmetrically intercalated so that in a width of 2-5 mm. antero- medianly of the dorsal umbo the costellae are arranged as in Table 8. Because of the flatness of these shells, and the frequency with which their anterior margins are broken, the best estimate of shell thickness is gained by measuring the height of the delthyrium (Table n). From the complete specimens available it is clear that this posterior region represents the region of greatest shell depth. Fine growth lines form minute ridges across the crests of the costellae which became increasingly prominent anteriorly, until in adult shells, the ridges are pro- longed into small spinose lamellae PI. 5, fig. 12. Concentric lamellae, formed by interruptions in growth, are variably developed, although they tend to be concen- trated towards the adult shell margins, presumably because of reduced shell growth. An unusual characteristic of the species, is the way in which the brachial valve commonly becomes flat, or slightly concave, over a distance of about 10 mm. immediately anterior to the initial convexity of the umbonal region. The peridel- tidium, which is best seen on calcareous shells (PI. 5, fig. 19), extends laterally for about one-half the width of the ventral interarea and is finely striated vertically, as well as bearing the sporadic growth lines that traverse the whole interarea and pseudodeltidium. It is possible that a similar area occurs upon the dorsal interarea. Clearly the periostracal shell covering was differentiated in the perideltidial region and the fine vertical striations are suggestive of a tight bonding to the shell surface, as might be expected under a periostracal pad (Williams 1956 : 257). The chilidium is best seen in adult shells, (PI. 5, figs. 6, 18) but its development can be followed from shells only about 3 mm. wide. In adult shells, with a dorsal in- terarea 1-5 mm. long, the chilidium curves around the base of the cardinal process lobes and is separated from them laterally by prominent grooves. A short chilidial ridge supports the structure between the cardinal process lobes and laterally it merges with the socket plates. Internally, the margins of adult shells are commonly secondarily thickened to a greater extent than the remaining surfaces, but never to the extent of those of Derby oides nebrascensis. This thickening, together with the closely spaced external lamellae it the shell margin, indicates periodic mantle retraction. This process increased both the thickness of shell substance and the total depth of the shell without appreciable increase to shell length or width. The development of the dental and median ridges is informative in indicating the affinity of these shells with stratigraphically younger forms, and helps to confirm the interpretation by Williams (1965 : 11404) of the delthyrial chamber of Orthotetes Fischer de Waldheim. The low trifid median ridge, which separates the ventral adductor scars from the diductor scars, arose umbonally and fused with the posterior ends of the dental ridges as a result of secondary shell deposition (Text-figs. 21-26). Shell deposition in adult stages increased the depth of the dental ridges until they approached the floor of the valve posteriorly (Text-fig. 26). Continued shell de- position umbonally could have buried the posterior ends of these ridges, together SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH 37 with the median ridge, so that in cross-section the ventral beak might appear to possess a thick " pseudospondylium ". A study of dorsal interiors varying from 1-5 mm. to 55 mm. wide shows certain changes in the cardinalia. The angel of the socket plates to the hinge-line varies, tending to decrease slightly with age. In an assemblage of variously sized shells the 1mm. 21 1mm. 22 1mm. 23 2 mm. 1 cm. 25 FIGS. 21-26. Illustrations of the ontogeny of the pedicle valve interior of Brochocarina wexfordensis (Smyth), postero- ventral aspect, showing the fusion of the dental ridges with the median septum, a, adductor scar; d, diductor scar; d.r, dental ridge; psd, pseudodeltidium; t, tooth; v.i, ventral interarea. angle is commonly between 20 and 25. The smallest shells show scarcely any inter- area, the cardinal process is but slightly differential into two lobes, the socket plates are straight, (PI. 5, figs. 20, 21) and there are only the slightest lateral swellings in- dicating the origins of the chilklium. By a width of 4-5 mm. all the essential elements of the cardinalia are distinguishable, save for the median ridge and ventral node between the cardinal process lobes and the slight thickening between the socket plates, bounding the postero-median edges of the subcircular adductor field (PI. 5, fig. 22). SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH TABLE 8 No. of ribs 4 5 6 7 8 A 4 6 3 3 B 2 5 3 I o TABLE 8. The number of ribs counted in 2-5 mm. at 5 mm. (A) and 10 mm. (B) antero- medianly of the dorsal umbo of Brochocarina wexfordensis (Smyth). TABLE 9 J mm. (var.) = 6-33 (77'93) w mm. (var.) = 10-03 (213-866) r = 0-998 a (var.) = 1-666 (o-ooin) w mm. (var.) = 10-03 (213-866) s mm. (var.) = 2-63 (8-032) r = 0-997 a (var.) = 0-194 (0-000023) TABLE 9. Statistics of length (1), maximum width (w) and maximum width of the socket plates (s) of 12 dorsal valves of Brochocarina wexfordensis (Smyth) from Co. Fermanagh. TABLE 10 1 mm. (var.) = 26-60 (70-203) w mm. (var.) == 38-61 (137-950) r = 0-983 a (var.) = 1-402 (0-01114) TABLE 10. Statistics of length (1) and maximum width (w) of 8 pairs of measurements from type dorsal valves of Brochocarina wexfordensis (Symth) from Hook Head, Co. Wexford. TABLE n I mm. (var.) = 9-56 (122-115) w mm. (var.) = 12-96 (226-31) r = 0-994 a (var.) = 1-361 (0-00079) I mm. (var.) = 9-56 (122-115) E mm. (var.) = 1-29 (1-652) r = 0-956 a (var.) = 0-116 (0-00042) fi mm. (var.) = 1-29 (1-652) cl mm. (var.) = 1-83 (3-873) r = 0-984 a (var.) = 1-531 (0-00268) TABLE n. Statistics of length (1), maximum width (w), height of delthyrium (h) and width of delthyrium (d) at the anterior margin of the interarea of 16 pedicle valves of Brocho- carina wexfordensis (Smyth) from Co. Fermanagh. SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH 39 fOrthotetinid gen. and sp. indet. (PI. 7, figs. 1-7) Three distinctive cardinalia have been recovered from the etched limestones of the Sillees River, Bunnahone, but no pedicle valves are known. Fortunately the three vary in size, viz. total widths of socket plates = 4-7 mm., 14-1 mm. and 17-6 mm., allowing ontogenetic changes to be observed. These cardinalia are quite unlike other davidsoniacean species from the faunas and are unusual in their slight strophomen- acean characteristics, i.e. external ornament and strong dorsal median septum. A cardinalia figured by Davidson (1861, pi. 27, figs. 6, 7) from Settle, Yorkshire is probably conspecific, but was included as Streptorhynchus crenistria; otherwise comparable material does not appear to have been described. The brachial valve was apparently gently convex with a wide straight hinge-line, well developed anacline interarea and arching chilidium from below which the cardinal process projected strongly. The external ribbing occurs with a frequency of about 10 ribs in 5 mm. width, 5 mm. from the umbo, and is apparently parvico- stellate. Between the ribs is a less distinct concentric ornamentation of minute ridges (PI. 7, fig. i), similar to that of strophomenaceans. Internally the cardinal process is typically davidsoniacean with two well developed incised lobes between which is a chilidial ridge terminating ventrally in a node. The socket plates are strongly recurved and nearly parallel to the interarea; medianly they merge to the cardinal process and prominent median septum, which is present even in the smallest specimen. The lack of pedicle valves make it impossible to be quite sure of familial placing but the form of the socket plates indicates either the Schuchertellinae or Ortho- tetinae as the most likely subfamilies. Of these the latter group seems more appro- priate as some members of the Orthotetinae have a poorly developed dorsal median septum. Until more material is available, in particular matching pedicle valves, a full generic or specific designation will not be attempted. Family SCHUCHERTELLIDAE Williams 1953 Subfamily SCHUCHERTELLINAE Williams 1953 Genus SERRATOCRISTA nov. DIAGNOSIS. Shell small, commonly ventribiconvex, pedicle valve strongly curved to conical in young shells ; hinge-line straight, commonly approximating to maximum width; ventral interarea elongate, apsacline to catacline, pseudodeltidium arched and entire, perideltidium obscure; dorsal interarea and chilidium much reduced; radial ornament multicostellate, spinose with costellae regularly intercalated; teeth supported by low dental ridges; muscle scars indistinct, rarely with slightly raised lanceolate adductor scars; cardinal process low, bilobed and supported by widely divergent socket-plates at about 25 to hinge-line; adductor field obscure, shell substance probably pseudopunctate. TYPE SPECIES. Serratocrista fistulosa sp.n. 40 SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH DISCUSSION. Serratocrista is included in the subfamily Schuchertellinae on account of its typically schuchertellid dorsal interior, including socket plates which diverge from the hinge-line acutely and which recurve slightly at their antero- lateral extremities. This is in contrast to the socket plates typical of the Strepto- rhynchinae, which diverge from the hinge-line less acutely, at 50 to 60, and continue antero-laterally fused to the brachial valve floor with no recurvature towards the posterior margin. Serratocrista differs from Schuchertella Girty, in being pseudo- punctate and having no dorsal median ridge, features which recall Orthopleura Imbrie, although it differs from this genus in being multicostellate and " spinose" . Unlike Schuchertellopsis Maillieux, representatives of the new genus were not com- pletely cemented by their pedicle valves to a foreign body during their life. Serratocrista fistulosa sp.n. (PI. 6, figs. 1-12) DIAGNOSIS. Biconvex Schuchertellinae bearing spinose, strong ribs; chilidium obsolescent, weak dental ridges and poorly impressed muscle scars. DESCRIPTION. Outline transversely semi-oval, approximately two-thirds as long as wide; biconvex, one-third as thick as long, slight dorsal median sulcus; strongly multi-costellate bearing about four crestal " spines " medianly between 9 and 10 mm. from dorsal umbo. About eight ribs occur per 2-5 mm. width antero-medianly at 5 mm. from dorsal umbo, pedicle valve costae commonly slightly stronger than costellae; ventral adductor scars posteriorly placed, lanceolate, enclosed by slight ridges; cardinal process low, lobes well separated by sulcus, socket plates diverge from hinge-line at about 25, prominent anteriorly, reaching almost one-third width of hinge-line; sockets arched postero-medianly by antero-lateral growth of vestigial chilidial plates; median septum absent, adductor scars obscure. MEASUREMENTS (in mm.) : length width HOLOTYPE. Complete shell (66.52739) 14-4 18-0 PARATYPES. Complete brachial valve (66.52740) 9-6 14-6 Complete pedicle valve (66.52741) 14-1 20-0 Complete pedicle valve (66.52744) 3-6 5-1 TYPE LOCALITY. Sillees River, about 300 yds. east of 6unnahone Lough (low D zone). DISCUSSION. The costellate ornamentation is distinctive with its short pointed " spines " commonly arising alternately from the crests of the ribs (PL 6, fig. 3). These " spines " become slightly more widely spaced anteriorly, but medianly be- tween 9 and 10 mm. from the umbo there are about four. Costellae were added by branching and intercalation, although the latter is rare on pedicle valves and the branching is predominantly median in origin. The costellae approximate to the size of the costae within about 5 mm. of their origin. At 5 mm. from the umbo 3, 3 SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH 41 and 9 valves have 6, 7 and 8 ribs per 2-5 mm. width antero-medianly. The ribbing is prominent with rounded crests and straight or slightly concave sides, up which fine growth-lines can be traced (PL 6, fig. 3), and both wave-length and amplitude of the ribs are commonly about equal. The radial ornamentation is comparable to that of the mid Devonian European species Xystostrophia umbraculum (Schlotheim) ; both species developed spinose outgrowths from their ribs, but in other respects, such as cardinalia, the two are quite distinctive. The shell interiors are unusually featureless, despite secondary thickening; the dental ridges show no accentuation with increased age, nor is there any sign of a median ridge in either valve. Although described as pseudopunctate, the shell structure is a little uncertain. The internal surfaces, of pedicle valves in particular, are covered by small pits which are confined neither to ribs nor interspaces. Unfortunately, unsilicified material is not available so microscopic examination of unaltered shell is impossible. One incompletely silicified specimen is broken across the ventral interarea and part of the valve. The inner and outer surfaces are completely silicified but internally there is only a silica lattice comprising lamellae held by more or less perpendicular fine rods (PI. 6, fig. n). This structure may be interpreted as being selective silicification along planes in the original shell structure which represented a form of punctation and the shell lamellae. Thomas (1958) describes Permian Streptorhynchus from Western Australia as having a shell structure that differs from his other David- soniacea. The conical flexures of the shell lamellae are directed outwards, rather than inwards as in normal pseudopunctate shells, and Thomas suspects that these flexures surrounded a fine canal (Thomas 1958, pi. 19). In the Australian material this " punctation " was confined to the ribs, as is the internal punctation of many enteletaceans and terebratuloids. If the shell structure of the Fermanagh material was comparable it would explain the minute pits on internal surfaces and could explain the selective silicification of the shell figured in Plate 6, fig. n. TABLE 12 I mm. (var.) = 10-83 (i7'53<>) I mm - ( var -) = I0 '^3 (*7'53o) wmm. (var.) = 14-52 (31-078) tn mm. (var.) = 3-02 (0-654) r = 0-970 r = 0-893 a (var.) = 1-332 (0-0262) a (var.) = 0-193 (0-0022) TABLE 12. Statistics of length (1), maximum width (w) and thickness (th) of 6 pedicle valves of Serratocrista fistulosa sp. n. TABLE 13 I mm. (var.) = 5-75 (12-22) w mm. (var.) = 8-33 (23-551) r = 0-988 a (var.) = 1-389 (0-0058) TABLE 13. Statistics of length (1) and width (w) of 10 brachial valves of Serratocrista fistulosa sp. n. 42 SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH Family MEEKELLIDAE Stehli 1954 Subfamily MEEKELLINAE Stehli 1954 [= Omboniinae Sokolskaja 1960] Genus SCHELLWIENELLA Thomas 1910 TYPE SPECIES. Spirifera crenistria Phillips 1836, by original designation of Thomas (1910 : 92). Schellwienella radialis (Phillips) (PI. 6, figs. 13-24. Text-figs. 27-35) 1836 Spirifera radialis Phillips: 220, pi. n, fig. 5. 1861 Streptorhynchus crenistria var. radialis (Phillips) Davidson: 129, pi. 25, figs. 16, 17, 18. 1930 ^Schellwienella aS. aspis Smyth: 555, pi. 16, figs. 6a, 6b. 1934 ? Schellwienella aspis var. radialiformis Demanet: 85, pi. 7, figs. 6-12. DIAGNOSIS (emended). Dorsibiconvex to slightly resupinate Schellwienella with strong parvicostellate ribbing, strong divergent dental plates, small complete chilidium, high cardinal process and deeply impressed dendritic dorsal adductor scars in adult. DESCRIPTION. Profile inequibiconvex, adult brachial valve strongly convex posteriorly, thickness about one-half shell width ; shell length about three-quarters width, adult anterior margin commonly slightly uniplicate; ribbing unevenly parvicostellate, commonly with seven ribs per 2*5 mm., 5 mm. antero-medianly of dorsal umbo, costae consistently stronger than intercalated costellae; concentric lamellae, becoming crowded marginally; ventral interarea apsacline, pseudodelti- dium arched, perideltidium indistinct ; dorsal interarea short with chilidium of equal length; dental plates receding, diverging to floor of valve, posteriorly enclosing muscle field consisting of postero-medianly placed adductor scars flanked by pair of rounded triangular diductor scars; cardinal process prominent, wide and bilobed; socket plates at about 50 from hinge-line and curved to valve floor to enclose sockets ; in adults ridges extend from socket plates to enclose oval dendritic adductor scars separated by slight median ridge; shell substance sparsely pseudopunctate. MEASUREMENTS (in mm.) : length width HOLOTYPE. Brachial valve (.2054) c. 30-0 0.42-0 Incomplete brachial valve (66.52746) c. n-8 c. 15-4 Complete brachial valve (66.52747) 30-6 42-0 Incomplete brachial valve (66.52748) c. 30-8 c. 40-0 Crushed, incomplete shell (66.52750) c. 50-0 c. 59-0 SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH 43 TYPE LOCALITY AND HORIZON: Holotype in the University Museum, Oxford; No. 2054 collected by Phillips from the " Base of the upper Irish limestone " at Florence Court, about 12 miles S.E. of Derrygonnelly, Co. Fermanagh. Other specimens from the argillaceous limestones and shales of Bunnahone and Carrick Loughs, 2 miles N.W. of Derrygonnelly, Co. Fermanagh, or from underlying shale | mile upstream from Milltown Bridge, I mile N.W. of Church Hill, Co. Fermanagh. Low D. zone. DISCUSSION. Although Thomas (1910 : 126) recorded the type material of Spin/era radialis Phillips as having been lost, the specimen figured by Phillips (1836, pi. n, fig. 5) is actually preserved in the University Museum, Oxford, No. .2054 and another specimen, No. E.2055, is possibly the second mentioned by Phillips on p. 220 as coming from Cumberland, but it is not as well preserved as the type specimen from Florence Court, Co. Fermanagh. Phillips described the Flor- ence Court locality as being at the " Base of the Upper Irish limestone ", which is the lateral equivalent of the " reefal " limestones about 12 miles N.W., near Derry- gonnelly, from below which the present material was collected. The lithology and fauna associated with the type specimen closely resembles the more shaly beds underlying the limestone horizon at Bunnahone from which the silicified fauna was collected. The type specimen itself shows only part of the dorsal exterior (PI. 6, fig. 24), but in all known details it is closely comparable with the schellwienellas recovered from Bunnahone and for these reasons the horizons are considered com- parable and the forms conspecific. Thomas (1910 : 126) referred Spin/era radialis, " as ascribed by some British authors " to Schuchertella, a view followed by Demanet (1934 : 87) and Sarycheva & Sokolskaja (1952 : 43). One of Davidson's figures, (1861, pi. 25, fig. 17) however, clearly shows schellwienellid dental plates in an illustration of Streptorhynchus crenistria, var. radialis from Gare, Lanarkshire, and it is probable that all three figures, viz. 16, 17 and 18, are of Schellwienella radialis. Short, but well developed dental plates are clearly visible in the Fermanagh specimens . (Text-figs. 27-30, PI. 6, fig. 17) The differentiation between costae and intercalated costellae is clear in shells longer than 5 mm. The ribs are adorned by short dart-like projections, usually arranged alternately, one on either side of the rib crest, with a modal frequency of 3 per mm. between 4 and 5 mm. from the umbo. There is no clear correspondence between these serrations and the growth-lines, but the latter do project forward in crossing each rib, showing that growth was more rapid in this region (PL 6, fig. 19). In order to have maintained a more or less equally developed anterior margin, without greatly extended ribs, the mantle must have retracted more strongly at the rib crests than between them where shell deposition would have continued more evenly. This retraction of the mantle probably resulted in the formation of the spinose serration. The ornament contrasts with the undifferentiated ribbing arrangement of Schellwienella aspis Smyth, from Hook Head, Co. Wexford, in rocks of K, Z and C age. Smyth (1930 : 555), however, says that there is a tendency for 44 SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH o n o a) rt a S ^\ *"! ^^ D 13 o *; O o " 3 H 5 T3 Jii* la" ' n3 CD <* 53 Si3^ CN p< .g .3 A "3 8 o g w rt 43 ^ f ^'. 8 '.2 I SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH 45 the costae of specimens from the strata of C age to be stronger and for "... every fourth one to be emphasized ". Thus, it is possible that the ornamentation became more differentiated through strata of C and S age to that seen on S. radialis in Upper S and D strata. The chilidium is well formed and in a brachial valve n mm. long was 2-7 mm. wide and 0-3 mm. long (Text-fig. 32) arching over the posterior face of the cardinal process in a postero-dorsal direction. A rudimentary chilidium can be distinguished 1mm 35 FIGS. 31-35. Illustrations of Schellwienella radialis (Phillips) showing the morphology of the external radial ornamentation, (Fig. 31); the chilidium of young and adult specimens (Fig. 32); a lateral view of an adult shell and the rotation of the juvenile portion of the shell (stippled) relative to the hinge line (Fig. 33); and the cardinalia, viewed dorsally, in young (Fig. 34) and adult (Fig. 35) specimens, i, costae; 2, first order costellae; 3, second order costellae; a.r, ridge surrounding the adductor scars; ch, chilidium; m.r, median ridge; s.p, socket plate. 46 SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH in valves only 2-5 mm. wide, as bulbous projections postero-laterally of the cardinal process lobes, similar to those seen in Brochocarina wexfordensis. During growth the distal edge of the chilidium became directed posteriorly and finally ventrally. This resulted not so much from a differential growth of the chilidium itself but by the progressive rotation of the dorsal hinge-line resulting from increasing valve con- vexity (Text-fig. 33), and the considerable thickness of secondary shell at the an- terior margins of gerontic valves. This angle of rotation may exceed 90 and in a specimen 52 mm. long approaches 110. The cardinalia is typically davidsoniacean in young shells (Text-fig. 34) but became considerably thickened in old age. In adult shells the anterior face of the cardinal process became thickened so as to extend beyond the youthful socket plates, leaving a distinct groove between the two. The socket plates extend antero-laterally from the hinge-line at about 45 to 55 enclosing the sockets medianly. Although the bases of the socket plates curve to the valve floor to bound the sockets antero-dorsally, they do not recurve towards the hinge-line as in Orthotetinae. In shells more than about 40 mm. wide shell deposition formed ridges which extended from the socket plates around the adductor field. Postero-laterally within each adductor scar is an oval area, about one-third as long as the complete scar, which has a differentiated ornamentation and may have been the scars of posterior adductor muscles (PL 6, fig. 22). In comparing the socket plates of different davidsoniacean subfamilies it must be recognized that while those of the Meekellinae are described as prolonged, as are those of the Streptorhynchinae and Derbyiinae, they do curve to the valve floor in a manner similar to the Schuchertellinae. However, the socket plates of the Schuchertellinae diverge from the hinge-line at a narrower angle than do those of the Meekellinae, while in the Orthotetinae they recurve towards the hinge-line with little anterior fusion to the valve floor. Superfamily GHONETACEA Bronn 1862 The chonetacids are not considered to be a separate suborder, but to be sufficiently closely related to the Productacea to belong to the suborder Productidina. Muir- Wood (1962) discussed the classification of the chonetacids and followed her earlier works of 1955, and with Cooper 1960, by separating them from the Productacea in the belief that productaceans never had a functional pedicle. This has been shown to be incorrect (Brunton 1965) and at least some genera of both groups had functional pedicles during their earliest stages of ontogeny. A pedicle sheath was previously unrecorded from chonetacids above the Devonian but is now described in Fermanagh rugosochonetids and globosochonetids of Visean age. It seems probable that Sarycheva & Sokolskaja (1959) are correct in uniting the Chonetacea and Productacea and their revertion to the previously held view that the Productacea were derived from the Chonetacea warrants careful consideration. The two groups are united by a comparable gross morphology, pseudopunctation and spine development and also by a similar phylogenetic trend to gigantism in the Lower Carboniferous. This may indicate a response to certain conditions by groups of organisms having arisen from the same ancestral gene pool. Probably during the SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH 47 Devonian period the Productacea and Strophalosiacea differentiated from a choneta- cean-like stock and rapidly diversified. The plectambonitaceans possibly provided the ancestral stock from which the chonetacids arose, possibly late in the Ordovician. Some of the earliest stropho- chonetids, from Anticosti Island, Canada, are from beds commonly correlated with the Upper Llandovery or Lower Wenlock. Eochonetes advena Reed, described from the Upper Ordovician, Dnimmuck Group of Girvan, is plectambonitid in character but had hollow canals, passing from the interior towards the exterior of the posterior margin, which closely resemble the canals leading to the spines of Chonetacea. It is not known whether the canals of Eochonetes extended to the outer surface, and spines are unknown. But it is no great evolutionary step for the epithelial processes, or evanginations, already present in Eochonetes to have remained generative at their tips and to have grown posteriorly, accompanied by the de- position of shell so as to have formed spines. Rib apertures have been observed and figured from the time of Davidson's mono- graph (1861) to Muir- Wood's recent chonetoid monograph (1962) in which she follows Dunbar & Condra (1932) in assuming that they are the bases of minute hollow spines. Muir- Wood (1962, pi. 6, fig. 6) illustrates the impression of the pedicle valve of a rugosochonetid which is said to show " spinules ". However, inspection of the specimen (66.20424) shows that fragments of shell adhere to the mould from which taleolae or endospines protrude. Besides these there are fine obliquely disposed ridges of sediment aligned along the rib impressions. These are the sedimentary infillings of the rib apertures (" spinule bases "), but neither they nor the taleolae are " spinules " protruding from the outer shell surface. A similar phenomenon has been recorded by Demanet (1934 : 52) on moulds of Schizophoria, where infillings of the punctae by iron oxides have left a minutely spinose surface. On no specimens, either from Fermanagh or those studied by Davidson (1884, pi. 20, fig. 21), have actual " spinules " been observed and it seems more likely that a rib aperture was never the base of a true spine. The formation of the apertures pro- bably took place by the sporadic inward sag of the mantle edge from the shell sur- face, and the resulting oblique hollows became sealed at their inner ends by the deposition of secondary shell. Anterior to each aperture, as growth continued, the rib regained its shape by the reversion of the mantle edge to its normal folded con- dition. The morphology of the chonetacid hinge spines has attracted attention and it is generally agreed that their formation was as described by Williams (1956 : 252). However, Muir- Wood (1962 : 5) considers that chonetid spines differ from pro- ductacid spines in that the latter were open at their distal end. Evidence in support of this inference is lacking and it seems more reasonable, since the spines of both groups were capable of growth, that the distal ends were sealed by the generative tip of epithelium, covered by periostracum. The angle of emergence of the spines from the hinge-line varied during the growth of the shell and they commonly curved so that the distal part of the spine was at a different angle from that at which it arose from the posterior margin. The early formed, more medianly placed spines, tend to have a higher angle to the hinge-line than have those towards the lateral 48 SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH extremities. A feature of spine orientation, noted on the Fermanagh shells, is that the spines commonly extended posteriorly at the time of their origin. As a result of valve curvature, and consequent rotation of the shell relative to the substratum, the spines did not all grow parallel to the adult commissural plane. Thus, on adult shells the median spines may be dorsally directed while those towards the lateral extremities are progressively more posteriorly directed. This pattern of spine growth probably assisted in the stabilization of the shells on the substratum through- out life and after the pedicle had ceased to be functional. Superfamily CHONETACEA Bronn 1862 nom transl. Shrock & Twenhofel 1953 Family CHONETIDAE Bronn 1862 Subfamily ANOPLIINAE Muir-Wood 1962 Genus GLOBOSOCHONETES nov. DIAGNOSIS. Small, strongly concavo-convex Anopliinae with strong ribbing and pair of ventrally serrated, anteriorly divergent septa in brachial valve. DESCRIPTION. Shell small, outline semi-elliptical with rounded prominent umbo, hinge-line widest part of shell; profile highly concavo-convex, medianly arched, adult shells with four pairs of spines at high angle to hinge; young furnished with pedicle sheath; multicostellate, commonly comprising sixteen costae branching dichotomously or with rarely intercalated costellae, ribs rounded and more pro- minent on pedicle valve ; ventral interarea orthocline, narrow with open delthyrium and indistinct arched apical pseudodeltidium, dorsal interarea rarely developed; teeth short and poorly differentiated from ventral interarea; median septum high, posteriorly confined but commonly extended anteriorly as low ridge for about one- third valve length; radially arranged tubercles correspond to external intercostal spaces ; cardinal process undifferentiated internally, externally with V-shaped myo- phore laterally supported by elongate, low socket ridges, almost parallel to hinge- line; short lateral septa variable developed; pair of high septa cross dorsal visceral disc almost to anterior margin, at about 12 from mid-line ; adductor scars indistinct, divided by lateral septa; radially tuber culate as dorsal valve; shell pseudopunctate. TYPE SPECIES. Globosochonetes parseptus sp. n. DISCUSSION. The small size of these shells, together with their great convexity and pair of prominent plate-like accessory septa across the dorsal interior, are fea- tures common to genera included by Muir-Wood (1962) in her subfamily Anopliinae. Although these genera are all described as having smooth shells, save for growth lines, she does appear to allow for costellation in her subfamilial diagnosis by saying "shell normally smooth", (1962:32). Thus the new genus, Globosochonetes, is here included within the Anopliinae and differs from Anoplia, Anopliopsis, Chonetina, Notanoplia and Tornquistia in being strongly ribbed. The ribbing and arrangement of internal tubercles is intimate, so that while the latter are more or less scattered within smooth genera, they are radially arranged in Globosochonetes. The genus differs from Plicochonetes , of the Rugosochonetinae, with which it may have been SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH 49 confused in the past, by its poorly differentiated cardinal process, strong dorsal septa, finer ribbing and smaller size. Globosochonetes parseptus gen. et sp. n. (PI. 7, figs. 8-27, Text-figs. 36-41) DIAGNOSIS. As for genus. DESCRIPTION. Small, deeply convex shells, one-third as deep as wide, four-fifths as long as wide, with narrow body cavity; ventral umbo of young shells flattened or grooved, provided with supra-apical pedicle sheath ; costation rounded, even and prominent except on umbones, costellae commonly dichotomously branched within first 2 mm. of ventral beak; five ribs occur in i mm. width, 2 mm. antero-medianly from ventral umbo ; adult hinge-spines slightly recurved towards mid-line, increasing in size laterally, ventral median septum prominent and thickened in beak adjacent to cardinal process; adductor scars oval, posteriorly placed, flanked by anteriorly spreading diductor scars; poorly differentiated cardinal process with small alveolus bordered by median ends of socket ridges that extend about one-half valve width and enclose shallow sockets; lateral septa indistinct, at about 45 to hinge-line and separate poorly defined posterior adductor scars from anterior adductor scars; pair of high accessory septa diverge from mid-line at 10 to 15, serrated distal edges commonly exaggerated in geronitc shells; small, posteriorly placed, lobate median septum developed late in life. MEASUREMENTS (in mm.) : length width HOLOTYPE. Complete shell (66.52751) 3-1 4-1 PARATYPES. Complete pedicle valve (66.52752) 3-5 4-8 Incomplete brachial valve (66.52753) 2-7 Complete brachial valve (66.52755) 1-3 1-6 Incomplete pedicle valve with pedicle sheath. (66.52756) 3-5 Incomplete pedicle valve with pedicle sheath. (66.52757) 1-7 Incomplete brachial valve (66.52754) 3-9 Complete shell (66.55498) 3-7 4-4 6rachial valve (66.55499) c. i-g c. 2-6 Incomplete shell (66.55783) 3-1 3-6 TYPE LOCALITY. Sillees River, about 300 yds. east of 6unnahone Lough (low D zone). DISCUSSION. Two small specimens in the Davidson Collection of the 6ritish Museum (Nat. Hist.) (6.14174) from Settle, Yorkshire, which are possibly the originals for figure 18, plate 47 of Davidson (1861), are externally indistinguishable from the Fermanagh shells. 6oth have the same shape and rib counts. Although GEOL. 1 6, I. 4 50 SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH the interiors of the Davidson specimens are not known, they are thought to be con- specific with G. parseptus. The Fermanagh species is apparently similar to Chonetes minuta Goldfussi sensu de Koninck (1847 : 219, pi. 20) from the Devonian Eifel region. However, C. minuta is longer (length is given as 12 mm. by de Koninck) and the ribbing apparently more coarse, i.e. 22 ribs in all. G. parseptus is comparable in size and shape to Leptaena (Chonetes) subminima M'Coy. However, inspection of the type specimens from the Sedgwick Museum, Cambridge (.6773-6780) shows that M'Coy's species has a finer costellation, viz. about 14 ribs per one mm., i mm. antero-medianly from the ventral umbo (cf. Table 14). The poorly preserved dorsal interior shows no sign of the strong septa present in the Fermanagh species and the two are not con- specific. Neither is M'Coy's material conspecific with the specimen " from the Namurian of the river Hodder, Yorkshire ' ' (6.53889) which Muir-Wood (1962 : 62) tentatively identified as "Chonetes [IPlicochonetes] subminimus (McCoy) ". The Hodder specimen has a rib count similar to that of G. parseptus and the two could be congeneric. Tornquistia polita (M'Coy) resembles the new species in size, shape and dorsal interior but differs in being devoid of all ribbing. Muir-Wood (1962 : 6) speaks of the young of some Devonian and Silurian chonetids having been attached by a pedicle which emerged through the ventral umbo and formed a " small pedicle pipe ". The present Visean chonetids are probably the first of this age to be recorded showing the structure, here called the pedicle sheath. It was almost certainly not functional in valves 3 mm. long because the ventral beak of such valves is filled by secondary shell at the posterior end of the median septum. With a maximum diameter of only about 0-03 mm., it is unlikely that the pedicle was functional for long after the spat had settled, or that its growth con- tinued beyond the neanic stage : certainly no internal opening has yet been distin- guished in valves longer than 1-2 mm. The pedicle sheath is essentially the same structure as is seen in several genera of the productacea, and it does seem that a functional pedicle was more common in the early stages of brachiopod development than is often supposed. Unlike Muir-Wood (1962 : 6) the writer considers the ped- icle sheath to be a feature of both strophomenoids and productoids, and one which indicates the close relationship of the two groups. During growth, the rate of shell deposition appears to have been greatest on the flanks, so that the pedicle valve became highly arched medianly and in these regions occurred the greatest proliferation of the costae. In some shells this pattern of growth led to a slight flattening of the antero-median venter. Costae are absent from the first 0-5 mm. of the shell and less prominent upon the brachial valve. 2, 6, 12, i and i specimens have respectively 14, 15, 16, 17 and 18 costae. Branching most commonly occurred within the first 1-5 mm. from the pedicle beak and was usually of a dichotomous nature, especially on the pedicle valve. However, about three- fifths of the costellae of both valves were added by external, (i.e. lateral) branching or by intercalation, and any one specimen may show all these types of rib addition. Of the four pairs of hinge-spines, the last formed are the largest, and although they arose from the hinge-line at an angle of about 120, they soon curved inwards to SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH 51 become parallel or even convergent to the mid-line. As would be expected, the spines arose at regular intervals, the third and fourth at valve lengths of about 2 and 3 mm. respectively. The means (with variances) of the distances between the spines are given in Table 15. The first pair of spines were of very small diameter, like the pedicle sheath, and were soon internally sealed. The second pair remain open in valves about 1-2 mm. long, but beyond this size soon became closed by the antero-lateral growth of the interarea and teeth. The third and fourth pairs of spines commonly retain their internal connections, opening anterior of the interarea (PL 7, fig. 14). The teeth are commonly indistinctly differentiated from the interarea by a slight ridge, although in some specimens they are more distinct and diverge from the hinge-line at an angle of up to 10. The ventral median septum is distinguishable in valves 1-2 mm. long, and arose from the beak (Text-fig. 37). At this growth stage the adductor scars from a sub- rounded, rather flat area within the ventral umbo. Beyond this stage convexity was such as to reorientate the muscle field from being dorsally to anteriorly directed and within these adult shells the adductor field is divided by the septum, which, while remaining confined to the umbonal region, is extended anteriorly as a low ridge for nearly one-third the length of the valve (measured parallel to the com- missural plane). The protegulal node is well seen on brachial valves, having been protected from abrasion by the shell convexity. It is commonly 0-3 mm. in length and about one- half the width, and is represented internally by the alveolus, lying between the car- dinal process base, the socket ridges and the posterior ends of the strong accessory septa, which are 0-15 mm. apart (Text- fig. 40). The septa are highest at about mid- valve length and always have serrated distal margins, the serrations being anteriorly directed and lobate in gerontic shells (Text-fig. 41). These septa were probably supporting structures to the brachial apparatus and within these small shells may have assisted in the separation of the water currents in the brachial cavity. A short median septum can be distinguished in dorsal valves of about 2 mm. in length. It continued to grow by secondary shell accretion over the median row of tubercles so that in valves about 3 mm. long it extended nearly i mm. anteriorly of the hinge-line. The alveolus always remained free of secondary structures (PL 7, figs. 21, 26). TABLE 14 Ribs 4 5 6 7 A o 23 41 10 B 8 21 6 o TABLE 14. The number of ribs counted in a width of i mm. at i mm. (A) and 2 mm. (B) antero-medianly of the ventral umbo of Globosochonetes parseptus gen. et sp. n. SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH 1mm. 39 FIGS. 36-39. Illustrations of the ontogeny of the pedicle valve of Globosochonetes par- septus gen. et sp. n., Fig 36 is the external view of the same specimen as Fig. 37 within which muscle scars, probably adductors, are clearly developed. FIGS. 40-41. Brachial valve interiors of young and adult specimens of G. parseptus. The depression anterior to the cardinal process of the young valve is represented externally by the protegulal node. SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH TABLE 15 53 Between Between Between Between Between Valve umbo and ist ist and 2nd 2nd and 3rd 3rd and 4th outer spines length Mean (mm.) (var.) 0-28 (0-0017) 0-40 (0-00069) 0-60 (0-0065) 0-74 (0-0125) 2-66 (0-190) 2-66 (0-266) n. 30 30 27 5 30 30 TABLE 15. Statistics of the distances between hinge-spines (numbered outwards from the umbo) of Globosochonetes parseptus gen. et sp. n., together with the total distance between the outer pair of spines and the length of the valves. TABLE 16 I mm. (var.) = 2-15 (0-266) r = 0-946 w mm. (var.) = 2-61 (0-960) a (var.) = 1-315 (0-00371) TABLE 16. Statistics of length (1) and maximum width (w) of 51 pedicle valves of Globosochonetes parseptus gen. et sp. n. TABLE 17 I mm. (var.) = 2-30 (0-272) w mm. (var.) = 2-89 (0-370) r = 0-959 a (var.) = 1-171 (0-00427) I mm. (var.) = 2-30 (0-272) {fit mm. (var.) = 0-99 (0-060) r = 0-895 a (var.) = 0-469 (000169) TABLE 17. Statistics of length (1), maximum width (w) and thickness (th) of 28 shells of Globosochonetes parseptus gen. et. sp. n. TABLE 18 I mm. (var.) = 1-98 (0-216) r = 0-729 s mm. (var.) = 0-52 (0-0147) a (var.) = 0-263 (0-00088) TABLE 18. Statistics of valve length (1) and the distance between the anterior ends of the accessory septa (s) of 39 brachial valves of Globosochonetes parseptus gen. sp. n. Subfamily RUGOSOCHONETINAE Muir-Wood 1962 Genus RUGOSOCHONETES Sokolskaja 1950 TYPE SPECIES. Orthis hardrensis Phillips 1841, pars, by original designation of Sokolskaja (1950 : 23). DISCUSSION. Diagnosis of the genus depends upon an understanding of R. hardensis. The species was discussed by Muir-Wood (1962) who selected a lectotype 54 SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH from amongst the Phillips specimens from Hardraw, Wensleydale, now at the University Museum, Oxford, (.1571). Neither this specimen nor the remaining Hardraw specimens at Oxford are particularly well preserved, being moulds or somewhat crushed specimens in shale. The lectotype, and two other specimens (E.I577, 1578), show distinct lobate areas on either side of the mid-line presumably accentuated by sediment compaction and slight crushing of the shell. These areas exactly match elevated regions seen on the dorsal interior of a specimen from Ray Gill, near Hawes, Wensleydale (Geol. Surv. Mus. 95131), which are assumed to mark the regions enclosed by the spirolophe. Further collecting is required to ascertain whether this dorsal morphology is a consistent and specific feature. The similarly sized specimens .1569 (Univ. Mus. Oxford) and 66.41147 (British Museum (Nat. Hist.)), figured by Muir-Wood (1962), show dorsal interiors without distinguishable brachial areas and such specimens may prove to be distinctive. In comparing the Fermanagh rugosochonetids with the types of R. celticus it became apparent that the specimens assigned by Muir-Wood to this species belong to three distinct groups. The holotype (36.41145) from Flintshire, North Wales, (PL 7, figs. 28-31) together with other specimens from Flintshire and elsewhere in Britain are distinguishable by their clear and fine ribs. Five, 25 and 8 specimens have respectively 4, 5 and 6 ribs per mm. at 4 mm. from the ventral umbo. Muir- Wood (1962 : 69) mentions a coarsely ribbed variant and these valves were figured as being conspecific. Three, 10 and 4 specimens have respectively 2, 3 and 4 ribs per mm. at 4 mm. from the ventral umbo (e.g. 6.53892 and 68475 in Brit. Mus. (Nat. Hist.) (PL 8, figs. 2-5), and although they have been found at the same loca- lities as the fine ribbed R. celticus s.s., appear to have other distinctive features. The coarse ribbed shells have more prominent rib apertures and a relatively longer ventral median septum than have the finely ribbed group, and the ventral adductor scars are distinctive in being slightly raised above the floor of the valve. The R. celticus picture is further complicated by specimens from Northumberland and Fifeshire which are poorly ribbed (e.g. 6.42046, 66.41100-01 and 6.53929-34) (PL 8, figs. 6-9). While the rib frequency is consistent with R. celticus s.s., the rib- bing is absent postero-laterally, near the posterior margin, and commonly replaced anteriorly, after a valve length of 7-9 mm., by irregular but prominent " growth- lines ". This anterior region is commonly infested by boring organisms and it may be that an ecological factor effected the growth of these shells. They further differ by their slightly greater width, relative to length; flatter umbo and smoother ventral diductor scars than in R. celticus s.s. Owing to the poorly developed ribbing, the internal valve margins are not strongly crenulated. The distinctions between R. celticus and R. hardrensis are slight. Muir-Wood (1962 : 70) says that the former is larger, more convex in profile, has spines extending from the hinge at a lower angle, and " has slight internal differences " from R. hardrensis. The few complete shells assigned to R. hardrensis from the Hardraw or Gayle shales of Wensleydale that are available for study (Geol. Surv. Mus. 93151- 93152; 8rit. Mus. (Nat. Hist.) 6.80965-80966, and 66.52661-52666) are almost indistinguishable from the holotype of R. celticus. One Wensleydale specimen in the Geological Survey Museum (93152) is 0-5 mm. longer and wider than the holotype SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH 55 of R. cdticm and differs in shape by being almost 20 % thicker! The rib frequency is 25 in 5 mm. at 5 mm. from the ventral umbo in both specimens. The difficulty in comparison lies in the poor preservation of the R. hardrensis lectotype and in deciding if this specimen is conspecific with the R. celticus-tike Wensleydale speci- mens. If this were so R. celticus would be a junior synonym of R. hardrensis. However, until a large localised collection can be studied to enable valid comparisons to be made, the two species must remain. Within R. celticus Muir-Wood distinction should be drawn between the finely ribbed holotype group; the coarsely ribbed group and those with poorly developed ribbing. These groups may well warrant at least subspecific designation. Rugosochonetes silleesi sp.n. (PI. 8, figs. 10-27; Text-figs. 42-50) DIAGNOSIS. Rugosochonetes with strongly convex pedicle valve and prominent umbo; multicostellate with 6 ribs per mm., 4 mm. from dorsal umbo, rib apertures present. DESCRIPTION. Outline semielliptical with length about two-thirds maximum width, hinge-line straight; shell unequiconcavo-convex with rounded ventral umbo extending beyond hinge-line, thickness approximately one-third hinge width; hinge spines extend posteriorly at about 30 to median plane, seven pairs on adult valves; multicostellate, ribs rounded, as wide as interspaces; about twenty-five costae, costellae commonly added by intercalation on brachial valve and by dicho- tomy on pedicle valve ; about six ribs per i mm. width, 4 mm. antero-medianly of dorsal umbo, rib apertures sparsely developed; fine concentric growth-lines in- distinct; ventral interarea anacline to orthocline, short, delthyrium quadrate to triangular, pseudodeltidium apical, much reduced; dorsal interarea hypercline, reduced, small chilidial plates flank notothyrium ; teeth set slightly below and parallel to plane of interarea, grooved on ventral surfaces ; median septum high umbonally, thickened below delthyrial apex, in adult shells extending one-third valve length as low ridge ; ventral muscle field flabellate, adductor scars pear-shaped, diductor scars elongately triangular, bounded postero-laterally by distinct shell thickening; hinge spines commonly communicating internally through oblique canals; cardinal pro- cess bilobed, poorly differentiated, myophores dorsally directed, V-shaped and in- cised; cardinal process laterally supported by socket ridges at about 20 to hinge- line, which enclose well defined sockets anteriorly; alveolus well defined; median septum extends about one-half length of adult valve; lateral septa prominent anteriorly, disposed at 30 to mid-line, and extending for about one-third length of adult valve; dorsal muscle field indistinct, posterior and anterior adductor scars pear-shaped and oval, separated by posterior ends of lateral septa; both valves internally ornamented by anteriorly directed radial rows of tubercles corresponding to external interspaces and pseudo-punctation, valve margins internally ribbed. 56 SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH MEASUREMENTS (in mm.) : length width HOLOTYPE. Complete shell (66.52758) 9-6 12-6 PARATYPES. Complete pedicle valve (66.52759) 9-6 12-7 Incomplete pedicle valve (66.52760) 13-0 Complete brachial valve (66.52761) 9-1 14-4 Incomplete brachial valve (66.52762) 10-3 Complete brachial valve (66.52763) 2-8 3-9 Complete brachial valve (66.52764) 7-7 n-8 Complete shell (66.52766) 9-8 13-0 Complete pedicle valve (66.52765) 7-0 8-9 Incomplete pedicle valve (66.52767) 3*7 c. 4-9 Complete shell with pedicle sheath (66.52768) 1-6 2-0 Shell crushed in shale (66.52769) c. n-i c. 17-2 Shell crushed in shale (66.55784) c. n-o c. 17-2 Incomplete shell (66.52770) 4-7 TYPE LOCALITY. Sillees River, about 300 yds. east of 6unnahone Lough (low D zone) DISCUSSION. The Fermanagh material is in general accordance with several features described or illustrated by Muir-Wood for R. celticm (1962 : 68). However, the shells only rarely reach the dimensions given by her, " about 19 mm. wide, 14 mm. long, and 3 mm. thick ", in the shales below the silicified limestone horizon which yields the present sample. More important distinctions are in the proportions of size and ribbing. Selecting 38 shells of R. celticus s.s. (i.e. holotype and con- specific specimens with the fine ribbing taken from a number of localities, in the 6ritish Museum (Nat. Hist.) collections) 5, 25 and 8 specimens have respectively 4, 5 and 6 ribs per i mm. width, 4 mm. antero-medianly. This compares with 6, 20 and 3 specimens of R. silleesi having respectively 5, 6 and 7 ribs per mm. (Table 21). The thickness of the shell, compared to length, is consistently greater in R. silleesi as a result of the deeper, more prominently rounded ventral umbo ; the rela- tive shell length is also slightly greater. The shell outline underwent little change during growth other than becoming relatively wider, although the cardinal ex- tremities were usually obtuse and only rarely represented the widest part of the shell. This variability seems to have resulted from an acceleration of growth in a lateral direction during the formation of each pair of spines. The spines, which number seven pairs in adult shells, arose with fairly regular spacing along the pos- terior margin of the ventral interarea (Table 22). It is frequently impossible to distinguish the sites of the first formed spines, and for this reason measurements were always taken from the mid-line of the valve to the second pair of spines. However, when the first pair were distinguishable, measurements were made and range from 0-35 to 0-6 mm., with a modal value of 0-4 mm. The spines become stronger later- ally, the sixth pair commonly being about 0-2 mm. in diameter. Most spines are inserted obliquely to the posterior margin of the valve but almost immediately SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH 57 continued to grow posteriorly at a high angle from the posterior margin of the valve. At each stage of growth the spines were posteriorly projecting so that in the adult shell the oldest, median spines, are nearly dorsally directed, while the youngest, lateral spines, project posteriorly (Text-fig. 42). This indicates the degree of rota- tion relative to the hinge-line during growth. Most commonly the spines retained hollow connection to the valve interior throughout adulthood (PI. 8, fig. 22). The p.sh. h.sp. 1mm. 43 FIG. 42. Posterior view of a rugosochonetid shell showing the way in which rotation of the commissural plane relative to the horizontal led to a swing in the orientation of the hinge-spines from being dorsally directed, medianly, to posteriorly directed, laterally, in adult shells; y and o indicate the spine orientation relative to the hinge-line axis of the spines formed in youth and old-age respectively. FIG. 43. Illustration of a young rugosochonetid shell viewed postero-dorsally; h.sp, hinge-spine; p.n, protegulal node; p.sh, pedicle sheath projecting from the tip of the ventral umbo. The cardinal process is bilobed and a rudimentary chilidium is commonly distinguishable. lateral two or three pairs of spines have broad direct openings to the interior, antero- ventral of the hinge-line, while the median three or four pairs retain connection by obliquely disposed canals through the interarea, so as to open ventro-laterally of the teeth. In a shell 13-0 mm. wide along the hinge-line, the second and third pairs of spines have canals, 0-8 mm. long, running through the interarea at about 70 to the mid-line. The convexity of the pedicle valve is regular in the mid region, but there is flatten- ing towards the cardinal extremities to form small ears. The brachial valve is flat for the first i-o mm., around the prominent protegulal node (Text-fig. 43). SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH Beyond this length concavity of the valve is gentle and regular so as to meet the pedicle valve towards the anterior margin as a short trail. The radial ornament is equally conspicuous on both valves, although obscure for about the first i mm. of both valves. The ribs are prominent, rounded and of much the same wave-length as the interspaces, each one slightly increasing in size towards the anterior margin. Table 23 shows the range in the number of costae observed on ,c.p. 46 FIGS. 44-47. Illustrations of principal internal morphological features of chonetids; brachial valve (Fig. 44), pedicle valve (Fig. 45); a reconstruction of the postero-median segment of the sylized lophophore and body wall supported by the lateral septa (Fig. 46); and a lateral view of the lateral septa (Fig. 47), a.a, anterior adductor scar; a, ventral adductor scar; av, alveolus; b i., brachial impression; b.w, body wall; ch, chilidium; c.p, cardinal process; d, ventral diductor scar; /, stylized lophophore; l.s, lateral septum; m.c, trace of a mantle canal; m.r, median ridge; m.s, median septum; p.a, posterior adductor scar; s, socket; sp, spine; sp.o, internal spine opening; t, tooth. brachial valves. The number counted on pedicle valves is consistently comparable, and within the same range fo four. On the brachial valve costellae are most com- monly added by intercalation ; this is almost invariably so over the median region of the valve, but on the flanks sporadic dichotomy of the ribs is usual. Intercalation is rare on the pedicle valves and dichotomy is the usual method of branching (Table 24). Thus the ribbing is complimentary and ventral dichotomy is usually accom- panied by dorsal intercalation during growth. Muir-Wood (1962 : 9) wrote of the " elongate-trigonal perforations " seen on the ribs of " most chonetids ", as being SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH 59 the " base of small hollow spinules which were very fine and delicate and are rarely preserved in place ". These apertures are irregularly and sparsely distributed on the ribs of R. silleesi as anteriorly directed arches temporarily terminating the rib. Anteriorly the rib regained its normal dimensions over a distance of less than 0-5 mm. (PL 9, figs. I, 2). The same sort of structure is to be seen on the ribs of Schizophoria and Rhipidomella from the same locality. The apertures were formed 48 FIGS. 48-50. Stylized reconstructions of the musculature and inferred position of the diagrammatic lophophore in Rugosochonetes silleesi sp. n. as seen in transverse section from the anterior (Fig. 48), in longitudinal section (Fig. 49), and the brachial valve interior (Fig. 50), a.a, anterior adductor muscle; d, diductor muscle; l.s, lateral septum with its prolongation showing as a discrete position of shell between the dorsally divi- ded adductor muscles; m.s, ventral median septum; p.a, posterior adductor muscle. by the temporary retraction or sagging of the mantle edge from the inner shell sur- face of the rib so that deposition ceased to form a rib until the mantle had once again become folded. Muir-Wood has referred to the taxonomic importance of these " spinulus ". Certainly there seems to be a genetical control within brachiopods as a whole, governing the formation of these apertures ; a control which is of system- atic importance amongst Lower Palaeozoic orthaceans and enteletaceans. The ventral beak of young shells is grooved, in a similar way to that of Globoso- chonetes, but a pedicle sheath is only rarely preserved (PI. 8, fig. 26). The median 60 SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH septum was developed from the earliest stages, but only in shells longer than about 5 mm. is the median ridge developed anteriorly of the high umbonal septum. Within the dorsal valve, the lateral septa, or anderidia of Sadlick (1965 : 157) became prominent in valves more than 5 mm. long, prior to which the septa are little more than raised tuberculate regions with a posteriorly placed ridge of about 0-3 mm. In adult shells the septa developed anteriorly forming distinct prongs. From their anterior ends indistinct reniform areas, enclosed by a slight ridge or by tubercles, can be seen extending beyond the median septum for about two-thirds of the valve length (Text-fig. 44). The dorsal median septum is low and flattened, except anteriorly (PI. 8, fig. 23). This flattening did not result from restriction with- in the body cavity of the shell as the valves are well separated in this region. The lateral septa (anderidia) are thought to have given support to the posterior ends of the primary loop of the spirolophe (Text-fig. 46), which was itself partly supported by the median septum and partly from the reniform markings antero-lateral of the median septum. Such an arrangement of the brachial apparatus would have been similar to that illustrated by Williams (1956) in fig. 5 (6) for Productus s.s. Text- figs 48-50 show the inferred gross anatomy of the species. If this interpretation is correct, the prolongations of the lateral septa (anderidia) protuded anteriorly of the visceral cavity, as defined anteriorly by the inferred paths of the adductor muscles. It is envisaged that the prolongations supported the anterior body wall at the points from which the lophophore was supported. Sadlick (1965 : 158) describes the anderidia as being in the coelomic cavity and well behind the body wall, and argues TABLE 19 I mm. (var.) = 6-n (87144) I mm. (var.) = 6-n (87144) w mm. (var.) = 8-02 (15-213) fn mm. (var.) = 2-29 (2-0567) r = 0-992 r = 0-920 a (var.) = 1-321 (0-00073) a (var.) = 0-486 (o-oono tn mm. (var.) = 2-29 (2-0567) x mm. (var.) = 7-08 (12-039) r = 0-972 a (var.) = 2-419 (0-00847) TABLE 19. Statistics of length (1), maximum width (w), thickness (th) and width of hinge- line (x) of 40 shells of Rugosochonetes silleesi sp. n. TABLE 20 I mm. (var.) = 6-77 (1-422) s mm. (var.) = 3-17 (0-739) r = 0-959 a (var.) = 0-721 (0-00350) TABLE 20. Statistics of length (1) and length of the median septum (s), measured from the hinge-line, of 14 brachial valves of Rugosochonetes silleesi sp. n. SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH TABLE 21 61 No. of ribs 5 6 7 8 At 2 mm. from umbo i ii 16 2 At 4 mm. from umbo 6 20 3 O TABLE 21. Ribs counted per i mm. width at distances of 2 mm. and 4 mm. antero- medianly from the dorsal umbo of R. silleesi sp. n. TABLE 22 Distances between spines Umbo and 2nd 2nd and 3rd 3rd and 4th 4th and 5th 5th and 6th 6th and 7th Mean (mm.) 0-90 0-74 1-018 1-22 1-26 i-35 (Var.) (0-01214) (0-0182) (0-0395) (0-0157) (0-0257) N 29 28 22 15 8 2 TABLE 22. Distribution of hinge-spines. Distances measured from the mid-line to the second spine and subsequently between additional spines of R. silleesi sp. n. TABLE 23 No. of costae on dorsal valves 20-23 24-27 28-30 No. of specimens 4 18 6 TABLE 23. The number of costae counted on 28 dorsal valves of Rugosochonetes silleesi sp. n. TABLE 24 Dichotomy Median Flanks sector Both Brachial valves 19 2 2 30 Pedicle valves 30 4 TABLES 24. Scoring for the method by which costellae were added on 53 brachial valves and 34 pedicle valves of R. silleesi sp. n. 62 SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH that they could not have been used for lophophore attachment. While this is agreed, nevertheless it is considered that these ridges developed functionally as posterior supports to the lophophore and that in life the anteriorly projecting processes were probably prominent in adult shells. Having restricted the anderidia to the coelomic cavity Sadlick can hardly suggest that " long anderidia undoubtedly helped form a channel for inhalent currents " (1965 : 158). Rugosochonetes delicatus sp. n. (PL 9, figs. 3-15, Text-figs 51, 52) DIAGNOSIS. Gently concavo-convex Rugosochonetes with flattened ventral umbo, thin-shelled; finely and indistinctly multicostellate with few rib apertures; muscle scars obscurely developed. DESCRIPTION. Outline subsemicircular, about two- thirds as long as wide, greatest width at straight hinge-line with poorly defined triangular ears; profile concavo-convex, pedicle valve evenly convex, umbo flattened, not extending beyond hinge-line, thickness one-quarter to one- third length, body cavity narrow; adult shells with four pairs of hinge-spines at 30 to 40 from mid-line; multi- costellate, ribs low and rounded, umbones smooth, costellae rarely added by dicho- tomy and intercalation, commonly 7 ribs per mm. width, 2 mm. or 4 mm. antero- medianly of pedicle umbo; rib aperture sparse, growth-lines indistinct; ventral interarea apsacline to orthocline, short, delthyrium open, pseudodeltidium reduced; dorsal interarea one-third length of ventral interarea, chilidial plates small, arcuate ; teeth subparallel to interarea, slightly crenulated distally; median septum short but high, extending about i mm. across ventral umbo and separating indistinct flabellate muscle field ; first 2 pairs of spine openings deflected laterally by semiconical screens of secondary shell; cardinal process lobes more or less fused medianly, myophore V-shaped, directed postero-dorsally and fused proximally ; deep alveolus flanked by socket ridges at about 20 to hinge-line and extending about one-third its width; lateral ridges short and low posteriorly; shell substance thin, pseudopunctate. MEASUREMENTS (in mm.) : length width HOLOTYPE. Complete shell (66.52771) 6-5 8-5 PARATYPES. Complete pedicle valve (66.52772) 6-5 9-3 Incomplete pedicle valve (66.52773) 8-3 Complete damaged shell (66.52776) 3-6 c. 5-8 Complete shell (66.52774) c. 5-0 7-6 Complete pedicle valve (66.52775) 5-0 6-6 TYPE LOCALITY. Sillees River, about 300 yds east of 6unnahone Lough (Low D zone). DISCUSSION. The species is similar in estimates of relative length and thickness to R. silleesi (Tables 19, 25) with which it occurs, and the two are probably closely SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH 63 related. In other respects, however, there are persistent clear differences. Thus, R. delicatus differs from R. silleesi in having a much flatter ventral umbo which does not project beyond the hinge-line, which constitutes the greatest width of the shell. The radial ornament, although of similar frequency, is less prominent, the ribs being low and costellae added on the pedicle valve by intercalation and dichotomy rather than almost entirely by dichotomy. The rows of tubercles are uniformly delicate over the entire ventral interior, about 4 occurring per mm. on the lateral flanks, whilst in this region of R. silleesi the tubercles are about twice the size with a frequency of 2 or 3 per mm. The dorsal median septum is ill defined and perhaps never fully developed. The body cavity is smaller and the shell substance thinner. The poorly defined ribbing and its absence close to the posterior margin is similar to the ornamentation of R. hindi Muir-Wood from the H zone of Cheshire, and to the poorly ribbed specimens of R. celticus Muir-Wood typical of the low E zone of Northumberland. However, the Fermanagh specimens differ from the former species in being concavo-convex, having fewer spines per unit length of hinge-line and in having 7 or 8 ribs per mm. at 4 mm. from the umbo as compared to 5 or 6 per mm. in R. hindi. The frequency of ribbing on 5, 13 and 5 specimens attributed to R. celticus from Northumberland is 4, 5 and 6 ribs per mm respectively. 4 mm. from the umbo. This frequency is comparable to that of R. celticus s.s., but is coarser that that of the two Fermanagh species R. silleesi and R. delicatus. The brephic shell was furnished with a supra-apical pedicle sheath (PL 9, fig. 14), extending ventro-posteriorly, which arose from the tip of the pedicle beak and posterior to the shallow V-shaped groove across the young shell. During growth each pair of hinge-spines was inserted at fairly regular intervals and projected posteriorly in the commissural plane at the time of their growth. As growth proceeded the com- missural plane rotated clockwise relative to the substratum (as viewed laterally with the umbo to the left) so that adult shells have their lateral spines directed posteriorly and their median, early formed spines, project dorsally as in R. silleesi (Text-fig. 42). Like R. silleesi, the spines retain their connection to the interior, but unlike that species, the interarea is only slightly thickened so that instead of oblique canals maintaining connection, localized deposits of secondary shell deflect the internal openings laterally to positions comparable to those of R. silleesi (Text-figs 51, 52). This deflection became less pronounced during growth so that younger spines have more direct openings to the interior. A valve 9-3 mm. wide has its first formed spines 0-5 mm. from the mid-line, but these do not open to the interior for a distance of 1-2 mm. from the mid-line; at this distance the second spines occur and these open internally 1-7 mm. from the mid-line. The slight amount of secondary shell deposition has resulted in poorly developed internal markings. The ventral muscle field has slight postero-lateral thickenings at its margin, but the median septum is rarely continued as a median ridge. Only two cardinalia are available for study and these have well developed socket ridges at about 20 to the hinge-line, extending about one-third of the hinge-width ; the lateral septa (anderidia) are clearly distinguishable, having raised prolongations anteriorly which are considered to have supported the posterior sections of the lophophore. There is no apparent indication of the development of a dorsal median septum, 6 4 SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH and it is certainly absent at a hinge width of about 8 mm. However, preservation of brachial valves is not sufficiently good to be able to say with certainty that no septum existed in old shells, especially as it is a structure which developed late in the ontogeny of Rugosochonetes. FIGS. 51-52. Illustrations of the pedicle valve interior of Rugosochonetes delicatus sp. n. (Fig. 51) and R. silleesi sp. n. (Fig. 52) showing the difference in the internal spine openings. TABLE 25 I mm. (var.) = 5-26 (1-367) w mm. (var.) = 7-63 (2-341) r = 0-980 a (var.) = 1-309 (0-00404) I mm. (var.) = 5-26 (1-367) tn mm. (var.) = 1-58 (0-315) r = 0-803 a (var.) = 0-480 (0-00481) TABLE 25. Statistics of length (1), maximum width (w) and thickness (th) of 19 pedicle valves of Rugosochonetes delicatus sp. n. TABLE 26 Ribs 6 7 8 9 at 2 mm. 4 9 3 3 at 4 mm. 4 8 7 i TABLE 26. Number of ribs counted per mm. width at 2 mm. and 4 mm. antero-medianly of the ventral umbo of R. delicatus sp. n. SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH 65 Rugosochonetes transversalis sp. n. (PI. 9, figs. 16-25) DIAGNOSIS. Wide Rugosochonetes with semi-elliptical outline, low rounded costellation; median ridges of cardinal process subparallel and narrowly separated; socket ridges prominent and divergent from hinge-line. DESCRIPTION. Outline transversely semi-elliptical, about one-half as long as wide, umbo flattened, not extending beyond hinge-line which constitutes greatest width of shell; profile concavo-convex, regular, about one-third as deep as long, body cavity narrow, commonly slightly sulcate; hinge-spines irregularly placed at high angle; multicostellate, ribs low rounded with rare apertures, costellae added by dichotomy on both valves, with about 3 ribs occurring per mm. width, 4 mm. antero-medianly from ventral umbo ; growth lines indistinct ; ventral interarea more or less orthocline, delthyrium about one-third closed by highly arched apical pseudo- deltidium; dorsal interarea orthocline to apsacline, about one-half length of ventral interarea, notothyrium with U-shaped chilidium ; teeth diverging slightly from inter- area; short high median septum separating elongate oval adductor scars, with flanking trigonal diductor scars ; median ridge may extend anteriorly from septum for 2 or 3 mm. ; two low ridges extend beyond median ridge from anterior ends of adductor scars for about two-thirds valve length (possibly traces of vascula media) ; cardinal process rather wide, median muscle ridges narrowly separated, lateral ridges divergent giving quadrified postero-dorsal surface; sockets deep, anteriorly bordered by prominent socket ridges extending about one-quarter hinge width; adult median septum partly fills alveolus, extending nearly one-half valve length, broad and low, anteriorly raised; lateral septa diverge at 25 from mid-line, and separate elongate oval anterior adductor scars from wider trigonal posterior scars ; internally radially tuberculate except postero-laterally; shell substance pseudo- punctate. MEASUREMENTS (in mm.) : length width HOLOTYPE. Complete shell (66.52778) 13-5 c. 23-0 PARATYPES. Incomplete pedicle valve (66.52779) c. n-o c. 22-0 Incomplete pedicle valve (66.52781) 5-5 Complete brachial valve (66.52783) 10-0 19-5 TYPE LOCALITY. Sillees River, about 300 yds east of 6unnahone Lough (Low D zone). DISCUSSION. The radial ribbing is almost as wide as that found within Plico- chonetes, as emended by Muir-Wood (1962 : 82), but differs in being poorly defined with low indistinct ribs. 6ranching is not common but almost invariably by dicho- tomy. Table 28 shows the distribution of costellation on pedicle valves. Growth lines are indistinct and may be impossible to distinguish on the silicified material. This poorly defined ornamentation cannot be attributed to abrasion, prior to silicifi- cation, as delicate structures, such as hinge spines and the pseudodeltidium are GEOL. 1 6, I. 5 66 SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH preserved, and the concave brachial valves would have been well protected. About one-half of the pedicle valves show sporadic concentric lamellae, probably indicating some irregular retardations of growth. Eight out of twelve shells have a slight median sulcation in their pedicle valves which dies out towards the anterior margin. This folding is even less marked on the brachial valves. Currie (1937 : 423) pointed out that a median sulcation of Chonetacea arose in the mid Carboniferous and it may be that the slight sulcation seen on several of the Fermanagh shells is an indication of this trend. In outline R. transversalis is similar to C. laguessiana de Koninck mut. 6 Hind from the Gin Mine Marine Band, N. Staffs. (Brit. Mus. (Nat. Hist.) 6.47309), but this shell is more finely ribbed, and in this respect is comparable to R. celticus s.s. It has about 8 spines in 10 mm. on either side of the umbo which contrasts with 5 or 6 spines in the same distance on the Fermanagh shells. In R. transversalis most of the spines retain internal openings, the more medianly placed spines having oblique canals leading to their openings which are lateral of the teeth. The internal surfaces of the ears, and regions immediately anterior of the interareas, are not tuberculate, but the ear regions are irregularly pitted. In old shells, the radial rows of tubercles tend to coalesce into low ridges with the tips of the tubercles still protruding from their crests. The ventral median septum terminates posteriorly in a thickened region between the bases of the teeth and below the apex of the delthyrium, but with- out the distinctly node-like callus of R. silleesi. The dorsal median septum is typical for the genus in its late development, and the lateral septa are again prominent anteriorly, protruding from the valve floor to the inferred position of the body wall. Like the ventral valve, tuberculation is confined to the mid and lateral regions, and towards the cardinal extremities the pair of slight knobs probably assisted in the articulation of this long-hinged species. Brachial ridges are not clearly distinguishable. TABLE 27 1 mm. (var.) = 10-70 (9-6943) 1 mm. (var.) = 10-70 (9-694) w mm. (var.) = 18-78 (40-640) fn mm. (var.) = 3-77 (4-257) r = 0-578 r = 0-770 a (var.) = 2-048 (0-0465) a (var.) = 0-663 (0-0298) TABLE 27. Statistics of length (1), maximum width (w) and thickness (th) of 8 shells or pedicle valves of Rugosochonetes transversalis sp. n. TABLE 28 Ribs 3 4 5 at 2 mm. o 6 5 at 4 mm. 9 3 o TABLE 28. Number of ribs counted in i mm. width at 2 and 4 mm. antero-medianly from the pedicle umbo of Rugosochonetes transversalis sp. n. SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH 67 Genus PLICOCHONETES Paeckelmann, 1930 TYPE SPECIES. Chonetes buchianus de Koninck, 1843, by original designation of Paeckelmann (1930 : 222). Plicochonetes buchianus (de Konick) (PL 9, figs. 27-32) DIAGNOSIS (emended). Strong concavo-convex Plicochonetes with narrow body cavity; prominent rounded ribs, not developed postero-laterally; small pseudo- deltidium and chilidial plates present ; dorsal median septum short and low. DESCRIPTION. Outline subsemicircular with straight hinge-line at widest part of shell, about two-thirds as long as wide; ears well developed and smooth; profile concavo-convex with narrow body cavity, shell about one-half as deep as long; radial ornament prominent and evenly developed from about 16 costae with rare additions of ribs by branching on pedicle valves and intercalation on brachial valves, about 5 ribs per 2-5 mm. at 4 mm. from ventral umbo, rib-apertures sparsely developed on both valves; growth lines finely developed; ventral interarea concave, more or less orthocline, delthyrium closed apically by small arched pseudodeltidium ; at least seven pairs of hinge spines subparallel to mid-line; dorsal interarea hyper- cline with notothyrium similarly sized to delthyrium and flanked by prominent chilidial plates; teeth suboval in outline; short high median septum extending as low ridge between elongately oval adductor scars ; diductor scars poorly impressed ; cardinal process bilobed and medianly fused, external face quadrifid with prominent median muscle boundaries separated by narrow groove; socket ridges extending about one-third hinge-line width; median septum low and broad, raised anteriorly and extending about one-quarter valve length, but continued as short ridge; lateral septa at 25 to 30 from mid-line, commonly prominent anteriorly; brachial im- pressions lobate, extending about three-fifths valve length and disc width; shell substance thin. MEASUREMENTS (in mm.) : length width Complete shell (66.52917) 7-8 12-8 Incomplete brachial valve (66.52918) 10-6 c. 16-0 Incomplete brachial valve (66.52919) 6-9 DISCUSSION. The species is rarely found in the limestones from Co. Fermanagh, but a few well preserved specimens warrant discussion. The genus was inadequately described by Paeckelmann (1930). In her description of the genus Muir-Wood (1962 : 82) makes no mention of the presence of chilidial plates. These are well developed arching the lateral flanks of the external face of the cardinal process so as partially to obscure the lateral muscle boundary ridges (PI. 9, fig. 30). The plates are barely fused medianly, but were well developed when the 68 SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH valve was 6 mm. long. The presence of a well defined apical pseudodeltidium in the present material indicates that this structure may be commoner on well preserved material than has been thought. This structure, together with the chilidial plates should be noted within a diagnosis of Plicochonetes. The correspondence between the ribbing of the brachial and pedicle valves is in- dicated by the way in which costellae are commonly added by intercalation on the brachial valve in a position opposite to a branched rib on the pedicle valve. An example of this can be seen on the shell illustrated on PL 9, figs. 29, 30. This is considered to be a common feature of ribbing, and is a necessity for a close fit of the anterior margin, but is difficult to demonstrate on more finely ribbed groups. Rib apertures are developed both on the ribs and sparsely on the smooth ears in a radial fashion. These structures are more fully discussed under Rugosochonetes. In common with other chonetaceids, the lateral septa developed at an early stage, prior to the differentiation of the median septum or clear development of the adductor scars (PI. 9, fig. 31). 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Morphology, classification and life habits of the Productoidea (Brachiopoda). Mem. geol. Soc. Amer., New York, 81 : 1-447, pis. I-I35- OEHLERT, D. P. 1890. Note sur differents groupes etablis dans le genre Orthis et en particul- ier sur Rhipidomella Oehlert ( = Rhipidomys Oehlert, olim). Jour. Conchyliologie (3) 30 : 366-374. PAECKELMANN, W. 1930. Die Fauna des deutschen Unterkarbons, Die Brachiopoden. i Teil. Abh. Preuss. geol. Landesanst, Berlin, 122 : 144-326, pis. 9-24. PARKINSON, D. 1954. Quantitative studies of Brachiopods from the Lower Carboniferous Reef Limestone of England. I Schizophoria resupinata (Martin). /. Paleont., Menasha, 28 : 367-381. PHILLIPS, J. 1836. Illustrations of the geology of Yorkshire: pt. 2, the Mountain Limestone District. 235 pp., 25 pis. London. ROWLEY, R. R. 1908. The Geology of Pike Country. Missouri Bur. Geol. Mines, 8, (2) : 1-122, pis. 1-20. RUDWICK, M. J. S. 1965. Sensory spines in the Jurassic brachiopod ^4 canthothiris. Palaeon- tology, London, 8 : 604-617, pis. 84-87. 70 SILICIFIED BRACHIOPODS FROM COUNTY FERMANAGH SADLICK, W. 1965. Andaridium, a new term for lateral septa of chonetids (Brachiopoda) . /. Paleont, Menasha, 39 : 157-159. SANDERS, J. E. 1958. Brachiopods and Pelycypods in a Mississippian Fauna in North-West Sonora, Mexico. Smithson, misc. Coll., Washington, 119, 3 : 4187, pis. 37. SARYCHEVA, T. G. & SOKOLSKAJA, A. N. 1959. The Classification of the Pseudopunctate Brachiopods (in Russian). Doklady Akad. Nauk SSSR, 125, i : 181-184. SCHUCHERT, C. & COOPER, G. A. 1932. Brachipod genera of the Suborders Orthoidea and Pentameroidea. Mem. Peabody Mus., Yale, 4 : 1-270, pis. 1-29. SCHUCHERT, C. & LE VENE, C. M. 1929. Brachiopoda (Generum et Genotyporum Index et Bibliographia) Fossilium Catalogus, 1, Animalia, 42 : 1-140 (Berlin). SMYTH, L. B. 1930. The Carboniferous Rocks of Hook Head, Co. Wexford. Proc. roy. Irish Acad., Dublin, 39, Sect. B. No. 26 i 523-566, pis. 15-20. SOKOLSKAJA, A. N. 1952. (in Sarycheva & Sokolskaja). A description of the Palaeozoic Brachiopods of the Moscow Basin (in Russian). Trans. Paleont. Inst. Moscow, 38 : 1-307 pis. 1-71. SOWERBY, J. de C. 1840-46. Mineral Conchology of Great Britain. 7 : 1-80, pis. 610-648. London. SPJELDNAES, N. 1957. The Middle Ordovician of the Oslo Region, Norway. 8, Brachiopods of the suborder Strophomenida. Norsk, geol. Tidsskr, Bergen, 37 : 1-214, pis. 1-14. THOMAS, G. A. 1958. The Permian Orthotetacea of Western Australia. Bull. Bur. Min. Res. geol., geophy., Canberra, 39 : 1-158, pis. 1-22. THOMAS, I. 1910. British Carboniferous Orthotetinae. Mem. geol. Surv. G. Brit., Palaeont. 1, 2 : 83-134, pi. 13. VEEVERS, J. J. 1959. Size and shape variation in the brachiopod Schizophoria from the Devonian of Western Australia. /. Paleont., Menasha, 33 : 888-901. WELLER, S. 1914. The Mississippian Brachiopods of the Mississippi Valley Basin. Mon. geol. Surv. III., Urbana, 1 : 1-508, pis. 1-83. WILLIAMS, A. 1956. The Calcareous Shell of the Brachiopoda and its Importance in their Classification. Biol. Rev., Cambridge, 31 : 243-287. WILLIAMS, A. et al. 1965. Treatise on Invertebrate Paleontology. (Ed. Moore, R. C.) Pt. H. Brachiopoda. 2 vols. xxxi + Hg27 pp., 746 figs. Kansas. WILLIAMS, A. & WRIGHT, A. D. 1963. The classification of the " Orthis testudinaria Dalman " group of Brachiopods. /. Paleont., Menasha, 37 : 1-32, pis. i, 2. WILLIAMS, J. S. 1943. Stratigraphy and Fauna of the Louisiana Limestone of Missouri. Prof. Pap. U.S. geol. Surv., Washington, 203 : 1-133, P^ s - I ~9- WRIGHT, A. D. 1963. The Fauna of the Portrane Limestone i . The Inarticulate Brachiopods. Bull. BY. Mus. nat. Hist. (Geol.) 8, 5 : 221-254, P^ s - I- 4- EXPLANATION OF PLATES Unless otherwise stated, all the specimens are housed in the British Museum (Nat. Hist.); were collected from the silicified limestone of Co. Fermanagh, and have been sprayed with ammonium chloride immediately prior to being photographed. PLATE I Crania quadrat a (M'Coy) FIGS, i, 2. External and internal views of broken brachial valve. 66.55599. Xi-5- FIG. 3. External view of brachial valve. 66.55601. X4-o. FIGS. 4, 5. External and internal views of brachial valve. 66.55600. X2-i. FIGS. 6, 7. Dorsal and lateral views of brachial valve. 66.55616. x6-2. FIG. 8. External view of brachial valve. 66.55602. X5-8. FIG. 9. External view of brachial valve. 66.55603. x 5-2. Acanthocrania cf. laevis (Keyes) FIG. 10. External view of brachial valve. 66.55605. X3'i. FIG. ii. External view of fragment of brachial valve. 66.55606. x 2-9. FIGS. 12-14. Lateral, dorsal and internal views of brachial valve. 66.55604. x 3-0. Philhedra trigonalis (M'Coy) FIGS. 15, 1 6. Dorsal and lateral view of brachial valve attached to a rugosochoneteid 66. 55607. x 2-0. FIGS. 17, 18. Lateral and dorsal views of brachial valve. 66.55608. X2-o. FIGS. 19-21. Lateral, internal (X2-5) and dorsal views of brachial valve. 66.55610. X2-0. FIGS. 22, 23. Internal and lateral views of brachial valve. 66.55609. x 2-0. FIGS. 24-26. Internal, dorsal and lateral views of brachial valve. 66.55611. x 2-0. FIGS. 27-29. Lateral, dorsal and internal views of brachial valve with a small portion of the pedicle valve still attached. 66.55612. X2'O, X 2-3 and x 3 -5 respectively. FIGS. 30, 31. Internal and external views of brachial valve. 66.55614. X5'2. FIGS. 32, 33. Dorsal and lateral views of brachial valve. 66.55613, x 3-0. Bull. Br. Mus. nat. Hist. (Geol.) 16, i PLATE i GEOL. 1 6, I PLATE 2 Schizophoria resupinata (Martin) FIGS. 1-3. Neotype, from Bolland (Gilbertson Colin.) viewed dorsally, ventrally and an- teriorly. BB.2420. x 0-5. FIGS. 4, 5. Part of brachial valve from the Visean of Cam Back, Yorks., viewed externally ( x 0-5) and internally ( x 0-95) . 6.56088. FIG. 6. Part of brachial valve from the Visean of Ulverstone, Lanes., showing the trilobed cardinal process and fulcral plates. 30113. Xo-95. Schizophoria resupinata dorsosinuata Demanet FIGS. 7-11. Incomplete shell viewed dorsally, ventrally, laterally, posteriorly and anteriorly. BB. 52701. xi-6. FIGS. 12, 13. Incomplete shell viewed postero-ventrally and dorsally. 66.52702. xi-6. FIG. 14. Incomplete brachial valve cardinalia. 66.52710. x 2-7. FIGS. 15, 16. Incomplete pedicle valve viewed posteriorly and dorsally. 66.52704. X2-3. FIG. 17. Cardinalia of brachial valve. 66.52705. X4 - o. FIG. 18. Ventral view of incomplete young brachial valve. 66.52712. x 3-3. FIG. 19. Ventral view of incomplete young brachial valve. 66.52706. x 6-0. FIG. 20. Incomplete brachial valve interior. 66.52922. X5-o. FIG. 21. Incomplete brachial valve interior. 66.52933. x 2-0. FIGS. 22-25. Young shell viewed posteriorly, anteriorly, dorsally and ventrally. 66.52716. x6-o. FIGS. 26, 27. Young pedicle valve interior and exterior. 66.52714. x 3-1. FIGS. 28, 29. Young brachial valve exterior and interior. 66.52708. x 6-0. FIG. 30. Juvenile brachial valve interior. 66.52707. X 6-0. FIGS. 31, 32. Juvenile pedicle valve exterior (x6>5) and interior (x8~5) 66.52713. FIGS. 33-36. Juvenile shell viewed ventrally, dorsally, anteriorly and posteriorly. 66.52717 x8- 75 . FIG. 37. Incomplete brachial valve interior. 66.52715. X 2-3. Bull. Br. Mus. nat. Hist. (Geol.) 16, i PLATE 2 GEOL. 1 6, I 6 PLATE 3 Rhipidomella michelini (L'Eveill6) FIGS. 1-3. Complete topotypic shell from Tournai, Belgium, viewed ventrally, dorsally and posteriorly. 36.55617 (reregd. from 6.18254). X i-i. FIGS. 4, 5. Brachial valve, from Tournai, Belgium, viewed antero-ventrally and ventrally. 66.55618. xi-i. FIG. 6. Pedicle valve interior, from Tournai, Belgium, 66.55619. Xi-i. FIGS. 7-10. Complete shell viewed dorsally, ventrally, laterally and posteriorly. 66.52718. X2-4. FIGS, n, 12. Incomplete pedicle valve viewed dorso-laterally and dorsally. 66.52719. X3-5- FIGS. 13, 14. Posterior portion of shell viewed internally and externally. 66.52727. X4'5- FIGS. 15-18. 6rachial valve exterior, interior (X2-87), posterior (X3-8) and lateral (X2-8) views. 66.52722. FIGS. 19, 20. Pedicle valve exterior (X2-5) and interior (X3-o) 66.52720. FIGS. 21, 22. Juvenile shell viewed dorsally and ventrally. 66.52724. x 3-8. FIG. 23. Incomplete brachial valve cardinalia. 66.52728. x 3-5. FIGS. 24, 25. Juvenile brachial valve exterior and interior. 66.52726. X4*5. Leptagonia analogia (Phillips) FIGS. 26, 27. Lectotype from the lower Carboniferous of 6olland, in the Gilbertson Colin, viewed dorsally and ventrally. 6.8936. Xi-o. FIG. 28. Incomplete pedicle valve interior, from the lower Carboniferous Redesdale limestone, Northumberland. 66.46524. x 3-0. FIGS. 29, 30. Internal mould, retaining fragments of shell, viewed anteriorly and dorsally, from the Gilbertson Colin. 66.55777. X i-o. FIG. 31. Complete shell from the Lower Carboniferous of Carrick-on-Shannon, Eire, viewed ventrally. Hunterian Museum L. 38 17/1. x i-o. Bull. Br. Mus. nat. Hist. (Geol.) 16, i PLATE 3 31 PLATE 4 Leptagonia analoga (Phillips) FIG. i. Brachial valve cardinalia from Carrick-on-Shannon. Hunterian Mus., L.3834/22. X3-o. FIG. 2. Brachial valve interior from Redesdale, Northumberland showing a mature cardina- lia and saccate pallial sinuses. 6.43708. Xi -i. FIG. 3. Incomplete silicified brachial valve exterior. 66.52921. X3'4. FIGS. 4, 5. Juvenile shell viewed dorsally (x 5-0) and ventrally (x 3-4). 66.52729. FIGS. 6, 7. Juvenile brachial valve interior and exterior. 66.52730. x 5-0. FIGS. 8, 9. Incomplete brachial valve from the Lower Carboniferous of Co. Sligo viewed posteriorly (Xi'3) and ventrally (xo-g). 66.52731. Derbyoides nebrascensis Dunbar & Condra FIGS. 10-12. Topotypic incomplete pedicle valve from the Upper Carboniferous near Nehawka, Nebraska, viewed externally, anterodorsally and dorsally. 66.55491. x i-o. FIGS. 13, 14. Topotypic incomplete brachial valve exterior and interior. 66.55490. X i -o. Tapajotia tapojotensis (Derby) FIGS. 15, 16. Topotypic incomplete pedicle valve from the Upper Carboniferous of Rio Tapajos, 6razil, viewed dorsally and anterodorsally. 66.55493. x i-o. FIGS. 17-19. Topotypic young pedicle valve viewed antero-dorsally, dorsally and ventrally. 66.55496. X2-i. FIGS. 20, 21. Topotypic incomplete brachial valve viewed posteriorly and ventrally. 66.55494. xi-5. FIGS. 22, 23. Topotypic young brachial valve exterior and interior. 66.55495. X2-I. Brochocarina wexfordensis (Smyth) FIG. 24. Paratype. Incomplete pedicle valve interior from Hook Head, Co. Wexford. Trinity College Dublin Colin. Xo-75. FIGS. 25, 26. Holotype. 6rachial valve viewed posteriorly (Xi'3) and externally (xo-7). Trinity College Dublin Colin. Bull. Br, Mus. nat. Hist. (Geol.) 16, i PLATE 4 26 PLATE 5 Brochocarina wexfordensis (Smyth) FIGS. I, 2. Incomplete pedicle valve exterior and interior. 66.55779. x i-o. FIGS. 3, 4. Pedicle valve exterior and interior. 66.55598. Xo75. FIG. 5. Incomplete pedicle valve interior. 66.55778. X i-o. FIG. 6. Incomplete shell viewed postero-dorsally. 66.55597. x 1-5. FIG. 7. Incomplete pedicle valve interior. 66.52733. x 1-7. FIG. 8. Juvenile pedicle valve interior. 66.52734. X 2-7. FIGS. 9, 10. Juvenile brachial valve exterior and interior. 66.55596. x 2-0. FIGS. 11-13. Incomplete pedicle valve exterior (xo-8) detail of external ornamentation (X3-o) and interior (xo-8). 66.52732. FIGS. 16, 17. Adult cardinalia viewed ventrally and posteriorly. 66.55595. X3-o. FIG. 18. Partially crushed shell from 6undoran, Co. Donegal, showing posterior view of cardinal process and chilidium. 66.52738. x 1-8 (not silicified). FIG. 19. Incomplete shell from Poll More, near 6oho, Co. Fermanagh, showing the ventral interarea. 66.52737. x 1-6 (not silicified). FIGS. 20, 21. Juvenile brachial valve interior and exteroir. 66.55594. X4-o. FIGS. 22, 23. Juvenile brachial valve interior and exterior. 66.55593. X3 - o. Bull. BY. Mus. nat. Hist. (Geol.) 16, i PLATE 5 18 PLATE 6 Serratocrista fist ulosa sp. n. FIGS. 1-3. Holotype. Complete shell viewed dorsally and ventrally (xi-8) and detail of external ornamentation (x6-o). BB. 52739. FIG. 4. Pedicle valve interior. 66.52741. Xi-6. FIG. 5. Incomplete brachial valve interior. 66.52743. xi-7- FIG. 6. Young brachial valve interior. 66.52740. x 1-8. FIG. 7. Juvenile pedicle valve exterior. 66.52744. x 4-4. FIG. 8. Incomplete pedicle valve interior. 66.52742. x 1-7. FIGS. 9, 10. Incomplete brachial valve exterior and interior. 66.55488. x 2-2. FIGS, ii, 12. Fragment of pedicle valve viewed laterally and dorsally. 66.55489. X2-2. Schellwienella radialis (Phillips) FIGS. 13-16. 6rachial valve viewed externally, internally and laterally (x 1-3) and detail of the external ornamentation (X2-3). 66.52747. FIG. 17. Incomplete pedicle valve viewed antero-dorsally. 66.52745. x 3-2. FIG. 1 8. Juvenile brachial valve interior. 66.52746. x 2-6. FIG. 19. Detail of external ornamentation on a crushed, unsilicified specimen from 6ohenvy, about i miles north of the Sillees R. locality. 66.52750. X2-4. FIG. 20, 21. 6rachial valve viewed posteriorly and ventrally. 66.52748. x 1-6. FIGS. 22, 23. 6rachial valve cardinalia from 6ohenvy, internally (xi-i) and externally (Xi'7). 66.52749 (unsilicified). FIG. 24. Holotype. 6rachial valve exterior, collected from Florence Court, Co. Fermanagh. The University Museum, Oxford. .2054. x i-o. Bull. Br. Mus. nat. Hist. (Geol.) 16, i PLATE 6 21 PLATE 7 Orthotetinid gen. et. sp. indet. FIGS. I, 2. Juvenile incomplete brachial valve exterior and interior. 66.55782. x 1-9. FIGS. 3, 4. Incomplete brachial valve exterior and internal view of cardinalia. 63.55780. Xi-o. FIGS. 5-7. Dorsal cardinalia viewed dorsally, ventrally and posteriorly showing the com- plete chilidium. 66.55781. + 1-0. Globosochonetes parseptus sp. n. FIGS. 8-1 1 . Complete shell viewed dorsally, ventrally, posteriorly and anteriorly. 66.55498. X5'7- FIGS. 12-14. Complete pedicle valve viewed externally, dorsally and antero-dorsally to show the short median septum. 66.52752. x 7-5. FIGS. 15-18. Holotype. Complete, disarticulated shell viewed posteriorly, dorsally, ven- trally and laterally. 66.52751. X7'5- FIGS. 19, 20. Incomplete shell viewed ventrally and dorsally. 66.55783. x 6-4. FIG. 21. Incomplete adult brachial valve interior showing short median septum. 66.52754. X7'7- FIG. 22. Incomplete brachial valve interior. 66.52753. x 7-5. FIG. 23. Juvenile pedicle valve viewed posteriorly to show pedicle sheath. 66.52757. Xio-i. FIG. 24. Young pedicle valve viewed posteriorly to show pedicle sheath. 66.52756,. X7-5- FIG. 25. Juvenile brachial valve interior. 66.52755. xii-5- FIGS. 26, 27. Young brachial valve with damaged accessory septum, interior and exterior. B6.55499. X55. Rugosochonetes celticus Muir-Wood FIGS. 28, 30. Holotype. Complete shell from the Visean of Flint, N. Wales, viewed ventrally, anteriorly, posteriorly and dorsally. 66.41145. X2-o. Bull. Br. Mus. nat. Hist. (Geol.) 16, i PLATE 7 PLATE 8 Rugosochonetes celticus Muir-Wood FIG. i. Complete shell viewed ventrally, identical to holotype and collected from the Lower Carboniferous of Cam Beck, Yorkshire. 3.48887. x 2-0. FIGS. 2, 3. Complete pedicle valve exterior and interior, also from Cam Beck, but of the coarsely ribbed group. 6.48894. X2-o. FIGS. 4, 5. Pedicle valve interior and exterior of coarsely ribbed specimen from the Visean of Beith, Ayrshire. 8.53892. x 2-0. FIGS. 6, 7. Dorsal and ventral views of poorly ribbed specimen from the Visean of Ancroft, Northumberland. 66.42045. X2-o. FIGS. 8, 9. Ventral and dorsal view of similar specimen from Aycroft. 66.42046. X 2-0. Rugosochonetes silleesi sp. n. FIGS. 10-13. Holotype. Complete shell viewed dorsally, ventrally, posteriorly and laterally. 66.52758. xi-7. FIGS. 14, 15. Complete brachial valve exterior and interior. 66.52761. X2-4. FIG. 1 6. Incomplete brachial valve interior. 66.52762. X2-9. FIGS. 17, 1 8. Pedicle valve viewed antero-dorsally and dorsally. 66.52759. X2'7. FIG. 19. Incomplete shell viewed dorsally. 66.52770. X5-o. FIG. 20. Juvenile brachial valve interior. 66.52763. x 7-5. FIG. 21. Young pedicle valve interior. 66.52765. X3'O. FIG. 22. Pedicle valve interior viewed anteriorly. 66.52760. x 2-7. FIGS. 23, 24. Incomplete brachial valve viewed postero-ventrally and postero-dorsally. 66.52764. X3-0. FIG. 25. Shell viewed postero-dorsally. 66.52766. X 2-7. FIG. 26. Juvenile pedicle valve exterior showing pedicle sheath. 66.52768. x 7-5. FIG. 27. Young pedicle valve interior. 66.52767. X4-I. Bull. Br. Mus. nat. Hist. (Geol.) 16, i PLATE 8 PLATE 9 Rugosochonetes silleesi sp. n. FIGS. 1,2. Two unsilicified slightly crushed shells from the shale below the silicified limestone at the Sillees river to show shell ornamentation. 63.52769. (x^'75), 66.55784 (X2-4) respectively. Rugosochonetes delicatus sp. n. FIGS. 3-5. Holotype. Incomplete shell viewed ventrally, dorsally and laterally. 66.52771. X375- \ FIGS. 6, 7. Complete shell viewed dorsally and ventrally 66.52774. x 3-8. FIGS. 8-1 o. Incomplete pedicle valve viewed ventrally, anteriorly and posteriorly. 66.52773. X3-75. Fig. ii. Pedicle valve exterior. 66.52775. X3-75. Figs. 12, 13. Pedicle valve viewed antero-dorsally and dorsally. 66.52772. X3-7- Fig. 14. Crushed juvenile shell with pedicle sheath, viewed ventrally. 66.52776. X3-75- Fig. 15. Incomplete brachial valve interior. 66.52777. x 5.0. Rugosochonetes transversalis sp. n. Fig. 16. Fragment of brachial valve interior. 66.52784. x 2.7. Figs. 17, 18. Incomplete pedicle valve viewed anteriorly and dorsally. 66.52779. x 1.7. Figs. 19-22. Holotype. Incomplete shell viewed posteriorly dorsally, ventrally and later- ally. 66.52778. Xi. 6. FIG. 23. 6rachial valve interior. 66.52783. Xi-7. FIGS. 24, 25. Dorsal cardinalia viewed ventrally and posteriorly. 66.52785. X2.75. FIG. 26. Incomplete young pedicle valve interior. 66.52781. X2.75. Plicochonetes buchianus (de Koninck) FIGS. 27-30. Shell viewed ventrally, laterally, postero-ventrally and dorsally. 66.52917. X2.4. FIG. 31. Incomplete juvenile brachial valve interior. 66.52919. X2.4. FIG. 32. Incomplete valve interior. 66.52918. X2-4- Bull. Br. Mus. nat Hist, (Geol.) 16, i ^^^ill 32 PRINTED IN GREAT BRITAIN BY ADLARD & SON LIMITED BARTHOLOMEW PRESS, DORKING S-H. A REVISION OF THE FORAMINIFE GENUS AUSTROTRILLINA PARR cN 2 C. G. ADAMS BULLETIN OF THE BRITISH MUSEUM (NATURAL HISTORY) GEOLOGY Vol. 16 No. 2 LONDON: 1968 A REVISION OF THE FORAMINIFERAL GENUS [ - S FEB AUSTROTRILLINA PARR BY C. G. ADAMS British Museum (Natural History Pp. 71-97; 6 Plates; 3 Text-figures BULLETIN OF THE BRITISH MUSEUM (NATURAL HISTORY) GEOLOGY Vol. 16 No. 2 LONDON: 1968 THE BULLETIN OF THE BRITISH MUSEUM (NATURAL HISTORY), instituted in 1949, is issued in five series corresponding to the Departments of the Museum, and an Historical series. Parts will appear at irregular intervals as they become ready. Volumes will contain about three or four hundred pages, and will not necessarily be completed within one calendar year. In 1965 a separate supplementary series of longer Papers was instituted, numbered serially for each Department. This paper is Vol. 16, No. 2 of the Geological (Palaeontological) series. The abbreviated titles of periodicals cited follow those of the World List of Scientific Periodicals. World List abbreviation Bull. Br. Mus. nat. Hist. (Geol.). Trustees of the British Museum (Natural History) 1968 TRUSTEES OF THE BRITISH MUSEUM (NATURAL HISTORY) Issued 6 February, 1968 Price i I2s. A REVISION OF THE FORAMINIFERAL GENUS AUSTROTRILLINA PARR By C. G. ADAMS MS accepted May i2th 1967 ABSTRACT The known species of Austrotrillina are redescribed and compared, and their geographical and stratigraphical distributions are discussed. It is concluded that the evolutionary changes observed in the wall structure are of value in stratigraphy. One new species, A . asmariensis, is erected. CONTENTS I. INTRODUCTION ......... 73 II. STRATIGRAPHICAL NOTES ....... 75 III. SYSTEMATIC PALAEONTOLOGY ...... 80 (a) Shell structure ....... 80 (b) Description of species ...... 82 (c) Outstanding problems ...... 93 IV. CONCLUSIONS ......... 93 V. REFERENCES ......... 95 I. INTRODUCTION Austrotrillina has long been recognized as an important mid-Tertiary index fossil in the Tethyan and Indo-Pacific regions. It is unknown from the Americas. Un- fortunately, the four species so far described, A. howchini (Schlumberger) , A. paucialveolata Grimsdale, A . brunni Marie, and A . striata Todd & Post, have never been adequately compared, their diagnostic characters have hitherto been uncertain and the stratigraphical value of the individual species has therefore been obscured. The purpose of this paper is to redescribe these species, to establish the facts about their geographical and stratigraphical distributions as accurately as possible, and to indicate the probable evolutionary history of the genus. Since Austrotrillina occurs in both the Tethyan and Indo-Pacific provinces, it is necessary to refer here to two schemes of classification for the Tertiary (Text-fig, i). Justification for the correlation between part of the East Indian letter stages (Tc-Te) and the European stages may be found in a recent paper (Adams 1965). It is thought wise to retain the two systems until a generally acceptable correlation becomes possible. GEOL. 1 6, 2 7 74 A REVISION OF AUSTROTRILLIN A o /> - Approximate Ifl 0) c U > c c o rrelat ion u "I O O _C wi th Q. O ,j n <-* CO ^ o o 2 u ro pean o a w) JE - r^ < < < < c < stages Ag e Age Q} Upper i z Tf "^ U () u O p (Tf 3 ) ^^ y Lower CO Tf Burd igalian i i ' "1 "i S s 5 ^ E 'S i-i T3 ^ en ^>,^> L^ "o ^a _^ . . CU CD rO "^ 13 rf O s. f Q t>-v ^ "-"} o3 Cy -^ ^ ^ H u~> o tfl '35 o o p .S H PH CO M I M 1 O M c a o d 7.' | 1 I "o bo. !l rms only, significant di A. paucialve r*-. js -*-> 8 s en cu "SL b '35 restricted t( few cham u a *p bo cu 3. I ~. CD a o o o , TJ d Ld of Austrotrillina A srs, not included as A howchini CD ->H It^3 ^3" ^ en g pj >3 cu A 3 cu lllll I/I birf urcating ; of te: very complex throughout test thick: 70-290^ often 200 ^ or more at chambe angles 00 much reduced en ,Q .CD g p CD ^ pj ^H f 6 bo U^ '1 | r^ VH p o o .^ <4H PH O E o k ^ | rx. IH i <^. >rH *^H X* O bo ej P S 4_J -. ^.S Q '35 o JS Js P 1 CJ o 32 v <2 -~ cu 1 .2 >> en 'i o Li r3 13 CD o .2 M ""^ ^ s? W "*"^ oo 1 i O o 2 OH -M" en CD A. asmarie't i a ^o .. CD CD O 'En cl g en 4-> P O p 2 J3 =H 'C 0) 3 03 S O en CJ "" g rt^ 1*8 a H Thickness outer sk Chamber 1 A REVISION OF AUSTROTRILLINA 95 Austrotrillina appeared in the Oligocene of the Middle East, its first recorded occurrence being with Nummulites fichteli. The earliest known forms can be assigned to A. asmariensis. In the Shurau Formation of Iraq, A. asmariensis occurs alongside A. paucialveolata. The latter species does not appear to have achieved a wide geographical or stratigraphical distribution; it is based on recrystallized or otherwise badly preserved specimens and may eventually prove to be synonymous with A. asmariensis or A. striata. A. asmariensis persisted virtually unchanged from the Middle Oligocene into the Lower Miocene (Aquitanian) . In the Indo-Pacific, A. striata appeared in late Td times and persisted through Te. It is possible that these are two forms of the same species. Present evidence indicates that the transition from A. striata to A. howchini began in Upper Te times in the Indo-Pacific and that this process was complete by Tf times. In Lower Tf times (" Burdigalian " in the Tethyan region) all known representatives of the genus were of the advanced A. howchini type. This last species was widely distributed, ranging from the western Tethys to Australia. The writer believes that all the species of Austrotrillina belong to a single lineage and that, in a sense, they all belong to one species. The evolutionary changes shown by the test will allow us to delimit a number of " species " which are of value strati- graphically. These specific names should be maintained for as long as they can be shown to be of stratigraphical value. V. REFERENCES ADAMS, C. G. 1965. The Foraminifera and stratigraphy of the Melinau limestone, Sarawak and its importance in Tertiary correlation. Q. Jl. geol. Soc., London, 121 : 283-338, pis. 21- 3- 1967. Tertiary foraminifera in the Tethyan, American and Indo-Pacific Provinces. Pp. 195-217. In: Aspects of Tethyan Biogeography , Eds. C. G. Adams & D. V. Ager, Systematics Association Publication No. 7, London. 336 pp. BANNER, F. T. & BLOW, W. H. 1965. Progress in the planktonic foraminiferal biostrati- graphy of the Neogene. Nature, London, 208: 1164-1166. BELLEN, R. C. VAN 1956. The stratigraphy of the " Main Limestone " of the Kirkuk, Bai Hassan and Qarah Chauq Dagh structures in north Iraq. /. Inst. Petrol., 42, no. 393: 233-263. 8 pis. BURSCH, J. G. 1947. Mikropalaontologische Untersuchungen des Tertiars von Gross Kei (Molukken). Schweiz palaeont. Abh., 65 : 1-69, pis. 1-5. CARTER, A. N. 1964. Tertiary Foraminifera from Gippsland, Victoria, and their strati- graphical significance. Mem. geol. Surv. Viet., 23 : 1-154, I 7 P^ s - CARTER, H. J. 1853. Description of Orbitolites malabarica, illustrative of the spiral and not concentric arrangement of chambers in d'Orbigny's Order Cyclostegues. Ann. Mag. nat. Hist., London (2) 11 : 142-144, pi. nA. CHAPMAN, F. 1908. On the Tertiary limestones and foraminiferal tuffs of Malekula, New Hebrides. Proc. Linn. Soc. N.S.W., 32 : 745-760, pis. 37-41. 1913. Description of new and rare fossils obtained by deep boring in the Mallee. Part i Plantae; and Rhizopoda to Brachiopoda. Proc. R. Soc. Viet, (n.s.) 26 : 165-191, pis, 16-19. 9 6 A REVISION OF AUSTROTRILLINA COLE, W. S. 1954. Larger foraminifera and smaller diagnostic foraminifera from Bikini drill holes. Prof. Pap. U.S. geol. Surv., 260-0 : 569-608, pis. 204-222. 1957- Larger foraminifera of Saipan Island. Prof. Pap. U.S. geol. Surv., 280-1 : 321- 360, pis. 94-118. 1958. Larger foraminifera from Eniwetok Atoll drill holes. Prof. Pap. U.S. geol Surv., 260-v: 743-7 8 4. P ls - 231-249. CLOUD, P. E., SCHMIDT, R. G. & BURKE, H. W. 1956. Geology of Saipan, Mariana Islands. Prof. Pap. U.S. geol. Surv., 280A : 1-126. CRESPIN, I. 1936. The larger foraminifera of the Lower Miocene of Victoria. Palaeont. Bull., Canberra, 2 : 3-13, pis. 1,2. 1954- Stratigraphy and Micropalaeontology of the Marine Tertiary rocks between Adelaide and Aldinga, South Australia. Bull. Bur. Miner. Resour. Geol. Geophys. Aust., Rep. No. 12 : 1-65, pis. 1-7. - !955- The Cape Range structure Western Australia: pt. 2 Micropalaeontology. Bull. Bur. Miner. Resour. Geol. Geophys. Aust., 21 : 49-82, pis. 7-10. EAMES, F. E., BANNER, F. T., BLOW, W. H. & CLARK, W. J. 1962. Fundamentals of Mid- Tertiary stratigraphical correlation. London (Cambridge University Press). DAVIES, A. M. 1927. Lower Miocene Foraminifera from Pemba Island, pp. 7-12. In: Stockley G. M. (see below). Report. Palaeont. Zanzibar Protectorate. DIZER, A. 1962^. Les foraminiferes de 1'Eocene et 1'Oligocene de Denizli. Rev. Fac. Sci. Univ. Istanbul (B) 27 : 39-47, pis. 1-7. - 19626. Foraminifera of the Miocene of the Sivas Basin (Turkey). Rev. Fac. Sci. Univ. Istanbul (B) 27 : 49-85, pis. 1-9. GORDON, W. A. 1961. Foraminifera from the 4CPR oil test well near Arecibo, Puerto Rico. Publ. Puerto Rico Mining Comm., 1961 : 25-40. GRIMSDALE, T. F. 1952. Cretaceous and Tertiary foraminifera from the Middle East. Bull. Br. Mus. nat. Hist. (Geol.) 1 : 221-248, pis. 20-25. HANZAWA, S. 1957. Cenozoic foraminifera of Micronesia. Mem. geol. Soc. Am., 66 : 1-163, pis. 1-38. HOTTINGER, L. 1963. Cjuelques Foraminiferes porcelanes oligocenes dans la serie sddimentaire prebetique de Moratalla (Espagne m6ridionale) . Eclog. geol. Helv., 56 : 963-972, pis. 1-5. HOUSE, M. R., DUNHAM, K. C. & WIGGLESWORTH, J. C. 1961. Geology and structure of the Maltese islands : 25-33. In: Bowd en- Jones, Dewdney & Fisher. Malta; Background for Development, Newcastle. JONES, T. R. & CHAPMAN, F. 1900. On the foraminifera of the orbitoidal limestones of Christmas Island: 226-264, pis. 20, 21. In: Andrews, C. W. A monograph of Christmas Island (Indian Ocean). Brit. Mus. (Nat. Hist.), London. LOEBLICH, A. R. & TAPPAN, H. 1964. Sarcodina chiefly " Thecamoebians " and Foramini- ferida. Treatise on Invertebrate Palaeontology, Pt.C, Protista 2. Geol. Soc. Amer. & Univ- ersity of Kansas Press. LUDBROOK, N. H. 1961. Stratigraphy of the Murray Basin in South Australia Bull. Geol. Surv. S. Aust., 36 : 1-96. 1963. Correlation of the Tertiary rocks of South Australia. Trans. Roy. Soc. S. Aust., 87 : 5-15- 1965. Tertiary fossils from Christmas Island (Indian Ocean) Jl. geol. Soc. Australia, 12 : 285-294, pis. 21, 22. MARIE, P. 1955. Quelques formes nouvelles de Polypiers et de Foraminiferes de 1'Oligocene et du Miocene du N.W. de la Grece. II Foraminiferes. Bull. Soc. geol. Fr. (6) 5 : 193-205, pis. 18-20. PARR, W. J. 1942. New genera of foraminifera from the Tertiary of Victoria. Min. geol. Jb., 2 : 361-363. RAO, S. R. N. 1941. The Tertiary sequence near Surat and Broach (Western India) with descriptions of foraminifera of the genus Pellatispira from the Upper Eocene of this region. Half yearly Jl., Mysore University (n.s.B), 2 : 5-17, pis. i, 2. A REVISION OF AUSTROTRILLIN A 97 RENZ, O. 1936. Stratigraphische und mikropalaontologische Untersuchung der Scaglia (Obere Kreide-Tertiar) im zentralen Appenin. Eclog. geol. Helv., 29 : 1-149, pis. 1-15. SCHLUMBERGER, C. 1893. Note sur les genres Trillina et Linderina. Bull. Soc. geol. Fr. (3) 21 : 118-123, pi. 3. SILVESTRI, A. 1920. Fossili rari o nuovi in Formazione del Paleogene. Boll. Soc. geol.., Ital 39 : 57-80, pi. 4. 1929. Osservazioni so Fossili Nummulitici. Riv. ital. Paleont., 35, fasc. i-n: 1-21, pis. i-3- I937- Paleontologia delle Somalia. V. Fossili dell'Oligocene e del Miocene. 3. Fora- miniferi deH'Oligocene e del Miocene della Somalia. Palaeontogr. ital., 32, supp. 2 : 45- 264, pis. 4-22. SMOUT, A. H. & FAMES, F. E. 1958. The genus Archaias (Foraminifera) and its stratigraphical distribution. Palaeontology,!: 207-225^13.39-41. STEFANINI, G. 1921. Fossili Tertiari della Cirenaica. Palaeontogr. ital., 37 : 101-143, pis. 16-28. STOCKLEY, G. M. 1927. Stratigraphy of the Zanzibar Protectorate. 5-6 Rep. Paleont. Zanzibar Protectorate. TISSOT, M. B. & NOESMOEN, A. 1958. Les Bassins de Noumea et de Bourail, (Nouvelle Caledonie). Rev. Inst. Pet. 13: 739-760. TODD, R. & POST, R. 1954. Smaller foraminifera from Bikini drill holes. Prof. Pap. U.S. geol. Sun., 260-N : 547-568, pis. 198-203. TODD, R. & Low, D. 1960. Smaller foraminifera from Eniwetok drill holes. Prof. Pap. U.S. geol. Surv., 260-X : 799-861, pis. 255-264. VLERK, I. M. VAN DER & UMBGROVE, J. H. F. 1927. Tertiare Gidsforaminiferen van neder- landisch oost-indie. Wet. Meded. Dienst. Mijnb. Ned.-Oost Indie, 6 : 3-31. WAYLAND, E. J. & DAVIES, A. M. The Miocene of Ceylon. Quart. Jl. geol. Soc. Land., 79 : 577- 602, pis. 28-9. PLATE i Austrotrillina astnariensis sp. nov. All x 50 approximately FIG. i. B form, P3943O. Kirkuk Well 56. Henson colln. FIG. 2. A form, P^66y. Bajawan limestone, Kirkuk. Smout & Eames colln. FIG. 3. A form, 39647. Kirkuk Well 56, Henson colln. (Figs. 2, 3 = A. howchini sensu Smout & Eames 1958). FIG. 4. Off-centre, axial section, P^ujg. Sample J.T.P.4943, Kuh e Pataq, Luristan. Oligocene. FIG. 5. Holotype, P47578. Sample J.T.P.4943, Kuh e Pataq, Luristan, Oligocene. FIG. 6. Off-centre, transve rsesection, P4758o. Sample J.T.P^Sgo Kuh e Pataq, Middle Oligocene. FIG. 7. A form, P4758i. Kirkuk Well K93, core 2, 2655 ft. 3 in. Ex. I.P.C. colln. FIG. 8. A form, 47582. Gach Saran Well 6, 4132-33 ft. Asmari limestone, Iran. FIGS. 9, 10. A forms, ?47583. Kirkuk Well Ki4, 2793-2808 ft. Ex. I.P.C. colln. FIG. II. A form, P47584. Kirkuk Well Kg3, core 2, 2655 ft. 3 in. Ex. I.P.C. colln. FIG. 12. B form. P47585. Gach Saran Well 6, 4135-36 ft., Asmari limestone, Iran. Bull. BY. Mus. nat. Hist. (Geol.) 16, 2 PLATE i \2 GEOL. 1 6. 2 PLATE 2 Austrotrillina howchini (Schlumberger) All from the Pata limestone- drill hole P.Q. 2, 273-75 ft., Chowilla Dam site, South Australia. Lower Miocene (Bairnsdalian). Ex. Geol. Surv. S. Australia collections. FIGS, i, 2. P47586. (i) External view of test x 35 ; (2) portion of wall more highly magnified showing finely pitted outer surface and sub-surface reticulation. See also PL 6, fig. 7. FIG. 3. Transverse section of A form, X48, P47587. FIG. 4. Transverse section of a more inflated A form, x 50, P47588. FIGS. 5, 7. Decorticated A form, P475QO (cf. Fig. i). Most specimens of Austrotrillina are found in this condition : (5) x 35 : (7) same specimen x 50. FIG. 6. A form, P4758g. Axial section of a specimen which closely resembled fig. i externally. For B form see Plate 6. Bull. Br. Mus. nat. Hist. (Geol.) 16, 2 PLATE 3 FIG. i. Austrotrillina paucialveolata. Syntype X48, P4o68i ; Kirkuk Well No. 14, Oligocene. Probably a B form. FIG. 2. A. paucialveolata. A form, x 50, P4759I ; Kirkuk Well 14, 2828-53 ft., Oligocene. FIG. 3. A. paucialveolata. A form, x 50, P40344 ; Kirkuk Well 14, 2828-53 ft., Oligocene. FIG. 4. A form, x 50, P4o68i (syntype) : Kirkuk Well 14. FIGS. 5, 6. A. paucialveolata. A form, Oligocene of Moratalla, Spain (= A. howchini of Hottinger 1963) (5) x 55 ; (6) x 50. Deposited in the Naturhistorisch.es Museum collections, Basle. FIG. 7. A. cf. striata x 50. Lower Coralline limestone, Malta, Brt. Petrol. Co., Colin. FIG. 8. A. striata, x 50. Wall partly destroyed by recrystallization. This specimen is indistinguishable from A. paucialveolata and is only determinable as A. striata from associated individuals. Tagpochau limestone, Saipan. U.S.G.S. colln., sample No. MSB 260. FIG. 9. A. striata/ howchini x 50. Bikini drill hole 2B 2038^-48 ft. This is one of the specimens figured by Cole (1954) as A. howchini and refigured in the Treatise (1964, fig. 362-8) under the same name. It is, in fact, intermediate between A . howchini and A . striata. U.S.N.M. Colln. Bull. Br. Mus. nat. Hist. (Geol.) 16, 2 PLATE 3 PLATE 4 Austrotrillina striata Todd & Post All x 50 unless otherwise stated FIGS. 1-3. A forms ^47592, P47593) from Eniwetok drill hole E-i, 1895-925 ft. Figs, i, 2 are of the same individual. Fig. 2 shows the external appearance of the test when immersed in oil ; decorticated specimens also look like this. FIGS. 4, 7. A forms from Eniwetok drill hole E-i, 1925-55 ft. U.S.N.M. colln. (4) trans- verse section, (7) longitudinal section. Note that the alveolar structure is not visible in the early chambers. FIGS. 5, 9, 11-13. All from Eniwetok drill hole E-i, 1925-55 ft. (5) P47594, A form; (9) surface view of typical specimen showing fine striae, P^j^gj ; (n) longitudinal section through A form; P47599; (12) wall of terminal chamber viewed from inside, X56, P476oo; (13) A form, terminal chamber broken off note ' step ', P476oi. FIGS. 6, 10. A forms from Eniwetok drill hole E-i, 1996^-2007 ft., ?47595 & 47598. All ex. U.S.G.S. collection. FIG. 8. A form (P47596) from Bikini drill hole 2B, 2049-2059^ ft. Topotype. Ex U.S.G.S. colln. Bull. BY, Mus. nat. Hist. (Geol.) 16, 2 PLATE 4 PLATE 5 The figures on this plate illustrate the difficulty in determining specimens from certain Indo- Pacific (Upper Te) limestones where transitional forms between A . striata and A . howchini occur, or where the range of variation of A. striata overlaps that of A. asmariensis. FIG. i. Austrotrillina sp. X5o, P46525. Intermediate between A. striata and A. how- chini. Upper Te, Melinau limestone, Sarawak. FIG. 2. A. striata X52, P4&526. Upper Te, Melinau limestone, Sarawak. FIG. 3. A. striata X5O, P^6^22. Lower Te, Melinau limestone, Sarawak. FIG. 4. A. cf. howchini x 50, P4&524. Upper Te, Melinau limestone, Sarawak. FIGS. 5, ii. A. cf. howchini x 50, P^j6o2, P4y6o6. Primitive forms from the Tagpochau limestone, Saipan. Sample No. MSB 413. U.S.G.S. colln. FIGS. 6, 7. Austrotrillina sp. X5o. Tagpochau limestone, Saipan U.S.G.S. colln. Sample No. MSB 397, Lower Te. These specimens are not strictly determinable In some respects they resemble A. asmariensis, in others A. striata / 'howchini (6) P476O3 ; (7) P476O4- FIG. 8. Austrotrillina sp. X5O. Tagpochau limestone, Saipan, Sample No. MSB 403, U.S.G.S. colln. Intermediate between A. striata and A. howchini. FIG. 9. A. cf. striata Todd & Post, B form, x 50, P476o5. Tagpochau limestone, Saipan. Ex Sample No. 6397, U.S.G.S. colln. FIG. 10. A. cf . howchini x 50. Part of wall of a specimen from the Tagpochau limestone, Saipan. Sample No. MSB 388, U.S.G.S. colln. Bull. Br. Mus. not. Hist. (Geol.) 16, 2 PLATE 5 PLATE 6 FIG. i. Austrotrillina howchini, A form X5O. Lower Chake beds, south end of Funzi Island, Pemba Island, Tanzania. PzzS^S. FIGS. 2, 4, 5. A. howchini. All x 50. 47607 (ex. P29878). All from the Lower Miocene of the Malabar coast, Cochin, Travancore, India. Associated with Taberina malabavica (Carter) for which this is the type locality : Carter collection. FIG. 3. A. howchini. B form, x/fo, 47608. Pata limestone, Chowilla Dam site, South Australia. Lower Miocene (Lower Tf). FIGS. 6, 8. A. brunni. Re-illustration of two of Marie's types : X 35 and x 50 approx. FIG. 7. A. howchini. Stereoscan electron microscope photograph showing surface pits. The subsurface reticulation is no longer visible as the specimen is coated with a fine gold film. Same individual as PI. 2, figs, i, 2. x 750, KV 20. FIG. 9. A. striata. Stereoscan electron microscope photograph showing surface striae and pits. Bikini Well 2b, 2091-2102 feet. P476O9 x 750, KV2O. Note that the pits are smaller than in A. howchini. Bull. Br. Mus. nat. Hist. (Geol.) 16, 2 PLATE 6 PRINTED IN GREAT BRITAIN BY ADLARD & SON LIMITED BARTHOLOMEW PRESS, DORKING BRITISH NEOCOMIAN RHYNCHONELLOID BRACHIOPc E. F. OWEN and R. G. THURRELL BULLETIN OF THE BRITISH MUSEUM (NATURAL HISTORY) GEOLOGY Vol. 16 No. 3 LONDON: 1968 BRITISH NEOCOMIAN RHYNCHONELLOID L 20FEB BRACHIOPODS ^ K\ BY ELLIS FREDERIC OWEN British Museum (Natural History) and REGINALD GEORGE THURRELL Institute of Geological Sciences Pp. 99-123; 4 Plates, 8 Text-figures BULLETIN OF THE BRITISH MUSEUM (NATURAL HISTORY) GEOLOGY Vol. 16 No. 3 LONDON : 1968 THE BULLETIN OF THE BRITISH MUSEUM (NATURAL HISTORY), instituted in 1949, is issued in five series corresponding to the Departments of the Museum, and an Historical series. Parts will appear at irregular intervals as they become ready. Volumes will contain about three or four hundred pages, and will not necessarily be completed within one calendar year. In 1965 a separate supplementary series of longer papers was instituted, numbered serially for each Department. This paper is Vol. 16, No. 3 of the Geological (Palaeontological) series. The abbreviated titles of periodicals cited follow those of the World List of Scientific Periodicals. World List abbreviation Bull. Br. Mus. nat. Hist. (GeoL). Trustees of the British Museum (Natural History) 1968 TRUSTEES OF THE BRITISH MUSEUM (NATURAL HISTORY) Issued 20 February, 1968 Price i is. BRITISH NEOCOMIAN RHYNCHONELLOID BRACHIOPODS By E. F. OWEN & R. G. THURRELL CONTENTS Page I. INTRODUCTION ......... 101 II. STRATIGRAPHICAL SUMMARY ....... 102 III. SYSTEMATIC DESCRIPTIONS ....... 108 Family RHYNCHONELLIDAE ....... 108 Subfamily CYCLOTHYRIDINAE Makridin ..... 108 Lamellaerhynchia rostriformis (Roemer) . . . . 108 Lamellaerhynchia walkeri (Davidson) . . . . . 113 Lamellaerhynchia walkeri claxbyensis subsp. n. . . . 114 Lamellaerhynchia rawsoni sp. n. . . . . . . 116 Lamellaerhynchia julenia sp. n. . . . . . . 116 Lamellaerhynchia cf. picteti Burri . . . . . 117 Rhynchonella parkhillensis sp. n. . . . . . 117 Rhynchonella speetonensis Davidson . . . . . ng IV. CONCLUSIONS .......... 121 V. REFERENCES .......... 122 SYNOPSIS A short stratigraphical account is given of the Lower Cretaceous, Neocomian beds of the southern part of the Lincolnshire Wolds. The Rhynchonellidae collected from these strata and beds of similar age in the northern Wolds, and from the Speeton Clay of Yorkshire are systematically described and compared with the corresponding fauna of the Brunswick and Hanover districts of north-west Germany, and also with faunas described from Neocomian horizons in Switzerland. INTRODUCTION IT was agreed at the Colloquium on the Lower Cretaceous held at Lyon, France in 1963 (p. 832) that the term Neocomian should not be used as a stage name, but that it should, perhaps, be preserved for a group of stages. It was further agreed that the term should be limited to represent three stages in the Lower Cretaceous namely, Berriasian, Valanginian and Hauterivian, and that the Barremian should be regarded as a separate stage midway between the top of the Hauterivian and the base of the Aptian. It is difficult when dealing with older classifications and groupings of beds to be precise about the geological age. For this reason, and because the term Lower Cretaceous has a somewhat broader connotation, the term Neocomian as used in this paper sometimes includes reference to the Fulletby beds, generally regarded as of Lower Barremian age. The material on which this paper is based was collected during the course of field surveys of the Lower Cretaceous rocks of the Lincolnshire Wolds, and from the cliff section at Speeton, Yorkshire. The descriptions of the formations in the GEOL. l6, 3. IO 102 BRITISH NEOCOMIAN southern Wolds are taken from a thesis submitted and approved in 1957 for the degree of Ph.D. of London University by one of the authors (R.G.T.). Many of the species of Rhynchonellidae described here from the Speeton Clay and from the Claxby Beds of Nettleton, Lincolnshire, were collected by Dr. P. Rawson during his study of the northern Wolds for a thesis submitted and approved for the Ph.D. degree of Hull University in 1967. Brachiopods appear sporadically throughout the British Neocomian but occur most frequently in the C 6 -D 2 Beds of Swinnerton at Speeton and in the condensed sequence of the Spilsby and Claxby series southeast of Nettleton. All the forms described here are from three main sources : Beds C 6 , Dj_ 2 of Speeton Cliff, York- shire; Claxby Beds at Nettleton, Lincolnshire [110980] ; and the Roach Stone of the Fulletby Beds at Cawkwell [280880], Belchford [290750] and Dalby Park [410700], Lincolnshire. All National Grid references quoted fall within the 100 km. square TF. Although the area occupied by the outcrop of the lower Cretaceous rocks in Lincolnshire far exceeds that of the Speeton Clay in Yorkshire, they have attracted much less attention. They are generally poorly exposed and even when brick-clay, iron-ore and building stone were being dug during the last century, useful occur- rences were few and far between. Efforts to correlate the strata below the Red Chalk were at first attempted on rather tenuous geological evidence. Judd (1870) was the first to employ palaeontological methods, using the ammonites to compare the English facies with rocks at localities he had visited in Europe. A zonal standard of reference had not been established in any region at that time, but later research, mainly at Speeton, resulted in the publication of a zonal scheme based on the belemnites (Lamplugh 1889, 1924), which has remained in use until the present with only minor modifications (see Swinnerton 1936-55). Lamplugh (1896 : 191-293) showed that the Speeton subdivisions were also recognizable in the Lincolnshire Neocomian, but other workers have preferred the more precise correlations afforded by the ammonite assemblages. Spath (1924) published a comprehensive system of zones for the Lower Cretaceous. Swinnerton (1935) recorded the presence of two additional ammonite faunas in the bottom three feet of the Spilsby Sandstone at Fordington Pumping Station [416714] Lin- colnshire and added considerably to knowledge of the stratigraphy and faunas of the Neocomian of the southern Wolds. He proposed (1935, 1936) the lithological subdivisions adopted here, which embody the nomenclature originally proposed in the Geological Survey's memoir (Jukes-Browne 1887) but with further subdivi- sions inserted and the system of grouping the formations under geological headings extended. In the absence of borehole data, the thicknesses quoted in the following table have been assessed from field mapping, supported by aneroid traverses with allowances made for the effects of superficial movements, structural complications and facies changes. The most complete and lithologically variable development of the Lower Creta- ceous rocks crops out in the southern Lincolnshire Wolds between Fulletby and Spilsby. The general north-westward attenuation of the strata may be attributed to continued uplift of the Market Weighton Axis during Neocomian times with the consequent development of additional non-sequences and changes of facies towards RHYNCHONELLOID BRACHIOPODS TABLE i 103 Langton Series : Carstone Beds Tealby Series : Fulletby Beds Tealby Beds Claxby Beds Spilsby Series : Spilsby Beds Carstone Grit Carstone Sands and Clay Sutterby Marl Upper Roach Roach Stone Lower Roach Upper Tealby Clay Tealby Limestone Lower Tealby Clay Upper Claxby Ironstone Hundleby Clay Lower Claxby Ironstone Ferruginous Grit Glauconitic Sands Basement Beds Estimated thickness in feet North Willingham Belchford Dalby 33 40 70 + 34 60 35 70 Go that area. A number of interpretations of the detailed interrelations and variations of the formations in Lincolnshire have been published (e.g. Wilson 1948 : 54, Swinnerton & Kent 1949 : 73). From the present six-inch survey, the base of the Carstone Grit appears to overstep northwards all formations successively from the Sutterby Marl down to the base of the Upper Tealby Clay, as shown in Fig. i. Thinning and change of facies within the Fulletby Beds in the same direction results in the disappearance of the Roach Stone north of Scamblesby [275788]. For the same reasons, the Hundleby Clay facies diminishes north-westwards and cannot be traced farther north than Belchford. The typical lithologies of the strata from which many of the Rhynchonellidae described in this paper have been obtained are outlined below. Claxby Beds These beds, named from their well-known occurrence in the old ironstone workings [112963] near Claxby-by-Caister, were first described by Judd (1867 : 245; 1870 : 329) although Dikes & Lee (1837) had previously noticed a " ferruginous band " . . . at the . . . " top of the Green Sandstone" [ = Spilsby Sandstone] at Nettleton. Ferruginous and non-ferruginous lithofacies are distinguishable in Lincolnshire. The former is present in the northern and central Wolds as the Claxby Ironstone; south-east of Belchford [290750] both facies have been mapped, the non-ferruginous Hundleby Clay being recognizable as pale, purplish-grey, silty clay which splits the ironstone at about the middle and appears progressively to replace the lower part, until in the extreme south-east of the Wolds it comes to rest directly upon the Ferruginous Grit of the Spilsby Beds. From a thickness of fourteen feet at Nettleton, there is no appreciable south- easterly thickening of the Claxby Beds at outcrop for twenty miles. At Harrington [365720] twenty-three feet are estimated to be present and almost thirty feet at io 4 BRITISH NEOCOMIAN FLAMBOROUGH HEAD FIG. i. Outcrop and sub-drift occurrences of the Lower Cretaceous rocks in east Lincolnshire and east Yorkshire. RHYNCHONELLOID BRACHIOPODS 105 Partney [410680]. The Hundleby Clay is estimated to be up to five feet thick at Belchford, fifteen feet at Hundleby [385640] and eighteen feet at East Keal [375645]. The ironstone fades is characterized by the ubiquitous presence, in varying con- centrations, of oolitic iron ore embedded in pale-grey to dark-brown, ferruginous silty clays with pink or cream, calcareous, siltstone bands at some levels. These harder bands contain much less oolitic material than the clays, but both rocks may be hardened and secondarily enriched by ferruginous impregnation and by the oxidation of iron salts to limonitic material which occurs commonly as flaky aggregations in irregular veins and as encrusting " iron pan ". Glauconite is rare but polished well-rounded pebbles of chert and subangular quartz grit are found, especially about the middle and near the base of the ironstone. Beds of round phosphatic nodules up to four inches across may contain moulds of ammonites, belemnites and " steinkerns " of bivalves. These, together with frequent evidence of contemporaneous erosion, such as the presence of thin beds of broken shells and aggregations of broken and abraded ooliths resting on churned, uneven surfaces suggest that a number of minor non-sequences may exist. Clusters of brachiopods are found more commonly in the oolitic clayey seams than in associ- ation with other faunal elements, which appear to have flourished more persistently in the silty environments. The Hundleby Clay fades normally comprises pale purplish-grey, mottled-brown, silty clay. It tends to become more arenaceous towards the top with yellow- stained shaly micaceous partings. At the type locality, near Spilsby, lenses of coarse, black, pyritous grit and others of white sand up to two inches thick and twelve inches long are present just below the Upper Ironstone, interbedded with irregular bands of decalcified, concretionary, buff-coloured siltstone nodules com- monly traversed by irregular fractures infilled by ochreous ferruginous matter. At lower levels the Hundleby Clay characteristically contains less silt and, between Belchford and Hundleby itself, the whole thickness of the formation comprises unctuous, plastic clay wherever it is thick enough to be separately mapped. The sparse macrofauna appears to be devoid of brachiopods. The Futtetby Beds Formerly referred to by the Geological Survey as " The Roach " (Jukes-Browne 1887 : 19), the Fulletby Beds were first so called by Swinnerton (1935) from their obvious presence in the cliff-like feature which distinguishes the northern part of Fulletby Hill [300750], the type locality. The formation is predominantly clayey, essentially ferruginous but rarely glauco- nitic, so that it is readily distinguishable in the Lower Cretaceous sequence. Ex- posures, though few, are usually of the Roach Stone. Characteristically reddish- brown clay loams are developed everywhere on these beds. The Fulletby Beds were subdivided by Swinnerton (1935 : 4) as follows: Estimated thickness in feet Fulletby /Belchford Tetford/Harrington Upper Roach 10-15 J 5 Roach Stone 4-6 15 Lower Roach 15-20 30 io6 BRITISH NEOCOMIAN Of all the Lower Cretaceous rocks which crop out in Lincolnshire, these are prob- ably the most variable in thickness and lithology. The clay or silty-clay matrix is commonly dark grey, though it may weather to brown and bright reddish-brown where concentrations of iron ore are particularly high. Grit grains and small rounded (lydite) pebbles are disseminated throughout. Churned horizons, as if brought about by contemporaneous erosion or by organisms, have been observed only rarely. The Roach Stone crops out just above the middle of the Fulletby Beds, where the predominantly clayey sequence rapidly becomes sandy, somewhat less ferruginous and markedly more calcareous. At a higher level, the arenaceous nature of the Roach Stone is continued into the heavily ferruginous, silty Upper Roach. The Roach Stone was originally described from the borehole at Alford (Swinnerton 1935 : 10) as a " hard calcreted ferruginous sandstone " approximately twelve feet thick. This description accords well with that given here for the sandstone facies at outcrop. The sandstone, however, is exposed infrequently and it is the ironstone facies which is seen at a number of localities over the whole area, and often it is the sole representative of the Roach Stone, especially in the ground northwest of Fulletby. These facts, especially the last, may suggest that the " ironstone " facies represents a lateral lithological development of the sandstone facies towards the northwest, as well as the indurated equivalent of those Roach beds which lie immediately above and below it in the southern part of the Lincolnshire Wolds. Accordingly, for practical reasons, the Roach Stone is here taken to include all the coherent strata at about the middle of the Fulletby Beds which give rise to mappable lithological and topographical features, irrespective of the previous lithological definition. The ferruginous content of these beds is predominantly in the form of black or dark-brown polished ooliths or limonite, although there is also a subordinate amount of amorphous and flaky ore, most of which appears to be secondary. The distri- bution of the indigenous limonite varies greatly; at the outcrop there is very little oolitic material in the Roach Stone or at the extreme base of the Fulletby Beds, but passing upwards in the Lower Roach, the oolitic content gradually increases to a maximum concentration in a bed just below the Roach Stone as defined by Swinnerton (1935) in boreholes. This rock is little more than a compact agglomera- tion of ooliths with subordinate silty-clay matrix which has sometimes been made coherent at the outcrop by secondary " iron-pan " deposits, but which is more usually friable, and less sandy than Roach Stone. Above the Roach Stone the concentration of oolitic iron ore is high but it appears to decrease, and the fraction of the variegated clay and silty-clay to increase inversely, as the beds are traced upwards towards the base of the Sutterby Marl. At the base of the marl, however, the Upper Roach is again strongly oolitic in some localities (Cawkwell and Sutterby [385720]) but predominantly clayey at others (Dalby Park). The Roach Stone occurs as two fairly distinct types; an earthy limonite rock and a calcareous sandstone. In the field, both rock types are recognizable in many small exposures, but it is not clear what the inter-relationship of these facies is, either in time or space. Both rock types may be examined in the same general area and both may be much disguised and hardened by secondary " iron-pan " deposits. RHYNCHONELLOID BRACHIOPODS 107 GEOL. 16, 3. io8 BRITISH NEOCOMIAN The sandstone fades is a hard fine-grained, yellowish-brown, evenly bedded silt- stone or sandstone cemented by a ferruginous and calcareous ground-mass enclosing scattered grit grains and a few limonite ooliths which are normally evenly distributed but may be more rarely confined to certain layers. The sandstone weathers along moderately strong, rectangular joints into flaggy fragments up to one foot square by about two inches thick, but more massive blocks can be picked up in ploughed fields. Fossils are extremely rare in this facies and no well preserved examples have been collected, but thin sections reveal a limited microfauna. The ironstone facies is a soft, earthy rock with less sandy material and more oolitic limonite disseminated throughout than in the sandstone facies. It is also much more variable in lithology: primary calcitic cement may be unevenly replaced by tenaceous "iron-pan " and ferruginous veining which makes the collection and development of the sparse shelly fauna a tedious process ; secondary calcite crystals may be present in cavities in the rock and encrust exposed blocks. With diminish- ing arenaceous content the ironstone facies tends to become even more strongly oolitic, softer, and to contain thin bands of broken shell debris, including disarticu- lated valves of brachiopods. This rock, when weathered, produces reddish-brown heavily ferruginous clayey loam, the true " roach " of the countryman, containing soft, crumbling boulders of ironstone from which a limited fauna of bivalves, belem- nites and brachiopods has been recovered. In the Belchford-Fulletby districts, this facies of the Roach Stone also contain fragments of woody debris and peculiar root-like concretions (" fucoids ") made of compact, silty ore. Hitherto the Fulletby Beds have been regarded as being poorly fossiliferous, and indeed very few fossil genera have been recorded specifically from this subdivision of the Tealby Series. Of a number of brachiopods collected during the field survey, the Rhynchonellidae are now recorded and described for the first time from the English boreal Cretaceous. The brachiopod fauna from the Claxby Ironstone was described in part by Davidson (1874), and a revision of the Rhynchonellidae des- cribed by him is given here, with additional descriptions of species from a similar horizon in the Speeton Clay and from the Hanover district of north-west Germany. SYSTEMATIC DESCRIPTIONS Superfamily RHYNGHONELLAGEA Schuchert 1896 Family RHYNGHONELLIDAE Gray 1848 Subfamily GYCLOTHYRIDINAE Makridin 1955 Genus LAMELLAERHYNCHIA Burri 1953 Lamellaerhynchia rostriformis (Roemer) (PL i, figs. 1-6; PL 2, figs. 1-9; PL 3, fig. 2; Text-figs. 3, 4) 1836 Terebratula rostriformis Roemer : 40, pi. 2, fig. 22. 1839 Terebratula multiformis Roemer : 19, pi. 18, fig. 8. 1839 Terebratula rostralina Roemer : 20, pi. 18, fig. 7. 1841 Terebratula multiformis Roemer; Roemer : 37. RHYNCHONELLOID BRACHIOPODS 109 1842 Terebratula rostralina & rostrata Roemer; Leymerie : pi. 15, fig. n. 1863 Rhynchonella multiformis (Roemer); de Loriol : 113, pi. 15, fig. 23. 1864 " Rhynchonella depressa Credner " (in part); Credner : 549, pi. 18, figs. 5-12. 1871 Terebratula depressa Quenstedt (non Sowerby, 1825); Quenstedt : 155, pi. 41, figs. 2, 6-10. 1872 Rhynchonella multiformis (Roemer); Pictet : 10, pi. 195, figs. 5-8. 1913 Rhynchonella multiformis (Roemer); Jacob & Fallot : 52, pi. 7, figs. 5-7. 1953 Lamellaerhynchia multiformis (Roemer); Burri : 275, fig. 2. 1956 Lamellaerhynchia rostriformis (Roemer); Burri : 652, pi. 7, figs, i, 2, pi. 10, fig. 3. DESCRIPTION. Biconvex Lamellaerhynchia varying from about 18-24 mm - l n g> 20-26 mm. wide and 12-15 mm. thick with a low median fold on the brachial valve and a correspondingly shallow sulcus in the pedicle valve. In some mature forms there is a marked tendency for the shell to become trilobate where the median fold is poorly developed. The uniplicate anterior margin shows some tendency to asymmetry and marginal thickening. The suberect beak is bordered by well- marked beak-ridges defining a broad, extensive interarea. Outward projections of the conjunct deltidial plates extend posteriorly and encircle a large foramen. In outline the shell varies from subcircular to elongate-oval to broadly triangular. The umbo varies from short and massive to produced and sharp with incurvature of the beak. In the typical form, the ornament consists of twenty to twenty-four sharply defined, strong, radiating, non-bifurcating ribs on each valve with four to five on the fold and a similar number in the sulcus. In some of the variants the number of costae on each valve depends on the type of rib ; some having fine, more rounded costae while others have more numerous but narrower, sharp ribs. Internal characters. In the original description of the genus Lamellaerhynchia Burri (1953 : 276, fig. 3), included a series of thirteen transverse serial sections through the umbo of a specimen under the specific name of L. multiformis, from the Hilsconglomerat of Berklingen, Brunswick, north-west Germany, and added a further single section of another specimen from the Lower Hauterivian of Bachbett des Arnon, Switzerland. In a subsequent description of the genus Burri (1956 : 652, 655), correctly quoting the valid name for the type-species of the genus as Terebratula rostriformis Roemer, included a further series of transverse sections of a specimen from Bachbett des Arnon, Switzerland. Comparison of the series of transverse sections made by the authors from topotype material, and those made and published by Burri reveals fundamental differences which are recorded here. Although in general outline the umbonal cavities appear similar, the main differences lie in the distal ends of the hinge-plates which, in the specimen figured by Burri (1953 : 276) from Berklingen, are seen to have a concave dorsal surface and are, in the broadest sense, Y-shaped. The Swiss specimen which Burri (1956 : 655) subsequently figured is shown to have gently curving hinge-plates with no discernible division at the distal ends. The fourteenth section in the series showing the posterior ends of the crura is taken from the same specimen in each case, as admitted by Burri in the legend. From this discrepancy in the description of the internal structure of Lamellaerhyn- chia rostriformis it must be concluded that Burri does not regard the shape of the hinge-plates as being of diagnostic importance, an assumption confirmed by his description of the genus which bears only a brief reference to that structure. The BRITISH NEOCOMIAN writers, however, do not share Burri's view and include here a series of transverse serial sections (Text-fig. 3) of a specimen of L. rostriformis from Roemer's type locality of Elligser Brink, near Hanover, north-west Germany. It will be seen from this series that the dorsal surfaces of the distal ends of the hinge-plates are OO o-4 \jl 0-6 l^jT 0-3 FIG. 3. A series of thirteen transverse serial sections through the umbo of a specimen of Lamellaerhynchia rostriformis (Roemer) from the Neocomian of the type locality at Elligser Brink, Hanover, Germany. 6.35702. X2. Numerals denote distance in millimetres between each section. concave or broadly Y-shaped (sections 8-10) and are, in fact, similar to those shown in Burri's original series (1953 : 276) from Berklingen. It may also be seen that the extreme posterior ends of the crura do not terminate in the manner of Burri's Swiss specimen i.e. acutely concave or U-shaped with the concave surface directed towards the floor of the dorsal valve. Instead they tend to narrow anteriorly, curving abruptly anteriorly with their concave surface both dorsally and ventrally directed. This stage is regarded as characteristic of L. rostriformis and may even be confined to this species since it is not shown in any of the transverse sections of other species of Lamellaerhynchia. A specimen from Gros Vahlberg, north-west Germany (Text-fig. 4), preserved in a crystalline limestone matrix, shows this feature and once again demonstrates the concave surface of the ends of the hinge-plates. It should be noted that the dorsal median septum in this specimen appears more strongly developed and this may prove to be a variable character. NEOTYPE. Terebratula multiformis Roemer 1839 is a synonym of the earlier T. rostriformis Roemer 1836, which therefore has priority and must be used even RHYNCHONELLOID BRACHIOPODS in though there is no evidence that Roemer ever used the name subsequent to 1836. The type material was housed in the Roemer Collection at the Hildersheim Museum, north-west Germany which was damaged and partly destroyed during the war (1939-45). In order to re-establish the species as Lamellaerhynchia rostriformis (Roemer), Burri (1956 : 653), selected a neotype from the remainder of the Roemer collection. This specimen, which he figured (Burri 1956, pi. 7, fig. i a-d) is in the Roemer-Museum at Hildersheim, registered number ySia. It is stated to have been collected from the ' ' Hilston ' (Astieria-zone = oberstes Valanginien oder Noricuszone = unterstes Hauterivien) " of Elligser Brink, near Hanover. REMARKS. Roemer's original definition of Terebratula multiformis (1839 : T 9> pi. 18, fig. 8) was so loosely expressed that it has hitherto been possible to include in it a large number of variable forms which, although they are doubtlessly closely interrelated genetically, may nevertheless be separated generically with advantage. Burri has found it practicable to differentiate between certain of these forms which are morphologically distinct in Switzerland and south-east France. He points out, however, that in north-west Germany the individual species of the genus Lamel- laerhynchia are less distinct so that the amount of morphological variation produces transitional forms which cannot be assigned with certainty to any of the established species. This observation is reinforced by our experience with the comparatively few specimens collected from Lincolnshire and Yorkshire. With such a variable species as L. rostriformis, and with so little material available from widespread localities, it is impossible to give any statistical data which would be of significance in determining the true morphological characteristics. Specimens collected from limestone localities, although in the main smaller, appear identical in every respect with those collected from the clays. Specimens collected from the Speeton Clay are comparatively rare, so a comparison has been made between limestone forms from Nettleton and those in a softer, more argillaceous, matrix from the " Elligser Brink Schiste " in the Hanover district of Germany. Likewise, specimens collected from limestone localities in Germany, such as Gros Vahlberg have been compared with similar forms from Nettleton in this country. In each case there has been perfect matching of both the typical form and intermediate variants. From the foregoing description it may appear that such morphological differences in thickness, sharpness and number of costae, overall outline, produced beak and relative size might constitute an argument in favour of taxonomic separation, but no stratigraphical advantage is yet apparent. The variants described as having more numerous rounded costae, more produced beaks and more triangular outline could, perhaps, be referred to a subspecies, but the paucity of well-collected material from the Neocomian in this country and in north-west Germany makes such a separation difficult. Burri (1956 : 695) does not record the geological range of this species, but it seems almost certain that the earliest record is from the Upper Valanginian and the latest from the top of the Hauterivian. Jacob & Fallot (1913, pi. 7, figs. 5-7) figured three specimens under the name BRITISH NEOCOMIAN 0-3 04^fcX " Vj|j^ 0-3 FIG. 4. Another series of fourteen transverse serial sections through the umbo of a speci- men of Lamellaerhynchia rostriformis (Roemer) from the Neocomian of Gros Vahlberg, north-west Germany. The dorsal septum is shown to be more highly developed and more persistent in this specimen. 6.35703. X2. Numerals denote distance in milli- metres between each section. Rhynchonella multiformis (Roemer). These resemble typical L. rostriformis, and illustrate perfectly the breadth of variation in size and type of costation to be found in this species. They were collected from the Upper Valanginian of the Jura Moun- tains, Switzerland. The specimen represented by fig. 5 is similar in general outline to extreme variants of the species collected at Gros Vahlberg, north-west Germany, and from the Claxby Ironstone at Nettleton and figured here (PI. 2, figs. 4, 5). They also represent the species T. rostralina which Roemer (1840, pi 18, fig. 7) briefly described and figured from the Hils of Schandelahe and Schoppenstedt, near RHYNCHONELLOID BRACHIOPODS 113 Hanover. This form is very often found in association with specimens which grade into the typical form and is here considered to be a variant and, therefore, a synonym of Lamellaerhynchia rostriformis. Another notable variant has been found in zone C 7 of the Speeton Clay and departs from the typical form in its type of costation. The costae are less acutely angular and less incised, giving them a more rounded appearance, but in general outline the shell follows the same morphological pattern as the typical form. A specimen illustrating this type of variation is figured on PI. 2, fig. 9. It is housed in the Hull Museum and registered as 61/64/9. A similar specimen is in the private collection of Mr. R. Clements of Hull University. In some smaller variants the dorsal fold appears to be more highly developed, with resulting inflation of this valve. These features are often accompanied by a more massive, truncated umbo, slightly smaller foramen and less extensive interarea in the ventral valve. In spite of its variability L. rostriformis can be readily distinguished from other species of Lamellaerhynchia, mainly by its larger dimensions, coarser angular costae in the typical form, massive umbo and extensive interarea. As in the case of many described species of Lamellaerhynchia, L. rostriformis has a tendency to asymmetrical development of the anterior commissure. It also exhibits marked growth-lines on the shell surface, a feature not particularly well developed in other forms of the genus. DISTRIBUTION. Apart from the English localities of Speeton, Yorkshire and Tealby and Nettleton in Lincolnshire, the species has been collected from the Lower Hauterivian at Auxerre, Yonne, France; Ste. Croix, Switzerland; and Schoppenstedt, Berklingen, Delligsen, Elligser Brink and Gros Vahlberg of the Brunswick and Hanover districts of north-west Germany. Lamellaerhynchia walkeri (Davidson) (PI. 4, figs. 3-8, Text-fig. 5) 1882 Rhynchonella walkeri Davidson : 68, pi. 8, fig. 33 only. 1964 " Rhynchonella " walkeri Davidson; Rudwick : 145, Text-fig. 6A. EMENDED DIAGNOSIS. Shell subcircular to oval in outline, biconvex. Dorsal valve inflated. Fold and sulcus broad and shallow. Twelve to fourteen coarse, angular ribs on each valve. Umbo short, suberect. Foramen moderate to small, hypothyrid. Deltidial plates conjunct. Beak-ridges distinct, interarea broad, extensive. LECTOTYPE. Davidson (1882) figured two specimens. Of these, his pi. 8, fig. 33 is a true representative of the species as it is widely known and was collected from the Claxby Ironstone at Acre House Mine, near Claxby, Lincolnshire. The second specimen, figured as pi. 8, fig. 34, departs from this form in ornament and outline and is not a true L. walkeri. It is housed in the Museum of the Institute of Geological Sciences (Geological Survey) and is registered as G.S.M. 110258. It is described elsewhere in this paper as L. walkeri claxbyensis subsp. n. H4 BRITISH NEOCOMIAN The specimen selected as lectotype is, therefore, that figured by Davidson on pi. 8, fig. 33; it is housed in the Sedgwick Museum, Cambridge and registered as S.M.B.H40I. Dimensions of lectotype. Length 18 mm., width 22 mm., thickness 15 mm. EMENDED DESCRIPTION. In the early growth stages the costation, which is characteristically angular, is already distinct. The curvature of both valves remains costant during development, so that the convexity of the valves is regular right up to the line of the anterior commissure in all but gerontic individuals, in which further growth produces a flattened anterior aspect. The low median fold on the dorsal valve and the shallow sulcus in the ventral valve both develop late and gradually become differentiated from the flanks. The adult shell is unequally biconvex, approaches an almost spherical outline, and is ornamented by strongly-developed, coarse, angular ribs. There is some variation but the typical form maintains an average length of 16 mm., width of 19 mm. and thickness of approximately 12 mm. The dorsal valve is strongly convex, becoming increasingly gibbous in the region of the fold which may be occupied by three or four ribs. The broad shallow sulcus in the ventral valve usually develops two or three ribs. A well-marked growth- line is often visible just anterior to the umbonal region, at a point approximately 2-3 mm. from the apex. Otherwise growth-lines are marginal and tend towards lamellar development in older individuals. Internal characters. These are consistent with those described for the type species with the exception of a somewhat more acute deflection of the hinge-plates towards the floor of the dorsal valve. The broad, concave ends of the radulifer crura are typical. DISTRIBUTION. Lamellaerhynchia walkeri occurs in the Claxby Beds of Lincoln- shire, where it is not common. It also occurs in the Neocomian of north-west Germany. Two examples are figured here. PI. 4, figs. 7, 8 from the Hauterivian of Elligser Brink for comparison with examples from Claxby Ironstone localities. REMARKS. The degree of variation exhibited by this species is not great and is confined to the coarseness and small number of ribs which are seen throughout all stages of growth, deeply incised on the surface of each valve. The general outline, which is subcircular in the typical form, varies only slightly, becoming more elongate-oval in some and perhaps faintly triangular in other variants. Al- though no other British Cretaceous species could be easily confused with L. walkeri there are other forms which approach this species in general morphology. They differ in their more numerous, less acutely angular ribs, less convex valves and more highly-developed median fold on the dorsal valve. Lamellaerhynchia walkeri claxbyensis subsp. n. (PI. 3, figs. 3, 4) 1882 Rhynchonella walkeri Davidson : 68, pi. 8, fig. 34 only. DIAGNOSIS. Oval to subcircular in outline. Umbo short, suberect. Foramen small. Beak-ridges well marked; interarea broad, short. Median dorsal fold well developed. Costa e sharp, undivided. Growth-lines marginal. RHYNCHONELLOID BRACHIOPODS X x 0-4 0-2 FIG. 5. Fifteen transverse serial sections through the umbo of a specimen of Lamellaerhyn- chia walkeri (Davidson) from the Claxby Ironstone, Nettleton, Lincolnshire. The last two sections show an enlargement ( X 5) of the distal ends of the crura. 36.44456. X 2. Numerals denote distance in millimetres between each section. HOLOTYPE. British Museum (Natural History) B.M. 66.42944, from the Claxby Ironstone, Top Mines, Nettleton, Lincolnshire. Dimensions of holotype. Length 18 mm., width 20 mm., thickness 15 mm. DESCRIPTION. Although similar in general outline to L. walkeri the new sub- species differs from it in having a more highly developed median fold on the dorsal valve, a shorter umbo, and a considerably smaller foramen. The deltidial plates are not well exposed and the broad interarea is shorter or less extensive than in L. walkeri. The costae, typically sharp or angular, are considerably more numerous than in L. walkeri, and average eighteen to twenty on both valves with four to five on the fold and three to four in the sulcus. Growth-lines are confined to the margins and often become lamellar. This development is well marked on specimens collected from the Claxby Ironstone at Nettleton (British Museum (Natural History), BB. GEOL. l6, 3. 12 n6 BRITISH NEOCOMIAN 42945-51). It is also noticeable in specimens from Elligser Brink in north-west Germany, and one specimen illustrating this character is now figured (PI. 3, figs. 3a-c). Lamellaerhynchia rawsoni sp. n. (PL 4, figs. 11-15) DIAGNOSIS. Small Lamellaerhynchia about 18 mm. long, 20 mm. wide and n mm. thick when fully grown. Distinctly triangular in general outline. Median fold well developed on dorsal valve. Umbo slightly produced, laterally excavated. Deltidial plates conjunct, well exposed. Foramen large, circular. Interarea short, broad, bounded by distinct permesothyrid beak-ridges. Ornament of eighteen to twenty coarse radiating, acutely angular, deeply incised costae. Fold and sulcus with three or four costae. HOLOTYPE. British Museum (Natural History), B.M. 66.44424, from the Roach Stone of Dalby Park, south Lincolnshire Wolds. Dimensions of holotype. Length 20 mm., width 21 mm., thickness 14 mm. PARATYPES. BB . 44421,66 . 44425, B6 . 42954 and 66 . 42955. DESCRIPTION. Although L. rawsoni bears a strong resemblance to L. hauterivi- ensis 6urri (1953), from the Lower Hauterivian of Switzerland, it can be readily distinguished by its fewer costae, less well-developed median fold on the dorsal valve, and slightly greater incurvature of the beak. It also has a well-developed growth-line at approximately 2-4 mm. anterior to the dorsal umbo. In older individuals there is a tendency to lamellar thickening of the margins. Internal characters. As for the type species L. rostriformis. DISTRIBUTION. In the same way that L. hauteriviensis 6urri is confined to the Lower Hauterivian it would seem that L. rawsoni is a species of limited vertical and horizontal range, being found only as a rare fossil in the Lower 6arremian, Fulletby 6eds, of this country. It has not been identified with certainty from any of the north German deposits though it probably exists in the 6arremian of the Hanover area. Lamellaerhynchia julenia sp. n. (PI. 3, figs. 6, 7) DIAGNOSIS. Elongate-triangular Lamellaerhynchia approximately 20 mm. long, 19 mm. wide and n mm. thick when fully grown. Produced, suberect beak, laterally excavated. Conjunct deltidial plates well exposed. Foramen large, circular. Acutely angular radiating costae, coarse and deeply incised. Interarea extensive. 6eak-ridges distinct, permesothyrid. Anterior commissure with marked tendency to asymmetry. HOLOTYPE. 6ritish Museum (Natural History), 6.M. 66.42984, from the Lower 6arremian, Fulletby 6eds of Dalby Park, south Lincolnshire Wolds. Dimensions of holotype. Length 21 mm., width 20 mm., thickness 15 mm. PARATYPE. 66.42985 RHYNCHONELLOID BRACHIOPODS 117 DESCRIPTION. The outstanding features of this species are its almost equal biconvexity and its constant eighteen to twenty costae on each valve. It is always elongate-triangular in general outline, varying only slightly in width, with a marked tendency to asymmetry of the anterior commissure. It bears a resemblance to L. gillieroni (de Loriol) but differs in its coarser, more deeply incised costae and more constantly elongate-triangular outline. It may, nevertheless, be the British equivalent of that species, occurring in the Lower Barremian, as L. gillieroni does in Switzerland. The morphological differences described above and the geographical difference would seem to justify the taxonomic separation accorded here. Internal characters. As for the type species L. rostriformis (Roemer). DISTRIBUTION. Although Lamellaerhynchia julenia occurs only in the Lower Barremian, Fulletby Beds in Britain, a similar form, differing only in relative size occurs in north-west Germany at Schoppenstedt, but the exact horizon has not been recorded. Three good examples of this species from Schoppenstedt are in the British Museum (Natural History), B.M. 66.44460-62. Lamellaerhynchia cf. picteti Burri (PI. 3, figs. 8, 9) DESCRIPTION. Acutely biconvex Lamellaerhynchia with short, massive umbo, suberect beak and short interarea. The beak-ridges are distinct and permesothyrid. Distinctly subcircular in general outline. Dorsal fold incipient or indistinct with fairly shallow but broad sulcus in the ventral valve. The costae vary in number from between twenty and thirty on each valve but there are some variants with slightly coarser costation and a corresponding reduction in number of costae. Most of the specimens ascribed here to this species show a tendency to asymmetry of anterior commissure. REMARKS. Although this species is compared here to L. picteti it is somewhat more circular in outline than the specimens figured by Burri (1956 : pi. 8, fig. 3, pi. 9, fig. i) but is nevertheless very similar in its type of costation, degree of con- vexity and general appearance. None of the specimens examined exactly matches those illustrated by Burri and it is for this reason that we have compared our species to the original to give a somewhat broader interpretation. DISTRIBUTION. Only three specimens of L. cf. picteti have been found in Britain so far and these were collected from the Claxby Ironstone at Nettleton, Lincolnshire. Genus RHYNCHONELLA Fischer 1809 Rhynchonella parkhillensis sp. n. (PI. 4, figs. 9, 10, Text-fig. 6) DIAGNOSIS. Species of Rhynchonella approximately 12 mm. long, 13 mm. wide, and 9 mm. thick when fully grown. Shell biconvex, outline subcynocephalous or n8 BRITISH NEOCOMIAN tetrahedral. Brachial valve with angular and prominent median fold containing two or three imbranched, simple, deeply-incised costae; sulcus with one or two costae. Beak-ridges distinct, hypothyrid. Umbo suberect. No cardinal process. Shallow septalium. Dental lamellae strong, subparallel. Radulifer crura. HOLOTYPE. British Museum (Natural History), B.M. 66.42952, from the Fulletby Beds, Roach Stone of Park Hill, Belchford, South Lincolnshire Wolds. Nat. Grid 28907685. Dimensions of holotype. Length 14 mm., width 14-1 mm., thickness 9 mm. PARATYPES. 66.52953-55. DESCRIPTION. In the early growth stages both valves are convex and smooth to within 3-5 mm. from the umbones. At this stage the costae gradually become discernible. A moderately deep sulcus develops and extends posteriorly with a linguiform extension averaging 6 mm. in length. The sulcus tapers gently to form a truncated V-shape. The lateral slopes of the fold are well marked anteriorly, separating the high median portion from the convex flanks, and subsiding completely where the costae arise. The number of costae on the fold varies from two to three. In forms where two costae are developed on the fold, one costa is developed in the sulcus. Likewise, when three costae are developed on the fold, two costae appear in the sulcus. FIG. 6. A series of twelve transverse serial sections through the umbo of a specimen of Rhynchonella parkhillensis sp. nov. from the Fulletby Beds, Dalby Park. 36.44405. X ij approx. Numerals denote distance in millimetres between each section. Internal characters. Serial sections made from undamaged examples of this species have been compared with a similar series from Rhynchonella loxia Fischer, the type species of the genus, published by Ager (1957 : 8, 9). Dr. Ager has kindly confirmed our assignment of the present species to Rhynchonella (s.s.). REMARKS. Rhynchonella parkhillensis is named from its most prolific locality at Park Hill, Belchford, Lincolnshire. The species is rare in the Roach Stone over the ten miles of its outcrop. Preservation is rarely excellent, but the paucity of natural exposures and the ferruginous nature of the matrix increase the value of the few specimens which can be found and extracted undamaged. Superficially, the species bears a resemblance to other species of Rhynchonella (s.s.) as re-defined by Ager (1957), particularly to R. rouillieri Eichwald, from the RHYNCHONELLOID BRACHIOPODS 119 Russian Upper Jurassic. Ager (1957 : 12) discussed the probable relationship of R. rouilleri to other species of Rhynchonella and assigned it to this genus. The species was further discussed and several subspecies described and figured by Makridin (1964 : 113, pi. 3, figs. 2-12) from the Upper Jurassic of the Russian Platform. Of these R. rouilleri eltonica bears a strong resemblance to R. parkhill- ensis, but the latter can be distinguished by its more acute, triangular outline, slightly more highly developed dorsal fold and more produced umbo. It differs from R. loxia in having a less acute, cynocephalous outline and more produced umbo but shares with that species the possession of fine, longitudinal striae, just visible on the surface of the shell in well-preserved specimens. These striae are crossed by transverse growth lines, equally faint in development, which give the appearance of a fine reticulation over the surface of the shell. DISTRIBUTION. Apart from the type locality at Park Hill, Belchford, specimens have been collected form the same horizon within the Fulletby Beds at Hoe Hill, Fulletby; Cloven Hill, South Ormsby; Dalby Park and Dalby Hill near Spilsby, South Lincolnshire. Rhynchonella speetonensis Davidson (PI. 3, fig. 5, PL 4, figs, i, 2. Text-figs. 7, 8) 1836 Terebratula varians Schlotheim; Roemer : 38, II, fig. 12. 1874 Rhynchonella speetonensis Davidson : 69, pi. 8, figs. 32a-c. EMENDED DESCRIPTION. Distinctive, subtrigonal, cynocephalous rhynchonelloid bearing a high fold in the dorsal valve at all stages of growth. Although the species is variable it maintains an average length of approximately 19 mm., width of 20 mm. and thickness of 16 mm. The variations are mainly confined to the width, which may exceed the length by as much as 3-6 mm, and the height of the dorsal fold, which is proportionately greater or more acutely arched in some variants. No costae are developed but the shell is ornamented by numerous fine, rounded costellae, averaging in number from sixteen to eighteen on the fold and fourteen to sixteen in the sulcus. The costellation varies in size and, in some of the German forms from Ellisger Brink, becomes coarse with a considerable reduction in the number of costellae. Internal characters. As in the case of Rhynchonella parkhillensis transverse serial sections have been made and compared with those of Rhynchonella loxia, as figured by Ager (1957 : 8, 9). LECTOTYPE. Davidson (1874 : 69) described Rhynchonella speetonensis from the Speeton Clay of Speeton, Yorkshire and illustrated his description by figuring a specimen (1874, pi. 8, figs. 32a-c) which he said was in the collections of the Wood- wardian Museum, Cambridge. In fact, three specimens labelled Rhynchonella speetonensis, 6.11426, 6.11427 & 6.11428, from the Speeton Clay are housed in the Sedgwick Museum. Of these, 6.11428 is nearest to the somewhat restored drawing of Davidson. It is assumed that all three specimens were used by Davidson and therefore rank as syntypes. 6.11428 is selected as lectotype; it is 15 mm. long, 16 mm. wide and 12 mm. thick. BRITISH NEOCOMIAN REMARKS. The assignment of this species to Rhynchonella (s.s.) was made after due consideration of both external and internal morphological features. R. speeton- ensis has many internal structures in common with R. loxia, including strong, 0-1 ^m^ 9 0-1 FIG. 7. Thirteen transverse serial sections through the umbo of a specimen of Rhynchonella speetonensis Davidson from the Speeton Clay, Speeton, Yorkshire. 66.44458. x ij approx. Numerals denote distance in millimetres between each section. slightly converging dental lamellae, shallow septalium, short dorsal median septum, similarly-shaped hinge-plates, and radulifer crura. Externally the two species have only two main morphological features in common, namely the general sub- trigonal outline and the high cynocephalous median fold in the dorsal valve. The ornament of fine costellae which distinguishes R. speetonensis does not appear on any of the other known species of Rhynchonella. However, Ager (1957 : 6) made special reference to faint striae observed on the shell surface of some specimens of R. loxia, and noted that Buckman (1918), in discussing the same species, placed sufficient emphasis on this character as to refer to it as capillation. Ager further pointed out that similar fine striae have been seen on specimens of R. rouillieri Eichwald from the Lower Volgian of Russia. We have also noted this feature in our description of R. parkhillensis sp. n. In his original description of R. speetonensis Davidson (1874 : 69) referred to the numerous growth-lines which cross the main costellation to form a reticulate orna- mentation. This is particularly noticeable [see PI. 3, fig. 5] in specimens from the Speeton Clay but is less well preserved in specimens from the Claxby Ironstone. The ornament of fine costellae and the high median fold in the dorsal valve, together with a more highly developed or slightly produced umbo, distinguish R. speetonensis from all other known species of Rhynchonella (s.s.). DISTRIBUTION. The species appears to be confined to the Speeton Clay (exact horizon uncertain), the Claxby Ironstone at Nettleton, and the Neocomian Beds at Elligser Brink and in the Hanover district of north-west Germany. RHYNCHONELLOID BRACHIOPODS FIG. 8. Eleven transverse serial sections through the umbo of a specimen of Rhynchonella speetonensis Davidson from Elligser Brink, north-west Germany. 6.11968. X2. Numerals denote distance in millimetres between each section. CONCLUSIONS Since the early descriptions by Roemer (1836; 1840) the north-west German Lower Cretaceous rhynchonelloid fauna has not been further investigated. The paucity of well-collected material from localities of known geological age has made any attempt to correlate the German species with the British forms from Lincoln- shire and Yorkshire difficult. A few species have been recognized as occurring on both sides of the North Sea and one of the most important of these is Lamellaerhyn- chia rostriformis (Roemer). This is a variable form, but an attempt is made here to define the broader limits of its variation and to draw a closer comparison between the north-west German specimens and those collected from British localities. In addition, comparison is also made between British and German forms and those described by Burri from the Neocomian of Switzerland. Although accepting a wide degree of variation within the limits of the species as defined here, it is pointed out that the precise geological range of L. rostriformis is unknown and the data obtained are based on specimens collected from Speeton and Nettleton by Dr. R. G. Thurrell and Dr. P. Rawson, and from museum material. It is thought that any differences in the internal characters between specimens sectioned by the authors (Text-figs. 3, 4) and those previously published by Burri (1953; 1956) are due, in the main, to differences in the technique of making and of presenting drawings of transverse sections. ACKNOWLEDGMENTS Our thanks are due to Dr. W. T. Dean and Dr. L. R. M. Cocks of the Department of Palaeontology, British Museum (Natural History), and to Dr. P. Rawson, Queen Mary College, London University. The photographs are the work of Mr. C. B. Keates to whom we also address our thanks. 122 BRITISH NEOCOMIAN REFERENCES ACER, D. V. 1957- The true Rhynchonella. Palaeontology, London, 1 : 1-15, pis. 1-2. ALLEN, P. 1954. Geology and Geography of the London-North Sea Uplands in Wealdon Times. Geol. Mag., Lond. 91 : 498. BOGG, F. 1819. A Sketch of the Geology of the Lincolnshire Wolds. Trans. Geol. Soc. Lond., 3 : 392-398. BOWER, C. R. & FARMERY, J. R. 1910. The zones of the Lower Chalk of Lincolnshire. Proc. Geol. Ass. Lond., 21 : 333-359. BURRI, F. 1956. Die Rhynchonelliden der Unteren Kreide (Valanginien-Barremien) im westschweizerischen Juragebirge. Eel. geol. Helv., Lausanne, 49 : 600-701, pis. 1-15. 1953. Beitrage zur systematik der Brachiopoden aus der untersten Kreide im west- schweizerischen Juragebirge. Eel. geol. Helv., Lausanne, 46 2 : 269-285. CASEY, R. 1962. The Ammonites of the Spilsby Sandstone, and the Jurassic-Cretaceous boundary. Proc. geol. Soc. Lond., 1598 : 95-100. Colloque sur le Cretace Inferieur. (Lyon, Septembre 1963). Mem. Bur. Rech. geol. min. 34 : xxi + 840. Paris. CREDNER, H. 1864. Die Brachiopoden der Hilsbildung im nordwestlichen Deutschland. Z. dtsch. geol. Ges., Berlin, 16 : 542-572, pis. 18-21. DAVIDSON, T. 1852. A Monograph of British Cretaceous Brachiopoda, 1 Palaeontogr. Soc. [Monogr.] London : 1-117, pis. 1-12. 1874. A Monograph of the British Fossil Brachiopoda, 4, i Supplement to the Recent, Tertiary, and Cretaceous Species. Palaeontogr. Soc. [Monogr.], London : 172, pis. 1-8. DIKES, W. H. & LEE, J. E. 1837. Outlines of the Geology of Nettleton Hill, Lincolnshire. Lines. Mag. Nat. Hist., 1837 : 561-566. HILL, W. 1888. On the Lower Beds of the Upper Cretaceous Series in Lincolnshire and Yorkshire. Q. Jl geol. Soc. Lond., 44 : 320-367. JACOB, C. & FALLOT, P. 1913. Etude sur les Rhynchonelles portlandiennes neocomiennes et mesocretacees du sud-est de la France. Mem. Soc. Paleont. Suisse, 39 : 1-82, pis. i-n. JUDD, J. W. 1870. Additional observations on the Neocomian Strata of Yorkshire and Lincolnshire with notes on their relations to beds of the same age throughout north Europe. Q. Jl geol. Soc. Lond., 26 : 326-348. 1868. On the Speeton Clay. Q. Jl geol. Soc. Lond., 24 : 218-250. 1867. On the strata which form the base of the Lincolnshire Wolds. Q. Jl geol. Soc. Lond., 23 : 227-251. JUKES-BROWNE, A. J. & HILL, W. 1900. The Cretaceous Rocks of Britain. The Gault and Upper Greensand of England x-499 pp. Mem. Geol. Surv. U.K., London. 1893. Recent borings through the Lower Cretaceous of East Lincolnshire. Q. Jl geol. Soc. Lond., 49 : 467-478. KEEPING, H. 1882. On some Sections of the Lincolnshire Neocomian. Q. Jl geol. Soc. Lond., 38 : 239-244. LAMPLUGH, G. W. 1891. On the Speeton Clays and their Equivalents in Lincolnshire. Ann. Rep. Brit. Ass., Leeds, 1890 : 808. 1896. On the Speeton Series in Yorkshire and Lincolnshire. Q. Jl geol. Soc. Lond., 52 : 179-220. 1922. A review of the Speeton Clays. Proc. Yorks. Geol. Soc., Leeds, 20 : 1-31. LEYMERIE, A. 1842. Suite du Memoire sur le terrain cretace du departement de 1'Aube. Mem. Soc. geol. Fr., Paris, (i) 5 i : 1-34, pi. 1-18. LINTON, D. L. 1954. The Landforms of Lincolnshire. Geography 39 : 67-79. LORIOL, P. de 1863. Description des animaux invertebres fossiles contenus dans I'etage Neo- comien Moyen du Mont Saleve. II : 113-214, pi. 15-22. Geneve. PICTET, F. J. 1872. Description des fossiles du terrain cretace des environs de Sainte-Croix. Mater. Paleont. suisse, Geneve (6) 1 : 1-158, pis. 195-208. QUENSTEDT, F. A. 1868-71. Petrefactenkunde Deutschlands, 2 : Brachiopoden, 1-60 (1868); 161-464 (1869); 465-748 (1870), pis. 37-61 (1871). Leipzig. RHYNCHONELLOID BRACHIOPODS 123 ROEMER, F. A. 1836. Die Versteinerungen des Norddeutschen Oolithen-Gebirges. 218 pp., 1 6 pis. Hannover. 1839. Die Versteinerungen des Norddeutschen Oolithen-Gebirges. 59 pp., 4 pis. Hannover. 1840. Die Versteinerungen des Norddeutschen Kreide-gebirges iv + J 45 pp-, 16 pis. Hannover. SPATH, L. F. 1941. On the boundary between the Upper and Lower Cretaceous. Geol. Mag., Lond., 77 : 309-315. 1924. On the Ammonites of the Speeton Clay and the subdivisions of the Neocomian. Geol. Mag., Lond., 61 : 73-89. SWINNERTON, H. H. 1936-55. A monograph of British Cretaceous Belemnites. Pt. 5. Palaeontogr. Soc., [Monogr.], London : xxxiii-xl, 63-68, pis. 16-18. 1941. Further observations on the Lower Cretaceous rocks of Lincolnshire. Proc. Geol. Ass. Lond., 52 : 198-207. 1937. The physical history of Lincolnshire. Lines. Nats. Union Trans. 1937 : 91-100. 1935. The rocks below the Red Chalk of Lincolnshire and their cephalopod faunas. Q. Jl geol. Soc. Lond., 91 : 1-46, pis. i-iv. THOMPSON, C. 1929. Speeton Clays and their southern equivalents; the Neocomian of southern England. Trans. Hull. Geol. Soc., 7 : 41-69. VERSEY, H. C. 1947. Presidential address. The structure of east Yorkshire and north Lincolnshire. Proc. Yorks. Geol. Soc., Leeds, 27 : 173-191. WEERTH, O. 1884. Die Fauna des Neocomsandsteins im Teutoburger Walde. Palaont. Abh., Berlin, 2 : 1-77, pis. i-n. GEOL. l6, 3. PLATE i a. Dorsal view. b. Lateral view. c. Anterior view. FIGS. ia, b, c. Lamellaerhynchia rostriformis (Roemer). Neocomian, Speeton Clay, D i Zone, Speeton, Yorkshire. Hull University Coll., H.U.C/S. 1590. FIGS. 2a, b, c. Lamellaerhynchia rostriformis (Roemer). Neocomian, " Elligser Brink Schist ", Elligser Brink, north-west Germany. B.M. 66.44406. FIGS. 3a, b, c. Lamellaerhynchia rostriformis (Roemer). Neocomian, Speeton Clay, Speeton, Yorkshire. Davidson Coll., B.M. 47262. FIGS. 4a, b, c. Lamellaerhynchia rostriformis (Roemer). Neocomian, " Elligser Brink Schist", Elligser Brink, north-west Germany. B.M. 66.44407. FIGS. 5a, b, c. Lamellaerhynchia rostriformis (Roemer). Neocomian, Speeton Clay, D2D Zone, Speeton, Yorkshire. Fletcher Coll., B.M. 66.44459. FIGS. 6a, b, c. Lamellaerhynchia rostriformis (Roemer). Neocomian, Claxby Ironstone, Top Mines, Nettleton, Lincolnshire. Hull University Coll., H.U.C/Rn.3O2. All figures at natural size unless otherwise stated. 6.M. = 6ritish Museum (Natural History) . Bull. Br, Mus. nat. Hist. (Geol.) 16, 3. PLATE i PLATE 2 a. Dorsal view. b. Lateral view. c. Anterior view. FIGS, i a, b, c. Lamellaerhynchia rostriformis (Roemer). Neocomian, " Elligser Brink Schist", Elligser Brink, north-west Germany. B.M. 66.44408. FIGS. 2a, b, c. Lamellaerhynchia rostriformis (Roemer). Neocomian, Claxby Ironstone, Top Mines, Nettleton, Lincolnshire. Rawson Coll., B.M. 66.44412. FIGS. 3a, b, c. Lamellaerhynchia rostriformis (Roemer). Neocomian, Acre House Mine, south of Nettleton, Lincolnshire. C.W. & E.V. Wright Coll., B.M. 66.44413. FIGS. 4a, b, c. Lamellaerhynchia rostriformis (Roemer). Neocomian, Acre House Mine, south of Nettleton, Lincolnshire. C. W. & E. V. Wright Coll., 6.M. 66.44411. FIGS. 5a, b, c. Lamellaerhynchia rostriformis (Roemer). Neocomian, Gros Vahlberg, north-west Germany. 6.M. 66.44410. FIGS. 6a, b, c. Lamellaerhynchia rostriformis (Roemer). Neocomian, Claxby Ironstone, Top Mines, Nettleton, Lincolnshire. Rawson Coll., 6.M. 66.44423. FIGS, ya, b, c. Lamellaerhynchia rostriformis (Roemer). Neocomian, " Elligser 6rink Schist ", Elligser 6rink, north-west Germany. 6.M. 66.9094. FIGS. 8a, b, c. Lamellaerhynchia rostriformis (Roemer). Neocomian, Speeton Clay, Speeton, Yorkshire. C. W. & E. V. Wright Coll., 6.M. 66.44409. FIGS, ga, b, c. Lamellaerhynchia rostriformis (Roemer). Neocomian, Speeton Clay, Speeton, Yorkshire. Hull Museum Coll., 61/64/9. Bull. Br. Mus. nat. Hist. (Geol.) 16, 3. II PLATE 2 8a 9a PLATE 3 a. Dorsal view. b. Lateral view. c. Anterior view. FIGS. ia, b, c. Larnellaerhynchia cf. picteti Burri. Neocomian, Claxby Ironstone, Top Mines, Nettleton, Lincolnshire. Rawson Coll. B.M. 66.42983. FIGS. 2a, b, c. Larnellaerhynchia rostriformis (Roemer). Neocomian, Claxby Ironstone, Acre House Mine, south of Nettleton, Lincolnshire. Institute of Geological Sciences Coll., G.S.M. 110257. FIGS. 3a, b, c. Lamellaerhynchia walkeri claxbyensis subsp. n. Neocomian, " Elligser Brink Schist", Elligser Brink, north-west Germany. B.M. 66.44417. FIGS. 4a, b, c. Lamellaerhynchia walkeri claxbyensis subsp. n. Neocomian, Claxby Ironstone, Top Mines, Nettleton, Lincolnshire. Rawson Coll., B.M. 66.42944. Holotype. FIG. 5. Enlargement of shell surface of Rhynchonella speetonensis Davidson to show the transverse lamellar ornament. B.M. 66.44457. Xi2approx. FIGS. 6a, b, c. Lamellaerhynchia julenia sp. n. Lower 6arremian, Fulletby 6eds, Dalby Park, Lincolnshire. Thurrell Coll. 6.M. 66.42985. Paratype. FIGS. 7a, b, c. Lamellaerhynchia julenia sp. n. Lower 6arremian, Fulletby 6eds, Dalby Park, Lincolnshire. Thurrell Coll., 6.M. 66.42984. Holotype. FIGS. 8a, b, c. Lamellaerhynchia cf. picteti 6urri. Neocomian, Gros Vahlberg, north- west Germany. B.M. 66.42987. FIGS, ga, b, c. Lamellaerhynchia cf. picteti 6urri. Neocomian, Schoppenstedt, north- west Germany. 6.M. 66.42986. Bull. Br. Mus. nat. Hist. (Geol.) 16, 3 PLATE 4 a. Dorsal view. b. Lateral view. c. Anterior view. FIGS. la, b, c. Rhynchonella speetonensis Davidson. Neocomian, Claxby Ironstone, Top Mines, Nettleton, Lincolnshire. Hull Univ. Coll. H.U.C./Rn.277. FIGS 2a, b, c. Rhynchonella speetonensis Davidson. Neocomian, " Elligser Brink Schist", Elligser Brink, north-west Germany. Davidson Coll. B.M. 66.44419. FIGS. 3a, b, c. Lamellaerhynchia walkeri (Davidson). Neocomian, Claxby Ironstone, Acre House Mine, near Claxby, Lincolnshire. C. W. Wright Coll. B.M. 66.42941. FIGS. 4a, b, c. Lamellaerhynchia walkeri (Davidson). Neocomian, Claxby Ironstone, Top Mines, Nettleton. Rawson Coll. B.M. 66.42943. FIGS. 5a, b, c. Lamellaerhynchia walkeri (Davidson). Neocomian, Claxby Ironstone, Acre House Mine, near Claxby, Lincolnshire. C. W. & E. V. Wright Coll. 6.M. 66.44414. FIGS. 6a, b, c. Lamellaerhynchia walkeri (Davidson). Neocomian, Acre House Mine. C. W. & E. V. Wright Coll., 6.M. 66.42942. FIGS, ya, b, c. Lamellaerhynchia walkeri (Davidson). Neocomian, " Elligser 6rink Schist", Elligser Brink, north-west Germany. Davidson Coll. 6.M. 66.44415. FIGS. 8a, b, c. Lamellaerhynchia walkeri (Davidson). Neocomian, " Elligser Brink Schist", Elligser Brink, north-west Germany. Davidson Coll. B.M. 66.44416. FIGS, ga, b, c. Rhynchonella parkhillensis sp. n. Neocomian, Lower Barremian, Fullet- by Beds, Roach Stone, Parkhill, Lincolnshire. Thurrell Coll. B.M. 66.42952. Holotype. FIGS. loa, b, c. Rhynchonella parkhillensis sp. n. Lower 6arremian, Fulletby 6eds, Roach Stone, Parkhill. Thurrell Coll. 6.M. 66.42953. FIGS, na, b, c. Lamellaerhynchia rawsoni sp. n. Neocomian, Lower 6arremian, Fulletby 6eds, Dalby Park, Lincolnshire. Thurrell Coll. 6.M. 66.44424. Holotype. FIGS. i2a, b, c. Lamellaerhynchia rawsoni sp. n. Neocomian, Lower 6arremian, Fullet- by 6eds, Cawkwell, Lincolnshire. Thurrell Coll. 6.M. 66.44421. FIGS. i3a, b, c. Lamellaerhynchia rawsoni sp. n. Lower 6arremian, Fulletby 6eds, 6elchford, Lincolnshire. Thurrell Coll. 6.M. 66.44425. Paratype. FIGS. i4a, b, c. Lamellaerhynchia rawsoni sp. n. Lower 6arremian, Fulletby 6eds, Dalby Park, Lincolnshire. Thurrell Coll. 6.M. 66.42954. FIGS. i5a, b, c. Lamellaerhynchia rawsoni sp. n. Lower 6arremian, Fulletby Beds, Dalby Park, Lincolnshire. Thurrell Coll. B.M. 66.42955. Bull. Br. Mus. nat. Hist. (Geol.} 16, 3. PLATE 4 Ib 6a 6c 7c - 7a lib Ik Ma PRINTED IN GREAT BRITAIN BY ADLARD & SON LIMITED BARTHOLOMEW PRESS, DORKING THE LOWER PALAEOZOIC BRACHIOPOD AND TRILOBITE FAUNAS OF ANGLESEY D. E. B. BATES BULLETIN OF THE BRITISH MUSEUM (NATURAL HISTORY) GEOLOGY Vol. 16 No. 4 LONDON: 1968 THE LOWER PALAEOZOIC BRACHIOPOD AND TRILOBITE FAUNAS OF ANGLESEY BY DENIS EDWIN BEECHING BATES University College, Aberystwyth Pp. 125-199; 14 Plates, 2 Text-figures BULLETIN OF THE BRITISH MUSEUM (NATURAL HISTORY) GEOLOGY Vol. 16 No. 4 LONDON: 1968 THE BULLETIN OF THE BRITISH MUSEUM (NATURAL HISTORY), instituted in 1949, is issued in five series corresponding to the Departments of the Museum, and an Historical series. Parts will appear at irregular intervals as they become ready. Volumes will contain about three or four hundred pages, and will not necessarily be completed within one calendar year. In 1965 a separate supplementary series of longer papers was instituted, numbered serially for each Department. This paper is Vol. 16, No. 4 of the Geological (Palaeontological] series. The abbreviated titles of periodicals cited follow those of the World List of Scientific Periodicals. World List abbreviation : Bull. Br. Mus. not. Hist. (Geol.) Trustees of the British Museum (Natural History) 1968 TRUSTEES OF THE BRITISH MUSEUM (NATURAL HISTORY) Issued 19 April, 1968 Price 3 THE LOWER PALAEOZOIC BRACHIOPOD AND TRILOBITE FAUNAS OF ANGLESEY By D. E. B. BATES CONTENTS Page I. INTRODUCTION AND ACKNOWLEDGMENTS . . . . . 129 II. SYNOPSIS OF STRATIGRAPHY . . . . . . . 130 (a) Eastern Anglesey . . . . . . . . 130 (b) The Berw Fault Complex 132 (c) The Llangwyllog Area . . . . . . . 132 (d) The Principal Area . . . . . . . 132 (e) The Gynfor Outliers . . . . . . . 137 (f) Faunal Lists ......... 138 III. FAUNAL AFFINITIES AND CORRELATIONS . . . . . 140 IV. SYSTEMATIC DESCRIPTION OF THE BRACHIOPODA .... 142 Superfamily Orthacea Woodward ..... 142 Family Hesperonomiidae Ulrich & Cooper . . . . 142 Hesperonomiella carmelensis sp. nov. . . . . 142 Monorthis typis gen. et sp. nov. . . . . . 144 Family Orthidae Woodward . . . . . . 145 Cyvtonotella sp. (i) . . . . . . . 145 Cyrtonotella sp. (2) . . . . . . . 146 Lenorthis proava (Salter) . . . . . . 146 Lenorthis sp. ........ 148 Orthambonites()} sp. (i) . . . . . . 148 Orthambonites(?) sp. (2) ...... 148 Pleurorthis costatus sp. nov. . . . . . . 149 Nicolella humilis Williams . . . . . . 150 Panderina lamellosa sp. nov. . . . . . . 151 Family Dolerorthidae Opik . . . . . . 152 Dolerorthis cf. tenuicostata Williams . . . . 152 Ptychopleurella sp. (i) . . . . . . . 152 Ptychopleurella sp. (2) . . . . . . . 153 Family Plaesiomyidae Schuchert . . . . . 154 Plaesiomys cf. robusta (Bancroft) . . . . . 154 Plaesiomys (Dinorthis] sp. . . . . . . 154 Family Plectorthidae Schuchert & Le Vene . . . 155 Plectorthis(l) sp. ........ 155 Platystrophia precedens major Williams . . . . 155 Family Skenidiidae Kozlowski . . . . . . 156 Skenidioides sp. (i) . . . . . . 156 Skenidioides sp. (2) ....... 156 Superfamily Enteletacea Waagen . . . . . 157 Family Paurorthidae Opik . . . . . . 157 Paurorthis(?) sp. ...... . 157 Family Dalmanellidae Schuchert . . . . . 158 Dalmanella(>} sp. ....... 158 Onniella(>} sp. ........ 158 Family Harknessellidae Bancroft . . . . . 159 Harknessella(?) sp. ....... 159 Horderleyella(l] sp. ....... 159 GEOL. 16, 4. 15 I 2 8 LOWER PALAEOZOIC BRACHIOPOD Page Family Linoporellidae Schuchert & Cooper . . . 159 Salopia salteri gracilis Williams . . . . . 159 Family Angusticardiniidae Schuchert & Cooper . . . 160 Rhynchorthis rotundus gen. et sp. nov. .... 160 Superfamily Clitambonitacea Winchell & Schuchert . . 161 Family Polytoechiidae Opik . . . . . . 161 Tritoechia sp. ........ 161 Family Clitambonitidae Winchell & Schuchert . . . 162 Clitambonites(?) sp. . . . . . . . 162 Ilmarinia sp. . . . . . * . 162 Apomatella(l} sp. . . . . . . . 163 Superfamily Gonambonitacea Schuchert & Cooper . . . 163 Family Gonambonitidae Schuchert & Cooper . . . 163 Antigonambonites pyramidalis sp. nov. . . . . 163 Estlandia(l] sp. ........ 164 Family Kullervoidae Opik . . . . . . 165 Kullervo aff. panderi (Opik) . . . . . . 165 Suborder Clitambonitidina Opik . . . . . . 165 Superfamily and genus unknown . . . . . . 165 Superfamily Plectambonitacea Jones . . . . . 166 Family Plectambonitidae Jones . . . . . 166 Ahtiella quadrata sp. nov. . . . . . . 166 Ahtiella concava sp. nov. . . . . . . 167 Reinversella monensis gen. et sp. nov. .... 169 Family Leptestiidae Opik . . . . . . 170 Palaeostrophomena sp. . . . . . . . 170 Palaeostrophomena(>} sp. . . . . . . 171 Family Leptellinidae Ulrich & Cooper . . . . 171 Leptestiina derfelensis (Jones) . . . . . 171 Bilobia aff. musca (Opik) . . . . . . 171 Family Sowerbyellidae Opik . . . . . . 172 Eoplectodonta lenis Williams . . . . . . 172 Ptychoglyptus sp. . . . . . . . . 173 Sericoidea abdita Williams . . . . . . 173 Superfamily Strophomenacea King . . . . . 174 Family Leptaenidae Hall & Clarke . . . . . 174 Leptaena sp. ........ 174 Dactylogonia sp. . . . . . . . . 175 Kiaeromena(l] sp. . . . . . . . 175 Superfamily Porambonitacea Davidson . . . . 176 Family Huenellidae Schuchert & Cooper . . . . 176 Rectotrophia globularis gen. et sp. nov. .... 176 Family Porambonitidae Davidson . . . . . 177 Porambonites (s.s.) sp. . . . . . . . 177 Family Camerellidae Hall & Clarke . . . . . 178 Camerella sp. . . . . . . . . 178 Superfamily Pentameracea M'Coy . . . . . 178 Family Parallelelasmatidae . . . . . . 178 Metacameralla cf. balcletchiensis (Davidson) . . . 178 Order uncertain . . . . . . . . . 179 V. SYSTEMATIC DESCRIPTION OF THE TRILOBITA . . . . 179 Family Asaphidae Burmeister . . . . . 179 Ogygiocaris selwynii (Salter) . . . . . . 179 AND TRILOBITES OF ANGLESEY 129 Family Thysanopeltidae Hawle & Corda . . . . 180 Protobronteus greenlyi sp. nov. ..... 180 Family Illaenidae Hawle & Corda . . . . . 181 Illaenus sp. ........ 181 Stenopareia cf. linnarssoni (Holm) . . . . . 182 Family Harpidae Hawle & Corda . . . . . 183 Selenoharpes(?) sp. ....... 183 Family Trinucleidae Hawle & Corda . . . . . 184 Bergamia(>} sp. ........ 184 Family Raphiophoridae Angelin . . . . . 185 Ampyx sp. (i) . . . . . . . 185 Ampyx sp. (2) . . . . . . . 186 Family Cheiruridae Salter . . . . . . 187 Ceraurinella sp. . . . . . . . . 187 Sphaerexochus sp. ....... 189 Family Pliomeridae Raymond ...... 190 Pliomerops sp. ........ 190 Placoparia sp. ........ 191 Family Calymenidae Burmeister . . . . . 192 Calymenid ......... 192 Family Homalonotidae Chapman ..... 193 Neseuretus monensis (Shirley) . . . . . 193 Family Lichidae Hawle & Corda . . . . . 194 Amphilichas sp. (i) ....... 194 Amphilichas sp. (2) . . . . . . . 195 Family uncertain . . . . . . . . 195 Monella perplex a gen. et sp. nov. . . . . . 196 VI. REFERENCES .......... 197 SYNOPSIS Arenig sandstones, grits and conglomerates rest unconformably on pre-Cambrian rocks and contain a shelly fauna with Baltic affinities, predominantly of brachiopods and trilobites. New brachiopods include Ahtiella quadrata sp. nov., Hesperonomiella carmelensis sp. nov., Monorthis typis gen. et sp. nov., Panderina lamellosa sp. nov., Rectotrophia globularis gen. et sp. nov., Reinversella monensis gen. et sp. nov., Rhynchorthis rotundus gen. et sp. nov. and Pleurorthis costatus sp. nov. A new trilobite, Monella perplexa gen. et sp. nov. is also present. Higher Arenig and Llanvirn shales, grits, conglomerates, shaley breccias and ironstones contain mixed graptolitic and shelly faunas, including one new brachipood, Ahtiella concava. Lower Caradoc rocks resting unconformably on older Ordovician or pre-Cambrian rocks comprise conglomerates and breccias with shelly faunas, and ironstones and graptolitic shales. A brachiopod-graptolite fauna from Llanbabo and Caregonen can be correlated with the Derfel Limestone fauna of the Arenig district. Limestone blocks in a breccia of the same age yielded a brachiopod-trilobite fauna, including Protobronteus greenlyi sp. nov. Graptolitic shales of Llandovery age at Parys Mountain rest on an acid volcanic group of Caradoc (?) age. I. INTRODUCTION AND ACKNOWLEDGMENTS ALTHOUGH Anglesey attracted the attention of several workers in the nineteenth century, our knowledge of the Ordovician stratigraphy is due mainly to the Geo- logical Survey Memoir of Greenly (1919), in which use was made of the standard graptolitic zoning developed by Lapworth, Elles and Wood to date the rocks. The i 3 o LOWER PALAEOZOIC BRACHIOPODS shelly faunas are under-represented in his collections; in particular the important Caradoc fauna from Llanbabo is not represented at all, though a large graptolite fauna is listed from the same locality (Greenly 1919 : 455). The Ordovician fossils have not been the subject of any intensive study since Greenly 's time, or indeed before it. Few species or genera have been erected from among them, and identification has been made in most cases by geologists who were not working on the island. Since the publication of Greenly 's memoir two papers have contained accounts of some of the fossils from his collection. Shirley (1936) in his account of the British Calymenidae referred the calymenids collected by Greenly from the basal beds of the Principal Area to the new species Synhomalonotus monensis (now Neseuretus monensis}, and Whittard (1956 : 17) commented on a specimen of Ampyx from the collection. The writer has already described a new species of gastropod, Mather ella(?) acuticostata, from the Arenig Treiorwerth Formation (1963). I wish to thank Professor A. Williams for his guidance throughout this work, and for his critical reading of the text. The following have commented on specific aspects of the palaeontology: the late Dr. L. R. Cox, Professor C. Poulsen, Professor G. Regnell, Dr. I. Strachan, Mr. R. P. Tripp, Professor H. B. Whittington and Professor A. Wood. Much of the work was carried out during the tenure of post-graduate scholarships of the Queen's University of Belfast and the Ministry of Education (Northern Ireland). Further aid was given by grants from the Systematics Association, and the Sir D. Owen Evans fund of the University College of Wales, Aberystwyth. I am grateful for the help given to me by many friends, including staff and students of the University College of Wales, for their aid in collecting specimens, and for discussions in the field and laboratory. II. SYNOPSIS OF STRATIGRAPHY The Ordovician rocks of Anglesey crop out in a number of areas, separated prin- cipally by upfaulted blocks of the Mona Complex. In general precise lithological correlations cannot be made between them, although two suites of arenaceous and rudaceous rocks are widespread, one of Arenig age and the other Caradocian. (a) Eastern Angelsey On the Menai Straits basal conglomerates and grits (the Garth Ferry Grits) rest on the Mona Complex at Garth Ferry, near Beaumaris, and are overlain by shales with Ptilograptus. The age of the succession is not known with precision, but since the Didymograptus extensus zone is present on the Caernarvonshire shore of the straits between the bridges (Greenly 1919 : 431) the Garth Ferry rocks are probably of approximately the same age. The area around Llangoed is poorly exposed, but a shelly fauna was collected from grey shales (the Tandinas Shales) at Caregonen. The shales are uncleaved and very soft, grey in colour, with plentiful mica flakes parallel to the bedding. The succession is complicated by north-dipping thrusts, though the shales appear to be dipping at low angles. Greenly found the faunas collected from them per- AND TRILOBITES OF ANGLESEY 132 LOWER PALAEOZOIC BRACHIOPODS plexing (1919 : 433), as they appeared to be of widely different horizons. This was due to Lake's identification of Ampyx nasutus Dalman from the shales, a form known to him only from the Didymograptus Ufidus zone in South Wales, while the graptolites found were typical of the Nemagraptus gracilis Zone. The Ampyx is however, possibly a new species, while the associated brachiopods are conspecific with those from the Derfel Limestone of the Bala district (Whittington & Williams 1955). The fauna is: Climacograptus antiquus Lapworth (?), Cl. scharenbergi Lap worth, Climacograptus sp., Nicolella sp., Platystrophia sp., Leptestiina derfelensis (Jones), Sericoidea abdita Williams, dalmanellid brachiopod, ogygiid trilobite, Ampyx sp. (2), Sphaerexochus sp., Amphilichas sp. (2), lamellibranch, Echinosphaerites sp. (b) The Berw Fault Complex Ordovician rocks (the Berw Group) incorporated in the Berw Fault complex, crop out at intervals from Pentraeth, at the head of Red Wharf Bay, to Tai Hirion, south-west of Holland Arms, a lower arenaceous division being succeeded by blue shales. Glanmorfa Shales Blue shales ? Berw Group Dryll Formation Greywackes with interbedded shales 300 ft. Berw-Uchaf Grits Quartz grits and sandstones 60-100 ft. North-east of Holland Arms the basal rocks are poorly exposed, but at Bwlch Gwyn a small exposure of sandstone and shale appears to rest on a pre-Ordovician felsite (Greenly 1919 : 435), though the junction is probably faulted. The sand- stone has yielded: Lenorthis proava (Salter), Skenidioides sp., Rhynchorthis rotundus gen. et sp. nov., Estlandia (?) sp. The same horizon is exposed in Rhyd-yr-arian ravine, where the stream is crossed by the road; the following list is from the collections of Greenly and the writer: Didymograptus hirundo Salter, Lenorthis proava (Salter), Pleurorthis(?) sp., Rhynch- orthis rotundus gen. et sp. nov., Monorthis(?} sp., Reinversella monensis gen. et sp. nov., Rectotrophia(?) sp., Antigonambonites(?) sp., polyzoan, crinoid ossicles. (c) The Llangwyllog Area The faulted outlier around Llangwyllog is also poorly exposed; though no shelly fossils have been found the succession commences with an arenaceous division which is at youngest Llanvirn (Greenly 1919 : 437). Higher shales are Caradoc in age, and an ironstone is present (the Ty'n-yr-onen Ironstone). (d) The Principal Area In the Principal Area the succession is more complete than elsewhere. The basal arenaceous beds of conglomerate, grit and current-bedded sandstone (the AND TRILOBITES OF ANGLESEY 133 i 3 4 LOWER PALAEOZOIC BRACHIOPODS Carmel Formation, the Foel Formation) crop out mainly along the south-east boundary lying unconformably on the Mona Complex. The Carmel Formation is exposed from Rhosneigr to within a mile of Llanerchymedd, and comprises a lower fossiliferous division of sandstones and conglomerates, and an upper sparsely fossili- ferous division with current bedding. The chief fossiliferous localities are: (i) by the roadside one-eighth of a mile north-west of Ty-hen (Greenly 1919 : 442). Lenorthis proava (Salter), Hesperonomiella carmelensis sp. nov., Neseuretus monensis (Shirley), Ogygiocaris selwynii (Salter), Monella perplexa gen. et sp. nov. (ii) in the scarp above Prys-owain-bach cottage, Carmel. L. proava, H. car- melensis, M. perplexa. (iii) small quarry pit 100 yds. north-west of Chaen-bach. Ogygiocaris sp., N. monensis. The type material of Monella perplexa comes from an old quarry, now filled in, 400 yds. north of Bryn Gollen Uchaf, half a mile west of Llanerchymedd. The Foel Formation is at least a partial lateral equivalent of the Carmel Forma- tion, and only occurs east of Llanerchymedd. It consists of conglomerates succeeded by flaggy sandstones with shale partings, but has so far proved unfossiliferous. Above the basal rocks are five variable rudaceous and arenaceous formations ranging in age from the D. extensus zone to the D. bifidus zone; they pass laterally and vertically into poorly exposed shales which contain faunas from the D. mur- chisoni zone. The Treiorwerth Formation is a thick series of sandstones, grits and conglomerates derived from Mona Complex schists and jaspers, exposed between Rhosneigr and Treiorwerth, and resting on the Carmel Formation. South-east of Ffynnon-y-mab, Trefor, the lowest horizons consist of grey-green siltstones with coarse micaceous shale partings, which pass up through 350 ft. of siltstones and sandstones to coarse grits and conglomerates which are typical of the formation. Three hundred yards south-east of Ffynnon-y-mab (Greenly 1919 : 442) graptolite fragments in the sandstones were identified by Elles as ITetragraptus headi (Hall). Sandstones in the same outcrop have a rich fauna, occurring as water-sorted lenticles of disarticu- lated valves: Lenorthis proava (Salter), Monorthis typis gen. et sp. nov., Pleurorthis costatus sp. nov., Panderina lamellosa sp. nov., Hesperonomiella(l} sp., Skenidioides sp. (i), Rhynchorthis rotundus gen. et sp. nov., Reinversella monensis gen. et sp. nov., Rectotrophia globularis gen. et sp. nov., Porambonites (s.s.) sp., Tritoechia sp., Antigonambonites Pyramidalis sp. nov., Mather ella(?) acuticostata Bates, Monella(?) sp., polyzoan fragments, crinoid ossicles. The Nantannog Formation is a thick sequence of shales, with a variable rudaceous content, mainly as scattered pebbles and slabs of phyllite, but sufficiently concen- trated at certain horizons to produce grits and conglomerates with a shaley matrix. The lithology persisted from the D. extensus to the D. murchisoni zones, and some of the lower horizons contain brachiopods of the Nantannog Formation fauna. A fauna indicative of the D. bifidus zone was found by Greenly at two localities, AND TRILOBITES OF ANGLESEY 135 on the same strike. From the first, west of the road at the bend 200 yards west of Fferam-uchaf farm, Llanbabo, Greenly's specimens were re-examined, no more having been found: D. bifidus (Hall), D. hirundo Salter, Orthambonites (?) sp. (i). A shelly fauna was found at the second locality, 190 yards south-east of the farm : D. bifidus (Hall)(?), D. hirundo Salter(P), Lingula sp., Orthambonites (?) sp., Skeni- dioides sp. (2), Ptychopleurdla sp., Dactylogonia sp., polyzoan fragments, crinoid ossicles. Two hundred and fifty yards west-south-west of Fferam uchaf Greenly (1919 : 452) found D. murchisoni (Beck), and his collection also contains: orthid brachiopod, illaenid pygidium, Bergamia(?) sp., Placoparia sp., Cyclopyge(?) sp. Laterally and vertically the Nantannog Formation passes into shales or the Treiorwerth Formation, except at Bod Deiniol, south of Llanbabo, where it is suc- ceeded by a thick succession of conglomerates, pebbly grits and sandstones, the Bod Deiniol Formation. The most prominent member is a conglomerate, 80 ft. thick, which occurs near the base of the formation and forms a scarp south of Bod Deiniol. The formation probably belongs to the D. bifidus zone, as Greenly records graptolites from low in the zone at Bodynolwyn-hir (1919 : 444) in beds underlying the grits, and beds about 100 ft. above the conglomerate member exposed in the bed of the River Alaw have yielded a pendent Didymograptus. The formation loses its topographic expression to the south-east towards Ty-bach cottage, and the grain size becomes finer, although the conglomerate may here be concealed by drift. Fifty yards north of the cottage the writer succeeded in obtaining a fauna from massive grits probably from a horizon above the conglomerate when a trench was being excavated in connection with the building of the Alaw reservoir: Lenorthis sp., Pander ina(?} sp., Paurorthis(?) sp., Apomatella(?) sp., Ahtiella concava sp. nov. North of Dulas Bay a succession of alternating sandstones and shales, the Dulas Formation, with worm burrowing, cone-in-cone concretions, neptunian dykes and current bedding, is well exposed on the shore and poorly inland. On the shore it is faulted against shales containing D. bifidus and D. murchisoni zone faunas. Over much of the Principal Area shales are poorly exposed, and Greenly records both lower Ordovician and Caradoc faunas from a number of localities; no formal stratigraphic name is however proposed for them. One new locality, 100 yards north of Gwredog-uchaf, Rhodogeidio, has a graptolite-trilobite fauna: Dictyonema sp., D. bifidus (Hall), D. artus Elles & Wood, D. stabilis Elles & Wood, Climaco- graptus cf. scharenbergi Lapworth, Climacograptus sp., Glossograptus hincksii fim- briatus (Hopkinson), Bergamia(!} sp. At Parys Mountain a volcanic suite (the Parys Group) rests on shales (the Parys Shales) of the D. bifidus zone or later: graptolites have been found in tips from shafts sunk beneath the volcanic rocks at the west end of the mountain (Greenly 1919 : 458). Although Greenly described the shales immediately beneath and to the north of the igneous rocks as Hartfell in age there is no palaeontological evidence for this. The igneous suite, described by Greenly as a felsite sill, is a complex of rhyolites, autobreccias, ignimbrites, tuffs and shales, intensively cleaved, sheared and silicified (Hawkins 1966 : 13). Above the Parys Group, in the core of the syn- 136 LOWER PALAEOZOIC BRACHIOPODS cline, is a succession of shales and mudstones of Silurian age whose relation to the older rocks is unknown. Llandeilo fossils (Greenly 1919 : 465) have been found associated with an iron- stone at Bonw, and also in a borehole at Llangoed (Greenly 1919 : 432). The extent and thickness of Llandeilo rocks is, however, unknown. Caradoc rocks are well exposed in the north-west of the Principal Area, where a variable group of basal rudaceous rocks overlies the Mona Complex. On Mynydd- y-garn and at Forth Padrig, north of Mynachdy, on both sides of the Carmel Head thrust a thick series of breccias, overlain by shales and alternating breccia beds (the Garn Formation), rests on several horizons in the Complex. The breccia contains slabs of schists and phyllites up to several feet long, and also rounded blocks of shelly limestone; at Porth Padrig, Greenly records a graptolite fauna from the N. gracilis zone in the shales, and the blocks have yielded: Cyrtonotella sp. (2), Palaeostrophomena(?) sp., Ptychoglyptus sp., Kiaeromena(l) sp., Camerella sp., Metacamerella cf. balcletchiensis (Davidson), Protobronteus greenlyi sp. nov., Illaenus sp., Stenopareia sp., Selenoharpes(?) sp., Pliomerops sp. On Pen-bryn-yr-eglwys, and on the coast to the south, the Mona Complex is overlain by a sandy and gritty formation, the Crewyn Formation, which varies in thickness between 60-150 ft. About 2 ft. above the unconformity, 300 yds. east of Trwyn y Crewyn poorly-preserved shells were found: Orthambonites sp., Plaesi- omys sp., Platystrophia(?) sp., lamellibranch, crinoid ossicles. West of Mynachdy, around an old barn called Ysgubor-gader, is a complicated region of folded and faulted shales, grits and pre-Cambrian rocks. Two small exposures of grit, apparently resting on the pre-Cambrian, are poorly exposed 225 yds. south-west and 400 yds. west-south-west of the barn, and contain Plaesi- omys cf. robusta (Bancroft), Orthambonites (?) sp. Dalmanella (s.l.) sp. and a cystid plate. In the Llanbabo region Caradoc rocks either rest on or are faulted against gritty beds of the D. murchisoni zone, but the contact is not exposed (Greenly 1919 : 451-456). The most complete section is seen at Fferam-uchaf where the rocks strike east- west through the farmyard: f Llanbabo Church Grits Pebbly grits alternat- I ing with shales 20 ft. + Llanbabo Formation ^ Fferam Shales Dark Blue shales 60 ft. Fferam Ironstone Ironstone and ferri- I ferous grit 20-40 ft. The ironstone and succeeding shales are also exposed in an old quarry south of Llanbabo (Greenly 1919 : 543), and graptolites of the N. gracilis zone were obtained from the shales in both areas by Greenly and his collectors. The Llanbabo Church Grits are best exposed in the old quarry 100 yds. south- west of the church, where 20 ft. of strata are exposed, pebbly graded grit beds up to 2 ft. thick alternating with silty blue-grey shales. The latter contain a graptolite fauna, regarded by Elles (in Greenly 1919 : 455) as being high in the N. gracilis zone, above the Fferam Shales. The grits contain a shelly fauna, mainly of dis- AND TRILOBITES OF ANGLESEY 137 articulated brachiopod valves, which correlates well with the Tandinas Shales at Careg-onen, and with the Derfel Limestone of the Arenig area (Whittington & Williams, 1955): Orthambonites (?) sp. (2), Nicolella humilis Williams, Cyrtonotella sp. (i), Dolerorthis cf. tenuicostata W'illiams, Platystrophia precedens major Williams, Ptychopleurella sp. (2), Plaesiomys (Dinorthis) sp., Salopia salteri gracilis Williams, Onniella(?) sp., Horderleyella(!} sp., Kullervo aff. panderi Opik, Clitambonites(l} sp., Ilmarinia sp., Palaeostrophomena sp., Eoplectodonta lenis Williams, Leptaena(l} sp., Echinosphaerites sp. The Llanbabo Church Grits are also exposed at Fferam-uchaf, in the north-east corner of the field immediately east of the farmhouse (Greenly 1919 : 451 and outcrop labelled 'conglm.' in fig. 207), with a similar fauna: Orthambonites (?) sp., Platystrophia(l] sp., Ptychopleurella sp. (2), Plaesiomys sp., Dolerorthis (?) sp., Salopia(?} sp., Bilobia aff. musca Opik, Leptestiina sp., Eoplectodonta lenis Williams, Leptaena sp. Above the basal Caradoc rocks of the N. gracilis zone are shales, poorly exposed and of uncertain extent. Greenly (1919 : 454-455) records graptolites from the zones of Cl. wilsoni and Dicranograptus clingani, from shales at Llanbabo which probably rest on the Llanbabo Church Grits. There is no evidence of the thickness of these zones, or of their relation one to another, though the close proximity of the outcrops to the older Caradocian rocks suggests that the zones are not very thick. In the Eilian sector no fossils have been found to add to Greenly's collection (1919 : 466), which contains Glyptograptus teretiusculus (Hisinger) and Placoparia sp. The section seen on the shore between the Carmel Head Thrust at Porth-y- corwgl and the gneisses south of Porth-y-gwichiaid contains a number of units, separated by faults. Between Porth-y-corwgl and Fresh Water Bay are a series of conglomerates, pebbly grits and shales (the Fresh W T ater Bay Group), all apparently younging south and overturned. Between Ogof Fach and Ogof Fawr are highly cleaved and sheared grey shales, intruded by acid sills. On the northern side of Porth-y-gwichiaid are fine siltstones and mudstones, with some worm burrows, also cleaved and folded; it is not known in which direction they young. On the south side of the Porth is a series of siltstones, shales, conglomerates and an iron- stone, partly slumped in some horizons, and disposed in a complex syncline. (e) The Gynfor Outliers On the north coast the Ordovician rocks are exposed in a number of faulted and folded outliers resting on the Mona Complex. Two groups are present, separated by a disconformity. The earlier (Porth \Ven Group), of Arenig Age, is of two conglomerate and grit formations, the lower being a purple conglomerate (the Hell's Mouth Conglomerate), absent from some exposures, and the upper a pale brown weathering sequence of conglomerates, grits and sandstones containing an Arenig fauna (the Torllwyn Formation). Brachiopods were obtained from some of the localities listed by Greenly (1919 : 469-470) : (i) 10 ft. above the unconformity on the north side of Ogof Gynfor (exposure 138 LOWER PALAEOZOIC BRACHIOPODS in Greenly op. cit., PI. XXIX): Rhynchorthis rotundus gen. et sp. nov., Estlandia(?) sp. (ii) about 40 ft. above the unconformity, 45 yds. north of the last locality, north of the faulted syncline containing Gynfor Shales in the core: Lenorthis sp., Hesperonomiella(l] sp., Monorthis sp., Panderina cf. lamel- losa sp. nov., Pleurorthis sp., Skenidioides sp., Rhynchorthis sp., Tritoechia sp., Antigonambonites sp., Inversella (Reinversellal] sp., Ahtiella quadrata sp. nov., crinoid ossicles, polyzoan fragments. (iii) Thirty to forty ft. above the unconformity, on the north side of the ridge of Mynydd-pant-y-gaseg, 85 ft. east of the summit: Orthambonites(l] sp., Ahtiella(?) sp. (poorly preserved). (iv) in the cutting of the Graig Wen tramway, 70 yds. below the winding house, collected from loose material: Lenorthis cf. proava (Salter), Panderina(?) sp., Rhynchorthis^} sp., Antigonambonites (?) sp. The specimens of Lenorthis examined include a number from the Geological Survey collection ^1470-1502). The upper group (Llanbadrig Group) is Caradoc in age, with an ascending se- quence of cherty shales (Gynfor Shales), an ironstone (Penterfyn Ironstone) and shales and ferriferous grits (Forth Pridd Formation). Faunas of graptolites from the lower and upper formations (Greenly 1919 : 470-471) come from the N. gracilis zone, and hence (it is unlikely that the Arenig fossils are derived) there must be a plane of disconformity within the Torllwyn Formation or at its top. Erosion surfaces are present within it, and the contact with the shales above is also abrupt, with the shales resting on a slightly irregular surface of coarse conglomerate. The Silurian shales of Parys Mountain lie above the volcanic Parys Group but the nature of the contact between them is unknown. Greenly (1919 : 481-482) lists graptolite faunas from all the Llandovery zones. There is no palaeontological evidence for Silurian rocks at Rhos-mynach (Greenly 1919 : 482-483), and the shales there are intercalated between rhyolites which are probably equivalent to the Parys Group. (f) Faunal Lists Explanation of symbols: ex. = Didymograptus extensus Zone; hi. = D. hirundo Zone; bi. = D. bifidus Zone; mu. = D. murchisoni Zone; te. = Glyptograptus teretiusculus Zone; gr. = Nemagraptus gracilis Zone. BRACHIOPODA ex. hi. bi. mu. te. gr. Ahtiella concava sp. nov. ... X Ahtiella quadrata sp. nov. ... X Antigonambonites pyramidalis sp. nov. . x Apomatella(>) sp. . Bilobia aff. musca (Opik) Camerella sp. ..... X ? Clitambonites(l) sp. . Cyrtonotella sp. (i) AND TRILOBITES OF ANGLESEY I 39 ex. hi. bi. mu. te. gr. Cyrtonotella sp. (2) X ? Dactylogonia sp. . Dalmanella(?) sp. X Dolerorthis cf. temncostata Williams Eoplectodonta lenis Williams . Estlandia(l) sp. . Harknessella(?) sp. X Hesperonomiella carmelensis sp. nov. . X ? Horderleyella(l] sp. X Ilmarinia sp. ..... X Kiaeromena(t) sp. .... X ? Kullervo aff . panderi (Opik) . Lenorthis proava (Salter) Lenorthis sp. Leptaena sp. ..... X Leptestiina derfelensis (Jones) . . X Metacamerella cf . balcletchiensis (Davidson) X ? Manor this typis gen. et sp. nov. . . X Nicolella humilis Williams ... X Onniella(l) sp. ..... Orthambonites(t) sp. (i) Orthambonites(?) sp. (2) ... Palaeostrophomena sp. . Palaeostrophomena(?) sp. Panderina lamellosa sp. nov. . Paurorthis(>} sp. . Plaesiomys sp. ..... X Plaesiomys cf . robusta (Bancroft) . . X Plaesiomys (Dinorthis) sp. ... X Platystrophia precedens major Williams . X Plectorthis(?) sp. . Pleurorthis costatus sp. nov. . Porambonites (s.s.) sp. . Ptychoglyptus sp. ..... X ? Ptychopleurella sp. (i) . Ptychopleurella sp. (2) . Rectotrophia globularis gen. et sp. nov. Reinversella monensis gen. et sp. nov. Rhynchorthis rotundus gen. et sp. nov. Salopia salteri gracilis Williams Sericoidea abdita Williams Skenidioides sp. (i) . . . X Skenidioides sp. (2) .... X Tritoechia sp. ..... X TRILOBITA Amphilichas sp. (i) X ? Amphilichas sp. (2) .... Ampyx sp. (i) ..... Ampyx sp. (2) ..... Bergamia(l] sp. ..... Calymenid ...... 140 LOWER PALAEOZOIC BRACHIOPODS Ceraurinella sp. Illaenus sp. Monella perplexa gen. et sp. nov. Neseuretus monensis (Shirley) Ogygiocaris selwynii (Salter) . Placoparia sp. Pliomerops sp. . Protobronfsus greenlyi sp. nov. Selenoharpes(l] sp. Sphaerexochus sp. Stenopareia sp. . hi. bi. tc. x? x? x? X? X? X? X? X X? III. FAUNAL AFFINITIES AND CORRELATIONS The basal rocks of the Principal Area, the Carmel Formation, have a fauna characterized by few species, but a large number of individuals, especially Lenorthis proava (Salter), which occurs in vast numbers as disarticulated valves. Similar species are found elsewhere in Wales at this horizon, at Arenig in the Henllan Ash, and at St. David's and the Carmarthen- Whitland region. In the latter regions they are described as Orthis carausii Salter, and are associated with Lenorthis alata (Salter) . Ogygiocaris selwynii (Salter) and Neseuretus monensis (Shirley) , which are found sporadically, belong to genera which are widespread throughout Wales at this time. Monella perplexa gen. et sp. nov. is at present cryptogenic, but may be a survivor of the Cambrian Corynexochida. Hesperonomiella carmelensis sp. nov. belongs to a genus described by Ulrich & Cooper (1938) from the upper Canadian (approximately upper Llanvirn) of much of North America. The genus is described as having chilidial plates, but in some cases they are very rudimentarily developed, and in this species are not developed at all. It is possible that later species of Hesperonomiella and its ally Hesperonomia have their origin in forms comparable with this species. Near the base of the overlying Treiorwerth Formation, and at the base of the system along the Berw Fault is a rich shelly fauna, consisting almost wholly of brachiopods. Three stocks, Lenorthis proava, Hesperonomiella carmelensis, and Monella(?) sp. persist from the Carmel Formation, but are joined by a variety of forms, some new, some with American affinities, and some very similar to contem- porary Baltic faunas. Rhynchorthis rotundus gen. et sp. nov., Porambonites sp. and Antigonambonites pyramidalis sp. nov. are closely related to contemporary Baltic stocks (Alichova 1953, Table i). Porambonites and Antigonambonites appear similar in morphological grade to the earliest Russian species (of Bj/? in Estonia, O 1 v 1 on the Russian platform) and one can correlate the Anglesey fauna with con- fidence with this horizon. Rhynchorthis is similar to Angusticardinia, also from this level, but appears to be more primitive in its features. Panderina lamellosa is more advanced than contemporary Russian species, again from this horizon. Reinversella monensis gen. et sp. nov. is closely related to Inversella Opik from Estonia and Norway, a later genus from the upper Arenig (B m and later) (Opik I 933 : 2 3)- Ahtiella quadraia sp. nov., is a member of a genus which is also found AND TRILOBITES OF ANGLESEY 141 later in the Baltic region (B^-C^. It is thus probable that the two faunas were closely linked at this time with migration possible in either direction. The stocks with American affinities, Pleurorthis costatus sp. nov. and Tritoechia sp., differ markedly from those just described. In America Pleurorthis is known from the much later Mystic conglomerate of Quebec and the Table Head Series of Newfoundland (both upper Llanvirn), with rather different species (Cooper 1956 : 330-333). Tritoechia ranges throughout the Arenig equivalents in North America (much of the Canadian of Twenhofel et al., 1954, chart 2). Monorthis typis gen. et sp. nov. is of uncertain affinities, and makes its only known appearance in this fauna. Skenidioides can probably best be regarded as indigenous, as it occurs in the Mytton Flags of Shropshire and at Tourmakeady, Co. Mayo (Professor A. Williams, personal communication), and is also present in the Whitland region. Rectotrophia globularis gen. et sp. nov. has affinities with both American and Bohemian forms. Mather ella, a sinistral gastropod, belongs to a small but widespread group of shells, with both American and Bohemian members. Llanvirn shelly faunas are sparse, as the sediments are predominantly shaley. Orthambonites(?) sp. (i) may be regarded as indigenous, being closely related to Lenorthis, as may Skenidioides sp. (2) descended from the Arenig species. Ahtiella concava sp. nov. either is descended from the Arenig species, or is a later migrant from the Baltic region. Ptychopleurella sp. (i) is an atypical member of the genus, possibly earlier than any of the American species. Trinucleids make their appear- ance in Anglesey at this time, but are indigenous south British elements which have been recorded widely within Wales (Whittard 1955-64; Whittington 1966), and may well have reached Anglesey earlier than this time. The dominant shelly fauna taken from rocks belonging to the Nemagraptus gracilis Zone is closely comparable with that found at Derfel, near Arenig (the Derfel Limestone fauna of Whittington & Williams 1955), which has been divided into a native association of elements known in Wales from older rocks, together with stocks which migrated from the east Baltic, Russia, Bohemia and the North Atlantic Province. As developed in Anglesey the fauna has similar elements. Native stocks include Orthambonites (?) sp. (2), Ptychopleurella sp. (2), Dinorthis sp., Eoplectodonta lenis Williams, Sericoidea abdita Williams, Salopia salteri gracilis Williams, Onniella(?) sp., Horderleyella sp., Amphilichas sp. (2), Ampyx sp. (2), and trinucleids. Elements regarded by Whittington & Williams as exotic include Nicolella humilis Williams, Cyrtonotella sp., Dolerorthis cf. tenuicostata Williams, Platystrophia precedens major W'illiams, Palaeostrophomena sp., Leptaena sp., Leptes- tiina derfelensis (Jones) and Kullervo aff. panderi Opik. Other stocks occurring in Anglesey, but not so far found at Derfel, provide further evidence of the Baltic affinities of the fauna. Bilobia aff. musca Opik has strong affinities with Opik's species, from this horizon in the east Baltic. Ilmarinia sp. and Clitambonites(l] sp. also belong to Baltic genera, though Ilmarinia occurs at a higher horizon in the east. In the light of the affinities of the Arenig faunas discussed above, the Derfel Limestone fauna is best regarded, not as an invasion of the region by an entirely new fauna during the N. gracilis transgression, but as the continuation of an association which existed in the lower Ordovician. 142 LOWER PALAEOZOIC BRACHIOPODS The fauna of the limestone blocks in the Garn Breccia at Forth Padrig is not younger than the N. gracilis Zone, and may be older. The trilobites of the lime- stone are similar to those of the Derfel Limestone, Ceraurinella, Amphilichas and Illaenus being common to both. Other trilobites in the fauna are Selenoharpes(?) sp., a calymenid, Piomerops sp. and Protobronteus greenlyi sp. nov. All these may be traced to the north Atlantic province, to which Whittington attributes Cerauri- nella(?}, Illaenus (s.l.) and Harpes (s.l.) from the Derfel Limestone. The brachiopods of the fauna are more ambiguous. Palaeostrophomena(l] sp., Cyrtonotella sp., and Kiaeromena(t} sp. have Baltic affinities, and the genera occur in the Derfel Lime- stone. Ptychoglyptus is known from slightly higher horizons in Norway (4b or the Climacograptus peltifer zone; Spjeldnaes 1957 : 61), and from the Girvan area in Scotland (Williams 1962 : 193). Camerella and Metacamerella are both found in Scotland and America. Thus these latter three brachiopod genera, together with the trilobites, may indicate an intermingling of the Baltic and Scoto-Appala- chian faunas, at least in the limestone facies, if not in the grits at Llanbabo or in the Careg-onen and Derfel sediments. It appears likely, from lithological evidence, that the source area of limestone deposition lay to the north of Anglesey, but prob- ably still on the upfaulted Irish Sea Landmass. The specimens examined either come from Greenly's collection or were collected by the author. Those with numbers prefixed by 'BB' (brachiopods) or Tn' (trilo- bites) have been donated to the British Museum (Natural History). Greenly's collection is now in the possession of the Geological Survey, and the specimen numbers bear the prefix 'Af. IV. SYSTEMATIC DESCRIPTION OF THE BRACHIOPODA Order ORTHIDA Schuchert & Cooper 1932 Suborder ORTHIDINA Schuchert & Cooper 1932 Superfamily ORTHACEA Woodward 1852 Family HESPERONOMIIDAE Ulrich & Cooper 1936 Genus HESPERONOMIELLA Ulrich & Cooper 1936 Hesperonomiella carmelensis sp. nov. (PI. i, figs. 1-6) 1919 Rafinesquina cf. llandeiloensis (Davidson); Matley in Greenly : 142. DIAGNOSIS. Semicircular to subquadrate Hesperonomiella about three-quarters as long as wide, hinge line equal to the greatest width, cardinal angles about 80-85; valves subequally and gently convex, lateral and anterior commissures plane; pedicle valve slightly carinate with convex lateral flanks, interarea wide, plane, apsacline, delthyrium open, width at teeth one-quarter the width of the valve; brachial valve with shallow rounded sulcus dying out anteriorly, interarea wide, shorter than the ventral one, anacline, notothyrium wide and open; neither umbo incurved; ornament finely and unequally multicostellate, costellae flat-topped with AND TRILOBITES OF ANGLESEY 143 narrow interspaces, numbering thirty per 5 mm. at 5 mm. from the umbo, arising by bifurcation, every fifth or sixth costella more prominent; teeth triangular, dental lamellae widely divergent forwards and slightly divergent to the floor of the valve, short but not receding, continued as low ridges around the muscle scars; muscle scars triangular in outline and relatively confined to the delthyrium, in length one-quarter that of the valve, adductor and diductor scars expanding forwards and equal in length; median trunks of the vascula media slightly impressed, con- verging forwards from the ends of the diductor scars to come in contact at half the length of the valve and then diverging again; cardinal process a simple lenticular septum with low lateral ridges parallel to its posterior half; brachiophores diverging at 80, short and triangular in cross section, ends bevelled, largely adpressed to the valve surface; muscle scars and mantle canals not seen; subperipheral rim present. TYPE SPECIMENS (measurements in mm.) Length Width HOLOTYPE. Internal mould of brachial valve (66.30529) 17-6 24-4 PARATYPES. Internal mould of pedicle valve (66.30530) 19-6 Internal mould of pedicle valve (66.30531) 19-2 26-9 Internal and external moulds of pedicle valve (66.30532a-b) .... External mould of brachial valve (66.30533) 19-3 HORIZON AND LOCALITY. Carmel Formation, sandstone 50 yds. north-east of Prys-o wain-bach, Carmel. N.G.R. 38878282. DISCUSSION. Although the family Hesperonomiidae as erected by Ulrich & Cooper (1938 : 114) was defined as comprising forms with a chilidium, some of the species described by them have only rudimentary chilidial plates, which may be interpreted as a thickening of the inner edge of the interareas, and a swelling of the brachiophores (cf. Ulrich & Cooper 1938, PI. 19, figs. 9, 10, 14, 17). Two genera were described, Hesperonomia with piano- or concavo-convex valves, and Hes- peronomiella with gently biconvex valves. The new species therefore belongs in the latter genus. All the described species have a uniform ornament, whereas the new species is unequally parvicostellate. Internally the closest species is Hespero- nomia louisensis Ulrich & Cooper, from the Sarbach formation, Alberta (Ulrich & Cooper 1938 : 120), which has almost identical ventral musculature and dorsal cardinalia, but has a concave brachial valve and equally parvicostellate ornament. The specimens from the type locality are all very uniform in size, and to some extent distorted. The smallest pedicle valve had a length of 9-1 mm., and in a sample of eleven pedicle valves the average length was 16-6 mm., with a variance of 4-42, suggesting that the sample was current drifted with good sorting. i 4 4 LOWER PALAEOZOIC BRACHIOPODS Genus MONORTHIS nov. DIAGNOSIS. Quadrate shells, widest at a long straight hinge line, alate, with slightly acute cardinal angles; lateral profile flatly biconvex, with very low pyra- midal pedicle valve and evenly convex brachial valve; pedicle valve with a low carinate fold with plane flanks, the rest of the surface evenly convex, almost flat; brachial valve with a deep rounded sulcus, swollen folds on either side of it, and concave lateral margins; lateral commissure flat, anterior commissure uniplicate; ventral interarea short and wide, apsacline to almost catacline, delthyrium open, dorsal interarea shorter, anacline, notothyrium open; surface finely multicostellate. Ventral interior with receding dental lamellae, teeth and musculature not seen. Dorsal interior with elevated notothyrial cavity; cardinal process a thin ridge; brachiophores thin and short, supported by a mass of callus, sockets thin and deep ; adductor scars not seen but separated by a large median ridge corresponding to the exterior sulcus. TYPE SPECIES. Monorthis typis sp. nov. from the Treiorwerth Formation. DISCUSSION. The simple cardinalia in the brachial valve, together with the transverse shape and the convexity of valves, form the distinctive features of the genus. Metorthis Wang is similar in shape, but has a thickened cardinal process and muscle scars like those of Dinorthis, whereas this genus seems to have the confined muscle scars of Orthis. The genus is tentatively placed in the Hesperono- miidae, since it agrees with the diagnosis of that family (Ulrich & Cooper 1938 : 114) except that neither chilidial plates nor a chilidium are present. The structure interpreted by Ulrich & Cooper as chilidial plates may be no more than the thick- ening of the inner edge of the interarea where it forms the posterior part of the brachiophores. Monorthis typis gen. et sp. nov. (PI. i, figs. 7-13) 1919 Orthis (Hebertella) vespertilio J. de C. Sowerby; Matley in Greenly : 442. DIAGNOSIS. Quadrate biconvex Monorthis, widest at a long straight hinge-line, alate, with slightly acute cardinal angles; lateral profile flatly biconvex, with very low pyramidal pedicle valve and an evenly convex brachial valve; pedicle valve with a low carinate fold with plane flanks, the rest of the surface evenly convex, almost flat, interarea short and wide, apsacline to almost catacline, delthyrium open; brachial valve with a deep rounded sulcus, swollen folds flanking it, and concave lateral margins, interarea shorter than the ventral one, anacline, noto- thyrium open; surface of both valves finely multicostellate, costellae numbering four per mm. at the shell margins but everywhere poorly preserved; ventral interior with receding dental lamellae, teeth not seen; musculature not seen but probably confined ; low ridges marking the sides of the fold are aligned with the dental lamellae ; dorsal interior with small elevated notothyrial platform; cardinal process a thin ridge; brachiophores short and thin, supported by a mass of callus cementing them AND TRILOBITES OF ANGLESEY 145 to the sides of the notothyrial cavity; sockets thin and deep; adductor scars prob- ably small, and separated by a large median elevation corresponding to the exterior sulcus. Length Width TYPE SPECIMENS (measurements in mm.) HOLOTYPE. Internal mould of brachial valve (BB. 30534) 7-1 PARATYPES. Internal and external mould of brachial valve (BB.30535a-b) . . . 6-9 Internal and external moulds of pedicle valve (BB . 30536a-b) . . . 7-1 n-o TYPE HORIZON AND LOCALITY. Treiorwerth Formation, sandstones 300 yds. south-east of Ffynnon-y-mab, Trefor. N.G.R. 36247950. DISCUSSION. The new species is generically distinct from other known ortha- ceans, and can be distinguished by features referred to in the generic description from various hesperonomiids with which it is most closely related. The poor preservation of the valves makes it impossible to carry out any analysis of the ribbing or of the various dimensions, except to remark that the average percentage length of five brachial valves relative to width was 62-6 (range 55 '3-73*4). Family ORTHIDAE Woodward 1852 Subfamily ORTHINAE Genus CYRTONOTELLA Schuchert & Cooper 1931 Cyrtonotella sp. (i) (PI. 2, figs. 9, 10, 13) FIGURED SPECIMEN (measurements in mm.) Length Width Internal and external mould of brachial valve (BB. 3 o52ia-b) .... HORIZON AND LOCALITY. Llanbabo Formation, Llanbabo Church Grits, Church Quarry, Llanbabo. N.G.R. 37758672. DISCUSSION. Two valves have been found, one being very incomplete, the other a brachial valve in fair condition. It is semi-circular, with a slight sulcus. The hinge-line is straight, with an anacline interarea and probably an open notothyrium. The ornament is multicostellate ; the margin has more than forty ribs but the details of the branching are obscure. Internally the cardinal process is simple and continuous with a median septum, the brachiophores are orthoid, diverging at 80, and the sockets are elongated parallel to the hinge-line. These characters agree well with those of the brachial valve figured by Williams (in Whittington & Williams 1955, pi. 38, figs. 14-16), and referred to Cyrtonotella aff. kukersiana (Wysogorski) . 146 LOWER PALAEOZOIC BRACHIOPODS Cyrtonotella sp. (2) (P.. 2, figS. 14-16) Length Width FIGURED SPECIMENS (measurements in mm.) Exterior of incomplete pedicle valve (BB . 30522) . 7-9 Exterior of incomplete brachial valve (66.30523) . 13-5 External mould of incomplete brachial valve (66.30524) . 8-9 HORIZON AND LOCALITY. Garn Formation, Limestone blocks in breccia beds, Forth Padrig, Mynachdy. N.G.R. 30539279. DISCUSSION. The valves have the external features of Cyrtonotella, but the interareas and the internal features are concealed. The pedicle valve is strongly convex, and is probably semi-circular in outline with a straight, slightly alate hinge-line ; the interarea cannot be very long. The brachial valve is gently concave, with a slight median sulcus in one specimen (66.30524). The ornament of both valves is slightly fascicostellate, with seven to twelve costellae per 5 mm. antero- medianly, and the interspaces have closely spaced fine growth lines. The pattern of the branching of the ribs cannot be made out. Owing to the incompleteness of the valves it is not possible to compare them closely with any other species. Genus LENORTHIS Andreeva 1955 Lenorthis proava (Salter) (PL i, fig. 21 ; PI. 2, figs. 1-8) 1866 Orthis calligramma var. proava Salter: Appendix 335-336, pi. 22, fig. i. 1868 Orthis Carausii (Salter ms.); Davidson : 315, pi. 16, fig. 23. 1869 Orthis Carausii (Salter ms.); Davidson : 229, pi. 33, figs 1-7. 1869 Orthis calligramma var. proava Salter; Davidson : 241, pi. 35, figs. 13-15. 1883 Orthis carausii Salter; Davidson: 182-184, pi- J 4- ^g 8 - 21-26. 1912 Orthis proava Salter; Matley : 78-79. DIAGNOSIS. Subquadrate biconvex Lenorthis five-sixths as long as wide and one-third as deep as wide, the pedicle valve being twice as deep as the brachial valve; widest at the hinge line, with cardinal angles of approximately 90, anterior and lateral commissures plane; pedicle valve convex, slightly carinate, interarea curved, apsacline, one-sixth the length of the valve; brachial valve gently convex with a shallow rounded median sulcus and concave flanks, interarea anacline, shorter than the ventral one ; ornament of simple rounded costae with equal rounded interspaces, numbering sixteen to twenty, with a wave-length of 0-93 mm. at 5 mm. from the dorsal umbo, the pedicle valve bearing a median costa and the brachial valve four costae in the sulcus ; costae covered by fine filae, growth lines rarely seen except at the margins of adult shells; ventral interior with blunt triangular teeth and small crural fossettes; dental lamellae vertical, receding; muscle scars confined to the delthyrium but details not seen, width three-twentieths that of the valve, length length unknown; dorsal interior with thick median septum running half the length of the valve; adductor scars quadripartite, on either side of the septum, AND TRILOBITES OF ANGLESEY 147 occupying four-tenths the width of the valve; margins of both valves crenulated. FIGURED SPECIMENS (measurements in mm.) Length Width Internal mould of brachial valve (BB. 30512) . 10-5 I5'i Internal and external moulds of pedicle valve (BB.305i3a-b) 11-7 15-8 Internal mould of pedicle valve (66.30514) . . distorted Internal and external moulds of brachial valve (BB.305i5a-b) . . . . n-o Internal mould of pedicle valve (Af . 1337) . . 11-4 15*0 HORIZON AND LOCALITIES. Carmel Formation, sandstones, 50 yds. north-east of Prys-owain-bach cottage, Carmel. N.G.R. 38878283. Specimen Af . 1337 is from the same horizon, 130 yds. north-west of Ty-hen, Treiorwerth. N.G.R. 35567872. DISCUSSION. The specimens of L. proava from all the localities in the Carmel Grits are preserved in a coarse sandstone, so that the finer detail of the ornament and of the mantle canal patterns is lost. It is seldom possible to count all the costae, since the finer ribs close to the hinge line are not preserved, and the anterior border of the ventral muscle scars is not seen. These scars may be triangular in shape, with the adductors not enclosed by the diductors and equal in length to them. In ten brachial valves the costae 5 mm. anteromedianly from the umbo have a mean wavelength of 0-93 mm. (var 0-0141). In the interior of the brachial valve the anterior and posterior adductor scars are equal in area, the posterior pair deeply sunk beneath the notothyrial platform. The brachiophores are closely adpressed to the edges of the platform, and the ends are bevelled. The majority of the figured specimens come from Prys-owain-bach, as here the species may be found in greatest abundance, and without much distortion. When first described by Salter, the locality was given as 'grits among the black shales of Llanerchymedd, Anglesey' (1866 : 336). No type locality is given for the figured specimens, which have since been lost. Earlier in the same work (259) the species, as Orthis calligramma var., is listed as occurring at a locality one mile north-west of Llanerchymedd, at Treiorwerth, and at Tyn-twr, 4 miles south of Llangefni. The first of these localities cannot easily be located, and good specimens are not found in that region; the second locality is that listed above at Ty-hen. TABLE i (a) (b) 1 (var. i) 10-36 (5-017) 9-44 (2-600) w (var. w) 12-12(5-438) 12-70(3-736) r 0-753 0-787 a (var. a) 1-041 (0-01339) i' J 99 (0-01092) a (var. b) i 34 (i 513) i 38 (i 0054) TABLE i. Statistics of length (1) and width (w) of (a) thirty-five pedicle valves and (b) fifty brachial valves of Lenorthis proava (Salter) from sandstones 50 yds. north-east of Prys-owain-bach, Carmel, 148 LOWER PALAEOZOIC BRACHIOPODS Lenorthis sp. (PI. 2, figS. 11-12) FIGURED SPECIMENS (measurements in mm.) Length Width Internal mould of pedicle valve (BB.3o6oia) Internal mould of brachial valve (BB . 30602) . 11-7 14-6 (est.) HORIZON AND LOCALITY. Bod Deiniol Formation, grits in temporary excavation 50 yds. north of Ty-bach cottage, Bod Deiniol. N.G.R. 37688528. DISCUSSION. The species is very similar to Lenorthis proava, and is probably closely related. The ratio of length to width of the brachial valve is very similar; in five valves the mean length is 9-56 mm. and width 12-68 mm. There may, however, be more costae, as at least twenty-four can be counted in some specimens, and their wavelength 5 mm. from the umbo in the brachial valves is approximately 0-75 mm. compared with 0-95 mm. in L. proava. Genus ORTHAMBONITES Pander 1830 Orthambonites (?) sp. (i) (PI. i, figs. 14, 16, 17) 1919 Orthis cf. proava Salter; Matley in Greenly : 452. FIGURED SPECIMEN (measurements in mm.) Length Width Internal and external moulds of brachial valve (Af. 1398-9) . 6-9 HORIZON AND LOCALITY. Nantannog Formation, gritty shales by well on the west side of the road, 220 yds. west of Fferam-uchaf. N.G.R. 36188667. DISCUSSION. The valve has about twenty rounded costae, with late internal and external bifurcations, and with fine parvicostellae in the interspaces. In shape the valve is semicircular, with rounded cardinal angles and the greatest width just anterior to them, gently convex and slightly sulcate. The internal details are similar to those of Lenorthis proava (Salter). Division of the costae is described by Cooper (1956) in two species, 0. bifurcatus and 0. divaricatus. The latter species, with its few late bifurcations, is very similar. Orthambonites (?) sp. (2) (PI. i, figs. 15, 18-20) DESCRIPTION. Small subcircular Orthambonites or Lenorthis with the more con- vex pedicle valve four-fifths as long as wide and one quarter as deep as long, orna- mented by about seventeen rounded costae with a wavelength of 07 mm. at 5 mm. from the ventral umbo. AND TRILOBITES OF ANGLESEY 149 FIGURED SPECIMENS (measurements in mm.) Length Width Internal mould of pedicle valve (66.30510) . . 10-7 12-0 Internal and external moulds of pedicle valve (BB.305na-b) 4-96-3 HORIZON AND LOCALITY. Llanbabo Formation, Llanbabo Church Grits, Church Quarry, Llanbabo. N.G.R. 37758672. DISCUSSION. A few pedicle valves of Orthambomtes(?) have been found from the Llanbabo Grits, together with a few fragmentary brachial valves. The numbers found are too few to analyse statistically, the mean length and width of three pedicle valves being 8-7 mm. and 10-1 mm. respectively. The species recalls 0. parvicrassi- costatus Cooper, from the Caradoc of the Girvan area (Williams 1962 : 98), which has about nineteen costae on the pedicle valve, angular in cross section. Neither this species nor the preceding one can be definitely assigned to Orthambonites, since the course of the vascula media has not been observed. Genus PLEURORTHIS Cooper 1956 Pleurorthis costatus sp. nov. (PI. 2, figs. 17-19; PI. 3, figs. 1-4, 6) DIAGNOSIS. Subequally biconvex, transverse, subquadrate to semicircular Pleurorthis, length seven-tenths the maximum width, which is at or just anterior to the hinge-line ; cardinal angles rounded to slightly acute ; lateral commissures almost straight, anterior commissure uniplicate; pedicle valve initially with a median fold, reversing to form a sulcus with gently curved flanks at about 3-4 mm. from the umbo; ventral interarea slightly curved, apsacline, about one-fifth the length of the valve; brachial valve initially with a slight sulcus, reversing to form a fold corresponding to the ventral sulcus, interarea wide, anacline, shorter than the ven- tral one, notothyrium open; ornament on both valves of sharp angular costae, about ten being primary, increasing by bifurcation and numbering about eight per 5 mm. antero-medianly at 5 mm. from the umbo, growth lines not seen; in ventral interior teeth blunt, triangular, dental lamellae descending vertically to the floor of the valve and slightly receding, diverging anteriorly at 70; muscle scars largely confined to the delthyrial cavity, elevated on a callosity ending anteriorly in a blunt forward pointing 'V; adductor track equal in width to one diductor scar, both sets of scars expanding forwards ; vascula media trunks parallel and submedian ; in dorsal interior notothyrial platform low, one-sixth the width of the valve ; cardinal process a simple ridge ; brachiophores blade-like, diverging from each other at more than 90, supported only by the notothyrial platform; sockets are pits just below the hinge-line; adductor scars extend to the midlength of the valve, separated by a median ridge of the same length, the posterior pair the smaller, wider than long, anterior pair triangular, coming to a blunt point close to the ridge; costellae im- pressed on the inner surface of young valves. i 5 o LOWER PALAEOZOIC BRACHIOPODS TYPE SPECIMENS (measurements in mm.) HOLOTYPE. Internal mould of brachial valve (BB. 30516) PARATYPES. Internal and external moulds of pedicle valve (BB.3o5i7a-b) Internal mould of pedicle valve (BB. 30518) Internal and external moulds of brachial valve (BB.30555a-b) Length Width 10-5 19-9 I2-O 7'9 TYPE HORIZON AND LOCALITY. Treiorwerth Formation, sandstones, 300 yds. south-east of Ffynnon-y-mab, Trefor. N.G.R. 36247950. DISCUSSION. The new species conforms to the generic diagnosis of Pleurorthis, but differs markedly from the species described by Cooper (1956 : 329-333). The ornament is much more coarsely costellate than even the coarsest described by him, the development of fold and sulcus is much more pronounced, and internally the described species have no excessive development of secondary calcite in the larger shells. This last trend in the new species gives rise to a pseudospondylium, and leads to the obliteration of all internal impressions of the costellae. I (var. 1) w (var. w) r a (var. a) b (var. b) TABLE 2 (a) 8-56(3-433) 12-26 (5-610) 0-867 1-124 (0-00653) 2-639 (0-509I) (b) 7-55 (2-891) 11-40 (6-181) 0-842 1-462 (0-01152) 0-368 (0-6392) TABLE 2. Statistics of length (1) and width (w) of (a) forty-eight pedicle valves, and (b) fifty-four brachial valves of Pleurorthis costatus sp. nov. from sandstones 300 yds. south-east of Ffynnon-y-mab, Trefor. Subfamily PRODUCTORTHINAE Schuchert & Cooper 1931 Genus NICOLELLA Reed 1917 Nicolella humilis Williams (PL 3, ngs. 5, 7-9) FIGURED SPECIMENS (measurements in mm.) Internal and external moulds of brachial valve (BB. 3 o 5 i9a-b) Internal and external moulds of brachial valve (BB.3052oa-b) Length Width 10-5 18-4 (est.) 10 -i AND TRILOBITES OF ANGLESEY 151 HORIZON AND LOCALITY. Llanbabo Formation, Llanbabo Church Grits, Church Quarry, Llanbabo. N.G.R. 37758672. DISCUSSION. Specimen 66.30520 has, as far as can be seen, an identical ribbing pattern to that of N. humilis, with possibly eighteen primary costae, though no secondary costae are developed, because of the small size of the valve. 66.30519 is also referred to this species; there appear to be only fourteen primary costae, allowing for state of preservation, and internal and external secondary costae originate at 5-6 mm from the umbo. Genus PANDERINA Schuchert & Cooper 1931 Panderina lamellosa sp. nov. (PL 3, figs. 10-18) DIAGNOSIS. A species of Panderina with semicircular alate valves, three-quarters as long as wide, the pedicle valve with the greater convexity, evenly convex medianly with concave lateral flanks; the brachial valve gently convex with a shallow sulcus, narrow posteriorly but rapidly widening; anterior commissure slightly uniplicate; radial ornament of low rounded costellae arising by implantation, crossed by im- bricate growth lamellae, which become crowded together at the shell margin in fully grown forms, especially on the brachial valve; ventral interior with stout dental lamellae descending directly to the floor of the valve, extended as low ridges bounding an ovate muscle area; teeth blunt, with large and prominent crural fossettes lying close beneath them and rimmed by accessory teeth ; dorsal interior with large cardinalia projecting above the hinge line, the width between the brachiophore tips being four-tenths the width of the valve; brachiophores blade-like, with massive knob-like ends, diverging at 90 and adpressed to the notothyrial plat- form; cardinal process a bulbous myophore without shaft, joined to the brachio- phores at its posterior end; muscle scars extend to the longitudinal midline of the valve, the anterior pair the larger, not bilobed. TYPE SPECIMENS (measurements in mm.) Length "Width HOLOTYPE. Internal and external moulds of brachial valve (66 . 30525a-b) . . . . 5-2 PARATYPES. Internal and external moulds of pedicle valve (66 . 30526a-b) . . . 4-8 6-7 Internal and external moulds of pedicle valve (88.30527a-b) ... 9-0 (est.) Internal and external moulds of brachial valve (66 . 30528a-b) . . . 6-8 9-0 (est.) TYPE HORIZON AND LOCALITY. Treiorwerth Formation, sandstones 300 yds. south-east of Ffynnon-y-mab, Trefor. N.G.R. 36247950. DISCUSSION. The known species of Panderina were all erected by Pander and Lamansky (Schuchert & Cooper 1932 : 82), and form a homogeneous group of shells with characteristics 'intermediate between Orthis s.s. and Productorthis . All have i 5 2 LOWER PALAEOZOIC BRACHIOPODS piano- or concave-convex shells, short interareas, simple cardinalia, and are im- bricate anteriorly. The new species has imbricate growth lamellae, but they are not confined to the front of the shell. The brachial valve is also distinctly convex, though the specimens are distorted and the degree of convexity cannot be accurately measured. The cardinalia approach the Productorthis type, and are larger than in the other described species. It can be seen therefore that the new species has characters which place it a little further towards Productorthis than the other species of Panderina. Family DOLERORTHIDAE Opik 1934 Subfamily DOLERORTHINAE Opik 1934 Genus DOLERORTHIS Schuchert & Cooper 1931 Dolerorthis cf. tenuicostata Williams 1955 (PI. 4) figs. 4, 6-7) FIGURED SPECIMEN (measurements in mm.) Length Width Internal and external moulds of pedicle valve (BB . 3o54ia-b) . . . . . . n-o HORIZON AND LOCALITY. Llanbabo Formation, Llanbabo Church Grits, Church Quarry, Llanbabo. N.G.R. 37758672. DISCUSSION. One specimen has been found, and shows the interarea and umbonal regions. Externally the ribs appear similar to those of D. tenuicostata, but since the specimen is not complete the patterns cannot be compared. Internally the muscle scars are of the same pattern, though the ridges bounding the diductor scars make an angle of 90 with each other while in the holotype of the species this angle is about 60. The vascula media are typical of the genus. Since the brachial valve has not been found, and the full ribbing pattern cannot be analysed, the specific identification is not certain. Subfamily GLYPTORTHINAE Schuchert & Cooper 1931 Genus PTYCHOPLEURELLA Schuchert & Cooper 1931 Ptychopleurella sp. (i) (PI. 3, figs. 19-23) FIGURED SPECIMENS (measurements in mm.) Length Width Internal and external moulds of pedicle valve (BB.30537a-b) . . 3 '5 Internal and external moulds of brachial valve (BB. 3 o5 3 8a-b) 4-5 AND TRILOBITES OF ANGLESEY 153 HORIZON AND LOCALITY. Nantannog Formation, fine sandstones and shales south-east of Fferam-uchaf farm, Llanbabo. N.G.R. 36518657. DISCUSSION. The valves have the typical form of Ptychopleurella : the pedicle valve is sub-pyramidal, with a long, almost catacline interarea, the brachial valve is convex, with a median sulcus and a shorter, almost orthocline interarea, and both valves have typical interiors for the genus. The ornament is of simple, angular costae, fourteen on the brachial valve, with two in the sulcus, originating just anterior to the umbo. It is crossed by imbricate growth lamellae, crowded together in the first 5 mm. of growth, subsequently occurring at three per mm. Only three pedicle valves and two brachial valves have been found, so that no good estimates of the size and shape parameters of the stock can be gained. The ratios of length to width as a percentage of the pedicle valve are 56 3, 58 8 and 79 7, and of the brachial valves 60-0 and 70-0. Without more material it is impossible to make any good comparisons with described species. In the simple ribs this species contrasts with Ptychopleurella sp. (2) from Llanbabo, and is similar to other early species, such as P. oklahomensis Cooper from the McLish formation, Llanvirn Series (Cooper 1956 : 388). Ptychopleurella sp. (2) (PL 4, figs. 1-3, 5) FIGURED SPECIMENS (measurements in mm.) Length Width Internal mould of incomplete brachial valve (BB. Internal and external moulds of incomplete pedicle valve (BB.3054oa-b) ..... 6-8 8-6(est.) HORIZON AND LOCALITY. Llanbabo Formation, Llanbabo Church Grits, Church Quarry, Llanbabo. N.G.R. 37758672. DISCUSSION. The valves found are small, biconvex and transverse, with a strongly convex pedicle valve with a median flattening and a strongly apsacline interarea, and a convex brachial valve with possibly a slight median fold and an almost ortho- cline interarea. The ornament is of coarse angular costae, increasing by implan- tation and crossed by close imbricate growth lamellae numbering eight per mm. at 6 mm. from the ventral umbo. Internally the dental lamellae are receding; the ventral musculature is well defined and elevated on a pseudospondylium, the adductor tracks being wide and shorter than the diductor tracks; the cardinalia are large, the cardinal process being a simple ridge somewhat thickened on its anterior edge. The species is similar to the later species of Ptychopleurella, e.g. P. bouchardi (Davidson) from the middle Silurian, which have ribbing patterns characterized by late developing secondary costae. The slight median fold of the brachial valve, if found on other specimens, may prove to be a diagnostic feature, since it is not found in other species of the genus. 154 LOWER PALAEOZOIC BRACHIOPODS Family PLAESIOMYIDAE Schuchert 1913 Subfamily PLAESIOMYINAE Schuchert 1913 Genus PLAESIOMYS Hall & Clarke 1892 Plaesiomys cf. robusta (Bancroft) (PI. 4> figs. 8-12) FIGURED SPECIMENS (measurements in mm.) Length Width Internal and external moulds of pedicle valve (BB.30544a-b) 23-5 32-5 Internal and external moulds of pedicle valve (BB.30545a-b) . 25-0 26-6 (est.) Internal and external moulds of brachial valve (BB.30543a-b) ... .15-0 HORIZON AND LOCALITY. Crewyn Formation, grits in small outcrop 420 yds. west-south-west of Ysgubor-gader, Mynachdy. N.G.R. 29589214. DISCUSSION. Both valves have the typical characters of Plaesiomys in shape, ventral musculature, and cardinalia. The very poorly preserved external moulds have costellate ribbing. The pedicle adjuster scars are very distinct, the diductor scars slightly bilobed, and the adductor scars not differentiated. The length of the two pedicle valves varies from 70-90 per cent, of their width. Strong internal plications extend inwards from the margin. These features are listed by Bancroft (1945 : 244-245) as characteristic of P. robusta. He gives little idea of the natural variation within the species, and unfortunately does not figure a typical pedicle valve, but only one described by him as abnormal. Plaesiomys (Dinorthis) sp. (PL 4, figs. 13-15) FIGURED SPECIMEN (measurements in mm.) Length Width Internal and external moulds of pedicle valve (BB . 30542a-b) . . . . . . 8-0 10-0 HORIZON AND LOCALITY. Llanbabo Formation, Llanbabo Church Grits, Church Quarry, Llanbabo. N.G.R. 37758672. DISCUSSION. The valve is of a subquadrate Dinorthis, convex at the umbo, but becoming flat towards the commissure, the interarea short and apsacline, with an open delthyrium, and a simple costate ornament of eighteen costae, becoming broad and flat-topped towards the anterior. In the interior the muscle scars are subquadrate and slightly indented medianly, though the individual scars cannot be separated. The dental lamellae are widely divergent. The shape of the valve, AN DTRILOBITES OF ANGLESEY 155 and the number of costae suggest a young specimen of D. flabellulum (J. de C. Sowerby) . Family PLECTORTHIDAE Schuchert & Le Vene 1929 Subfamily PLEGTORTHINAE Schuchert & Le Vene 1929 Genus PLECTORTHIS Hall & Clarke 1892 Plectorthis (?) sp. (PI. 4, figs. 16, 19) 1919 Orthis (Dalmanella) testudinarial Dalman; Matley in Greenly : 452. FIGURED SPECIMENS (measurements in mm.) Length Width Internal mould of pedicle valve (Af. 1377) . . 6-6 8-0 Internal mould of pedicle valve (Af. 1462) . . 8-5 HORIZON AND LOCALITY. Nantannog Formation, gritty shales 250 yds. west- south-west of Fferam-uchaf, Llanbabo. N.G.R. 36178655. DISCUSSION. The valves are convex, suboval in outline with a straight hinge- line narrower than the maximum width, and a short curved apsacline interarea and open delthyrium. The ornament is finely costellate. The teeth are not seen, the dental lamellae are thin and sub-parallel, the muscle scars extend one-third the length of the valve with the adductor and diductor scars the same length and with a rectangular end. Subfamily PLATYSTROPHIINAE Schuchert & Le Vene 1929 Genus PLATYSTROPHIA King 1850 Platystrophia precedens major Williams 1955 (PL 4, figs. 17-18) FIGURED SPECIMEN (measurements in mm.) Length Width Internal and external moulds of pedicle valve (BB.30546a-b) 13-5 HORIZON AND LOCALITY. Llanbabo Formation, Llanbabo Church Grits, Church Quarry, Llanbabo. N.G.R. 37758672. DISCUSSION. Isolated valves referable to Platystrophia have been found at Careg-onen, Trwyn y Crewyn and Llanbabo. Only at the last locality are the valves complete enough for a specific identification, and appear to be identical with specimens from the Derfel Limestone (Whittington & Williams 1955 : 402, pi. 38, figs. 24-29). The other specimens, in all probabliity from the same horizon, also belong to the bicostate species group. 156 LOWER PALAEOZOIC BRACHIOPODS Family SKENIDIIDAE Kozlowski 1929 Genus SKENIDIOIDES Schuchert & Cooper 1931 Skenidioides sp. (i) (PI. 5, figs. 1-2) FIGURED SPECIMENS (measurements in mm.) Length 2-3 Width Internal mould of pedicle valve (BB . 30547) . Internal mould of brachial valve (BB . 30548) . 3-2 HORIZON AND LOCALITY. Treiorwerth Formation, sandstones 300 yds. south- east of Ffynnon-y-mab, Trefor. N.G.R. 36247950. DISCUSSION. The specimens are preserved as internal and external moulds in a coarse grit, and are too poorly preserved to identify specifically. In particular the costae are hardly preserved at all, though they are probably few in number, between 13 and 16, and simple. The pedicle valve is semicircular, pyramidal, with a long strongly apsacline interarea and a high-standing shallow spondylium supported by a short receding median septum. The brachial valve is gently convex and sulcate, and bears a well developed median septum running the length of the valve. TABLE 3 1 mm. (var. 1) w mm. (var. w) r a (var. a) b (var. b) 2-47 (0-203) 3'53 (0-306) 0-723 1-245 (0-0493) 0-45 (0-3126) TABLE 3. Statistics of length (1) and width (w) of fifteen pedicle valves of Skenidioides sp. (i) Skenidioides sp. (2) (PI. 5, figs. 3-5) FIGURED SPECIMENS (measurements in mm.) Internal and external moulds of brachial valve Length Width ) 2-3 Internal and external moulds of pedicle valve (BB.3055oa-b) 2-6 HORIZON AND LOCALITY. Nantannog Formation, fine sandstones and shales 190 yds. south-east of Fferam-uchaf, Llanbabo. N.G.R. 36518657. DISCUSSION. The specimens are typical of the genus, but are very small. The pedicle valve is sub-pyramidal, with a shallow, largely free spondylium. The brachial valve has a good septalium, the supporting plates converging on a high median septum which runs most of the length of the valve. The ornament of both valves is of simple costae, apparently about fourteen in number. AND TRILOBITES OF ANGLESEY 157 This species is very similar to Skenidioides sp. (i) from the D. hinmdo zone, but there seem to be minor differences between the interiors of the two species. The earlier species has a well developed median septum in the pedicle valve, possibly with a larger delthyrium. The dorsal sulcus also seems to be better developed in this species. Superfamily ENTELETACEA Waagen 1884 Family PAURORTHIDAE Opik 1933 Genus PAURORTHIS Schuchert & Cooper 1931 Paurorthis (?) sp. (PI. 5, ngs. 6-9) DESCRIPTION. Pedicle valve subcircular, evenly convex, about one-third as deep as long and slightly longer than wide ; hingeline slightly less than the maximum width; interarea curved, apsacline, delthyrium open; ornament fascicostellate but not well preserved; umbonal cavity deep; muscle scars extending forwards beyond the umbonal cavity to almost half the length of the valve, elevated anteriorly; central (adductor?) scars occupying most of the width between the dental lamellae, flanked by narrow, slightly depressed (diductor?) tracks which extend onto the sides of the dental lamellae, which extend alongside them as ridges ; teeth apparently aligned along the dental lamellae, crural fossettes present; vascula media at first converging from the ends of the diductor scars, then diverging; margin of valve crenulate. FIGURED SPECIMENS (measurements in mm.) Length Width Internal mould of pedicle valve (BB . 3o6o3a) . 9-5 10-2 Internal and external mould of pedicle valve (BB . 3o6o4a-b) 10-3 9-4 HORIZON AND LOCALITY. Bod Deiniol Formation, grits in temporary excavation 50 yds. north of Ty-bach Cottage, Bod Deiniol. N.G.R. 37688528. DISCUSSION. Although a number of pedicle valves were collected, no brachial valves were found, nor was it possible to examine a thin section of the shell to determine the nature of the shell material. The fascicostellate ornament, disposition of the muscle scars and vascula media, and the short median ridge are all found in Paurorthis. Williams (1962 : 141) has commented on the development of the latter feature, which is better developed in the allied genus, Cydomyonia. The valves also show some similarities to certain dalmanellid-like members of the Orthidae and Finkelnburgiidae. "Pedicle valves of Nanorthis have a similar shape, with sometimes a fasciculate ornament, but internally the shell is not thick- ened under the muscle scars; Nothorthis is similar but more transverse. Archae- orthis also has a Dalmanella-like exterior, but the muscle scars, although elevated, do not extend forwards from the umbonal cavity as in the Anglesey specimens. Diparelasma is another dalmanellid-like form, with the muscle scars elevated in a GEOL. 1 6, 4. 17 158 LOWER PALAEOZOIC BRACHIOPODS pseudospondylium in front, and a short median ridge, but with a finely costellate ornament. In many respects the muscle scars and pseudospondylium are very similar. Family DALMANELLIDAE Schuchert 1913 Genus DALMANELLA Hall & Clarke 1892 Dalmanella (?) sp. (PL 5, figs. lo-n) FIGURED SPECIMENS (measurements in mm.) Length Width External mould of brachial valve (BB . 30568) . 8.2 (est) External mould of pedicle valve (66.30569) . . 7-2 8-4 (est.) HORIZON AND LOCALITY. Crewyn Formation, grits 420 yds. west-south-west of Ysgubor-gader. N.G.R. 29589214. DISCUSSION. The valves are small, and the interiors are very badly preserved, so that it is impossible to make out the details of the cardinalia in the brachial valve. Owing to the small size of the brachial valve the ribbing pattern is not fully developed, so that only the first internal and external branches are developed. The pedicle valve is deeply convex, and only slightly carinate, the brachial valve very gently convex with a shallow median sulcus. Genus ONNIELLA Bancroft 1928 Onniella (?) sp. (PL 5, figs. 12-14) FIGURED SPECIMENS (measurements in mm.) Length Width Internal and external moulds of pedicle valve (BB.3057oa-b) 8-1 Internal mould of brachial valve (66.30571) . 5-5 6-4 HORIZON AND LOCALITY. Llanbabo Formation, Llanbabo Church Grits, Church Quarry, Llanbabo. N.G.R. 37758672. DISCUSSION. The valves are subcircular, biconvex, the pedicle valve having the greater convexity and the brachial valve a shallow sulcus. The ornament is only seen on the pedicle valve and is slightly f ascicostellate with forty to fifty costellae on the margin and a wavelength of 0-23 mm. at 5 mm. from the ventral umbo. The ventral adductor scar is shorter than, but not enclosed by the diductor scars, from the ends of which run widely separated and diverging vascula media. The brachiophores are widely divergent, but the details of the fulcral and supporting plates are not seen. The former may not be present. The adductor scars in the brachial valve are quadripartite. The valves recall Onniella (Soudleyella] cf . avelinei 6ancroft (Whittington & Williams 1955 : 407). AND TRILOBITES OF ANGLESEY 159 Family HARKNESSELLIDAE Bancroft 1928 Genus HARKNESSELLA Reed 1917 Harknessella (?) sp. (PI. 5, ng. 16) FIGURED SPECIMEN (measurements in mm.) Length Width Exterior of pedicle valve (Af . 1492) . . . . 10 i 14-7 HORIZON AND LOCALITY. Garn Formation, limestone block in breccia bed, 300 yds. south-east of the summit of Mynydd-y-garn. N.G.R. 31759062. DISCUSSION. The valve is convex and slightly carinate, with a costellate orna- ment, no other details can be seen. A carinate pedicle valve is a feature of Hark- nessella. Genus HORDERLEYELLA Bancroft 1928 Horderleyella (?) sp. (PL 5, fig- 15) FIGURED SPECIMEN. Incomplete internal mould of pedicle valve (66.30572). HORIZON AND LOCALITY. Llanbabo Formation, Llanbabo Church Grits, Church Quarry, Llanbabo. N.G.R. 37758672. DISCUSSION. An internal mould of a pedicle valve from Llanbabo agrees with Horderleyella? sp. from the Derfel Limestone (Whittington & Williams 1955, pi. 38, fig. 30) in having similar small subcordate muscle scars, and possibly belonging to an undescribed species. Family LINOPORELLIDAE Schuchert & Cooper 1931 Genus SALOPIA Williams 1955 Salopia salteri gracilis Williams (PL 5, figs. 17-18) FIGURED SPECIMEN. Incomplete internal mould of brachial valve (66.30573.) HORIZON AND LOCALITY. Llanbabo Formation, Llanbabo Church Grits, Church Quarry, Llanbabo. N.G.R. 37758672. DISCUSSION. The cardinalia and the median septum are well preserved, and show that the specimens belong to the genus Salopia. Since the cardinalia are small, with a length of less than 20 per cent, of the valve length, it can be placed in the subspecies S. salteri gracilis. i6o LOWER PALAEOZOIC BRACHIOPODS Family ANGUSTICARDINIIDAE Schuchert & Cooper 1931 Genus RHYNCHORTHIS nov. DIAGNOSIS. Rostrate biconvex shells, the brachial valve with the greater con- vexity; rectimarginate or slightly uniplicate; hinge-line narrow; ventral interarea long and narrow, almost orthocline, delthyrium open; dorsal interarea shorter, almost orthocline, notothyrium open; ornament on both valves of simple rounded costae becoming vague towards the flanks. Ventral interior with receding, almost obsolete dental lamellae; strong teeth, oval in shape and aligned along the lamellae; orthoid muscle scars, the adductor and diductor scars expanding forwards, the former not enclosed by the latter. Dorsal interior with deep notothyrial cavity, cardinal process a simple ridge; brachiophores plate-like, short and thick, with supporting and socket plates ; adductor muscle scars orthoid, differentiated into anterior and posterior pairs, the anterior pair the larger. TYPE SPECIES. Rhynchorthis rotundus sp. nov. from the Treiorwerth Formation. DISCUSSION. Schuchert & Cooper (1931 : 244) erected the subfamily Angusti- cardiniinae, with their new genus Angusticardinia, for orthids evolving towards the rhynchonellids, but still retaining more orthid characters than those of the rhynchonellids. Rhynchorthis conforms to the description of the subfamily in having interareas on both valves, together with both orthid and rhynchonellid characters. It differs, however, from Angusticardinia in a number of important features. The interareas, though narrow, are long, the dental lamellae are weak or obsolete, and there is no median ridge inside the brachial valve. It is not known whether the shell material of either genus is punctate; Opik (1933 : 5, 6) thought that Angusticardinia was probably punctate. Apatorthis (Opik 1933 : 5, from the middle and upper Ordovician of Estonia) is another rhynchonelliform shell, but has short and narrow curved interareas of equal length, a well marked fold and sulcus, and angular costae. The shell is punctate and is placed by Opik in the Enteletacea. Schuchert & Cooper (1932 : 84) suggested that Angusticardinia, being 'the earliest rhynchonelliform shell known', may have been the ancestor of the rhynchonellids, evolving into Rhynchotrema. Rhynchorthis is contemporary with Angusticardinia, but seems to be closer in structure to the ancestral orthids. The hinge-line is not quite so narrow, the interareas are long, and the cruralium-like structure of Angusticardinia, in which the supporting plates meet a median ridge, is not developed. Rhynchorthis rotundus gen. et sp. nov. (PI. 5, figs. 19-26) DIAGNOSIS. Species of Rhynchorthis, six-fifths as long as wide, dorsi-biconvex with brachial valve one-fifth as deep as long, pedicle valve one-eighth as deep as long, ornamented by about twelve simple costae; internal details as for genus. AND TRILOBITES OF ANGLESEY 161 TYPE SPECIMENS (measurements in mm.) Length Width HOLOTYPE. Internal mould of brachial valve (BB 30551) PARATYPES. Internal mould of brachial valve (BB 30552) Internal mould of brachial valve (BB 30553) Internal mould of pedicle valve (BB 30554) Internal mould of pedicle valve (BB 10-1 8-4 ii-l 12-4 9'5 30556) TYPE HORIZON AND LOCALITY. Treiorwerth Formation, sandstones 300 yds. south-east of Ffynnon-y-mab, Trefor. N.G.R. 36247950. DISCUSSION. The new species is known from a number of rather poorly preserved moulds, particularly so in the case of the external moulds. The mean length per cent, of 5 pedicle valves relative to the width is 121-0 (variance 195-0). The cor- responding figures for 5 brachial valves are 107-4 an d 121-5. In the five brachial valves the mean depth per cent, relative to length is 20-6 (variance 29-2). Suborder CLITAMBONITIDINA Opik 1934 Superfamily CLITAMBONITACEA Winchell & Schuchert 1893 Family POLYTOECHIIDAE Opik 1934 Genus TRITOECHIA Ulrich & Cooper 1936 Tritoechia sp. (PI. 6, figs. 1-3, 5) FIGURED SPECIMEN (measurements in mm.) Length Width Internal and external moulds of pedicle valve (BB . 30557a-b) 17-0 19-8 (est.) HORIZON AND LOCALITY. Treiorwerth Formation, sandstones 300 yds. south- east of Ffynnon-y-mab, Trefor. N.G.R. 36247950. DISCUSSION. Only one well preserved pedicle valve, the figured specimen, and a few other poorly preserved pedicle valves have been found. No brachial valves have been found which can definitely be assigned to the genus. The valve conforms externally to the genus Tritoechia. In outline it is semi- circular, widest at the hinge-line, with cardinal angles just acute. The surface is evenly convex, the umbo not incurved or inflated, and the interarea plane, apsacline but almost catacline. The delthyrium is covered by a strongly convex deltidium, but the foramen is not preserved. The ornament, which is poorly preserved, is finely multicostellate, with about fourteen costellae in 5 mm. both at the margin i62 LOWER PALAEOZOIC BRACHIOPODS and near the umbo. Internally the teeth are strong and rounded, supported by receding dental lamellae which diverge ventrally. The form and extent of the muscle scars are not known. Among the species of Tritoechia described by Ulrich & Cooper (1938 : 162-169) are a number which approach the valve closely, the nearest being T. transversa, which has an interarea more inclined towards the orthocline. Family CLITAMBONITIDAE Winchell & Schuchert 1893 Subfamily CLITAMBONITINAE Winchell & Schuchert 1893 Genus CLITAMBONITES Pander 1830 Clitambonites (?) sp. (PL 6, fig. 4) FIGURED SPECIMEN. Fragmentary external mould of brachial valve (66.30558). HORIZON AND LOCALITY. Llanbabo Formation, Llanbabo Church Grits, Church Quarry, Llanbabo. N.G.R. 37758672. DISCUSSION. The external mould is of a large, probably subquadrate brachial valve in excess of 18 mm. long by 26 mm. wide, gently convex, becoming flat or slightly sulcate medianly. The ornament is mulitcostellate, with perhaps four costellae per cm. at 5 mm. from the umbo, and at the margin eighteen per cm. At least ten more prominent ribs divide the ornament into sectors, each with four to six smaller ribs, arising both by implantation and bifurcation. Strong thick growth lamellae occur at intervals. The convex shape, and prominent growth lamellae, are both features of Clitambonites. Clinambon and Vellamo both have much less prominent growth costellae. Genus ILMARINIA Opik 1934 Ilmarinia sp. (PL 6, figs. 6-7) FIGURED SPECIMEN. Internal and external moulds of incomplete pedicle valve (BB. 3 o55 9 a-b). HORIZON AND LOCALITY. Llanbabo Formation, Llanbabo Church Grits, Church Quarry, Llanbabo. N.G.R. 37758672. DISCUSSION. Two counterpart moulds of the pedicle valve of a clitambonitaceid from Llanbabo show a subquadrate outline, a long apsacline interarea, and a slight sulcus. The delthyrium is possibly open, or constricted by deltidial plates, because there are certainly traces of a large foramen, and the ornament is finely multicostellate. Internally there is a good spondylium, one-third the width of the valve, and elevated by its own depth from the floor of the valve. It has a flat floor, and (though the specimen is broken) shows what may be the beginning of a thin receding median septum. Ilmarinia is the only clitambonitaceid genus with a ventral sulcus, and hence the specimen probably belongs here. AND TRILOBITES OF ANGLESEY 163 Subfamily ATELELASMATINAE Cooper 1956 Genus APOMATELLA Schuchert & Cooper 1931 Apomatella (?) sp. (PI. 6, figs. 8-n) DESCRIPTION. Pedicle valve subquadrate, wider than long, widest at the hinge- line with the cardinal angles right angles; deeply pyramidal, slightly flattened medianly, interarea catacline or strongly apsacline, slightly curved, twice as wide as long ; delthyrium probably open ; ornament finely costellate ; spondylium simplex high, shallow in cross-section; median septum receding. FIGURED SPECIMENS (measurement in mm.) Length Width Internal and external moulds of pedicle valve (BB.3o6o5a-b) 8-8 Internal and external moulds of pedicle valve (BB . 3o6o6a-b) . . . . . . 10-9 I3'4(est.) HORIZON AND LOCALITY. Bod Deiniol Formation, Grits in temporary excavation 50 yds. north of Ty-bach Cottage, Bod Deiniol. N.G.R. 37688528. DISCUSSION. A number of pedicle valves have been found at this locality, none with any trace of plates restricting the delthyrium, suggesting that the absence of plates is more than an accident of preservation. Superfamily GONAMBONITACEA Schuchert & Cooper 1931 Family GONAMBONITIDAE Schuchert & Cooper 1931 Subfamily GONAMBONITINAE Schuchert & Cooper 1931 Genus ANTIGONAMBONITES Opik 1934 Antigonambonites pyramidalis sp. nov. (PL 6, figs. 12-18) DIAGNOSIS. Outline sub-rectangular, wider than long, hinge-line just less than maximum width, anterior and lateral commissures rectimarginate ; biconvex, pedicle valve pyramidal, with a long almost catacline interarea, slightly curved, brachial valve slightly convex, with a shallow median sulcus, interarea short and anacline; delthyrium probably closed or restricted by convex deltidial plates; notothyrium restricted but not closed by chilidial plates; ornament costellate, costellae numbering four per mm. at 5 mm. from the umbo, stronger ribs appearing at intervals, ribs crossed by well marked growth lines giving a slightly imbricate appearance; teeth not seen in ventral interior, but muscle scars impressed on a largely sessile spondylium triplex, supported at its anterior end by two lateral septa, the median septum being almost obsolete, adductor and diductor scars expanding forwards, the adductor tracks separated from the diductor tracks by raised ridges ; dorsal interior with brachiophores long and widely divergent, measuring between 164 LOWER PALAEOZOIC BRACHIOPODS their tips over half the width of the valve, median septum very short or absent, cardinal process simple ; adductor muscle scars within a semicircular track bounded by the brachiophores and by an indented ridge; margin crenulated. TYPE SPECIMENS (measurements in mm.) Length Width HOLOTYPE. Internal and external moulds of brachial valve (BB.3056ia-b) . . . . 5-8 7-5 PARATYPES. Internal mould of pedicle valve (BB. 30562) Internal mould of brachial valve (B . 30563) 9 9 Internal mould of pedicle valve (BB. 30564) 6-8 TYPE HORIZON AND LOCALITY. Treiorwerth Formation, sandstones 300 yds. south-east of Ffynnon-y-mab, Trefor. N.G.R. 36247950. DISCUSSION. The poor preservation of the specimens, and the fact that they are preserved as natural moulds and not as complete specimens with the original shell material, means that it is impossible to study the form and structure of the spondylium in detail. Since, however, it is a spondylium triplex the specimens belong to the Gonambonitidae. Antigonambonites Opik is the closest described genus, being biconvex and having a largely sessile spondylium. The described species are generally flatly lenticular, with an apsacline interarea in the pedicle valve. The ornament is similar to that of A. costatus Opik (1934 : 156), in which the costellae are conspicuous and angular, though in this species some costellae are accentuated. The pedicle valve is also deeper, in shape like that of Skenidioides , and has a similarly inclined interarea. The deltidial plates are poorly preserved in the moulds, and it is impossible to say whether they meet medianly or not. The mean percentage length relative to width of 5 brachial valves is 76-0, with a range from 58-2 to 92-9. Genus ESTLANDIA Schuchert & Cooper 1931 Estlandia (?) sp. (PI. 7, figs. 2-4, 6-9) 1919 Petraia sp. Greenly : 435. FIGURED SPECIMENS (measurements in mm.) Internal and external moulds of incomplete pedicle valve (Af. 238, Af. 225) Internal mould of brachial valve (Af .214) Internal and external moulds of brachial valve (BB.3056oa-b) Length Width 5'4 distorted HORIZON AND LOCALITY. Berw-uchaf Grits, 90 yds. north of Bwlch-gwyn farm, Holland Arms. N.G.R. 48207303. AND TRILOBITES OF ANGLESEY 165 DISCUSSION. The pedicle valve is strongly pyramidal, with a long apsacline interarea, possibly with an open delthyrium and with a costellate surface, the costellae having the 'chain-sculpture' characteristic of Estlandia. The interior has a well developed spondylium triplex, with a thick median septum, and thinner lateral septa parallel to the median septum. The interior of the brachial valve has long widely divergent brachiophores, thickened at their outer ends. The adductor muscle scars are half the length of the valve, pentagonal in form, with crenulated antero-lateral margins. They are separated by a thin median septum which joins the brachiophores at their inner ends to form an anchor-shaped structure. The valves are provisionally placed in Estlandia as the ornament of the pedicle valve is quite characteristic of that genus. The side septa of Estlandia, however, are usually short and widely spaced, rather than close to the median septum. Family KULLERVOIDAE Opik 1934 Genus KULLERVO Opik 1932 Kullervo aff. panderi (Opik) (PI. 6, figs. 19-22; PI. 7, fig. i) FIGURED SPECIMENS (measurements in mm.) Length Width Internal mould of pedicle valve (BB . 30565) . . distorted Internal mould of pedicle valve (BB . 30566) . . 3-3 7-5 Internal and external moulds of brachial valve (BB. 3 o56 7 a-b) 4-5 8-5 HORIZON AND LOCALITY. Llanbabo Formation, Llanbabo Church Grits, Church Quarry, Llanbabo. N.G.R. 37758672. DISCUSSION. The specimens are certainly conspecific with Kullervo aff. panderi (Opik) described by Williams (Whittington & Williams 1955 : 412, pi. 30, figs. 56-62) and, like it, differ from Opik's species only in the poorer development of the hemi-syrinx. The cardinal angles are slightly alate, and on them the concentric ornament is more pronounced than medianly (cf. Opik 1934 text-fig. 37). The ventral interarea is almost catacline and appears to have an open delthyrium; since the specimens are small this is probably a characteristic of young stages, as suggested by Williams (Whittington & Williams 1955 : 412). There are no sub- spondylial septa. Suborder CLITAMBONITIDINA Opik 1934 Superfamily and genus uncertain (PI. 7, figs. 5, lo-n) FIGURED SPECIMENS (measurements in mm.) Length Width Internal mould of pedicle valve (BB . 30607) . Internal and external moulds of brachial valve (BB.3o6o8a-b) 8-0 14-6 166 LOWER PALAEOZOIC BRACHIOPODS HORIZON AND LOCALITY. Bod Deiniol Formation, grits in temporary excavation 50 yds. north of Ty-bach Cottage, Bod Deiniol. N.G.R. 37688528. DISCUSSION. Two valves found in the Nantannog Beds at the site of the Alaw reservoir cannot be assigned to any clitambonitid species. In particular it is not certain whether they belong together. The pedicle valve has a very long interarea, with deltidial plates, dental lamellae which converge to the floor of the valve, possibly with side septa, and with a prominent central groove in the floor of the delthyrium; the ornament is coarsely costellate. If the structure is a spondylium simplex then the valve may belong to the Polytoechiidae, as the median septum seems only to be rudimentary. The brachial valve is quadrate in outline, slightly alate, convex with a shallow median sulcus, and a short, almost orthocline interarea, possibly with a small chilidium; the ornament is coarsely costellate and imbricate. Internally the cardinalia are elevated on a notothyrial platform, which passes into a broad median septum ; the cardinal process is a simple ridge, with widely divergent socket ridges; the muscle scars have two pairs of septa lying lateral to them, parallel to the median septum. Order STROPHOMENIDA Opik 1934 Suborder STROPHOMENIDINA Opik 1934 Superfamily PLECTAMBONITACEA Jones 1928 Family PLECTAMBONITIDAE Jones 1928 Subfamily AHTIELLINAE Opik 1933 Genus AHTIELLA Opik 1932 Ahtiella quadrat a sp. nov. (PL 8, figs. 1-9) DIAGNOSIS. Alate, subrectangular Ahtiella, two-thirds as long as wide; brachial valve convex, with a median sulcus widening and deepening anteriorly, flanked by rounded folds and slightly concave flanks near the cardinal angles; anterior commissure bent ventrally in some specimens; interarea anacline, notothyrium possibly covered by a small convex chilidium at its apex; pedicle valve flat or concave, with a low carinate median fold, and the anterior and lateral commissures bent ventrally; delthyrium open, possibly covered by a small arched plate at its apex; interarea strongly apsacline, eight times as wide as long; ornament of about fifteen costellae in 5 mm. at 5 mm. from the ventral umbo, every third or fourth costella accentuated, pedicle valve with about three very oblique and indistinct wrinkles near the cardinal angles; teeth angular, aligned along the hingeline, sup- ported by very short receding dental lamellae diverging to the floor of the valve; muscle scars rectangular, wider than long, adductor scars not enclosed by diductor scars, both pairs expanding linearly forwards, adductors enclosing an angle of 60 with an arcuate anterior margin, diductors blade-like, extending beyond the ad- ductors, enclosing an angle of 75 between their outer margins; small depressions AND TRILOBITES OF ANGLESEY 167 beneath teeth are either pedicle adjuster scars or depressions to accommodate the socket ridges ; two pairs of vague ridges radiate from the ends of the diductor scars ; anterior and lateral margins abruptly deflected ventrally ; cardinalia orthid, elevated on a notothyrial platform; cardinal process a simple ridge, thickened along its anterior edge, highest midway along its length and triangular in outline; socket ridges short and rod-like, diverging at about 90, resting directly on the notothyrial platform and possibly continuous with an incipient chilidium ; sockets broad excava- tions in the hinge-line, diverging at about 90 and each enclosing an angle of 20; prominent median septum separating the muscle scars, which are disposed in an arc about the umbo, extending just less than half the length of the valve, one pair lateral to the other. TYPE SPECIMENS (measurements in mm.) Length Width HOLOTYPE. Internal mould of pedicle valve (66.30609) 10-9 15 -8 PARATYPES. Internal mould of pedicle valve (BB. 30610) . . . . . . 13-3 21-2 (est.) Internal and external moulds of pedicle valve (BB.3o6na-b) ... 22-0 (est.) Internal and external moulds of brachial valve (BB . 3o6i2a-b) Internal and external moulds of brachial valve (BB . 3o6i3a-b) Internal and external moulds of brachial valve (BB . 3o6i4a-b) TYPE HORIZON AND LOCALITY. Torllwyn Formation, sandstones 50 ft. above the base of the succession on the north side of the faulted syncline, 45 yds. north of Ogof Gynfor, Llanbadrig. N.G.R. 37859490. Ahtiella concava sp. nov. (PI. 7, figs. 12-22) DIAGNOSIS. Semicircular slightly alate Ahtiella, six-tenths as wide as long; brachial valve evenly convex in lateral view, with a narrow median sulcus having a V-shaped cross-section, flanked by rounded folds; interarea anacline to almost orthocline, very short, notothyrium possibly covered by a small convex chilidium at its apex; pedicle valve convex in lateral view, becoming more strongly bent towards the anterior commissure, but with the convexity broken by a narrow carinate fold which becomes more rounded and vaguer away from the umbo; del- thyrium covered by a small arched plate at its apex; interarea procline or catacline, one-thirteenth as long as wide; ornament on both valves too fine to be observed, but growth lines present near the margins of valves; teeth triangular, aligned along the hinge-line, supported by very short receding dental lamellae diverging to the floor of the valve; muscle scars rectangular, diductors extending further forwards 1 68 LOWER PALAEOZOIC BRACHIOPODS than adductors, but details not seen; vague ridges radiating from the diductor scars; anterior and lateral margins deflected ventrally in some specimens; dorsal cardinalia orthid, elevated on a notothyrial platform; cardinal process a simple ridge, triangular in side view and thickened along its anterior margin; socket ridges short and rod-like, diverging at 90, sockets shallow excavations under the hinge- line; muscle scars separated by a prominent median septum, posterior scars rounded and set in excavations under the notothyrial platform, anterior scars elongate and lying along each side of the median septum, extending to almost half the length of the valve, flanked by three ridges on each side, radiating from the posterior scars; median septum cusp-shaped in lateral outline, highest at its mid-point, thickened and swollen in its anterior half. TYPE SPECIMENS (measurements in mm.) HOLOTYPE. Internal and external moulds of pedicle valve (BB . 3o6i5a-b) PARATYPES. Internal and external moulds of brachial valve (BB . 3o6i6a-b) Length Width 17-2 23-8 (distorted) 19-8 (distorted) 13-0 20-7 (est.) n-7 22-2 Internal and external moulds of brachial valve (BB . 3o6i7a-b) Internal and external moulds of brachial valve (BB.3o6i8a-b) Internal and external moulds of pedicle valve (BB.3o6i9a-b) (distorted) TYPE HORIZON AND LOCALITY. Bod Deiniol Formation, grits in temporary excavation 50 yds. north of Ty-bach Cottage, Bod Deiniol. N.G.R. 37688528. DISCUSSION. The two Anglesey species of Ahtiella differ from each other mainly in external shape and ornament, and in the development of the internal ridges in the brachial valve. A. quadmta has a rectangular outline, with the pedicle valve almost flat across the visceral disc and the brachial valve gently convex; both fold and sulcus are shallow. The ventral interarea is apsacline, and the orna- ment unequally costellate. In contrast A. concava is semicircular in outline, the pedicle valve has a concave visceral disc, and the brachial valve is strongly convex ; both fold and sulcus are carinate, and higher and deeper. The ventral interarea is procline to catacline, and the ornament, though not preserved, is probably much finer. Both species differ in their combinations of characters from the Baltic species described by Cpik (1932; 1933) and Hessland (1949). Most of these are relatively much wider, with prominent rugae close to the hinge-line. The fold and sulcus of A. concava are much better developed than in any Baltic species, although in outline and covexity it is similar to A. lirata Opik. A. quadrata is more quadrate than any of the Baltic forms, and less convex. AND TRILOBITES OF ANGLESEY 169 The mean percentage of length relative to width of five pedicle valves of A. quadrata was 64-7 (range 57'3~^9*)' For A. concava the corresponding value for thirteen pedicle valves was 59-8 (range 51 7-77 -o) and for eight brachial valves 62-1 (range 54-9-78-4). Correlation coefficients between length and width for these specimens were not significant, due to poor preservation and distortion of the specimens. For similar reasons it was not possible to make any accurate estimate of the thickness of the valves. Genus REINVERSELLA nov. DIAGNOSIS. Semicircular plectambonitaceans with small postolateral wings; abruptly geniculate, with the border deflected ventrally ; ventral disc convex, dorsal disc flat, the anterior and lateral commissures with a frill or gutter deflected dorsally ; ventral interarea apsacline, short and wide, dorsal interarea short, anacline, both delthyrium and notothyrium open; ornament of fine bifurcating costellae, crossed by irregular concentric rugae on the visceral disc. Ventral interior with dental lamellae diverging widely both laterally and ventrally, continuous with low ridges round the muscle scars; muscle scars triangular, adduc- tor and diductor scars equal in length. Dorsal interior with cardinalia raised on a low notothyrial platform; cardinal process low, thin and blade-like, slightly swollen anteriorly; brachiophores short and triangular in section, continuous on their ventral faces with the interarea. TYPE SPECIES. Reinversella monensis sp. nov. from the Treiorwerth Formation. DISCUSSION. This genus is separated from Inversella Opik because of the develop- ment of a second deflection of the anterior and lateral borders of the shell, which forms a sort of frill or gutter. A similar, but more elaborate frill is characteristic of Limbimurina Cooper (1956 : 851-852), which bears the same relationship to the strophomenacean Leptaena as the new genus does to Inversella. Two of the des- cribed species of Inversella, I. borealis Opik and /. angulata Opik, have a chilidium, and it may be present in the third species /. perundosa Opik. In contrast the new genus has an open notothyrium. Reinversella monensis gen. et sp. nov. (PI. 8, figs. 10-17) 1919 Leptaena rhomboidalis (Wilckens), partim.; Matley in Greenly : 442. DIAGNOSIS. A species of Reinversella three-quarters as wide as long, and about one-third as deep as wide, ornamented with fine bifurcating costellae numbering fourteen to seventeen per 5 mm. on the rim of the visceral disc, crossed by seven to nine rugae, continuous or anastomosing across the midline ; in the ventral interior the width of the muscle scars is about one-fifth the width of the valve and their length one-quarter the length of the valve; the width of the cardinalia is one-fifth the width of the brachial valve. 170 LOWER PALAEOZOIC BRACHIOPODS TYPE SPECIMENS (measurements in mm.) Length Width HOLOTYPE. External and internal moulds of brachial valve (BB . 30574a-b) . PARATYPES. External and internal moulds of pedicle valve (BB . 30575a-b) External and internal moulds of brachial valve (BB.30576ab) . . . 15-3 21-3 (distorted) 15-5 i8-o(est.) TYPE HORIZON AND LOCALITY. Treiorwerth Formation, sandstones 300 yds. south-east of Ffynnon-y-mab, Trefor. N.G.R. 36247950. DISCUSSION. In addition to bearing a frill, the new species shows detail differences from the described species of Inversella. I. perundosa Opik from the Expansus- schiefer, D. hirundo zone (Opik 1939 : 128, 142, PL 5, fig. 6) is the closest species, but has a prominent broad median costella. Family LEPTESTIIDAE Opik 1933 Subfamily LEPTESTIINAE Opik 1933 Genus PALAEOSTROPHOMENA Holtedahl 1916 Palaeostrophomena sp. (PI. 9, figs. 2, 4-5) FIGURED SPECIMENS (measurements in mm.) Internal and external moulds of pedicle valve (BB. 3 o57 9 a-b) Internal mould of brachial valve (BB . 30580) Length Width 7-6 HORIZON AND LOCALITY. Llanbabo Formation, Llanbabo Church Grits, Church Quarry, Llanbabo. N.G.R. 37758672. DISCUSSION. The pedicle valve is subquadrate, and gently convex. The orna- ment consists of fine costellae, divided into sectors each containing five to seven costellae separated by stronger costellae numbering about thirty. Internally there appear to be no dental lamellae, other details have been obliterated. The brachial valve shows the cardinalia, the cardinal process is a rounded mass (as preserved) passing into a median septum, the sockets and accessory sockets are conspicuous. The specimens agree in all visible details with P. magnified Williams, but the form of the ventral muscle scars, one of the diagnostic features of that species, is not visible in the Llanbabo specimens. AND TRILOBITES OF ANGLESEY 171 Palaeostrophomena (?) sp. (PL 9, %. i) FIGURED SPECIMEN (measurements in mm.) Length Width Exterior of pedicle(?) valve (BB.3058ia-b) . . 11-7 24-0 (est.) HORIZON AND LOCALITY. Garn Formation, limestone blocks in breccia beds, Forth Padrig, Mynachdy. N.G.R. 30539279. DISCUSSION. The valve is semicircular and gently convex. The posterior margin forms a slight angle at the umbo, the cardinal angles are acute, produced into small wings, and the lateral and anterior margins evenly curved. The ornament is of fine parvicostellae, separated into sectors containing sixteen in each by sharp accentuated costellae, about twelve in number in the whole valve, all the costellae arising by implantation. The surface of the valve is wrinkled along the posterior margin by radial rugae, which are more faintly developed over the whole surface. The valve cannot be closely compared with Palaeostrophomena sp., as the interior is not exposed, but it agrees with the genus in exterior details. The closest species is P. magnifica Williams, though the number of parvicostellae in each sector is different. It could also belong to Glyptambonites Cooper, in which the pedicle valve has the same outline, convexity and ornament. Family LEPTELLINIDAE Ulrich & Cooper 1936 Subfamily LEPTESTIININAE Havlicek 1961 Genus LEPTESTIINA Havlicek 1952 Leptestiina derfelensis (Jones) (PL 9, figs. 7-9) FIGURED SPECIMENS (measurements in mm.) Length Width Internal mould of pedicle valve (BB . 30577) . . 4-8 Internal mould of brachial valve (66.30578) HORIZON AND LOCALITY. Tandinas Shales, by the track 50 yds. west of Tandinas quarry, Careg-onen. N.G.R. 58248187. DISCUSSION. Both valves show the internal characters well, particularly the brachial valve, in which the cardinalia and the lophophore platform are perfectly preserved. The papillae are not visible in the pedicle valve. Genus BILOBIA Cooper 1956 Bilobia aff. musca (Opik 1930) (PL 9, figs. 10-13) DESCRIPTION. Triangular Bilobia with rounded cardinal angles and an anterior tongue, four-fifths as long as wide; the brachial valve evenly concave and the \-/i LOWER PALAEOZOIC BRACHIOPODS pedicle valve slightly carinate with flattened flanks; teeth double, the posterolateral pair the larger; dental lamellae divergent, continuous with a raised rim to the muscle scars which is indented medianly in a right angle; diductor scars large and flabellate with small auxiliary lobes under the teeth, possibly just meeting anterior to the adductor scars and extending one-third the length of the valve; vascula media converging anteriorly from the ends of the diductor scars ; dorsal lophophore platform prominent, one-half the length of the valve, elevated and free anteriorly, markedly bilobed with each lobe rounded. FIGURED SPECIMENS (measurements in mm.) Length Width Internal mould of pedicle valve (BB . 30582) . . 10-3 10-6 Internal mould of brachial valve (BB . 30583) HORIZON AND LOCALITY. Llanbabo Formation, Llanbabo Church Grits, 180 yds. east of Fferam-uchaf, Llanbabo. N.G.R. 36548673. DISCUSSION. The pedicle valve is very similar to that of Bilobia musca (Opik) in the general shape, the form of the teeth, and the muscle scars. In the brachial valve the lophophore platform has similar rounded anterior lobes. None of the specimens shows the cardinalia, and there are no external moulds well enough preserved to show the ornament. Family SOWERBYELLIDAE Opik 1930 Subfamily SOWERBYELLINAE Opik 1930 Genus EOPLECTODONTA Kozlowski 1929 Eoplectodonta lenis Williams (PL 9, figs. 14-18) FIGURED SPECIMENS (measurements in mm.) Length Width Internal and external moulds of pedicle valve (BB. 3 o584a-b) Internal and external moulds of brachial valve (BB. 3 o585a-b) . . 5-7 External mould of brachial valve with interarea of pedicle valve (BB . 30586) .... HORIZON AND LOCALITY. Llanbabo Formation, Llanbabo Church Grits, Church Quarry, Llanbabo. N.G.R. 37758672. DISCUSSION. The interior of the pedicle valve conforms to that of E. lenis from the Derfel Limestone, though the denticles are only poorly seen on the right side. The dorsal muscle scars are raised on low platforms, and are flabellate in form with one pair outside the other. The median and submedian septa are almost parallel, and between the scars are distinct depressions running their full length. AND TRILOBITES OF ANGLESEY 173 Subfamily PTYGHOGLYPTINAE Cooper 1956 Genus PTYCHOGLYPTUS Willard 1928 Ptychoglyptus sp. (PI. 10, figs. 1-2) DESCRIPTION. Pedicle valve semicircular, slightly alate, gently convex; brachial valve concave medianly with flattened wings; ornament divided into sectors by sharp accentuated costae and costellae, 8 at the margin of valve 4 mm. long, possibly three primary, the others arising about 1-5 mm. from the umbo; between are fine parvicostellae, too poorly preserved to be counted; concentric ornament of prominent rugae, faint at less than 2mm. from the umbo, slightly asymmetrical in cross section, steeper towards the umbo; divided into sectors by the sharp costellae which they do not cross or fold, in the median part of the valves alternating between them, laterally tending to coincide across them, bent convex to the umbo; fine concentric growth lines follow the rugae, hence the valve margin is scalloped. FIGURED SPECIMENS (measurements in mm.) Length Width Exterior of pedicle valve (BB . 30590) . . . 4-4 Exterior of brachial valve (BB . 30589) . HORIZON AND LOCALITY. Garn Formation, limestone blocks in breccia beds, Porth Padrig, Mynachdy. N.G.R. 30539279. DISCUSSION. The valves are all small, none being above 5 mm. long; since most described members of the genus are up to four times this length it is possible that these are all young specimens, not affording adequate material upon which to erect a new species. Ptychoglyptus kindlei Cooper (1956 : 816) appears similar, but grows to a much larger size and develops a geniculation. P. virginiensis Willard (Cooper 1956 : 818) is also similar though the rugae seem to become prominent at an earlier growth stage. P. valdari (Spjeldnaes 1957 : 58; Williams 1962 : 194) has rugae with both faces sloping anteriorly, with the posterior face undercut, and this is also true of P. cf. valdari from Girvan (Williams 1962 : 194). P. cf. virgini- ensis, also from Girvan (Williams 1962 : 193), has similar rugae and costae, and is Caradoc in age. Subfamily AEGIROMENINAE Havlicek 1961 Genus SERICOIDEA Lindstrom 1953 Sericoidea abdita Williams (PL 9, figs. 3, 6) FIGURED SPECIMENS (measurements in mm.) Length Width Interior of brachial valve (BB . 30587) . . . 1-7 Interior mould of brachial valve with shell material adhering (BB . 30588) GEOL. l6, 4. iS i 7 4 LOWER PALAEOZOIC BRACHIOPODS HORIZON AND LOCALITY. Tandinas shales, on the shore by the powerhouse 100 yds. west of the pier, Careg-onen. N.G.R. 58208193. DISCUSSION. Specimen 66.30587 shows the pattern of septules characteristic of this species, three pairs of lateral septules and a narrow, more prominent median septule. 66.30588 shows the cardinalia but is not complete enough to show the septules. Superfamily STROPHOMENACEA King 1846 Family LEPTAENIDAE Hall & Clarke 1892 Genus LEPTAENA Dalman 1828 Leptaena sp. (PL 10, figs. 3-6) DESCRIPTION. Outline semicircular, slightly auriculate; pedicle valve with con- cave visceral disc bounded by a sharply raised ridge passing to a sharp geniculation ; interarea apsacline, extending the width of the valve and about one-fifteenth as long as wide, delthyrium enclosing an angle of about 135, open, pseudodeltidium not observed; brachial valve with flat visceral disc, bounded by rounded depression before the geniculation; interarea narrower than on the pedicle valve; notothyrium covered by a conspicuous convex chilidium with a median depression; interior of pedicle valve with teeth as narrow outgrowths from the hinge-line, elongated parallel to it, dental lamellae not seen, muscle scars elliptical in outline, with lance- olate adductor scars enclosed by diductors, the latter separated by a septum an- teriorly; brachial interior with bilobed cardinal process tapering forwards to a point, the outer edges parallel and the inner ones diverging at 60, sockets bounded by vague ridges forming the posterior edge to the muscle scars and uniting with a low median ridge to produce an anchor-like structure, with the median ridge passing into a short sharp median septum just before the edge of the disc, which is raised and crossed at intervals by radial grooves. FIGURED SPECIMENS (measurements in mm.) Length Width Internal mould of pedicle valve (66.30591) . . 10-3 19-6 (est.) Internal mould of brachial valve (66 . 30592) Internal mould of brachial valve (66 . 30593) HORIZON AND LOCALITY. Llanbabo Formation, Llanbabo Church Grits, 180 yds. east of Fferam-uchaf, Llanbabo. N.G.R. 36548673. DISCUSSION. The material compares well with that from the Derfel Limestone (Whittington & Williams 1955 : 419, pi. 39, figs. 86-90). There is no septum preserved between the lobes of the cardinal process in the Angelsey specimens, and their exteriors are unknown. AND TRILOBITES OF ANGLESEY 175 Genus DACTYLOGONIA Ulrich & Cooper 1942 Dactylogonia sp. (P. 10, figs. 7-8) DESCRIPTION. Brachial valve incomplete, broken along a growth line, possibly along a line of geniculation ; slightly concave in longitudinal view, almost plane in anterior view; outline semi-circular, slightly alate, hinge-line straight, the greatest width; interarea very short, wide, anacline, notothyrium apparently lacking a chilidial cover; ornament of very faint concentric rugae, developing at about 3 mm. from the umbo, costellae if present too fine to be preserved; cardinal process short, bilobed, uniting with a low median ridge that bifurcates anteriorly; socket ridges diverging at 110 to each other, adpressed to the valve surface, bounding sockets which are not raised above the general interior; muscle scars bounded by a series of septa, two prominent sub-median septa parallel to each other becoming thickened and diverging at their posterior ends, separated by a slot from low thick diverging septa, which are separated from the socket ridges by a narrow depression ; anterior ends of the sub-median septa separated by two triangular raised areas, between which is a thin median septum; inner surface outside the septa covered by a series of coarse pustules. FIGURED SPECIMEN. Internal and external moulds of an incomplete brachial valve (BB.3o596a-b). HORIZON AND LOCALITY. Nantaiinog Formation, fine sandstones and shales 190 yds. south-east of Fferam-uchaf, Llanbabo. N.G.R. 36518657. DISCUSSION. Without more material it is impossible to place this specimen more exactly. The pattern of septa recalls those of Dactylogonia (cf. Cooper 1956 : pi. 225, fig. 4), though the septa here are nearer the socket ridges, and are separated only by narrow slots. The three pairs of raised areas together form a rim, locating within it the visceral mass of the animal. The slots between the septa were probably for the passage of the various vascula, the vascula media between the anterior pair, and the vascula myaria posterior to the long prominent pair. The inner margins of the two pairs of septa slope obliquely inwards, and are probably the seats of attach- ment of the adductor muscle scars. ? Dactylogonia sp. has been described by MacGregor (1961 : 204) from the upper Llandeilo of the Berwyn mountains. His specimen does not greatly resemble that described above, the septa being weakly developed, the cardinal process large, and the pustules less distinct and drawn out radially. Genus KI AERO MEN A Spjeldnaes 1957 Kiaeromena (?) sp. (PI. 10, figs. 9, 10) FIGURED SPECIMENS. Exterior of incomplete pedicle(?) valve (66.30594). Exterior of incomplete brachial(P) valve (66.30595). 176 LOWER PALAEOZOIC BRACHIOPODS HORIZON AND LOCALITY. Garn Formation, limestone blocks in breccia bed, Forth Padrig, Mynachdy. N.G.R. 30539279. DISCUSSION. The valves are semicircular, slightly alate and geniculate, and as neither the hinge-lines and interareas nor the interiors are preserved the valves have been determined on their transverse profile and ornament. The pedicle valve is convex, with the disc slightly carinate along the midline, the brachial valve with a slightly concave disc. The ornament on both valves is of fine parvicostellae, approximately ten per mm. on the valve margins, divided into sectors by stronger costellae, of which six arise near the umbo and fifteen are present at the margin of a valve about 9 mm. long. Both types of ribs arise by implantation. There are no rugae on the disc. Order PENTAMERIDA Schuchert & Cooper 1931 Suborder SYNTROPHIIDINA Ulrich & Cooper 1936 Superfamily PORAMBONITACEA Davidson 1853 Family HUENELLIDAE Schuchert & Cooper 1931 Subfamily RECTOTROPHIINAE nov. Globular huenellids with parallel dental lamellae, and with parallel supporting plates in the brachial valve, without cardinal process. Genus RECTOTROPHIA nov. DIAGNOSIS. Globular subtriangular biconvex shells with deep pedicle valve and less convex brachial valve, rectimarginate commissure and narrow hinge-line; ornament unknown. Ventral interior with parallel dental lamellae, the muscle scars confined between them and elevated on a low pseudospondylium. Dorsal interior with parallel, receding supporting plates, without a cardinal process, adductor muscle scars hexagonal in outline, expanding anteriorly from the anterior ends of the supporting plates. TYPE SPECIES. Rectotrophia globularis sp. nov. from the Treiorwerth Formation. DISCUSSION. The Heunellidae, into which the new genus falls, at present com- prises two subfamilies, the Huenellinae, without a cardinal process, and the Meso- nomiinae, with a rudimentary cardinal process and recumbent brachiophore plates. Both families are also characterized by the development of a fold and sulcus, and by having non-parallel supporting plates. The disposition of the supporting plates in the new genus, together with the shape of the valves and the absence of fold or sulcus, necessitate the erection of a new sub-family. Rectotrophia globularis gen. et sp. nov. (PI. 10, figs. 11-17) DIAGNOSIS. As for genus. AND TRILOBITES OF ANGLESEY 177 TYPE SPECIMENS (measurements in mm.) Length 6-7 Width 7-0 6-7 (est.) 5'7 HOLOTYPE. Internal mould of pedicle valve (Af.i436) PARATYPES. Internal mould of brachial valve (Af . 1436) Internal mould of brachial valve (Af . 1442) 6 7 TYPE HORIZON AND LOCALITY. Treiorwerth Formation, sandstones 300 yds. south-east of Ffynnon-y-mab, Trefor. N.G.R. 36247950. DISCUSSION. The genus is known only from a few internal moulds, from Greenly's collection, the writer having found no well-preserved specimens. As a result no mean estimates of proportions can be included in a precise specific diagnosis. The holotype is 2-8 mm. thick, and the dental lamellae are 1-7 mm. apart. In the first paratype (Af.i436) the supporting plates are 1-9 mm. apart, in the second they are 1-5 mm. apart and the adductor muscle scars are 1-9 mm. long. Family PORAMBONITIDAE Davidson 1853 Genus PORAMBONITES Pander 1830 Porambonites (s.s.) sp. (PI. n, figs. 1-6, 8) FIGURED SPECIMENS (measurements in mm.) Length Width Internal and external moulds of pedicle valve (BB.30598a-b) 18.0 Internal and external moulds of brachial valve (BB.30599a-b) 20-5 23-2 Internal mould of brachial valve (BB . 30600) . 13 -3 12-5 HORIZON AND LOCALITY. Treiorwerth Formation, sandstones 300 yds. south- east of Ffynnon-y-mab, Trefor. N.G.R. 36247950. DISCUSSION. The specimens are all disarticulated, incomplete, and have suffered some distortion. Since the species of Porambonites are to a large extent based on external form it is not possible to make a close comparison with any described species. In addition the fold and sulcus do not develop until the shell is well grown, and of the figured specimens only BB . 30599 has a good fold. The valves are roughly circular in shape, and so do not belong to the subgenus Equirostra (Isorhynchus). The pedicle valve is lenticular, without a swollen umbo, the brachial valve more convex. The internal features of both valves are well preserved, but only the dorsal muscle scars are visible. The adductor scars are bluntly wedge-shaped and form an arc lying anterior to the ends of the supporting plates. The diductor scars are four(?) in number forming a narrower central pair flanked by two wider scars. Allied species, from the lower Ordovician of the Baltic are P. broggeri Lamansky, P. altus Pander and P. planus Pander, 178 LOWER PALAEOZOIC BRACHIOPODS Family CAMERELLIDAE Hall & Clarke 1894 Subfamily CAMERELLINAE Hall & Clarke 1894 Genus CAMERELLA Billings 1859 Camerella sp. (PL n, figs. 7, 9-11) FIGURED SPECIMEN. Complete shell (66.30597), length 4-8 mm., width 5-1 mm., thickness 2-9 mm. HORIZON AND LOCALITY. Garn Formation, limestone blocks in breccia beds, Forth Padrig, Mynachdy. N.G.R. 30539279. DISCUSSION. The figured specimen is the only complete one known, the others being only fragments of smaller valves. It is sub-triangular, slightly wider than long, with both valves approximately equally convex. The dorsal fold at the anterior margin is two-thirds the width of the valve, and originates at 2-6 mm. anterior to the umbo. It comprises two bounding costae, separated by a shallow depression which corresponds to a low costa or fold in the pedicle valve. The ventral sulcus is flanked by a pair of subangular costae. A few growth lines on the pedicle valve show the outline to have been sub-circular until the fold and sulcus started to develop. The majority of described species of Camerella have three or more costae developed on the fold, all the costae appearing at the same time, that is, when the fold starts to appear. C. unicostata (Cooper 1956 : 583, pi. 113, B, figs. 6-9) has a similar development of costae on the fold and sulcus, but has more costae on the flanks, and, at the same size, seems to be more tumid and is suboval in outline. Suborder PENTAMERIDINA Schuchert & Cooper 1931 Superfamily PENTAMERACEA M'Coy 1844 Family PARALLELELASMATIDAE Cooper 1956 Genus METACAMERELLA Reed 1917 Metacamerella cf. balcletchiensis (Davidson) (PL n, figs. 12-14) 1919 Camarella? [cf. Stricklandinia? balcletchiensis (Dav.)] ; Matley in Greenly : 478. FIGURED SPECIMEN. Complete shell (Af.isgo) length 21-1 mm., width 20-0 mm., thickness 15-0 mm. HORIZON AND LOCALITY. Garn Formation, limestone blocks in breccia beds, Forth Padrig, Mynachdy. N.G.R. 30539279. DISCUSSION. The only specimen so far found, a complete shell from Greenly's collection, is very similar to the Girvan species (Williams 1962 : 232). The outline is comparable, with 'false interareas' extending just over half the length of the shell, and, so far as can be seen, a very low fold on the antero-median part of the brachial valve, The ornament is also very similar, consisting of about six low rounded AND TRILOBITES OF ANGLESEY 179 costae, with a wavelength of 2 mm. at 13 mm. from the umbo. The interior details are not seen and hence cannot be compared with M. balcletchiensis. Order uncertain (PI. 10, figs. 18-24) FIGURED SPECIMENS (measurements in mm.) Length Width Internal and external moulds of pedicle valve (BB . 55792a-b) 18-9 18-6 Internal and external moulds of brachial valve (BB.5579ia-b) . 20-5 HORIZON AND LOCALITY. Torllwyn Formation, sandstone 50 ft. above the base of the succession on the north side of the faulted syncline, 45 yds. north of Ogof Gynfor, Llanbadrig. N.G.R. 37859490. DISCUSSION. The valves are rostrate and convex, roughly circular in outline. The pedicle valve bears a strongly marked sulcus with a flattish floor, flanked by angular folds, and has a narrow curved interarea. The delthyrium is apparently open. The brachial valve bears a corresponding fold, and both valves are costellate, with flat-topped costellae interspersed with narrow interspaces. In the ventral interior the dental lamellae are almost parallel, the muscle scars raised on a wad of callus extending anterior to the lamellae on a pseudospondylium which is rounded at its anterior end. The dorsal cardinalia are not fully preserved, though supporting plates diverge to the floor of the valve. The external shape and ornament of the valves suggests the syntrophiid Rhyso- strophia, but the internal structures differ considerably, and the specimens may well belong in the Orthida. V. SYSTEMATIC DESCRIPTION OF THE TRILOBITA Family ASAPHIDAE Burmeister 1843 Subfamily OGYGIOCARIDINAE Raymond 1937 Genus OGYGIOCARIS Angelin 1854 Ogygiocaris selwynii (Salter) (PI. 12, figs. 1-2, 5-6) 1919 Ogygia selwyni Salter; Lake in Greenly : 442, 446. DESCRIPTION. Cranidium quadrilateral, wider than long, evenly convex (tr.). Glabella almost as long as cranidium, sides almost parallel but slightly constricted opposite the eyes, anterior margin semicircular; evenly convex (tr.), slightly con- vex (longit.) with a dome-shaped anterior lobe; glabellar furrows almost obsolete; one pair faintly impressed midway along the glabella. Axial furrows weak, ending in shallow hypostomal pits; occipital ring reduced to a pair of triangular raised portions pointing inwards to the tubercle, with a narrow articulating ring formed by a faint furrow behind the triangular facets (following Harrington & Leanza's interpretation, 1957 : 177). Preglabellar field absent. Fixigenae triangular shaped r8o LOWER PALAEOZOIC BRACHIOPODS areas behind the eyes. Posterior border sloping slightly backwards; posterior border furrow broad and shallow, opposite the occipital ring adaxially. Eyes semicircular, very close to and centred on the transverse midline of the glabella. Facial suture isoteliform, with the anterior branches widely divergent in front of the eyes, meeting in an even curve without any apparent acumination; posterior branches oblique backwards and outwards, sigmoidal. Pygidium transverse, one and one-half times as wide as long; anterior margin convex forwards, postero-lateral margins convex, with the greatest curvature across the midline. Axis tapering backwards, not extending onto the posterior border and with the end rounded; probably with eight or more axial rings; narrow (longit.) articulating half ring. Marked anterior border. Pleural fields with pleural furrows marking more than four segments, each bearing oblique ridges near their outer ends. Border of uniform width, one-fifth the length of the whole pygidium, concave but with a convex ridge against the pleural fields. Doublure convex ventrally and of the same width as the border. FIGURED SPECIMENS (measurements in mm.) Length Width Internal mould of cranidium (Af . 842) . . . distorted Internal mould of cranidium (Af. 823) . . . 31-5 36-0 Internal mould of pygidium (Af . 820) . . . 37*5 54-0 (est.) Internal mould of pygidium (Af . 821) HORIZON AND LOCALITY. Carmel Formation, sandstones. Af .820-823 from the scarp west of Bryn Gollen Uchaf (Bryn Gwallen of Greenly), N.G.R. 40558380; Af.842 from quarry 400 yds. north-north-west of Bryn Gollen Uchaf, N.G.R. 40508425. DISCUSSION. The cranidia correspond closely with that of 0. selwynii as des- cribed by Whittard (1964 : 233) though it is difficult to recognize the glabellar furrows. In particular the anterior portions of the facial sutures diverge at the same angle, and their course close to the median suture is also similar. Af .820, the internal mould of the pygidium differs in that the posterior border is more strongly curved across the midline than laterally, whereas the reverse is true of 0. selwynii (Whittard 1964 : 235). Af.82i shows oblique ridges in addition to the pleural furrows. Family THYSANOPELTIDAE Hawle & Corda 1847 Genus PROTOBRONTEUS Snajdr 1960 Protobronteus greenlyi sp. nov. (PI. 12, figs. 3-4, 7) 1919 Illaenus caecus Holm (partim) ; Lake in Greenly : 478. DIAGNOSIS. A species of Protobronteus with no inner anterior border furrow, and an ornament of coarse terrace lines without intervening pits, transverse in alignment over the anterior part of the fixigenae. DESCRIPTION. Both cranidia incomplete, probably semicircular with truncated AND TRILOBITES OF ANGLESEY 181 corners. Glabella clavate, reaching to the anterior border, evenly convex (sag. and tr.); narrowest just behind the midline (sag.), just longer than wide; without glabellar furrows. Axial furrows convex inwards, well defined. Occipital ring not seen. Fixigenae incomplete, evenly convex (long.), palpebral lobe and course of facial suture not seen. Anterior border not separated from glabella mesially, but present in front of the nxigenae; anterior border furrow well defined, meeting the axial furrow in a right angle, and continuing a little way adaxially to define the anterolateral corner of the glabella. Ornament of coarse terrace lines, averaging five to eight per 5 mm., becoming crowded together on the anterior border, trans- verse across the glabella, borders and anterior part of the fixigenae, not preserved elsewhere. Librigena incomplete, triangular, convex (long.), with prominent anterolateral border furrow, no posterior border furrows. Eye lobe large, semicircular. Genal spine long, circular in cross-section. Ornament of distant terrace lines, diverging on either side of eye. TYPE SPECIMENS (measurements in mm.) Length Width HOLOTYPE. Incomplete cranidium (In. 58291) . . 28-8 PARATYPES. Incomplete cranidium (In . 58292) . Internal mould and interior of incomplete librigena (In . 58293a-b) TYPE HORIZON AND LOCALITY. Garn Formation, limestone blocks in breccia beds, Forth Padrig, Mynachdy. N.G.R. 30539279. DISCUSSION. Protobronteus was erected by Snajdr (1960 : 245-246) to include only Eobronteus reedi Sinclair (1949 : 51-52). In this species, as in P. greenlyi the glabella is clavate, without any glabellar furrows, and coalesces with the anterior border. E. curtus Sinclair (1949 : 50-51) is very similar and could well be included in Protobronteus as the glabellar furrows are indistinct and the anterior border furrow fades out mesially. P. greenlyi differs from both these species in that the inner anterior border furrow is absent (the cheek furrow of Sinclair 1949 : 51), and the ornament is differently developed. In P. reedi the terrace lines are longitudinal between the two border furrows, and in E. curtus they are not developed in the same place, only coarse punctae being present. Family ILLAENIDAE Hawle & Corda 1847 Subfamily ILLAENINAE Hawle & Corda 1847 Genus ILLAENUS Dalman 1827 Illaenus sp. (PL 12, figs. 8-13, 15) 1919 Illaenus caecns Holm (partim); Lake in Greenly : 478. DESCRIPTION. Cranidium quadrangular, evenly convex (tr.), longitudinal con- vexity strong posteriorly, weak anteriorly. Glabella short and wide, with slight 182 LOWER PALAEOZOIC BRACHIOPODS independent convexity (tr.), two-thirds the width of the cranidium. Axial furrows curve inwards for two-thirds of their length, and end in an outwards curve. Pal- pebral lobes one-third the length of the cranidium, situated less than their own length from the posterior margin. Posterior branches of the facial sutures short, running directly backwards, anterior branches slightly divergent. Dorsal surface of cranidium smooth. Pygidium parabolic, the anterior margin slightly convex forwards, width four- thirds the length, convex, the inner pleural fields gently convex and the margins deflected at about 45. Axis short, sub-triangular, with independent convexity (tr.), four-tenths the width of the pygidium. Axial furrows shallow posteriorly, meeting at about 60. Short (long.) articulating half ring. Pleural fields with anterior borders slightly swollen, marked off by shallow depressions. Articulating facets sharply bevelled, with terrace lines extending beyond them. Rest of dorsal surface finely pitted. Doublure close to the dorsal shield, convex ventrally at its outer margin, almost half the length (sag.) and one-tenth the width of pygidium at anterior margin. Inner margin commencing near midline of facet (tr.), swinging in a curve gradually decreasing in radius to the midline of the pygidium, where a forward pointing cusp is found. Ventrally deflected median ridge strongly marked. Doublure bears terrace lines running parallel to its margins about 0-7 mm. apart. FIGURED SPECIMENS (measurements in mm.) Length Width Cranidium (^.58294) ..... 9-9 Pygidium (In. 58295) 23-7 32-7 Pygidium (In. 58296) 22-6 33-5 DISCUSSION. The species resembles Illaenus revaliensis (Holm 1886 : 87-92, pi. 2, figs, i-io) particularly in the shape and other features of the pygidium. The axis is similar, and the inner margin of the doublure has a forward pointing cusp at the midline. The cranidium is poorly preserved, and may possibly be a crushed and distorted cranidium of Stenopareia cf. linnarssoni (Holm), but the glabella is relatively wider, the palpebral lobes are much larger, and the anterior margin seems to be sharply truncated. Genus STENOPAREIA Holm 1886 Stenopareia cf. linnarssoni (Holm) (PI. 12, figS. 14, 16-23) 1919 Illaenus caecus Holm (partim); Lake in Greenly : 478) DESCRIPTION. Cranidium quadrangular, the frontal area domed, strongly and evenly convex (long, and tr.). Glabella with slight independent convexity (tr.), half the length of cranidium. Two pairs of oval muscle scars between the axial furrows, the anterior pair indistinct. Axial furrows poorly defined on dorsal, but well defined on ventral surface, extending forwards half the length of cranidium, widening in their anterior half to be well defined on the ventral surface. Palpebral lobes less than one fifth the length of cranidium, less than their own length from AND TRILOBITES OF ANGLESEY 183 the posterior border. Posterior braches of facial suture short, straight, running diagonally outwards, anterior branches straight, converging slightly forwards. Glabella and fixigenae with smooth dorsal surfaces, frontal margin with faint terrace lines on the ventral surface. Librigena twice as long as wide, tapering to a point anteriorly, with vertically deflected border present anteriorly. Genal angle very broadly rounded. Rostral plate triangular, anterior margin gently convex outwards, the posterior margins concave rearwards, meeting in a central cusp with an angle of less than 90. Ventral surface with terrace lines. Pygidium semi-oval, just over half as long as wide, weakly convex except at the sides where almost vertically deflected. Axis one-third the anterior width, un- defined posteriorly, evenly convex (tr.). Axial furrows shallow, only seen at anterior margin. Dorsal surface smooth. Articulating facets convex, almost vertical. Doublure lies close to the dorsal surface, with a faint median ridge, anterior margin monocuspid(P). FIGURED SPECIMENS (measurements in mm.) Length Width Cranidium (In . 58297) 15-5 18 6 Cranidium (In. 58298) 14-6 (est.) Librigena (^.58299) . . . . . . 19-7 Rostral plate (In . 58300) 8-9 22-6 Pygidium (In. 58301) 23-4 42-4 (est.) Pygidium (In. 58302) . . . . 13-5 22-5 HORIZON AND LOCALITY. Garn Formation, limestone blocks in breccia beds, Porth Padrig, Mynachdy. N.G.R. 30539279. DISCUSSION. The cranidium is very similar to that of Stenopareia linnarssoni (Illaenus linnarssoni Holm in Warburg 1925 : 115-123, pi. 2, figs. 14-18). The glabellar proportions and the axial furrows are the same, with an anterior swelling of the furrows. The palpebral lobes are the same size and equally far back. The pygidia are approximately similar in proportion; the inner margin of the doublure is unknown, though it also has a ventrally deflected median furrow. The facets are narrow and rounded in both cases, but the axis is relatively narrower in the Anglesey specimens. Stenopareia camladica Whittard (1961 : 216-217, pi. 30, figs. 10-13) nas a similar cranidium, but the axial furrows are poorly preserved, and the pygidium is differently proportioned in the Shropshire species. Family HARPIDAE Hawle & Corda 1847 Genus SELENOHARPES Whittington 1950 Selenoharpes (?) sp. (PL 13, ngs. 1-2, 5-6) DESCRIPTION. Outline of cephalon oval; greatest width probably behind the occipital ring. Glabella tapering forwards, width at its base seven-ninths of its length, rounded 1 84 LOWER PALAEOZOIC BRACHIOPODS anteriorly; sharply convex and carinate, in height equal to its width; in lateral profile becoming vertical anteriorly. Basal lobes triangular, very vague, one-third the length of the glabella, marked by shallow furrows running inwards and back- wards. Axial, preglabellar, and occipital furrows all shallow. Occipital ring one- ninth length of the glabella, bent up with it. Pre-glabellar field one-third length of the glabella, sloping anteriorly. Eye tubercles prominent and elevated above the cheeks, opposite the anterior one- fifth of the glabella. Eye ridges broad, running directly inwards. Genal ridges fine, running outwards and backwards to the girder. Alae one-third the length of the glabella, depressed, marked by semicircular alar furrows. Cheek lobes bent down anterolaterally and laterally. Posterior border with sharply raised convex rim, continuous with a similar rim on the inward side of the prolongations. Cheek roll not separable from the cheeks. Brim equal in width anteriorly to the glabellar length, convave, with a row of prominent pits just inside the rim marking the inner edge of a downward bevel round the rim. Girder smooth, with prominent pits forming a single row on both sides ; girder possibly meeting the internal prolonga- tions. Glabella and alae smooth; preglabellar field and cheek lobes anterior and lateral to the eyes with radiating ridges with fine pits between them; on the rest of the cheeks and on the brim are similar fine pits but without ridges or arrangement. FIGURED SPECIMEN. Incomplete cranidium (^.58303). HORIZON AND LOCALITY. Garn Formation, limestone blocks in breccia beds, Forth Padrig, Mynachdy. N.G.R. 30539279. DISCUSSION. The two closest genera are Selenoharpes and Aristoharpes , the former of Middle Ordovician (post-Llandeilo) age and the latter of Llandovery age. In Selenoharpes the glabella tapers forwards, the eye ridges are prominent and genal ridges are present. In Aristoharpes the glabella is sub-parallel sided, eye ridges are weak and genal ridges absent. It also has much smaller alae than Selenoharpes, which are one-quarter the length of the glabella compared with one-half. There is thus some doubt as to where to place these specimens, which compare closely with Selenoharpes, except for the smaller alae, a difference that is probably trivial. The specimens are certainly not conspecific with the type species, S. youngi (Reed) from the lower Caradoc of Girvan, in which the brim is convex upwards. Family TRINUCLEIDAE Hawle & Corda 1847 Subfamily CRYPTOLITHINAE Angelin 1854 Genus BERGAMIA Whittard 1955 Bergamia (?) sp. (PI. 13, figs. 3-4, 9> 13) DESCRIPTION. Cephalon twice as broad as long. Glabella pyriform, swollen, tapering markedly posteriorly, second and third furrows fairly well marked, pit- like in form ; well marked alae bounded laterally by deep furrows, ending laterally against the posterior border in well marked knobs ; glabellar furrows not well marked AND TRILOBITES OF ANGLESEY 185 against the alae. Genae swollen, crossed by a ridge running obliquely back from the front of the glabella to the genal angle. Occipital ring very narrow, arched and convex posteriorly; posterior borders from a narrow sharp ridge posterior to a wide shallow furrow. Glabella and genae posterior to the ridge bear a strong reticulate pattern, becoming faint towards the front of the glabella. Fringe of uniform width throughout except at the genal angle ; pits sunk in deep radial sulci ; girder not seen in any of the specimens; sulci number eighteen on each side of the centre-line, with up to four pits in each ; interradial sulci numbers i and ii present ; some twin pits. Thoracic segments not well preserved; axis strongly convex with axial rings convex posteriorly; pleural regions with strong oblique pleural furrows; pleural spines strong and directed posteriorly. Pygidium over twice as wide as long, triangular in outline; axis tapers at 30 with at least five axial rings, well defined and strongly arched; pleural lobes divided by at least four faintly marked oblique interpleural furrows; anterolateral angles bevelled as an articulating facet; posterior margins with a broad border of uniform width, slightly raised over the centre-line. FIGURED SPECIMENS. Counterpart moulds of cranidium and pygidium (In. 58304a-b). Length of cranidium (sag.) 3-4 mm., width 7-0 mm. Length of pygi- dium i -7 mm., width 4-2 mm. Counterpart moulds of complete dorsal carapace (In.58305a-b). Length (sag.) 2-5 mm. Ventral mould of dorsal carapace (In. 58306) Distorted. HORIZON AND LOCALITY. Shales, D. bifidus zone, quarry 100 yds. north of Gwredog-uchaf farm, Rhodogeidio. N.G.R. 40488628. DISCUSSION. The preservation of the specimens, in particular of the fringe, is not good enough to make a certain generic identification. However, the simplicity of the fringe suggests that the specimens belong to Bergamia, which ranges from the uppermost Arenig through the Llanvirn, and possibly into the Caradoc (Whittard I 955 : 3 1 )- The species resembles B. rhodesi Whittard (1955 : 32) in the arrange- ment of the pits on the fringe. The smallest specimen illustrated (PI. 13, fig. 3) is a meraspid of probably degree two. There is little difference in characters from the larger specimens. Family RAPHIOPHORIDAE Angelin 1854 Genus AMPYX Dalman 1827 Arnpyx sp. (i) (PI. 13, %. 8) 1919 Ampyx cf. domains (Angelin); Lake in Greenly : 446. 1955 Ampyx sp.; Whittard : 17. FIGURED SPECIMEN. Cranidium (Af .824). Length 9-0 mm., width 12-4 mm. i86 LOWER PALAEOZOIC BRACHIOPODS HORIZON AND LOCALITY. Carmel Formation, sandstones on the escarpment 300 yds. west of Bryn Gollen Uchaf. N.G.R. 40558380. DISCUSSION. This specimen remains the only one collected from the basal grits, and there is nothing that can be added to Whittard's opinion that it probably belongs to an undescribed species. Ampyx sp. (2) (PL 13, figs. 7, 10-12) 1919 Ampyx nasutus Dalman; Lake in Greenly : 433. DESCRIPTION. Cranidium quadrilateral in outline, length four-tenths the width, the anterior border very well developed. Glabella pyriform, widest near the anterior end and broadly rounded in front, one-third to one-quarter the width of the cranidium in front, tapering to the occipital ring, exceptionally weakly swollen, overhanging only part of the preglabellar field. One pair of glabellar furrows almost isolating long narrow lobes, the furrows running back parallel to the axial furrows, starting just anterior to the transverse midline of the glabella; alae (cf. Whittard 1955 : 15) crescentic, starting anterior to the glabellar furrows and extending backwards to meet the posterior border furrow, axial and alar furrows faint; glabellar spine at least half as long as the cephalon, circular in cross section, possibly concave dorsally. Fixigenae triangular, gently convex. Facial suture runs in a gentle sigmoidal curve convex outwards as it crosses the posterior border, convex inwards forwards of this and again convex outwards in its anterior third. Occipital ring narrow, occipital furrow shallow, both convex backwards. Posterior border furrow broad and shallow, running obliquely outwards and backwards, but sweeping forwards again near the genal angle ; posterior border widening laterally. Pre-glabellar field comparatively long, about one-sixth the length of the cephalon, flattened. Thorax of six segments, broad and flat. Axis convex, axial rings each with a shallow groove defining small lobes at each side. Pleurae parallel-sided, each with an oblique furrow curved forward at the tip, sharply deflected ventrally at prominent fulcral processes which appear as tubercles. First or macro-pleurae longer than the others with outer margins not deflected but sloping backwards and out to the fulcrum. Other pleurae with blunt terminations. Pygidium triangular, twice as wide as long. Anterior margin straight, postero- lateral borders slightly convex, deflected, with terrace lines parallel to the margins. Axis convex, with narrow articulating half-ring, tapering from one-fifth the width of the pygidium anteriorly to a point at the posterior end, occasionally a few axial rings present. Pleural lobes smooth, except for strongly developed anterior borders, marked off by sharp furrows running obliquely backwards and outwards, becoming concave forwards laterally to meet the anterolateral angle of the pygidium. Pro- minent fulcral tubercle at the inner end of the articulating facet. AND TRILOBITES OF ANGLESEY 187 FIGURED SPECIMENS (measurements in mm.) Length Width Internal and external moulds of cranidium (In. 58ao7a-b) 16-0 356(est.) External mould of cranidium (In . 58308) Internal mould of thoracic segments and pygidium (Af.3653) . 16-3 19-3 External mould of pygidium (In . 58309) . . 7-0 16-8 (est.) HORIZON AND LOCALITY. Tandinas shales, by the track leading down to the quarry, and on the shore behind the power house, at Tandinas quarry, Careg-onen. N.G.R. 58248187. DISCUSSION. The species is similar to A. linleyensis Whittard of the Shelve area (D. bifidus zone), but differs in having a short, weakly swollen glabella, a pre-glabellar field, and having terrace lines on the pygidium. A. salteri Hicks (D. extensus zone?) also has terrace lines to the pygidium, but lacks a pre-glabellar field. Family CHEIRURIDAE Salter 1864 Subfamily CHEIRURINAE Salter 1864 Genus CERAURINELLA Cooper 1953 Ceraurinella sp. (PI. 13, figs. 14-22) DESCRIPTION. Cranidium roughly triangular in outline, broader than long. Glabella evenly convex (tr.), gently convex (sag.) becoming more convex along the anterior lobe. Length equal to the maximum width, the latter across the anterior lobe, sides slightly tapering towards the occipital ring, front margin convex forwards. Three pairs of narrow well marked glabellar furrows; ip inclined ob- liquely backwards, bent back to join the occipital furrow nearer the midline than the axial furrows; 2p and 3p parallel to each other, curving obliquely backwards and crossing one-third the width of the glabella (tr.). Basal lobes with independent convexity, one and a half times the length (exsag.) of the second and third lobes; the latter subequal in length without independent convexity. Occipital furrow not well seen, shallow. Fixigenae triangular convex, eye lobe on the highest part, opposite and close to the second glabellar lobe, equal in length to that lobe (exsag.). Anterior part of fixigenae parallel sided, anterior branch of facial suture running in to meet the axial furrows just in front of 3p glabellar furrows. Posterior branch of facial suture runs transversely out from the eye, and curves round to meet the anterolateral border of the cranidium. Posterior border furrows deep and wide, bending sharply forwards to meet the lateral border furrow. Posterior border widening laterally towards genal spine, length of latter unknown. Glabella and borders smooth, fixigenae coarsely tuberculate. Librigenae unknown. Hypostome slightly longer (sag.) than maximum width (tr.) across anterior wings, i88 LOWER PALAEOZOIC BRACHIOPODS tapering backwards to a width at the posterior border half the maximum. Median body convex (sag. and tr.) widest in front of anterior wings. Anterior, lateral and posterior border furrows broad and shallow. Middle furrows faint, running in from opposite shoulders to end in shallow pits. Posterior lobe crescentic, independ- ently convex where marked off by the middle furrows. No anterior border medianly. Anterior wing slopes steeply dorsoposteriorly, tip narrow and spine-like. Lateral border commences opposite anterior wing, widens rapidly to prominent and sharp shoulder (in ventral view) wh'ch is just less than half the way back (exsag.) from the anterior border, continuous with the posterior border. Short denticle or spine on the posterolateral corners, posterior border straight. Posterior wing not seen. Entire surface smooth. Thorax of unknown number of segments. Axis arched, most sharply convex over the midline, length (sag.) one-fifth the width, width one-quarter that of the whole segment. Anterior margin convex forwards over the midline, concave forwards laterally above the apodemes, which are deflected ventrally (no articulating half -ring seen). Inner part of pleura horizontal, divided in two by a furrow parallel to the axial furrow, the inner part being one-third the width of the whole, and crossed by a diagonal furrow, the outer part bent abruptly ventrally and forming a gradually tapering pleural spine. No ornament on the segments. Pygidium poorly preserved. Convex axis with four axial rings, or three axial rings and an articulating half ring. Margin not preserved, except for one long tapering spine probably commencing opposite the second axial ring and curving backwards towards its tip. No ornament present. FIGURED SPECIMENS (measurements in mm.) Length Width Incomplete glabella (In. 58310) .... 8-7 Incomplete glabella (In. 58311) .... 10-3 Incomplete cranidium (In. 58312) . . . 13-6 Hypostome (111.58313) Hypostome (In. 58314) 7-9 5 '4 Hypostome (^.58315) 9.1 Thoracic segment (In. 58316) .... Thoracic segment (In . 58317) Incomplete pygidium (In. 58318) .... HORIZON AND LOCALITY. Garn Formation, limestone blocks in breccia beds, Porth Padrig, Mynachdy. N.G.R. 30539279. DISCUSSION. The specimens are assigned to Ceraurinella since the eyes are opposite the 2p lobes and near the glabella, the genal spines though not complete are short, the pygidium has the long spines typical of that genus (and Ceraurus), and the thoracic segments and hypostome also are of the same type. The species described by Cooper (1953 : 29-30) and by Whittington & Evitt (1953 : 62-70) differ in their ornament, which is more pervasive, and possibly also in other minor details. None of the species of Ceraurus (Raymond & Barton 1913; Barton 1913) AND TRILOBITES OF ANGLESEY 189 corresponds. Ceraurinella? sp. has been recorded by Whittington from the Derfel limestone (in Whittington & Williams 1955 : 422-423, pi. 40, figs. 102, 107 and in), but the two species are not the same, as in his figures the eyes, not preserved, cannot have been farther back than opposite the 3p glabellar lobes, and the 3p lobes seem to be longer (sag.) than the others. Subfamily SPHAEREXOCHINAE Opik 1937 Genus SPHAEREXOCHUS Beyrich 1845 Sphaerexochus sp. (PL 14, figs. 1-2) DESCRIPTION. Cranidium only preserved, distorted by flattening, crescent shaped in outline, original convexity not known. Glabella subcircular to pentagonal in outline, widest opposite the second glabellar furrow (2p). Occipital ring narrower than the glabella at its maximum, one-eighth of glabella length (sag.), convex, posterior margin concave backwards. Occipital furrow broad and deep, uniformly curved throughout. First glabellar furrows (ip) transverse with a gently concave backwards curve, curving sharply at their inward ends towards the occipital furrow, running to meet it in another gentle curve convex sagittally. The first lateral glabellar lobes isolated, subquadrate in outline, possibly without independent con- vexity, four-ninths the length of the glabella (sag.), approximately two-ninths its width. Second glabellar furrow (preserved only on one side) very short, straight. Second glabellar lobe one-half length of the first. No third glabellar lobes or furrows. Anterior border not preserved. Fixigenae small, triangular, convex. Palpebral lobe very narrow, opposite to ip furrow, two-thirds the length of the first lobes. Facial suture not seen forward of the eye. Posterior branch runs outwards and then backwards to meet the posterior border at right angles. Posterior border equal in width to the occipital ring at its inner end, widening towards the genal angle. Posterior border furrow concave forwards, dying out towards the genal angle. FIGURED SPECIMEN (measurements in mm.) Length Width Cranidium (^.58319) . . . . 6-0 (sag.) 9-5 HORIZON AND LOCALITY. Tandinas shales, on the shore by the powerhouse, 100 yds. west of the pier, Careg-onen. N.G.R. 58208193. DISCUSSION. The specimen differs from all described species of Sphaerexochus by having two pairs of lateral glabellar furrows. 5. bilobatus (Whittard 1958 : no) has only the basal pair developed, otherwise three pairs seem to be the rule. The preservation of the specimen has resulted in accentuation of the anterior furrow on one side, and its obliteration on the other. It is possible, though unlikely that a third pair of furrows may be present, but obliterated. GEOL. 16, 4. 19 igo LOWER PALAEOZOIC BRACHIOPODS Family PLIOMERIDAE Raymond 1913 Subfamily PLIOMERINAE Raymond 1913 Genus PLIOMEROPS Raymond 1905 Pliomerops sp. (PI. 14, figs. 3-4, 6-7) DESCRIPTION. Cranidium incomplete. Glabella quadrangular, expanding for- wards from the occipital ring to midway between the pre-occipital and middle furrows, forwards of this having a domed margin, slightly flattened in the centre. Dorsal furrows deeply impressed. Pre-occipital furrows (ip) commencing at one- third the length of the glabella forwards from the occipital ring, running obliquely inwards and backwards for one-quarter the width of the glabella, at that point turning abruptly to run slightly forwards, finally curving round to point obliquely backwards at their inner tips, which are separated by one-eighth the width of the glabella. Middle furrows (2p) commencing just forwards of two-thirds the length of the glabella, running inwards and backwards to as near the midline as the pre- occipital furrows, the tips of the inner ends of the two pairs of furrows being much closer together than their outer ends. Anterior furrows (3p) located on the anterior margin, half way between the midline and the anterolateral corner of the glabella, faint and short, being little more than indentations of the margin. Rear two pairs of glabellar lobes with independent convexity. Axial furrows of the same depth as the glabellar furrows, curving smoothly into the anterior border furrow. Occipital furrow convex forwards at centre, becoming concave forwards towards the axial furrows. Occipital ring not completely preserved, lengthening (sag.) towards the midline. Anterior border strongly arched dorsally over the midline, widest at the midline and at the anterolateral angles of the cephalon. Fixigenae incompletely preserved. Hypostome shield-shaped, anterior border convex, lateral and posterior borders with a sigmoidal curve ending in a posterior point, slightly wider than long, almost flat. Middle body of same shape. Anterior lobe produced into lateral wings, posterior lobe crescentic, defined by middle furrows commencing just behind the wings, broad and shallow, curving gradually inwards. Anterior border poorly preserved, widest at the anterior wings. Lateral and posterior borders of uniform width except at their anterior ends. All border furrows wide and shallow. Pygidium with shape of an extremely taut bow, just longer than wide, anterior margin very convex forwards. Convex (tr.), the margins deflected ventrally at angles up to 90, almost flat (sag.), but convex (exsag.). Axis convex, of five flat- topped (sag.) axial rings, tapering backwards, followed by a terminal axial piece one and one half times as long as the rings, parallel sided for half its length and tapering to a point in the posterior half. Pleural portions of five pleural lobes, without a border, each lobe widening to the margin and truncated to produce a smooth lateral and posterior border ; the last pair surrounding the axis and separated by a median furrow. AND TRILOBITES OF ANGLESEY 191 FIGURED SPECIMENS (measurements in mm.) Length Width Incomplete cranidium (In. 58320) . . . 16-5 Hypostome (In. 58321) 14-5 Pygidium (^.58322) 39-0 Internal mould and interior of pygidium (In. 58323a-b) . 17-0 (est.) HORIZON AND LOCALITY. Garn Formation, limestone blocks in breccia beds, Forth Padrig, Mynachdy. N.G.R. 30539279. DISCUSSION. The above descriptions are of isolated pieces from the limestone blocks, and, assuming they belong together, they are assigned to the genus Pliomerops Raymond on the basis of the diagnosis given by Harrington (in Moore 1959 : 440). The anterior border is not denticulate, there is no median indentation of the glabella, and the terminal axial piece is long and enclosed. The cranidium resembles that of P. canadensis (Billings) illustrated in the Treatise (Moore 1959 : fig. 345, 2b) but the pygidia do not. As far as can be seen, most of the described species of Pliomerops have short terminal axial pieces and usually a denticulate margin, though the diagnosis in the Treatise (Moore 1959 : 440) states that the terminal axial piece is long. Reed (1906 : 153, Plate XIX, fig. 16) figures a pygidium very like this as Pliomera sp. B. N. Cooper (1953) has described a pliomerid from Virginia, Pliomerella ameri- cana, which is somewhat similar to the Anglesey specimens. The pygidium appears to be identical, to judge from PL 10, fig. 4 of his paper. This is a crushed specimen, but the long axial piece is apparently enveloped by the posterior pleurae. Another pygidium is illustrated in fig. I of the same plate, in which the terminal axial piece is quadrate and reaches the posterior margin, though it may be that the posterior part is missing, and the caption states that the specimen is incomplete. Cooper's text does not indicate whether the axial piece is enveloped or not, and the specimen of his PI. 10, fig. i is re-illustrated on p. 445 of the Treatise (Moore 1959 : fig. 348, 2b) as being in fact complete. The accompanying text in the Treatise (Moore 1959 : 0445) states that a pygidium of this sort is diagnostic of Pliomerella. The genus was erected by Reed (1941 : 269) for trilobites with two pairs of glabellar furrows 'combined with some characters of Pliomera' ' , but he did not describe a pygidium. It is thus probable that Pliomerella americana Cooper does not belong to Pliomerella, but possibly to Pliomerops, though there is no sign in Cooper's figures of the anterior glabellar furrows, nor does he describe them in the text. Subfamily PLACOPARIINAE Hupe 1953 Genus PLACOPARIA Hawle & Corda 1847 Placoparia sp. (PI. 14, fig. 5) 1919 Placoparia sp. : Lake in Greenly : 466. FIGURED SPECIMEN. Dorsal carapace (Af.i3i9). Length 23-1 mm. GEOL. 16, 4. !Q I 9 2 LOWER PALAEOZOIC BRACHIOPODS HORIZON AND LOCALITY. Shales of the Gl. teretiusculus zone, 80 yds. north of the streamlet, on the shore at Porth-y-gwichiaid (Greenly 1919 : 466). N.G.R. 48799160. DISCUSSION. The species P. zippei (Boeck) has recently been divided into two species, P. zippei and P. barrandei Prantl & Snajdr, differing in a number of small features, including the glabellar shape, details of the glabellar and occular furrows, and the development of vincular notches (Whittard 1966 : 283-284). P. barrandei itself is a synonym of P. cambriensis Hicks (1875 : 186, pi. 9, figs. 1-2) (Dr. W. T. Dean, personal communication). The Anglesey specimen belongs more probably to P. cambriensis, as the glabella is quadrate rather than trapezoidal in outline, though the evidence of the other features is equivocal, probably due to crushing of the specimen. Family CALYMENIDAE Burmeister 1843 Subfamily CALYMENINAE Burmeister 1843 Calymenid undet. (PI. 14, figs. 8-9, 12-13) FIGURED SPECIMENS (measurements in mm.) Length Width Hypostome (^.58324) 6-7 5-6 Pygidium (In. 58325) . 9-3 H'5 HORIZON AND LOCALITY. Garn Formation, limestone blocks in breccia bed, Porth Padrig, Mynachdy. N.G.R. 30539279. DISCUSSION. The material found consists of one complete pygidium, and one complete and one incomplete hypostome. It is assumed that they all belong to one species. The pygidium is oval in outline, and strongly convex. The axis gradually tapers backwards, not reaching the posterior border, with six well defined axial rings, a terminal piece and an articulating half ring. The pleural portions show deep pleural furrows with much shallower interpleural furrows, extending to the margin but becoming much fainter on the border. The border is marked by faint depres- sions running from the tip of the axis to the anterior margins. There are well defined and almost vertically deflected articulating facets, with the foremost pleural groove extending onto them. In posterior view the lateral and posterior margins show a strongly marked arch across the midline. The entire surface, except for the articulating facets and the furrows, is finely tuberculate. The hypostome is longer than wide, rectangular in outline. The middle body is parallel-sided, with faint diagonal middle furrows dividing off a crescentic posterior lobe, convex longitudinally and sharply convex transversely, without a raised central portion to the anterior lobe. The anterior border is flexed ventrally, con- tinuous with large anterior wings. The lateral borders have a wide gently curved notch extending from the anterior wings to opposite the anterior end of the posterior lobe. The lateral and posterior borders behind this are wide and flat, produced AND TRILOBITES OF ANGLESEY 193 into points almost one-third of the length of the hypostome, separated by a deep median notch extending to the end of the middle body. The tips of the points and the notch are all sharp, each with an angle of about 50. Subdivision of the Calymeninae is based mainly on cephalic characters, so it is not possible to give a generic designation. The upper Ordovician calymenid species have been assigned to five different genera by Shirley (1936 : 400), and of these Platycalymene , Gravicalymene and Flexicalymene agree in their pygidal characters. Flexicalymene is the closest in character, and the pygidium described and figured by Shirley (1936 : 406, pi. 29, fig. 7) looks similar, though it is more angular in outline. Family HOMALONOTIDAE Chapman 1890 Subfamily EOHOMALONOTINAE Hupe 1953 Genus NESEURETUS Hicks 1872 Neseuretus monensis (Shirley) (PI. 14, figs, n, 16) 1919 Calymene parvifrons Salter; Lake in Greenly : 442, 446. 1919 Calymene tristani Brongniart; Lake in Greenly : 442. 1936 Synhomalonotus monensis Shirley : 401. FIGURED SPECIMENS (measurements in mm.) Length Width Internal and external moulds of pygidium (In. 58326a-b) 16-9 21-0 (est.) Internal mould of pygidium (In . 58327) . . distorted HORIZON AND LOCALITY. Carmel Formation, sandstones ; In . 58326a-b from 440 yds. north of Ty-hen, Treiorwerth, N.G.R. 35767891; In. 58327 from 120 yds. north-west of Chwaen-bach, Llanerchymedd, N.G.R. 39468378. DISCUSSION. Shirley described this species from specimens in Greenly's collection (G.S.M. Af. 930-2). The thorax, librigenae and pygidium were not represented in the collection, so only the cranidium was described. Pygidia have been found from the same horizon, and give additional information on the species. The speci- men from Chwaen-bach is distorted, and the description is based on that from near Ty-hen (^.58326). The pygidium is broader than long, roughly elliptical but with the anterior margin more strongly curved than the borders. The axis bears an articulating half ring and furrow. The axis is funnel-shaped, the tapering portion containing at least six rings, followed by an almost cylindrical portion terminating in a rounded end not quite reaching the posterior margin. The pleural lobes are gently convex, and bear six rounded unfurrowed pleurae, separated by well marked interpleural furrows. The border is sharply rounded, but the form of the doublure is unknown. The pygidium from Chwaen-bach shows pleural furrows which may be the result of crushing. 194 LOWER PALAEOZOIC BRACHIOPODS Family LICHIDAE Hawle & Corda 1847 Subfamily TETRALIGHINAE Phleger 1936 Genus AMPHILICHAS Raymond 1905 Amphilichas sp. (i) (PL 14, figs. 10, 14-15, 17) DESCRIPTION. Cranidium roughly pentagonal, strongly bent down at the an- terior and posterior lateral corners. Glabella rounded, axe-shaped, as broad as long, strongly convex, overhanging in front. Frontero-median lobe prominent, expanded in front to more than twice its basal width; anteriorly strongly convex; anterior lateral angles rounded; posteriorly parallel sided and less convex. First lateral (longitudinal) furrows run inwards towards centre of lobe, curving steadily round to become parallel and meet the occipital furrow at right angles. Lateral lobes gently convex, a little less elevated than the median lobe; bluntly pointed in front, strongly bent down with the antero-median lobe; posterolateral angles extend considerably further back than the median lobe. Axial furrows as strong as longitudinal furrows, posteriorly parallel to them, diverging slightly in front of the eyes. Occipital furrow straight and horizontal behind median lobe, directed obliquely backwards behind the lateral lobes, and less obliquely behind the fixigenae. Occipital ring not completely preserved but possibly widest behind the median lobe. Fixigenae posteriorly equal in width to the lateral lobes, narrowing to less than half that width opposite the eye; expanding in front of the eye; expanding in front of the eye but not completely preserved. Course of facial suture only seen round eye, running outwards behind it. Palpebral lobe semicircular, convex inwards; its length is one-fifth that of the glabella and its posterior end level with the occipital furrow. Entire cranidium, except for the furrows, covered with tubercles of varying size, irregularly placed. Hypostome oval in outline, broader than long. Posterior border broad, posterior margin indented. Middle body circumscribed. Posterior lateral lobes well defined by median furrows running inwards slightly posteriorly with short bifurcations at their inner ends. Lateral borders broad, with short triangular wings opposite the posterior border furrow. Anterior border appears to be lacking. Anterior part of middle body pitted; anastomosing ridges or terrace lines on remainder of surface. FIGURED SPECIMENS (measurements in mm.) Length Width Incomplete cranidium (In . 58328) . . . 14-9 Hypostome (In. 58329) .... 5 -8 (sag.) 7-9 HORIZON AND LOCALITY. Garn Formation, limestone blocks in breccia beds, Porth Padrig, Mynachdy. N.G.R. 30539279. DISCUSSION. No thoracic segments have been found, and the only remains of pygidia so far found are too incomplete to describe; they only show the typical development of tubercles, The cranidium shows similarities to A, wahlenbergi AND TRILOBITES OF ANGLESEY 195 Warburg from the Leptaena Limestone in Dalarne, and also to Lichas (Amphilichas) hibernicus (Portlock) (Reed 1906 : 106, pi. 15, fi. I non 2-3). Amphilichas sp. (2) (PI. 14, figs. 18-19) DESCRIPTION. Outline possibly semicircular, weakly convex both longitudinally and transversely, probably crushed. Frontero-median lobe convex, expanding forwards to over twice its posterior width; the longitudinal furrows being parallel posteriorly and curving outwards to diverge at more than 90 where they meet the axial furrow, not reaching the occipital furrow but ending in a pit. Tri composite lobe widening very slightly forwards, at its posterior end the same width as the median lobe posteriorly; axial furrows concentric with the longitudinal furrows but with smaller radius of curvature. Fixigena incomplete, narrow, posterior to the eye less than half the width of the tricomposite lobe, cut into by the eye lobe, which is one-fifth the length of the cranidium. Only a fragment of the occipital ring preserved. Surface evenly pitted. FIGURED SPECIMEN (measurements in mm.) Length Width Incomplete external mould of cranidium (Af. 3000) 17 app. HORIZON AND LOCALITY. Tandinas shales, by the track 50 yds. west of Tandinas quarry, Careg-onen. N.G.R. 58248187. DISCUSSION. There appear to be no basal lobes, so that the specimen belongs to Amphilichas, although there is little to compare closely with Amphilichas sp. (i) from Forth Padrig. Family uncertain Genus MONELLA nov. DIAGNOSIS. Genus similar to Glossopleura Poulsen, but differing in having more strongly marked glabellar furrows, the anterior ends of the palpebral lobes not touching the glabella, and eleven (compared with eight) thoracic segments. TYPE SPECIES. Monella perplexa sp. nov. from the Carmel Formation. DISCUSSION. The specimens assigned to the new genus were referred by Lake (in Greenly 1919) to Ogygia, but certainly do not belong to the suborder Asaphina. The thorax consists of eleven segments and the glabella is distinctly furrowed, a combination of characters that is quite different from any contemporary trilobites, but generally characteristic of the Order Corynexochida, though the rostral plate and hypostome have yet to be found. The glabella is clavate and reaches the anterior margin, the eyes are large and semicircular, with prominent palpebral lobes, though eye ridges are not present. The closest genera are found in the family Dolichometopidae, of the order Corynexochida. Athabaskiella has a similar cephalon, but a smaller pygidium with only four segments differentiated in the pleural regions ig6 LOWER PALAEOZOIC BRACHIOPODS and fewer in the axis. Bathyuriscus has smaller eyes which are not semicircular, and a very narrow border to the pygidium. Dolichometopsis has a pygidium without a border and with a terminal indentation, and Glossopleura has very faint glabellar furrows, only eight thoracic segments, and differs in the position of the palpebral lobes. Monella perplexa gen. et sp. nov. (PL ii, figs. 15-21) 1919 Ogygia sp. (pars) ; Lake in Greenly : 446. DIAGNOSIS. As for genus. DESCRIPTION. Outline ovate, cephalon larger than pygidium. Cephalon semi- circular, over twice as broad as long. Glabella clavate, between one and one- quarter and two times as long as broad, convex transversely and slightly convex longitudinally; glabellar lobes with independent convexity; three pairs of glabellar furrows, one quarter the width of the glabella, shallow at their abaxial ends ; posterior pair (ip) at one quarter the length of the glabella forwards, inclined obliquely backwards and becoming shallower and wider at their adaxial ends; 2p inclined slightly backwards, situated just forward of half the length of the glabella; 3p transverse or slightly inclined forwards, nearer 2p than the front of the glabella; anterior margin of glabella convex forwards, lateral margins and the distinct axial furrows evenly and gently convex adaxially, with well marked fossulae midway between 3p and the front of the glabella. Occipital ring continues the convexity of the glabella, one sixth its length (sag.) ; occipital furrow distinct. Fixigenae smaller than the glabella or the librigenae. Palpebral lobes semicircular, posterior extremities just anterior to the base of the glabella; anterior extremities between the 2p and 3p furrows, separated from the axial furrows at each end by one-third the width of the glabella. No preglabellar field. Anterior border furrow narrow, anterior border with a vertically deflected margin. Facial sutures opisthoparian, posterior branches diverging backwards to cut the posterior margin midway between the axial furrow and the genal spine; anterior branches run directly forwards from the eye to the margin. Librigenae convex, genal spine equal in length to the glabella. Posterior border straight to the facial suture, then curving abaxially from it evenly round to the genal spine; posterior and lateral furrows well defined, posterior border half the width of the occipital ring (sag.) ; the lateral border with a vertical deflection. Doublure wide. Hypostome and rostral plate unknown. Thorax of eleven segments. Axis cylindrical, tapering slightly, equal in width to the pleural regions, articulating half-rings equal in length (sag.) to the axial rings; interpleural furrows curving slightly forwards towards the axial furrows. Pleural regions flat adaxially, deflected ventrally in their abaxial regions; pleural furrows transverse, dying out between fulcra and extremities; short, backwardly directed pleural spines formed by the extremities of the pleurae being tapered. AND TRILOBITES OF ANGLESEY 197 Anterior three(?) segments narrower (tr.) than the rest and undeflected at their ends. Pygidium semicircular. Axis convex, tapering to a point and extending onto the border but not reaching the posterior margin, eight or possibly more axial rings present. Pleural lobes gently convex with pleural furrows only. Border broad, concave, doublure equal to it in width. TYPE SPECIMENS (measurements in mm.) Length Width HOLOTYPE. Counterpart moulds of complete dorsal carapace (Af. 827-8) .... 13-7 PARATYPES. Internal mould of cranidium (Af .834) Internal mould of cranidium (Af . 836) Internal mould of pygidium (Af . 839) OTHER FIGURED SPECIMEN External mould of incomplete dorsal cara- pace (In. 58290) .... TYPE HORIZON AND LOCALITY. Carmel Formation, sandstones in old quarry (now filled in), 400 yds. north-north-west of Bryn Gollen Uchaf, Llanerchymedd. N.G.R. 40508425. Other figured specimen from same horizon, on the escarpment 50 yds. north-east of Prys-o wain-bach, Carmel. N.G.R. 38878283. DISCUSSION. The generic position of M. perplexa has already been discussed, and it is at present the only species known of the genus. VI. REFERENCES. ALIKHOVA, T. N. 1953. Rukovodyashchaya fauna brakhiopod Ordovitskikh otlozheniy severo- zapadnoi chasti Russkoi Platformy. Vses. Nauchno-Issledov. Geol. Inst. (VSEGEI), Minist. Geol. i Okhrany Nedr., SSSR, Trudy, 162 pp., 17 pi. BANCROFT, B. B. 1945. The brachiopod zonal indices of the stages Costonian to Onnian in Britain. J . 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