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Z _l z HSONIAN INSTITUTION NOIiniliSNI NVINOSHillMS S3IHVaan LIBRARIES SMITHSONIAN INSTI CO osHims' S3 iavaan“LiBRARi es“'smithsonian“ institution ^NoiiniiiSNi nvinoshhins s3 i a CO Z to 2 , c/5 Z to ? , , V- 5 1 y- - i-iriPif > ~'W' 2 > x^OiM^^ 2 2 xO\oC^ ^ Z t/5*Z CO*^ Z to z 3S0NIAN INSTITUTION NOIiniliSNI NVINOSHimS S3iavaan LIBRARIES SMITHSONIAN INSTI - CO _ to Q " _ '<^ua‘=^ Q x^Ai DX--^ O DSH1IIAIS"'S3 lava a n~LI B RAR I ES^SMITHS0NIAN~’lNSTITUTI0N^N0linillSNl“'NVIN0SHlllNS_S3 I a CO ^ x^tvAsv^ m ^ m xcfVQsv^jx ^ HS0NIAN~INSTITUTI0N^N0linillSNI~NVIN0SHilWS^S3 I ava a 11 ~LI B RAR I ES SMITHSONIAN INSTI Z r CO Z CO Z > ^ Z < '->9, S s s o S ' 1>F'’ >' 5 >■' OSHlItMS^^Sa lavaan^LIBRARI Es'^SMITHSONIAN institution 'NOIinillSNI_NVINOSHlllA!S ’ S3 I a ~ ‘ CO 2: HSONIAN INSTITUTION NOIiniliSNI NVINOSHIIWS S3iavaail LIBRARIES SMITHSONIAN INSTI osHiiiNS S3iavaan libraries Smithsonian institution NoiiniiisNi nvinoshiiins S3ia CO z CO z V, CO z ^ CO VOLUME 15 Palaeontology 1972 PUBLISHED BY THE PALAEONTOLOGICAL ASSOCIATION LONDON Dates of publication of parts of Volume 15 Part 1, pp. 1-185, pis. 1-38 Part 2, pp. 187-380, pis. 39-65 Part 3, pp. 379A-518, pis. 66-105 Part 4, pp. 519-693, pis. 106-132 February 1972 June 1972 September 1972 December 1972 THIS VOLUME EDITED BY N. F. HUGHES, GWYN THOMAS, ISLES STRACHAN, ROLAND GOLDRING, J. D. HUDSON, D. J. GOBBETT AND L. R. M. COCKS Dates of publication of Special Papers in Palaeontology Special Paper No. 1 Special Paper No. 2 Special Paper No. 3 Special Paper No. 4 Special Paper No. 5 Special Paper No. 6 Special Paper No. 7 Special Paper No. 8 Special Paper No. 9 Special Paper No. 10 Special Paper No. 11 21 June 1967 31 January 1968 7 October 1968 1 May 1969 17 October 1969 26 April 1970 6 August 1970 11 November 1971 11 December 1971 10 February 1972 7 December 1972 © The Palaeontological Association, 1972 Printed in Great Britain at the University Press, Oxford by Vivian Ridler Printer to the University CONTENTS Part Page Ambrose, T., and Romano, M. New Upper Carboniferous Chelicerata (Arthropoda) from Somerset 4 569 Ash, S. R. Marcouia gen. nov., a problematical plant from the Late Triassic of the south-western U.S.A. 3 423 Late Triassic plants from the Chinie Formation in north-eastern Arizona 4 598 Baker, P. G. The development of the loop in the Jurassic brachiopod Zeilleria leckeiibyi 3 450 Banks, H. P. The stratigraphic occurrence of early land plants 2 365 Bate, R. H. Fossil and living Hemicypris (Ostracoda) from Lake Rudolf, Kenya 1 184 Phosphatized ostracods with appendages from the Lower Cretaceous of Brazil 3 379A Bates, D. E. B. A new Devonian crinoid from Australia 2 326 Bishop, G. A. Moults of Dakoticancer overanus, an Upper Cretaceous crab from the Pierre Shale of South Dakota 4 631 Black, C. C. Review of fossil rodents from the Neogene Siwalik beds of India and Pakistan 2 238 Black, M. Crystal development in Discoasteraceae and Braarudosphaeraceae (plank- tonic algae) 3 476 Brett, D. W. Fossil wood of Platanns from the British Eocene 3 496 Brunton, C. H. C., and Mackinnon, D. L. The systematic position of the Jurassic brachiopod Cadomella 3 405 Clayton, G. Compression structures in the Lower Carboniferous miospore Dictyo- triletes admirabilis Flayford 1 121 Cocks, L. R. M. The origin of the Silurian Clarkeia shelly fauna of South America and its extension to West Africa 4 623 Creber, G. T. Gymnospermous wood from the Kimmeridgian of East Sutherland and from the Sandringham Sands of Norfolk 4 655 Eager, R. M. C. Use of the pictograph 2 378 Elliott, G. F. Cretacicrusta gen. nov., a possible alga from the English Cretaceous 3 501 Trinocladus exoticus, a new dasycladacean alga from the Upper Cretaceous of Borneo 4 619 Earrow, G. E. Periodicity structures in the bivalve shell: analysis of stunting in Cerastoderma edide from the Burry inlet (South Wales) 1 61 Hancock, J. M., Kennedy, W. J., and Klaumann, H. Ammonites from the trans- gressive Cretaceous on the Rhenish Massif, Germany 3 445 Jackson, D. E., and Lenz, A. C. Monograptids from the Upper Silurian and Lower Devonian of Yukon Territory, Canada 4 579 Jago, j. B. Two new Cambrian trilobites from Tasmania 2 226 Jeletzky, j. a. Morphology and taxonomic status of the Jurassic belemnite "Rhopalo- teuthis' somaliensis Spath 1935 1 158 Kaueeman, E. G. Ptychodus predation upon a Cretaceous Inoceramus 3 439 Keen, M. C. The Sannoisian and some other Upper Palaeogene Ostracoda from north- west Europe 2 267 Kennedy, W. J. The affinities of Idiohamites ellipticoides Spath (Cretaceous ammon- oidea) 3 400 and Klinger, H. C. A Texanites-Spinaptychus association from the Upper Cretaceous of Zululand 3 394 Hiatus concretions and hardground horizons in the Cretaceous of Zululand 4 539 CONTENTS iv Part Page Kennedy W. J. See Hancock, J. M. Klaumann, H. See Hancock, J. M. Klinger, H. C. See Kennedy, W. J. (two papers) Lane, P. D. New trilobites from the Silurian of north-east Greenland, with a note on trilobite faunas in pure limestones 2 336 Layman, M. See Taylor, J. D. Lenz, a. C. See Jackson, D. E. Lord, A. iVicherella and Gramannella, two new genera of Lower Jurassic Ostracoda from England 2 1 87 MACKINNON, D. L. See Brunton, C. H. C. Matthews, S. C., Sadler, P. M., and Selwood, E. B. A Lower Carboniferous cono- dont fauna from Chillaton, south-west Devonshire 4 550 Mishra, V. P. See Sahni, A. Morton, N. The Bajocian ammonite Dorsetensia in Skye, Scotland 3 504 Nichols, D. The water-vascular system in living and fossil echinoderms 4 519 Paul, C. R. C. Morphology and function of exothecal pore-structures in cystoids 1 I Peel, J. S. Observations on some Lower Palaeozoic tremanotiform Bellerophontacea (Gastropoda) from North America 3 412 Rigby, J. F. On Arberia White, and some related Lower Gondwana female fructifications 1 108 Romano, M. See Ambrose, T. Sadler, P. M. See Matthews, S. C. Sahni, A., and Mishra, V. P. A new species of Protocetus (Cetacea) from the Middle Eocene of Kutch, western India 3 490 Sellwood, B. W. Regional environmental changes across a Lower Jurassic stage- boundary in Britain 1 125 Selwood, E. B. See Matthews, S. C. SoRAUF, J. E. Skeletal microstructure and microarchitecture in Scleractinia (Coelen- terata) 1 88 Taylor, J. D., and Layman, M. The mechanical properties of bivalve (Mollusca) shell structures 1 73 Thulborn, R. a. The post-cranial skeleton of the Triassic ornithischian dinosaur Fabrosaurus australis 1 29 Tozer, E. T. Observations on the shell structure of Triassic ammonoids 4 637 Tucker, M. E. See Van Straaten, P. Van Straaten, P., and Tucker, M. E. The Upper Devonian Saltern Cove goniatite bed is an intraformational slump 3 430 Wade, M. Hydrozoa and Scyphozoa and other medusoids from the Precambrian Ediacara fauna. South Australia 2 197 WooTTON, R. Nymphs of Palaeodictyoptera (Insecta) from the Westphalian of England 4 662 Wright, A. D. The brachiopod Acanthocrania in the Ordovician of Wales 3 473 Notes for authors submitting papers for publication in Palaeontology 4 676 VOLUME 15 • PART 1 Palaeontology FEBRUARY 1972 PUBLISHED BY THE PALAEONTOLOGICAL ASSOCIATION LONDON THE PALAEONTOLOGICAL ASSOCIATION The Association was founded in 1957 to further the study of palaeontology. It holds meetings and demonstrations, and publishes the quarterly journal Palaeontology and Special Papers in Palaeontology. Membership is open to individuals, institutions, libraries, etc., on payment of the appropriate annual subscription: Institute membership ..... £10-00 (U.S. $26.00) Ordinary membership £5-00 (U.S. $13.00) Student membership £3-00 (U.S. $8.00) There is no admission fee. Institute membership is only available by direct appli- cation, not through agents. Student members are persons receiving full-time instruc- tion at educational institutions recognized by the Council; on first applying for membership, they should obtain an application form from the Membership Treasurer. All subscriptions are due each January, and should be sent to the Membership Treasurer, Dr. A. J. Lloyd, Department of Geology, University College, Gower Street, London, W.C. 1, England. COUNCIL 1971-2 President: Dr. W. S. McKerrow, Department of Geology, Oxford Vice-Presidents: Professor M. R. House, The University, Kingston upon Hull, Yorkshire Dr. Gwyn Thomas, Department of Geology, Imperial College, London, S.W. 7 Treasurer: Dr. J. M. Hancock, Department of Geology, King’s College, London, W.C. 2 Membership Treasurer: Dr. A. J. Lloyd, Department of Geology, University College, Gower Street, London, W.C. 1 Secretary: Dr. W. D. I. Rolfe, Hunterian Museum, The University, Glasgow, W. 2 Editors Mr. N. F. Hughes, Sedgwick Museum, Cambridge Dr. Isles Strachan, Department of Geology, The University, Birmingham 15 Dr. R. Goldring, Department of Geology, The University, Reading, Berks. Dr. J. D. Hudson, Department of Geology, The University, Leicester Dr. D. J. Gobbett, Sedgwick Museum, Cambridge Other members of Council Dr. E. N. K. Clarkson, Edinburgh Dr. L. R. M. Cocks, London Dr. R. H. Cummings, Abergele Dr. Julia Hubbard, London {co-opted) Dr. W. J. Kennedy, Oxford Mr. M. Mitchell, Leeds Dr. Marjorie D. Muir, London Dr. B. Owens, Leeds Dr A. D. Wright, Belfast Dr. W. H. C. Ramsbottom, Leeds Dr. Pamela L. Robinson, London Dr. E. P. F. Rose, London Dr. C. T. ScRUTTON, Newcastle Dr. V. G. Walmsley, Swansea Overseas Representatives Australia: Professor Dorothy Hill, Department of Geology, University of Queens- land, Brisbane Canada: Dr. B. S. Norford, Institute of Sedimentary and Petroleum Geology, 3303- 33rd Street NW., Calgary, Alberta India: Professor M. R. Sahni, 98 The Mall, Lucknow (U.P.), India New Zealand: Dr. C. A. Fleming, New Zealand Geological Survey, P.O. Box 30368, Lower Hutt West Indies and Central America: Mr. John B. Saunders, Geological Laboratory, Texaco Trinidad, Inc., Pointe-a-Pierre, Trinidad, West Indies Western U.S.A.: Professor J. Wyatt Durham, Department of Paleontology, Univer- sity of California, BerKeley 4, California Eastern U.S. A.: Professor J. W. Wells, Department of Geology, Cornell University, Ithaca, New York © The Palaeontological Association, 1972 MORPHOLOGY AND FUNCTION OF EXOTHECAL PORE-STRUCTURES IN CYSTOIDS by c. R. C. PAUL Abstract. Humatirhombs, humatipores, and diplopores have external respiratory exchange surfaces. Their thecal canals open internally and body fluids flowed through them in life. Four types of humatirhomb are dis- tinguished on morphology and arrangement of canals. Raised and buried humatipores occur and diplopores may have had extensile podia in life. All cystoid pore-structures were respiratory. Exothecal pore-structures were individually less efficient in exchange than endothecal (dichoporite) pore-structures. Their relative inefficiency is due to requirements of protection and is counteracted by their large number per theca. Cystoids with exothecal pore-structures attain great size. Less efficient pore-structures (humatirhombs, humatipores) have shorter stratigraphic ranges and become extinct before more efficient types (pectinirhombs, cryptorhombs, diplopores). Recent echinoderms as a group lack a specialized circulatory system and utilize varied exchange surfaces as did cystoids. Efficient exchange surfaces must be thinner than 1-3 mm: cystoid exchange surfaces are 0 01- OT mm thick. Diplopores and humatipores may have been connected to an internal water vascular system but humatirhombs were not. Rhombifera probably had external radial water vessels but Diploporita lacked them. Some Rhombifera may have had both internal and external branches of the water vascular system. Classes Rhombifera and Diploporita are defined and cystoid classification is reviewed. The cystoids constitute a heterogeneous grouping of primitive echinoderms which range from the basal Ordovician just into the Upper Devonian. The vital organs of cystoids (and other primitive echinoderms) were completely enclosed within a rigid cup or theca which provided them with protection. At the same time the theca restricted communication with the ambient sea water from which both food and oxygen neces- sary for life were obtained. The purpose of this paper is to show that three major types of pore-structure which occur in cystoids evolved in response to the respiratory ‘prob- lems’ created by the rigid theca. These pore-structures in cystoids, and by implication similar pore-structures in other primitive echinoderms, were effectively gills. Traditionally cystoid pore-structures have been grouped into ‘diplopores’ and ‘pore- rhombs’ on morphological grounds. Functionally however division of all echinoderm pore-structures into endothecal and exothecal groups, where primary exchange from sea water to body fluids took place within and outside the theca respectively, is more appropriate (text-fig. 1). The morphology and function of endothecal (dichoporite) pore- structures in cystoids have been described (Paul 1968). The present paper considers exothecal pore-structures for which Hudson (1915, p. 166) originally proposed the term ‘exospires’. Three basic types of exothecal pore-structures occur in cystoids : one type of rhomb and two types of dipore. Brief descriptions of their morphology were given in Paul (1968). In the next two sections the morphology of exothecal pore-structures in cystoids is described and they are analysed functionally as exchange structures. Since the most likely form of exchange is oxygen and carbon dioxide transfer a section on respiration [Palaeontology, Vol. 15, Part 1, 1972, pp. 1-28, pis. 1-7.] C 8472 B 2 PALAEONTOLOGY, VOLUME 15 in recent echinoderms follows. The last two sections deal with the water vascular system in cystoids and with the taxonomic and evolutionary implications of this study. Acknowledgements. Thanks are due to the following for the loan of, or access to, specimens in their care: Dr. R. L. Batten, American Museum of Natural History (AMNH); Drs. R. P. S. Jefferies and H. G. Owen, British Museum, Natural History (BMNH); Drs. R. V. Melville and A. Rushton, Insti- tute of Geological Sciences, London (GSM); Dr. H. Mutvei, Naturhistoriska Riksmuseum, Stock- holm (RM); Mr. A. G. Brighton and Dr. C. L. Forbes, Sedgwick Museum, Cambridge (SM); and Dr. P. M. Kier and Mr. T. Phelan, United States National Museum (USNM); Dr. E. S. Richardson, Field Museum of Natural History, Chicago (FMNH). Parts of this work were undertaken during the tenure of a Harkness Scholarship and a Natural Environment Research Council research scholarship at the Sedgwick Museum, Cambridge. Both are gratefully acknowledged. Dr. Jefferies kindly read the manuscript and suggested several improvements; however, I accept responsibility for all opinions expressed in the work. TEXT-FIG. 1. Diagrammatic representations of endothecal (a) and exothecal (b) canals. In a sea-water flows through the canal and exchange takes place within the theca; in b body fluids flow in the canal and exchange takes place outside the theca. Thecal wall shown with vertical lines. In this and following diagrams the external medium is towards the top of the figure. TEXT-FIG. 2. Simple (a) and compound (b) thecal canals. In a a single tangential canal (tc) connects a pair of perpendicular canals (pc); in b three tangential canals connect the perpendicular canals. Thecal canals open in internal pores (ip) in all exothecal pore-structures. MORPHOLOGY OF EXOTHECAL PORE-STRUCTURES IN CYSTOIDS All cystoid pore-structures are composed of U-shaped thecal canals (text-fig. 2) with one or more connections (tangential canals) between the limbs of the U (perpendicular canals). The openings (thecal pores) of exothecal canals are internal. The three types of exothecal pore-structures in cystoids are humatirhombs, humatipores, and diplopores s.s. (Paul 1968, p. 700). 1. Humatirhombs (text-figs. 3a-d, Pis. 1-4) Humatirhombs (humare: Lat. to bury) are composed of a set of thecal canals pores, fistula, Lat. a canal), all of which arise from pores on the inner surface of one PAUL: EXOTHECAL PORE-STRUCTURES IN CYSTOIDS 3 plate, pass through the plate, and cross a plate suture to pores on the internal surface of an adjacent plate (text-fig. 3). The pores are always simple and circular (PI. 4, fig. 2). The tangential canals may be single (simple fistulipores, text-fig. 2>a-b) or multiple (compound fistulipores, text-fig. Zc-d) and they lie either just below the external sur- TEXT-FiG. 3. Four types of humatirhomb. a, simple humatirhombs with simple fistulipores (sf), b, complex humatirhombs with simple fistulipores, c, simple humatirhombs with compound fistulipores (cf), d, complex humatirhombs with compound fistulipores. In humatirhombs with simple fistulipores (a, b) the tangential canals (xc) are raised in ridges; humatirhombs with compound fistulipores (c, d) have tangential canals buried beneath plate surfaces. Complex humatirhombs (b, d) have both principal fistulipores (pf) and shorter intermediate fistulipores (if), pc = perpendicular canal. face (Pis. 3-4) or in the crests of ridges on the external surface of the theca (PI. 1). Usually only simple fistulipores are associated with ridges (text-fig. 3a-b). Four types of humatirhomb may be distinguished on the structure and arrangement of fistulipores. In simple humatirhombs all the fistulipores run the entire length of the rhomb from margin to margin (text-fig. 3a, c). Complex humatirhombs (text-fig. 3b, d) have additional shorter fistulipores within the intra-rhomb area. Both types of humati- rhomb may be composed of either simple or compound fistulipores. Thus four types of humatirhomb may be recognized : 4 PALAEONTOLOGY, VOLUME 15 Simple humatirhombs with simple fistulipores (text-fig. 3a) Complex humatirhombs with simple fistulipores (text-fig. 2>b) Simple humatirhombs with compound fistulipores (text-fig. 3c) Complex humatirhombs with compound fistulipores (text-fig. 2d) Humatirhombs are characteristic of, and confined to, the superfamily Caryocystitida, members of which have thecae composed of an indefinite and usually large number of thecal plates which are randomly arranged. The number of thecal plates often increases TEXT-FIG. 4. Camera lucida drawings of the humatirhombs of Caryocystites lagenalis Regnell to show principal (pf) and intermediate (if) fistulipores. A, traces of tangential canals (SM A57362). b, traces of perpendicular canals (SM A30656) to show that intermediate fistulipores define smaller rhombs within the main rhomb, s = plate suture. during growth and it is impossible to describe the position in a theca of an individual plate or rhomb. However since all plate sutures have rhombs developed across them and all rhombs of any one theca are invariably the same, distinction of individual rhombs is unnecessary. No part of a theca is better provided with rhombs than any other part. EXPLANATION OF PLATE 1 Stereophotos of simple humatirhombs with simple fistulipores. Figs. 1, 2, 7. Lophotocystis granatum (Wahl.). 1, 2, Two small weathered examples to show fine granules on external surface. 1, RM Ec4353; 2, RM Ec4352; 7, SM A57330, Part of a large example with well-developed humatirhombs. All x 3. Eigs. 3-6. Ulrichocystis eximia Bassler. 3, 4, Unweathered isolated plate; 3, oblique sutural view to show tangential canals beneath external ridges, x 6; 4, external surface, x 4. 5, 6, Another isolated plate ; 5, weathered external surface to show exposed tangential canals and positions of perpendicular canals ; 6, internal surface to show canals partially covered near plate centre, both X 4 (cf. text-fig. \2b). Specimens in author’s colln. Eig. 8. Lophotocystis sp. nov. (Shole’shook, S. Wales). SM A53070c. Latex impression of fragmentary example. X2. Fig. 9. Lophotocystis malaisei (Regnell). SM A 50361. Latex impression of part of theca. X2. All figures whitened with ammonium chloride sublimate. Palaeontology, Vol. 15 PLATE 1 PAUL, Simple humatirhombs with simple fistulipores PAUL: EXOTHECAL PORE-STRUCTURES IN CYSTOIDS 5 The distribution of the four types of humatirhomb within the superfamily Caryo- cystitida does not correspond to taxonomic subdivisions. The first two types of humati- rhomb (text-fig. 3>a-b) are confined to the genera Ulrichocystis Bassler and Lophotocystis nov. (= Heliocrinites of the ‘planata’ group of Regnell 1951, p. 22; Bather 1906, p. 18; see Appendix 2, p. 26). Lophotocystis has tangential canals developed in prominent ridges on the external surface of the theca (PI. 1). The humatirhombs of Ulrichocystis are simple and their tangential canals are less distinctly raised (PI. 1, figs. 3-4). The third and most common type of humatirhomb (text-fig. 3c) occurs in all species of Heliocrinites s.s. (i.e. Regnell’s ‘plicata’ group, 1951, p. 22), all Echinosphaeritidae and Caryocystites dubia (Angelin) = C. angelini Auctt. The fourth type (text-fig. M) occurs only in C. lagenalis Regnell as far as is known. TEXT-FIG. 5. Two possible interpretations of the structure of the canals in Stichocystis Jaekel as seen in longitudinal section. In a each pair of perpendicular canals (pc) is connected by a separate tangential canal (tc). In b a single tangential canal connects all perpendicular canals. The tangential canals were made entirely of soft tissue and are not preserved. Both the pairing of the perpendicular canals and the efficiency of currents (indicated by arrows) favour interpretation a. s = plate suture. The genus Stichocystis Jaekel which on other morphological grounds belongs in the Caryoeystitida bears unusual rhombs with sets of perpendicular canals developed in ridges on the external surface of the plates. Not all details of the structure of these rhombs are known but they seem to be functionally and morphologically related to humatirhombs. I interpret them as having a rhomb-in-rhomb structure (text-fig. 5a) but this is not certain. These rhombs may bear the same relationship to simple humati- rhombs that multi-disjunct pectinirhombs bear to disjunet pectinirhombs. The next two types of exothecal pore-struetures (diplopores and humatipores) are dipores which consist of a single thecal canal, not a set of canals (Paul 1968, p. 700). 2. Diplopores (text-figs. 6-8, Pis. 5-6) Diplopores are dipores composed of a simple thecal canal, the tangential portion of which was not normally calcified and probably formed a papula or podium in life. As a result only the pair of perpendicular canals is preserved in fossils, which led Muller (1854) to propose the term ‘Doppelporen’ or diplopore (see Huxley 1854). If a diplopore is considered as a functional rather than a morphological unit, the pores are internal and the supposed podium represents the tangential portion of the thecal canal (text-fig. 6). No podium has yet been found preserved but diplopore 6 PALAEONTOLOGY, VOLUME 15 tangential canals are sometimes calcified in the Aristocystitidae and Sphaeronitidae. Normal diplopores show as two pores which are usually paired within a shallow depres- sion {peripore) on the external surface of the theca. Peripores may have rims, or peripheral or central tubercles (text-fig. la-d). In general morphology, diplopores strongly resemble the pore-pairs of echinoids. Only the two perpendicular canals of a diplopore are preserved in most fossils. They may pass straight through the plates, follow sinuous courses, or unite with one or more other perpendicular canals (text- fig. 8). Previously it has been assumed that when two perpendicular canals unite to form a Y-shaped canal both branches fed the same diplopore (e.g. Chauvel 1941, figs. 39c-c, p. 100). However, in the only example where I have been able to trace the course of the two branches they fed separate diplopores (text-fig. 8Z>). Functionally this is a more efficient arrangement since it allows circulation. In Codia- cyslis Jaekel and Sphaeronites Hisinger large pits, off which a number of perpendicular canals branch, occur on the internal surfaces of the plates. These pits could be centres of radiation for afferent and efferent canals but this is not certain. They show up as prominent tubercles on internal moulds (e.g. Barrande 1887, pi. 19, figs. 30, 32-33, 35-36). Diplopores show wide variations in morphology but no clearly defined types exist. Diplopores of certain genera and families may have characteristic morphology however (e.g. Haplosphaewnis, PI. 6, figs. 1-3; Sphaeronites s.s. PI. 5, figs. 1-2). Diplopores occur in all superfamilies of the Diploporita. They are usually randomly distributed over a theca but may be more prolific on certain parts of the theca (or of individual thecal plates) than on other parts. In the Aristocystitidae certain areas of the theca may have sealed canals. Usually these areas were permanently in contact with something solid TEXT-FIG. 6. Diagrammatic representa- tion of the structure of a diplopore. The two perpendicular canals open into a depression, the peripore, over which a podium or papula extended in life. EXPLANATION OF PLATE 2 Complex humatirhombs with simple fistulipores. Fig. 2. Lophotocystis araneus (Sehlotheim), RM Ec5370. Note intermediate fistulipores in rhombs. Fig. 7. Lophotocystis sp. RM Ec25233a. Simple humatirhombs with compound fistulipores. Fig. 1. Heliocrinites stellatus RegneU, RM Ec25985. Note compound fistulipores with pairs of tan- gential canals. Fig. 3. Echinosphaerites aiirantiurn aiirantium (Gyll.), SM A57365. Note fistulipores reach plate centres. Fig. 5. Echinosphaerites aurantium suecicus Jaekel, SM A57343. Note large area without fistulipores in centres of large plates. Figs. 4, 6. Heliocrinites ovalis Angelin. Two examples with weathered surfaces revealing tangential canals in groups of two and three, 4, RM Ec3324; 6, RM Ec3327. Figs. 1, 2, 4, 6, 7, x3, whitened with ammonium chloride sublimate; Figs. 3, 5, x5, photographed under water. Palaeontology, Vol. 15 PLATE 2 PAUL, Complex humatirhombs with simple fistulipores PAUL; EXOTHECAL PORE-STRUCTURES IN CYSTOIDS 7 TEXT-FIG. 7. Four diplopores with different arrangements of tubercles and ridges associated with their peripores. a, Sphaeronites pomum (Gyll.). Oval peripores deeply impressed into the plate surface and with spine-like tubercles on the ridges between them (PI. 5, fig. 2). b, Sphaeronites globulus (Ang.). Polygonal peripores with a large flat-topped central tubercle which produces moat-like channels within the peripore (PL 5, fig. 3). c, Archegocystis sp. nov. (Shole’shook, S. Wales). Oval peripores with simple raised rims (cf. PI. 6, fig. 4). d, Haplosphaeronis sp. nov. (Shole’shook, S. Wales). Peripore divided into pyriform and circular depressions by a subcentral ridge, peripheral ridge with two tubercles between pores (PI. 6, fig. 2). A B TEXT-FIG. 8. Two possible arrangements of Y-shaped perpendicular canals in diplopores. Current systems (indicated by arrows) are more efficient in b than in A. p = podia, pc = perpendicular canal. during life (e.g. ambulacral facets, attachment areas, etc.). In the Dactylocystidae diplopores are confined to five ambulacral tracts. 3. Humatipores (text-fig. 9, PI. 7) A humatipore is a dipore which consists of a wholly calcified compound thecal canal (text-fig. 9). In undamaged humatipores no pores show on the external surface. Two internal circular pores lead to two or more tangential canals which may lie either 8 PALAEONTOLOGY, VOLUME 15 beneath the flat external surface of the plates (buried humatipores, text-fig. 9b, PI. 7, figs. 1, 5-10), or in a prominent external tubercle (text-fig. 9a, PI. 7, figs. 2-4). Humatipores are characteristic of, and confined to, the family Holocystitidae Miller. Buried humatipores occur in all five genera of Holocystitidae but tubercular humati- pores are confined to the genera HoJocystites s.s. and Pustulocystis Paul. Humatipores are always evenly developed over a theca. TEXT-FIG. 9. Diagrammatic representations of the morphology of a, raised, and b, buried humatipores. In both, part of one tangential canal (tc) is cut away for clarity, pc = perpendicular canal, t = tubercle. 4. Haplopores A number of species of the Aristocystitidae have been claimed (Bather 1900; Chauvel 1941) to bear haplopores: a type of pore-structure which consists of a single perpen- dicular canal. Since I have not examined all the relevant species I cannot state that haplopores do not occur in cystoids. However I have not seen a single specimen of a cystoid which characteristically bears haplopores and hence their functional mor- phology is not analysed. In the last fifty years or so Chauvel is the only person to have EXPLANATION OF PLATE 3 Simple humatirhombs with compound fistulipores. Figs. 1, 7. Heliocrinites sp. nov. (Rhiwlas, N. Wales). 1, GSM 102326, Part of an unweathered theca with tangential canals filled with dark sediment, x 5, photographed under water. 7, GSM 102325, Stereophotos of weathered theca to show tangential canals in groups of two to four, x 3. Fig. 3. Echinosphaerites aurantium americanum Bassler. Example with tangential canals reaching plate centres (cf. PI. 4, fig. 1), x4 (author’s colb.). Figs. 4, 6. Caryocystites dubia (Angelin). 4, SM A51333, A large weathered theca. 6, SM A57335, Stereophotos of a small example to show tangential canals in groups of two to four, both x 2. Fig. 5. Heliocrinites guttaeformis Regnell. RM Ec4780. An example with prominent tangential canals, x3. Complex humatirhombs with compound fistulipores. Fig. 2. Caryocystites lagenolis Regnell. SM A57362. Stereophotos to show details of rhombs (cf. PI. 4 fig. 6), X 6. All figs, except fig. 1 whitened with ammonium chloride sublimate. Palaeontology, Vol. 15 PLATE 3 PAUL, Simple humatirhombs with compound fistulipores PAUL: EXOTHECAL PORE-STRUCTURES IN CYSTOIDS 9 examined cystoid species which may bear haplopores. He wrote (1941, p. 60): ‘If one reserves the name haplopores (canaux haploporiques) for these sinuous ramifying canals, the canals of Arislocystis [sic], even though united in pairs, are incontestably haplopores’ (my italics). But if the perpendicular canals were paired circulation was possible and whatever modifications occurred within the plates, functionally the struc- ture is the same as a typical diplopore (text-fig. 6). Hence I regard the pore-structures of Aristocystites as diplopores. Only one true haplopore has come to my notice in an isolated plate of Eucystis sp. from Knock, Westmorland which also bears several typical diplopores. I interpret this as a damaged or incompletely developed diplopore. FUNCTION OF EXOTHECAL PORE-STRUCTURES IN CYSTOIDS Untestable functional interpretations are inherently weak, since they can be neither substantiated nor disproved, and undesirable since they cast doubt on the validity of all functional interpretations. Many functional hypotheses are open to test however, by Rudwick’s paradigm method (Rudwick 1964). To test a functional hypothesis the detailed morphology of a fossil structure is compared with that of an ideal structure (paradigm) which would serve the supposed function with maximum efficiency. Close comparison indicates that the fossil structure could have served the supposed function efficiently but does not prove that in fact it did so. The paradigm method can be used to test the mechanics, but not the physiology of the structures investigated. It depends on acceptance of ‘mechanical uniformity’ (i.e. that the ‘laws’ of mechanics applied in the past as they do now) but may be totally independent of knowledge of living organisms. All morphological structures have more or less well-defined mechanical effects. Their function is taken to be that effect which is most beneficial to the vital needs of the organism or which confers most selective advantage on the organism. By considering effects rather than function, analysis may be made more rigorous and conclusions stated more positively. For example rigidity is an undeniable mechanical property of triangles. The triangulation ‘ornament’ of ridges connecting plate centres which is so commonly found in echinoderms undoubtedly increased the strength and rigidity of the test. This is not an interpretation: it is a fact. If we try to explain this effect in terms of function or selective advantage, then we make interpretations. In doing so we may draw sound conclusions if we can demonstrate that a vital function necessary for the survival of the organism (e.g. nutrition, protection, respiration, excretion, etc.) was performed more efficiently with, than without, the structure involved. Echinoderm tests with triangulation ‘ornament’ provided better protection for the enclosed vital organs than those without this ‘ornament’, by virtue of their increased strength and rigidity. Thus we may conclude that most probably the function of triangulation ‘ornament’ was protection but un- doubtedly its effect was to increase the strength and rigidity of the test. The following analysis is an attempt to estimate the mechanical efficiency of cystoid pore-structures as exchange systems and they are compared with the appropriate para- digm. Any exchange system must have an exchange surface to prevent mixing of fluids. The amount of exchange is controlled by the following factors : 1. The area of the exchange surface: the larger the area the greater the amount of exchange. 2. The resistance to exchange of the exchange surface: the thinner the surface the less its resistance will be. 3. The concentration gradient across the exchange surface: the higher the gradient (i.e. the greater the difference in concentration of the exchange substance on either side of the exchange surface) the greater the potential exchange. A counter-current system (text-fig. lOu) is the most efficient method of maintaining a high concentration gradient. 10 PALAEONTOLOGY, VOLUME 15 Thus the paradigm of an exchange system will have a large area of exchange surface which is as thin as is compatible with its strength and a counter-current system. A more detailed account of the above is presented in Paul 1968, pp. 708-709. Detailed functional analysis In exothecal pore-structures the fluids within the canals were body fluids. A healthy animal presumably had control over both their composition and circulation. Hence devices to prevent recirculation and choking of the canals by foreign particles were unnecessary and cannot in fact be recognized. The exchange surfaces were outside the theca and therefore liable to mechanical damage. This brings into opposition two requirements of the paradigm: the thinner the exchange surface the greater the amount of exchange but the greater the chances of rupture and mixing. With the above ideas in mind the detailed morphology of exothecal pore-structures in cystoids will be compared with the paradigm of an exchange system and estimates of the efficiencies of the various types made. 1. The area of the exchange surface. Four of the five basic types of cystoid pore- structures have calcified exchange surfaces which are frequently preserved in fossils and the areas of which can be measured or at least estimated fairly accurately. Echinoderm skeletal material is a meshwork of fine calcite rods and soft tissue fibres ; exchange would have taken place through the latter. Only about half the exchange surface area (the soft tissue half) functioned actively in exchange during life. In cystoids individual calcified exothecal pore-structures are much less efficient than endothecal (dichoporite) pore-structures in terms of the area of exchange surface. The 50 70- 90- II 50 >30 -»I0 100 . TEXT-FIG. 10. Idealized exchange systems, a, counter current; b, concurrent. Maximum potential exchange in b is half that of a. Figures represent percent concentration of the exchange substance. Heavy arrows indicate current directions, light arrows indicate ex- change. EXPLANATION OF PLATE 4 Stereophotos of simple humatirhombs with compound fistulipores. Fig. 1. Echinosphaerites aurantiiim americanum Bassler. Weathered example with fistulipores which do not reach plate centres in largest plates, x 4 (author’s coUn.). Figs. 2, 3. Echinosphaerites aurantiiim s.l. 2, BMNH E7803, Internal surface of part of theca to show openings of perpendicular canals (cf. PI. 1, fig. 6), x2. 3, BMNH (unreg.), Weathered portion of theca, x3. Fig. 4. Heliocrinites giittaeformis Regnell. RM Ec4763. Portion of weathered theca with large rhombs, X3. Fig. 5. Caryocystites dubia (Angelin). SM A57332. Example with unweathered external surface show- ing outlines of rhombs, x 2. Stereophotos of complex humatirhombs with compound fistulipores. Fig. 6. Caryocystites lagenalis Regnell. SM A57362. Note intermediate fistuhpores, X 2. Palaeontology, Vol. 15 PLATE 4 PAUL, Simple humatirhombs with compound fistulipores PAUL; EXOTHECAL PORE-STRUCTURES IN CYSTOIDS 11 ratio AJA( where A^ is the area of the exchange surface and Ai is the area of the thecal surface occupied by the pore-structure is a measure of the efficiency of an individual pore-structure. In endothecal pore-structures this ratio is always greater than one and in one measured pectinirhomb was 7-84. Table 1 shows that this ratio varies from 0-28-0-86 in humatirhombs. All three types of exothecal pore-structure in cystoids exhibit modifications of their basic design which increase the ratio AJA( but no evo- lutionary trends towards increased efficiency are apparent in contrast to pectinirhombs (Paul 1968). TABLE I . Estimates of the ratio AJAt in humatirhombs Species Ratio Humatirhomb type Lophotocystis angustiporus (Regnell) 0-37 Simple rhombs with simple fistulipores L. granatum (Wahl.) 0-30-0-42 „ „ „ L. sp. (Shole’shook) 0-28 „ „ „ L. malaisei (Regnell) 0-28-0-41 ,, ,, ,, Ulrichocystis eximia Bassler 0-59-0-67 ,, ,, ,, L. sp. nov. (Skalberget) 0-42 Complex rhombs with simple fistulipores Heliocrmites ovalis Ang. 0-58-0-68 Simple rhombs with compound fistulipores FI. guttaeformis Regnell 0-38-0-80 ,, ,, ,, H. sp. nov. (Rhiwlas) 0-43 „ „ ,, Echiuosphaerites aurantium (Gyll) 0-29 „ „ „ E. a. suecicus Jaekel 0-75 ,, >9 99 E. a. americamm Bassler 0-57-0-77 99 99 99 Caryocystites dubia (Ang.) 0-71 99 99 99 C. lagenalis Regnell 0-86 Complex rhombs with compound fistulipores For simple fistulipores raised in ridges: Ag ~ (\-5xFW), and At = {RS+RW) where RS = ridge separation, RW = ridge width, and FW = fistulipore width. For compound fistulipores buried in plates; Ag ~ FW and At ^ FW+IFW. (IFW = separation of fistulipores.) For complex rhombs the area covered by intermediate fistulipores is calculated and the ratio Ag/At doubled for that area, i.e.{4e (total) + 4;, (complex)}//! (.Thus if the complex rhomb area is half the total rhomb area the total exchange area = \-5Ag/At- In an ideal simple humatirhomb without raised ridges the ratio of the width of the tangential canals to the width of the gap between them is a close approximation to AglAf. When the two widths are equal AJAi is approximately 0-5. Humatirhombs with compound fistulipores generally have more closely spaced tangential canals than those with simple fistulipores. However, the latter are usually raised in ridges and have a larger area of exchange surface than buried tangential canals (text-fig. 11). The increase in area due to the ridges is as much as 50%. Both arrangements (i.e. raised simple fistulipores and buried compound fistulipores) seem to be alternative methods of increasing the ratio AgjA,, In terms of exchange surface area humatirhombs are individually much less efficient than dichoporite pore-structures. However, every plate suture bears a humatirhomb in all Caryocystitida and there are thus several hundred rhombs per theca. The total exchange area per theca was probably as high as in dichoporite cystoids with only 1-25 rhombs per theca. Since almost all the thecal surface is covered with humatirhombs the ratio AgjAt is only slightly greater than the ratio of the total exchange area to the total thecal surface area. Thus anything from about 25% to 75% of the thecal surface area 12 PALAEONTOLOGY, VOLUME 15 was exchange surface in humatirhomb-bearing cystoids but only about half aetively functioned in exchange. Humatipores are very similar to humatirhombs in terms of exehange area but it is much more difficult to measure or estimate AJAi. An increase in the number of tan- gential canals increases the exchange area per humatipore (text-fig. 9b). Equally, raising the humatipore into a prominent tubercle increases exchange area (text-fig. 9a). With regard to exchange area per humatipore buried humatipores are less efficient than tubercular humatipores. However, the former are frequently more densely packed than the latter. Again this seems to reflect two alternatives: fewer, more efficient structures or a larger number of less efficient structures. In humatipore-bearing cystoids total A <— 2r — ► TEXT- FIG. 11. Diagram to illustrate the exchange areas of (a) buried, and (b) raised tangential canals (tc) in fistulipores. Width of exchange area in one canal in a is 2r, in b it is nr. In rhomb width W and length / areas are 6rl in A and Inrl in b. Since 77 ~ 3 two canals in b have the same exchange area as three canals in a. exchange area per theca probably lies within the same limits as for humatirhomb-bearing cystoids. Some diplopores resemble echinoid pore-pairs very strongly and probably gave rise to podia analogous, if not homologous, to echinoid tube-feet. The podia are never EXPLANATION OF PLATE 5 Stereophotos of diplopores. Fig. 1. Sphaeronites sp. nov. (Raback, Vastergotland, Sweden). SM A35317. A small theca with densely packed diplopores over entire surface. Fig. 2. Sphaeronites pomum (Gyll.) SM (unreg.). Note spinose tubercles between deeply sunken peri- pores (cf. text-fig. 6a). Fig. 3. Sphaeronites globulus (Angelin). SM A57321. Note polygonal peripores with large flat-topped central tubercle (cf. text-fig. 6b). Fig. 4. Sphaeronites sp. nov. (Skalberget, Dalarna, Sweden). SM A57407. Note irregular diplopores like those of S. globulus. Fig. 5. Sphaeronites pyriformis (Forbes). BMNH E16340. Fig. 6. Sphaeronites litchi (Forbes). GSM 7431. Note very prominent central tubercles (cf. fig. 8 this plate). Stereophotos of echinoid pore-pairs. Fig. 7. Arbacia punctulata (Lam.). Note tubercles around pore-pairs (author’s colln.). Fig. 8. Echinocorys scutatus (Leske). SM (unreg.). Pore-pairs of buccal tube-feet. Note large central tubercle (cf. fig. 6, this plate). Figs. 1-6 X 3, 7, 8 x4. All whitened with ammonium chloride subfimate. Palaeontology, Vol. 15 PLATE 5 PAUL, Diplopores PAUL: EXOTHECAL PORE-STRUCTURES IN CYSTOIDS 13 preserved, so measurement of their surface area is impossible. Nevertheless the area of podium wall could not have been less than the area of the peripore and since it was entirely made of soft tissue all the area could have functioned in exchange. Thus in diplopores AJAirmxst have been greater than or equal to 1. Most diplopores have rims and tubercles associated with their peripores as do most echinoid pore-pairs. In the latter the rims and tubercles are attachment structures for the longitudinal muscles of the tube-feet (Nichols 1959, p. 70). As a broad generalization, the more strongly developed the rims, etc. are, the stronger the muscles and the greater the flexibility of the tube-feet. For example, many regular sea urchins have much more prominent rims and tubercles associated with pore-pairs on the oral surface up to the ambitus, and the tube-feet on this surface are the main ones used in locomotion. In some cases the com- parison between diplopores and pore-pairs is so strong (e.g. Sphaeronites and Echino- corys oral tube-feet, PI. 5, cf. figs. 3-6 with fig. 8) that the conclusion that they represent almost identical structures seems inescapable. Although impossible to prove, available evidence strongly suggests that some diplopores had extensile podia. This would increase their efficiency as exchange surfaces in two ways: it increases the area and it decreases the thickness of the exchange surface. The density of packing of diplopores varies from genus to genus or even species to species. In Archegocystis the number of diplopores could apparently increase or decrease during life (Paul 1971). This forms a very delicate exchange mechanism that could respond to changes of the environment. Such was definitely not the case in Sphaeronites, all species of which have diplopores evenly developed all over the theca. The latter genus shows an interesting evolutionary trend towards larger diplopores throughout the Middle and Upper Ordovician. Many representatives of the Aristocystitidae have sealed diplopores in some part of the theca. Chauvel (1966, p. 109) has interpreted this as a ‘maladie calcaire’ reminiscent of W. D. Lang’s fatalistic trends in various calcium carbonate secreting organisms (Lang 1923n, b). Calcification of diplopores decreases their efficiency by at least halving their exchange surface area but it does not necessarily render them useless. Indeed calcifica- tion is much more likely to represent protection against predators eating soft tissue podia than ill health. Cystoids lacked spines, at least as far as is known; so podia were not mechanically protected as sea urchin tube-feet are. The following conclusions can be drawn as regards area of exchange surface : (i) Individual exothecal pore-structures are very much less efficient than individual endothecal pore-structures but far more of them are developed on any one cystoid. The total area for exchange per theca was probably the same for both endothecal and exo- thecal pore-structures. In humatirhombs available measurements indicate that the total exchange area was between 25% and 75% of the total thecal surface area. (ii) In humatirhombs the raising of tangential canals in ridges, and the development of compound and additional fistulipores increase exchange area. In humatipores production of many tangential canals and development of tubercular humatipores both increase exchange area. Some diplopores may have had extensile podia which also increased exchange area. Within the limits of their geometry all three types of exothecal pore- structure tend to maximize their exchange area. Diplopores were probably the most efficient of the three but were liable to predation since their exchange surfaces were made entirely of soft tissue. 14 PALAEONTOLOGY, VOLUME 15 (iii) Although individually inefficient all exothecal pore-structures probably provided adequate exchange area per theca by sheer weight of numbers. 2. The resistance to exchange of the exchange surface. For maximum efficiency the exchange surface should be as thin as possible; however, rupture and mixing of fluids must be prevented. Exothecal pore-structures are much more susceptible to mechanical damage than endothecal pore-structures since their exchange surfaces are external. It is not surprising therefore that measurable exothecal exchange surfaces are thicker (0-05-0-10 mm) than endothecal exchange surfaces (always less than 0-03 mm and reaching as little as 0-007 mm). Nevertheless the thecal wall in most cystoids with exo- thecal pore-structures is 1-3 mm thick and often much thicker in aristocystitids. Chauvel (1966, p. 27) records a maximum thickness of 26 mm in Maghrebocystis. Although exchange surfaces of humatipores and humatirhombs are thicker than those of endo- thecal pore-structures they are still very much thinner than the thecal wall. Since no measurements of thickness are possible in diplopores their efficiency in terms of re- sistance to exchange cannot be estimated. However, extensible podia would have had very thin walls in all probability. Exothecal pore-structures do not seriously weaken the theca and no strengthening structures have been recognized. Again this contrasts with pectinirhombs (Paul 1968). 3. Maintenance of a concentration gradient. The most efficient method of maintaining a concentration gradient is a counter-current system (text-fig. lOn). The best evidence for current directions is given by protective devices and devices to prevent recirculation. Unfortunately neither type of device is necessary with exothecal pore-structures since the fluids flowing in the thecal canals were body fluids. Neither type of device has been recognized. Some indirect evidence of currents and their directions of flow is available, however. Nearly all recent echinoderms have ciliated external epithelia and cystoids probably had too. From purely hydrodynamic considerations fluids within the canals would not have moved without cilia due to the viscous effect of the boundary layer (Paul 1968, pp. 719, 721). Almost certainly both internal and external ciliary currents were present in cystoids. The humatirhombs of Lophotocystis granatum (Wahlenberg) have fine granules developed on the ridges. In the best preserved example the granules are elongate parallel to the rhomb axes (PI. 1, figs. 1-2). If a ciliated epithelium was present EXPLANATION OF PLATE 6 Stereophotos of diplopores. Figs. 1, 3. Haplospliaeronis obloiiga (Angelin). 1, SM A57381, An example with oval peripores without rims. 3, SM A57356, An example with peripores with strongly raised rims. Fig. 2. Haplospliaeronis sp. nov. (Shole’shook, S. Wales). SM A57520. Latex impression of theca showing asymmetrical diplopores (cf. text-fig. 6d). Fig. 4. Archegocystis steUiilifera (Salter). BMNH E16200. Latex impression showing elongate and oval diplopores with simple rims (cf. text-fig. 6c). Fig. 5. Aristocystites bohemicus Barrande. SM A49868c. Latex impression showing irregular peripores between gonopore (left) and hydropore (right). Even though the peripores are very irregular it is still possible to see that the perpendicular canals are arranged in pairs as in typical diplopores. Eig. 6. Triamara sp. USNM 166580. Example with small oval peripores. x4. Eigs. 1-5 X 3. All whitened with ammonium chloride sublimate. Palaeonlology, Vol. 15 PLATE 6 PAUL, Diplopores PAUL: EXOTHECAL PORE-STRUCTURES IN CYSTOIDS 15 these granules would have increased the area of ciliated surface and enhanced the cur- rents parallel to the rhomb axis. Such granules are similar to those on the periplastronal areas of recent spatangoid sea urchins and are present on other species of Lophotocystis. Granular ornament is also characteristic of most species of humatipore-bearing cystoids although the granules are not elongate. Since all the thecal surface is covered with humatirhombs in caryocystitid cystoids, external currents of different rhombs would interfere with each other. Nevertheless, water in contact with the external surface of the theca would be continually changed. Evidence for the presence and direction of currents in Diploporita is virtually non- existent. However the genera Holocystites and Haplosphaeronis regularly have asym- metrical dipores and this asymmetry may be associated with current flow. Clearly, internal fluids came up one perpendicular canal and descended down the other. Which canal was efferent and which afferent is not certain in either genus. In Holocystites, which bears humatipores, one perpendicular canal is subcentral and one peripheral (text-fig. 9a, PI. 7, figs. 2, 3). I suggest that body fluids ascended the subcentral perpen- dicular canal but the alternative direction seems equally plausible. From the point of view of exchange either direction would seem to be equally efficient. Some species of Haplosphaeronis have asymmetrical diplopores. The peripore rim is thickened and raised and the peripore floor raised between the perpendicular canals, but closer to one than the other. Thus one canal opens in a roughly circular depression and the other in a pyriform depression (text-fig. Id, PI. 6, fig. 2). The diplopores of Haplosphaeronis are elongate and most are aligned in an oral-aboral direction. In the oral half of the theca the pyriform depression is adoral in the diplopore but the converse is true in the aboral half of the theca. If the theca was orientated with the mouth upwards, surface ciliary cleaning currents may have moved in an aboral direction on the upper half of the theca as they do in many recent sea urchins. A current in the reverse direction in the aboral half of the theca would also help to keep the theca clean (text-fig. 12). If such external currents were present, alignment of the diplopores parallel to them would allow internal counter-currents to operate. Recent sea urchins with specialized respiratory tube-feet have opposed exter- nal and internal currents. Again the opposite current directions would seem equally plausible and equally efficient in exchange. The pattern of external currents proposed for Haplosphaeronis involves flow from the oral and aboral extremities towards the ambitus. Precisely similar current patterns were proposed for the external currents of dichoporite rhombiferans (Paul 1968). Since the two groups are not closely related, similar external cleaning currents may have preceded the evolution of internal respiratory currents. The latter probably developed in a fixed relationship to the former, namely counter to them. In summary, there is little direct evidence for the presence or direction of currents in exothecal pore-structures. However, in at least one example of each major type there TEXT-FIG. 12. Possible surface current directions in Haplosphaeronis Jaekel. Such currents would help to clean the thecal surface. 16 PALAEONTOLOGY, VOLUME 15 is some indirect evidence for currents. Indeed the basic morphology of thecal canals is ideal for current flow since one perpendicular canal could act as the afferent canal and the other as the efferent. In all but two genera the two perpendicular canals are identical and it is generally impossible to say which canal was which. Conclusions All three exothecal pore-structures (humatirhombs, humatipores, and diplopores) differ from the paradigm of an exchange system to some degree and they were indi- vidually less efficient than endothecal pore-structures in terms of the area and thickness of the exchange surface and possibly of current systems too. This relative inefficiency can be explained in terms of the need to prevent rupture of the exchange surface. Although individually less efficient than endothecal pore-structures, exothecal pore- structures still allowed exchange to take place. Indeed if currents were present this would inevitably have been their effect. Large numbers of exothecal pore-structures are developed in any one theca which compensates for their individual inefficiency. For example, the ratio AJAi is an estimate of individual efficiency in terms of exchange surface area. An average value for humati- rhombs is probably about 0-5, for pectinirhombs about 10. In equal-sized thecae with equal-sized rhombs there should be 20 times as many humatirhombs as pectinirhombs to achieve the same amount of exchange. This ratio of humatirhombs to pectinirhombs is easily exceeded in practice since humatirhombs are developed in all available space on a theca. The exchange surfaces are thicker in humatirhombs than in pectinirhombs and hence the ratio should be higher than 20 to 1 . There can be little doubt that the mechanical effect of exothecal pore-structures in cystoids was to allow exchange between sea water and body fluids. Since oxygen and carbon dioxide transfer constitute the most likely form of this exchange, exothecal pore-structures were respiratory structures. It is now pertinent to consider respiration in more detail. EXPLANATION OF PLATE 7 Humatipores. Figs. 1, 5, 7. Trematocystis globosus (Miller). 1, USNM S3058b. Note tangential canals exposed by weathering. 5, 7, FMNH 8766a; 5, General view of plate, X 6 approx. 7, Detail of humatipores to show plate meshwork in weathered tangential canals, x 25 approx. Figs. 2-3. Stereophotos of Holocystites alteniatiis (Hall). BMNH E7629. 2, Detail of single humati- pore, X 25 approx. 3, General view of plate showing tubercular humatipores with radiating tan- gential canals, x 6 approx. Fig. 4. Holocystites scutellatiis Hall. Detail of some weathered tubercular humatipores, X 10 (author’s colln.). Fig. 6. Brightonicystis gregarius Paul. SM A32814a. Detail of humatipores with 6-8 tangential canals, X5. Fig. 8. Stereophotos of Pentacystis sphaeroidalis (Miller and Gurley). FMNH 6000. Detail of weathered humatipores, Xl3. Fig. 9. Stereophotos of Pentacystis simplex Paul. AMNH 20271a. Detail of pit bored into cystoid by parasite which shows tangential canals of three humatipores parallel to the sides of the pit. These canals were formed after the pit was bored, X 10. Fig. 10. Stereophotos of Trematocystis rotundas (Miller). All figures whitened with ammonium chloride sublimate. Palaeontology, Vol. 15 PLATE 7 PAUL, Humatipores PAUL: EXOTHECAL PORE-STRUCTURES IN CYSTOIDS 17 RESPIRATION IN RECENT AND EOSSIL ECHINODERMS A specialized respiratory system consists of three distinct parts. The respiratory system in vertebrates, for example, includes : (i) an external exchange surface (lungs or gills) whereby oxygen is gained from (and carbon dioxide lost to) the surrounding medium, (ii) a circulation system (blood stream) to distribute oxygen internally, and (iii) internal exchange surfaces (the capillaries) whereby oxygen is transferred from the circulation system for use in cellular metabolism. Unless sites of metabolism are very close to the external exchange surfaces some system of oxygen transport is vital for efficient respiration. Most triploblastic metazoa have a specialized circulation system but recent echinoderms do not. The preceding analysis of exothecal pore-structures in cystoids considered only the first part, i.e. the external exchange surfaces, and depended on paradigmatic methods. This section considers the internal portions of the respiratory system, and depends more on biological uniformitarianism. It is pertinent to consider what is known of respiration in recent echinoderms. Recent echinoderms Relatively little systematic information is available on respiration in recent echinoderms. Farman- farmaian (1966, p. 245) in his summary uses Harvey’s (1928) equation for the dilTusion of oxygen into a spherical organism to prove conclusively that no echinoderm could rely on diffusion alone to gain oxygen from sea-water. Harvey’s equation is as follows: Co = Ar^-I6D where €„ is the concentration in atmospheres of oxygen in sea water; A is the rate of oxygen con- sumption by the organism in ml Oa/grm/minute ; r is the radius of the sphere in cm; and D is the diffusion coefficient in atmospheres/cm/cm^. Using the following values, the equation can be solved for r (which is the depth to which oxygen will penetrate into an echinoderm by diffusion alone). Co = 0-21 (Farmanfarmaian 1966) D = 0000011 (Krogh 1941) A = 0 001233 maximum and 0 000166 minimum (Farmanfarmaian 1966) ___6D.Cq ' A _ 6x0000011 X 0-21 6x000001 lx 0-21 ” 0001233 “ 0000166 - 0 0112408 or 0 0834939 r =106 mm or 2-89 mm Farmanfarmaian argues that the success of the echinoderms is to a large extent dependent upon the development of specialized respiratory surfaces (i.e. external exchange surfaces) since they are clearly essential to survival. For efficient respiration these surfaces must be significantly less than 1-3 mm thick. Recent echinoderm respiratory surfaces include respiratory trees and tentacles (holothurians), podia (all classes), papulae (asteroids), peristomial gills (regular echinoids), genital bursae (ophiuroids), and the general external surface (all classes). All but the last fall well within the thickness limits estabhshed above. An efficient external exchange surface requires currents to replenish depleted fluids. Such currents are either oscillatory, involving current reversals, or circulatory. Oscillatory currents occur in blind structures, for instance in the respiratory trees of holothurians and the peristomial gills of regular echinoids. Circulatory currents occur in closed ring-shaped structures such as the tube-foot/ampulla system of echinoids. Recent echinoderms possess no specialized circulation system to distribute C C 8472 18 PALAEONTOLOGY, VOLUME 15 oxygen internally. Oxygen must be transferred into the fluids of the major eoelomic pouches via the external exchange surfaces and all organs involved in metabolism are either bathed in these fluids or directly in sea water. The role of the water vascular system in respiration needs some clarification. Farmanfarmaian (1966, p. 250) has conclusively shown that in sea urchins the tube-foot/ampulla systems transfer oxygen from sea water to eoelomic fluids. But the radial water vessels are much less involved in respiration than the tube-foot/ampulla system because they are not directly in contact with sea water and are blind struc- tures without circulatory currents. The water vascular system can only transfer oxygen into eoelomic fluids efficiently where there is a tube-foot/ampulla system in which the tube-foot is external and the ampulla is internal (text-fig. 13). Hence the respiratory contribution of the water vascular system in crinoids, which have an almost totally external water vascular system, is negligible. This would be equally true of external branches of the water vascular system in cystoids if these were present. In crinoids with large calyces and no calycal pore-structures, migration of coelomocytes would seem the only plausible way to oxygenate organs within the calyx. However, the role of coelomocytes in respiration (summarized in Endean, 1966) among recent echinoderms is not understood. Systematic movement of coelomocytes could explain the absence of a distinct circulation system in echinoderms. However, it is almost impossible to observe whether such movements of coelomocytes actually occur. One type of coelomocyte found in recent holothurians contains haemoglobin (i.e. the haemocytes). Wandering haemocytes would inevitably carry oxygen and carbon dioxide with them but again the actual course of wandering is impossible to observe. Haemocytes are unknown in recent crinoids and were presumably absent in fossil groups such as cystoids. It may be noted that Farmanfarmaian (1966, p. 246) rejects the suggestion that the digestive traet can be involved in respiration. In summary: recent echinoderms respire through a variety of specialized external exchange surfaces but lack any internal circulation system to distribute the oxygen so gained. No recent echinoderm relies exclusively on one type of external exchange surface and all types are made entirely of soft tissue. Efficient external exchange surfaces in recent echinoderms must be significantly less than 1-3 mm thick. Comparison of recent and fossil echinoderms Comparison of primary exchange surfaces in recent echinoderms and cystoids demonstrates both similarities and differences. Perhaps the most obvious difference is total lack of calcified exchange surfaces in recent echinoderms whereas these are com- monly present in four of the five basic types of cystoid pore-structures and occur rarely in the fifth. A second important difference is the apparent lack of oscillatory currents in cystoids. These two features may be correlated. It is difficult to develop an oscillatory current in a rigid calcified structure whereas soft tissue is ideally suited to produce the expansions and contractions necessary for oscillation. Perhaps the most important similarity is the wide variety of respiratory exchange surfaces which may be internal (e.g. holothurians) or external (e.g. asteroids and echinoids) among recent echinoderms just as in cystoids. The over-all efficiency of a respiratory system depends not only on the external exchange surfaces but also on the internal distribution of oxygen. It is relevant therefore to speculate on the nature of the internal connections of cystoid pore-structures. If a cystoid relied on diffusion alone to distribute oxygen internally it would be advan- tageous to have pore-structures developed evenly over the entire surface. All internal organs would then be approximately equidistant from an oxygen source. The dichopores of pectinirhombs and cryptorhombs extended into internal eoelomic spaces. In the Hemicosmitida, cryptorhombs are more or less evenly developed over the theca and probably no internal circulation was developed. The supposed internal ciliary counter- currents in the cryptorhombs and movement of organs may have provided adequate PAUL: EXOTHECAL PORE-STRUCTURES IN CYSTOIDS 19 circulation of coelomic fluids within any one coelomic pouch. In the Glyptocystitida, however, there is a progressive reduction in the number of pectinirhombs per theca and all Silurian and Devonian species have four or fewer pectinirhombs. This is believed to be correlated with the development of a specialized internal circulation system. Grooves on internal moulds of Callocystitidae from the Middle Silurian of North America pro- vide some evidence as to the path of this circulation system (Paul \961a). Since the grooves are apparently connected to the hydropore the supposed circulation system is believed to have been associated with the water vascular system. The thecal canals of exothecal pore-structures could represent simple evaginations of internal coelomic pouches in which case all the canals could have been connected to one coelomic pouch. Alternatively each coelomic pouch could have had a number of such evaginations. Both humatirhombs and humatipores are always developed over the entire thecal surface and hence the latter alternative would seem more likely. However, Nichols (1962, p. 135, figs. 18, 1968) suggested that the Diploporita and Rhombifera be recognized as distinct classes but without presenting all the evidence or defining the classes. Now that detailed evidence, at least as regards the pore-structures, has been presented, formal definitions of the major taxa of cystoids may be given as follows: CLASS DIPLOPORITA Mullcr 1854, nom. transl. Definition. Crinozoa with exothecal pore-structures (dipores) which consist of a single thecal canal, globular or pyriform theca generally composed of a large number of randomly arranged plates, which are usually all pierced by pore-structures. With or without a true stem, ambulacral appendages uniserial but very rarely preserved, water vascular system probably internal. The lower divisions within the class are as in Kesling (1963, 1968) except that the Holocystitidae is separated from the Aristocystitidae and the latter is elevated to Superfamily rank (Paul 1971). CLASS RHOMBIFERA Zittcl 1880 nom. transl. Definition. Crinozoa with exothecal or endothecal pore-structures (rhombs) which consist of rhombic sets of thecal canals, globular pyriform or oval theca, with true stem at least early in development, ambulacral appendages biserial (arms or brachioles), water vascular system probably with external radial branches. ORDER DiCHOPORiTA Jackel 1899 emend. Paul 1968 Definition. Rhombifera with endothecal pore-structures (pectinirhombs and cryptorhombs) composed of dichopores, with theca composed of a small number of plates arranged in three to five circlets, pore-structures only developed across certain sutures, true stem throughout life. This order contains two superfamilies, the Glyptocystitida and the Hemicosmitida. The family Polycosmitidae is assigned to the Hemicosmitida, otherwise the classification is as given in Kesling 1963, 1968. ORDER EisTULiPORiTA Paul 1968 Definition. Rhombifera with exothecal pore-structures (humatirhombs) composed of fistulipores, with theca composed of a large number of plates which may be added during growth and are randomly arranged, pore-structures developed across all possible sutures, true stem lost in adult or possibly totally absent in rare examples. This order contains one superfamily, the Caryocystitida. Detailed classification as in KesUng 1963, 1968 except that the family Stichocystidae is added. Kesling’s superfamily Polycosmitida thus becomes defunct. Even this classification, which is more complex than previous classifications, may oversimplify cystoid evolution. In particular the relationship between the two rhombi- feran orders is more assumed than real. The only character unique to the two orders is the presence of rhombs. However fistulipores could not have evolved from dichopores nor vice versa. Rhombic structures or ornament may develop in any animal or plant group with a tesselated pavement of polygonal units. Rhombs can be recognized in PAUL: EXOTHECAL PORE-STRUCTURES IN CYSTOIDS 25 most classes of echinoderms, in fish with heavily armoured bodies, in tortoiseshell scutes, even in some calcareous algae. The rhombic outline is a geometrical result of the mode of growth of closely fitting polygons and has no other significance. The presence of respiratory rhombs in the Dichoporita and Fistuliporita is due to parallel or convergent evolution and, in the absence of other shared characteristics, implies no particularly close relationship. APPENDIX 1 List of species with exothecal pore-structures examined in this study. Class RHOMBiFERA Muller Type of pore-structure Order fistuliporita Paul Superfamily caryocystitida Family caryocystitidae Lophotocystis granatum (Wahl.) L. malaisei (Regnell) L. augustiporus (Regnell) L. sp. nov. (Haverfordwest, Wales) L. araueus (Schlotheim) L. sp. (Skalberget, Sweden) Heliocrinites ovalis (Angelin) H. guttaeformis Regnell H. stellatus Regnell H. balticus Eichwald H. sp. nov. (Rhiwlas, Wales) Coryocystites dubia Angelin (= C. angelini Auctt.) C. lageualis Regnell Humatirhombs Fistulipores Rhombs simple simple „ complex compound simple complex Family Echinosphaeritidae Echiuosphaerites aurautium (Gyll.) compound simple E. aurautium suecicus Jaekel ,, „ E. aurautium americauum Bassler „ „ E. arachuoides Forbes „ „ Family Ulrichocystidae Ulrichocystis eximia Bassler simple Class Diploporita Muller Superfamily Sphaeronitida Family Sphaeronitidae Pore-structures Sphaerouites pomum (Gyll.) Diplopores s.s. S. sp. nov. (Raback, Sweden) „ S. globulus (Angelin) „ S. sp. nov. (Skalberget, Sweden) „ S. litcbi (Forbes) „ S. pyriformis (Forbes) „ S. sp. (Glyn Ceiriog, Wales) „ Haplosphaerouis oblouga (Angelin) ,, H. kiaeri Jaekel „ //. sp. nov. (Haverfordwest, Wales) „ Eucystis barreudeua Haeckel „ F. (Barrande) ,, 26 PALAEONTOLOGY, VOLUME 15 E. munitus (Forbes) Diplopores s.s. E. quadrangularis Regnell „ E. angelini Regnell „ E. raripimctata Angelin „ Archegocystis stellulifem (Salter) „ ''Sphaeronis' dalecarliciis Angelin „ '' Sphaeronis' punctatus Forbes „ Family Holocystitidae Holocystites cylindricus (Hall) Humatipores H. alteniatiis (Hall) „ H. obnormis Hall „ H. scutellatus Hall „ Pentacystis simplex Paul „ P. wykqffi (Miller) „ P. sphaeroidalis (Miller & Gurley) „ Trematocystis globosiis (Miller) „ T. rotimdus (Miller) „ Pustidocystis pentax Paul „ P. omatissimus (Miller) „ Brightonicystis gregariiis Paul „ Superfamily Aristocystitida Family Aristocystitidae Aristocyslites bohemicus Barrande Diplopores A. siibcyliiidriciis Barrande „ A. sp. (Knock, England) „ Trianwra titmida (Miller) „ T. ventricosa (Miller) „ T. multiporata Paul „ T. laevis Paul „ T. sp. (Big Creek, Indiana, U.S.A.) „ Sinocystis loczyi Reed „ '’Sphaeronis' shihtienensis Reed „ Superfamily Glyptosphaeritida Family Glyptosphaeritidae Glyptosphaerites leuchtenbergi (Volborth) Family Dactylocystidae IRevalocystis kearsargensis (Stauffer) „ Family Gomphocystitidae Gomphocystites indianensis Miller „ Family Protocrinitidae IRegnellicystis sp. (Rye Cove, Virginia, U.S.A.) APPENDIX 2 Formal definitions of Lophotocystis nov. and Heliocrinites s.s. : Genus Lophotocystis nov. (Lophotos, Gr. crested). Type species. Echinosphoerites granatum Wahlenberg. PAUL; EXOTHECAL PORE-STRUCTURES IN CYSTOIDS 27 Definition. A genus of Caryocystitidae with globular theca, fifty to several hundred thecal plates not folded about rhomb axes; humatirhombs with simple fistulipores raised in distinct ridges on external surface of plates. Genus Heliocrinites Eichwald 1840. Type species. Echinosphaerites balticum Eichwald. Definition. A genus of Caryocystitidae with oval to globular theca, fifty to several hundred plates usually folded about rhomb axes to produce a surface ornament of triangular depressions; humati- rhombs with compound fistulipores almost completely or totally buried within plates. REFERENCES BARRANDE, J. 1887. Systeme Silurien du centre de la Bolieme. E partie: Recherches paleontologiqiies. 7. Classe des Echinodennes. Ordre des Cystides. xviH-233 pp., 39 pis. Leipzig and Prague. BATHER, F. A. 1900, The echinoderms. In lankester, e. r. A treatise on zoology, 3, vi + 344 pp., London. 1906. Echinodermata, In reed, f. r. c. Lower Palaeozoic fossils of the Northern Shan States, Burma. Mem. geol. Surv. India. Palaeont. indica, n.s. 2 (3), 6-40, pis. 1-2. CHAUVEL, J. 1941. Recherches sur les Cystoides et les Carpoides Armoricaines. Mem. Soc. geol. miner. Bretagne, 5, 286 pp., 7 pis. 1966. Echinodermes de TOrdovicien du Maroc. Cahiers Paleont. 120 pp., 16 pis. DURHAM, J. w. 1967. Notes on the Helicoplacoidea and early echinoderms. J. Paleont. 41, 97-102, pi. 14. and CASTER, k. e. 1963. Helicoplacoidea: a new class of echinoderms. Science, 140, 820-822. EICHWALD, E. 1840. Siir le Systeme Silurien de TEsthonie. 222 pp. St. Petersburg. ENDEAN, R. 1966. The coelomocytes and coelomic fluids. In boolootian, r. a. (ed.). Physiology of Echinodermata. Ch. 13, 301-328. FARMANFARMAIAN, A. 1966. The respiratory physiology of echinoderms. Ibid. Ch. 10, 245-265. HARVEY, E. N. 1928. The oxygen consumption of luminous bacteria. J. gen. Physiol. 11, 469-475. HUDSON, G. H. 1915. Some fundamental types of hydrospires with notes on Porocrinus smithi Grant. Bull. N.Y. St. Mus. Ill, 163-173, 2 pis. HUXLEY, T. H. (Translator) 1854. On the structure of the echinoderms, by Prof. J. Muller. Ann. Mag. nat. Hist. (2 ser.) 13, 1-24, 112-123, 241-256. HYMAN, L. H. 1955. The Invertebrates. 4. Echinodermata. The coelomate Bilateria, 763 pp., 280 figs. New York, London, and Toronto. JAEKEL, o. 1899. Stammesgeschichte der Pelmatozoen. I. Thecoidea and Cystoidea, 442 pp., 18 pis., 88 figs. Berlin. 1918. Phylogenie und System der Pelmatozoen. Paldont. Z. 3, 1-128, 114 figs. KESLiNG, R. V. 1963. Key for the classification of cystoids. Contr. Mus. Paleont. Univ. Mich. 18, 101- 116. 1968. Cystoids, In moore, r. c. (Ed.) Treatise on invertebrate Paleontology. S. Echinodermata, 1. S85-S267. KROGH, A. 1941. The comparative physiology of respiratory systems. 172 pp., 84 figs. Philadelphia. LANG, E. D. 1923o. Evolution: a resultant. Proc. geol. Ass. Lond. 34, 7-20. 19236. Trends in British Carboniferous corals. Ibid. 34, 120-136. MULLER, J. 1854. liber den Bau der Echinodermen. Abh. preuss. Akad. IL/s'S'. (1854), 123-219, pis. 1-9 (see Huxley, T. H. above). NICHOLS, D. 1959. Mode of life and taxonomy in irregular sea-urchins. Pubis. Syst. Ass. 3, 61-80. 1962. Echinoderms. 200 pp., 26 figs. London. PAUL, c. R. c. 1967fl. Hallicystis attenuata, a new callocystitid cystoid from the Racine Dolomite of Wisconsin. Contr. Mus. Paleont. Univ. Mich. 21, 231-253, 4 pis., 8 figs. 19676. Cyclocystoidea, Eocrinoidea, Rhombifera, Diploporita and Paracrinoidea, In harland, w. B. et al. (Eds.) The Fossil Record. London (Geol. Soc.), pp. 566-570. 1968. The morphology and function of dichoporite pore-structures in cystoids. Palaeontology, 11, 697-730, pis. 134-140. 28 PALAEONTOLOGY, VOLUME 15 PAUL, c. R. c. 1971. Revision of the North American Holocystites fauna (Diploporita). Fieldiaua, Geology, 24, 166 pp. REGNELL, G. 1951. Revision of the Caradocian-Ashgillian cystoid fauna of Belgium with notes on isolated pelmatozoan stem fragments. Mem. Inst. r. Sci. not. Belg. 120, 1-47, 6 pis. RUDWiCK, M. J. s. 1964. The inference of function from structure in fossils. Br. J. Phil. Sci. 15 (57), 27-40. ziTTEL, K. A. VON, 1880. Hondbucli der Palaeontologie. 1. Protozoa, Coelenterata, Echinodermata and Molluscoidea. 765 pp., 558 figs. Miinchen and Leipzig. C. R. C. PAUL Dept, of Geology University of Reading Revised typescript received 6 May 1971 Reading, RG6 2AB THE POST-CRANIAL SKELETON OF THE TRIASSIC ORNITHISCHIAN DINOSAUR FABROSA URUS AUSTRALIS by R. A. THULBORN Abstract. The post -cranial skeleton of the ornithischian dinosaur Fabrosaums australis, Ginsburg 1964, is described for the first time from material from the Upper Triassic Red Beds of Lesotho. Certain skeletal features (e.g. the tibio-femoral ratio) indicate that Fabrosawus should be assigned to the family Hypsilophodontidae of the suborder Ornithopoda. Fabrosawus is envisaged as a small, unarmoured and habitually bipedal dinosaur with distinct cursorial potential. Muscle scars on the femora and pelvic girdle bones point to a system of pelvic musculature not unlike that proposed by Romer (1927) for Thescelosaurus and by Gallon (1969) for Hypsilo- phodon. The problem of ornithischian origins is briefly examined. Fabrosawus presents few primitive characters and is of little assistance in any attempt to locate the possible ancestors of the Ornithischia. It is concluded that Fabrosaiiriis represents the earliest known portion of a hypsilophodont stock which persisted through the greater part of the Mesozoic era and which gave rise, even if indirectly, to such varied ornithischian groups as the iguanodonts, hadrosaurs, and ceratopsians. Triassic relatives of Fabrosaurus may be discerned as far afield as China (Tatisaurus) and Argentina (Pisanosaiirus). Lycorhimts [Fleterodoutosaiirus], also from the Upper Trias of southern Africa, appears to represent an extremely early, rather specialized, and short-lived hypsilo- phodont divergence. Knowledge of the earliest recorded (Upper Triassic) ornithischian dinosaurs is based upon rare and fragmentary fossils. In only two cases, Lycorhimts [Heterodonto- saurus] and Fabrosaurus, are the skulls at all well known (Crompton and Charig 1962; Thulborn 1970n, 1970Z?). Post-cranial bones have been described only in the South American Pisanosaurus (Casamiquela 1967), and these are far from complete. The genus Fabrosaurus was established by Ginsburg (1964) on the basis of a jaw fragment from the Upper Triassic Red Beds of Basutoland (now Lesotho). Subsequent discoveries have permitted description of the Fabrosaurus skull in near-entirety (Thul- born 1970n). This paper concerns the previously unknown post-cranial skeleton of Fabrosaurus. Hence Fabrosaurus becomes perhaps the best known pre-Jurassic orni- thischian. Material The material described below is preserved in the collection of the Zoology Department at University College, London. It was collected by Dr. K. A. Kermack and Mrs. F. Mussett during the 1963-1964 expedition from University College to Basutoland. The material was obtained from the Upper Triassic Red Beds of the Stormberg Series on the northern flank of Likhoele Mountain, near the settlement of Mafeteng (see map, text-fig. 1). Greater stratigraphic precision is not possible for two reasons: firstly, because the classic subdivisions of the Trias, established upon marine faunas, cannot be extended into continental deposits such as the Red Beds, and secondly, because of the lack of suitable zone fossils within the Upper Trias of southern Africa. Such zonation as has been achieved in the late Trias of this area is not at all detailed and cannot be extended successfully over large areas. The bones described below are all from ‘assemblage B. 17’ mentioned in separate accounts of the Fabrosaurus skull and dentition (Thulborn 1970u, 1971). This assemblage (text-fig. 2) contains at least [Palaeontology, Vol. 15, Part 1, 1972, pp. 29-60.] 30 PALAEONTOLOGY, VOLUME 15 two individuals of Fabrosaurus, the smaller one being the better represented. Assemblage B. 17 com- prises: skull fragments (both individuals), numerous isolated teeth, 44 vertebrae or parts of vertebrae (? both individuals), rib fragments and ossified tendons (? both individuals), left and right scapulae, left scapula (larger individual), left humerus, left humerus (larger individual), right radius and ulna, left radius (larger individual), parts of right carpus and manus, paired ilia, ischia, and pubes, paired femora, tibiae, and fibulae, 2 left tarsal bones, left metatarsus and parts of right metatarsus, phalanges of left and right feet. TEXT-FIG. 1. Maps showing provenance of assemblage B. 17 {Fabrosaurus australis). The material was collected at locality a, on the northern flank of Likhoele Mountain. Shaded areas (larger map) repre- sent outcrops of Drakensberg volcanics overlying the Red Beds. Preservation and preparation of material The matrix is a tough medium-grained sandstone of bright red colour. The bones are preserved in grey or white calcareous material which is usually stained black, brown, or red. Nearly every bone is traversed by numerous fine cracks — the ‘checkering’ noted by Simmons (1965) in his account of reptiles from the Chinese Trias. These fissures doubtless represent sun-cracking acquired by the bones prior to burial. Similar effects may be observed at present in southern Africa, where even the stoutest bones (e.g. those of horses and oxen) are completely shattered after a few weeks’ exposure. Each bone is enclosed within a coat of reddish-black ferruginous material. This coating is usually one or two millimetres thick and tends, where it is weathered, to part from the underlying bone very easily (a feature which is of considerable use in preparation). When freshly exposed, however, this encrustation adheres very firmly to the bone by virtue of innumerable intrusive veinlets. This is especially noticeable at the ends of the long bones and elsewhere at points of incomplete ossification (e.g. the dorsal margin of the scapula). It is also in these regions that the ferruginous cortex is thickest. The material was prepared by both mechanical and chemical means. Soft or weathered matrix was THULBORN: POST-CRANIAL SKELETON OF FABROSAURUS 31 removed with a mounted needle. Tougher matrix was removed rapidly by the use of a light hammer with small cold chisels and straight dental probes. A variable-speed vibro-tool was used to the same effect; this lent itself to much finer control and was safely employed very close to the bone. Prior to chemical treatment all exposed bone was coated in a thin (1 part to 4) solution of polybutyl meth- acrylate in ethyl acetate. This protective coating, which also served to consolidate friable bone surfaces, may be removed at any time by washing in ethyl acetate. Subsequently the material was very thoroughly dried and then immersed in cold dilute (10-15%) solutions of either acetic or formic acids in water. The period of immersion varied between 30 minutes and 3 hours. After thorough washing and drying the material was further prepared mechanically. These processes were repeated until no more matrix could safely be removed (ideally until individual bones were freed from the matrix). TEXT-FIG. 2. Fabrosaurus australis. Assemblage B. 17. X0 38. Several bones (mainly fragments of vertebrae) have been omitted for clarity. Two individuals are present, the larger one being represented by the humerus {h I) and the scapula (s I) at left. DESCRIPTION Explanation of abbreviations used in text-figures ac acetabular margin cleft between proximal trochanters of acet acetabulum femur a e anterior embayment of ilium fc facet for coracoid a pr anterior process fib fibula art proximal articular surface fib 1 left fibula c cranial fragments fib r right fibula c2 second distal carpal fl left femur c3 third distal carpal fr right femur cap capitulum g glenoid cavity cf facet for chevron bone gd grooved dorsal margin of ischium eg claw groove g t greater trochanter cn c cnemial crest h head d diapophysis hdr bones of right hand d c distal condyle hi left humerus dp c delto-pectoral crest ig intermalleolar groove 32 PALAEONTOLOGY, VOLUME 15 ill left ilium P if posterior intercondylar fossa Up iliac process of ischium p U posterior iliac shelf Ur right ilium P 1 left pubis i m medial malleolus po postzygapophysis is 1 left ischium pop postpubis is p ischiadic peduncle of ilium PP prepubis is r right ischium ppd pubic peduncle of ilium 1 c lateral condyle ppr posterior process It lesser trochanter P r right pubis m insertion of flexor tibialis (ischium) P t insertion of coccygeo-femoralis longus m c medial condyle (femur) mcl to mc4 metacarpals i to iv pub p pubic process of ischium mtl to mt4 metatarsals i to iv pz prezygapophysis mt 1 left metatarsus r c radial condyle of humerus mt r right metatarsus rd radius n notch in scapular margin rd r right radius n c neural canal s 1 left scapula n s neuro-central suture s r right scapula n sp neural spine tf fourth trochanter ob obturator process of ischium t 1 left tibia ob f obturator foramen t P transverse process o m lateral malleolus t r right tibia 0 t ossified tendons tub tuberculum pa parapophysis u ulna p e insertion of ilio-femoralis externus u c ulnar condyle of humerus (femur) u r right ulna Vertebral column (text-figs. 3, 4, and 5) The material includes vertebrae from most regions of the column. It is impossible to estimate the vertebral formula with any accuracy since the material, which is rather fragmentary, may have been derived from more than one anhoal. The best-preserved cervical vertebrae (text-fig. 3a) come from the middle of the neck. Their long and narrow centra have deeply excavated flanks and give the impression, in ventral view, of having been ‘pinched in’. These excavations probably represent areas of origin for the rectus capitis muscula- ture (running forwards to insert on the occiput) and serve to distinguish the neck vertebrae from others in the column. Each centrum bears a prominent median keel on its ventral surface. The terminal articular faces of the centra are in most cases obscured by thick crusts of haematite; these faces are shield-shaped, wider than high. The foremost centrum shown in text-fig. 3 tends slightly to the opistho- coelous condition; the succeeding cervical centra are distinctly amphicoelous. The parapophysis is a poorly defined rugosity near the antero-dorsal corner of the centrum; it occurs at successively higher levels as it is traced back through the neck vertebrae. The other area of rib attachment, the diapophysis, is a small rounded eminence situated on, or slightly above, the mid-point of the persistent neuro-central suture. In the hindmost neck vertebrae the diapophysis is at a somewhat higher level and is extended into a short ventro-lateral process. The neural arch is about as high as the centrum whilst the neural spine is merely an insignificant median ridge. The rounded and tongue-like prezygapophyses overhang the front of the centrum; the postzygapophyses are shorter and are rather angular in outline. The articular faces of the zygapophyses are inclined at about 15° from vertical. The dorsal vertebrae (text-figs. 3 and 5) are distinguished from the neck vertebrae by virtue of their more robust construction, principally through their broad centra and stout transverse processes. Each spool-shaped centrum has smoothly rounded flanks and bears a very faint median keel on its ventral surface. At their extreme anterior and posterior ends the lateral and ventral faces of the centra bear traces of wrinkling and weak longitudinal fluting. This ornament probably marks the former attachment of hypaxial trunk muscles. All of the dorsal centra are amphicoelous and have terminal articular faces of sub-circular outline. The very distinctive transverse processes are remarkably thick and massively constructed where they merge with the neural arch. Each process extends horizontally and terminates in an elliptical and convex facet (the diapophysis) for the attachment of the tuberculum from the associated rib. The facet for the capitulum of the rib (i.e. the parapophysis) is located on the THULBORN: POST-CRANIAL SKELETON OF FABROSAURUS 33 TEXT-HG. 3. Fabrosaurus australis. Cervical and dorsal vertebrae, xl-5. a, parts of three cervical vertebrae in right lateral view, b, two dorsal vertebrae in left ventro-lateral view, c-f, reconstructed cervical vertebrae in dorsal, right lateral, anterior, and ventral views, g-k, reconstructed dorsal vertebra in left lateral, anterior, ventral, and dorsal views. C 8472 D 34 PALAEONTOLOGY, VOLUME 15 anterior edge of the transverse process. In the hindmost dorsal vertebrae the parapophysis is found much closer to the diapophysis. The neural spines are best illustrated by three examples together with a number of ossified tendons (text-fig. 5F). Each blade-hke spine arises from the entire length of the neural arch and is of consistent antero-posterior width for its entire height. Faint vertical striae on the flanks of these spines indicate the former attachment of epaxial trunk muscles. The thickened dorsal TEXT-FIG. 4. Fabrosaiirus australis. Sacral and caudal vertebrae, X 1-5. a-d, sacral centrum in ventral, left lateral, dorsal and anterior views, e, partial neural arch, from sacral region, in dorsal view, f, sagittal section through a sacral centrum, g, partial neural arch, from anterior caudal region, in right lateral view, h, anterior caudal vertebra in dorsal view. J, neural arch, from middle caudal region, in left lateral view, k, posterior caudal vertebra in right lateral view. margins of the neural spines were probably embedded, during life, in the fibrous tissues of the dermis. The postzygapophyses are stout spatulate processes which overhang the rear end of the centrum ; the prezygapophyses are similar in outline, but shorter. In the anterior and middle dorsal vertebrae the articular faces of the zygapophyses are inclined at about 20° from horizontal; in the posterior dorsal region these articular faces are practically horizontal. The sacral vertebrae (text-fig. 4) are represented by five centra and parts of two neural arches. Attachment scars on the ilium (text-fig. 8c) suggest that the Fabrosaurus sacrum incorporated five vertebrae. The sacral centra are distinguished by their remarkable width. Each one is constricted in the middle and bears a distinct median keel on its ventral surface. The terminal articular faces of the THULBORN: POST-CRANIAL SKELETON OF FABROSAURUS 35 centra are quite flat, crescentic in outline, and wider than high. There are no indications of any fusion between the centra. The dorsal view of a centrum (text-fig. 4c) shows four large facets for neural arch attachment and the deep basm-Uke excavation which represents the floor of the neural canal. A for- tuitous sagittal section through one centrum (text-fig. 4f) reveals the full extent of the ventrally inflated neural canal. The neural arches of the sacral series are represented by fragments found at some distance from the nearest centrum. Depressed areas flanking the extremely thin neural spine merge imperceptibly with the flat dorsal surfaces of the transverse processes. Each stout and horizontal transverse process is some 7 mm long and is of uniform width to its free end. The prezygapophyses are situated close to the midfine, indicating that the postzygapophyses (not preserved) must have been very close together. Each prezygapophysis has a sub-rectangular profile and bears an articular face which is ahnost vertical. The caudal vertebrae (text-fig. 4) are rather poorly represented. The anterior tail vertebrae are dis- tinguished by their long and extremely thin transverse processes. These processes are directed laterally and slightly to the front. The spool-shaped centra have flat terminal faces of sub-circular outline. At its postero-ventral margin each centrum is bevelled to form a crescentic facet for the attachment of a chevron bone (haemal arch); a similar, though smaller, facet is present at the antero-ventral margin. Each tall and blade-like neural spine is inclined to the rear and arises only from the posterior half of the neural arch. The bluntly rounded prezygapophyses overhang the front of the centrum ; the postzy- gapophyses are represented merely by raised areas flanking the postero-ventral part of the neural spine. The articular faces of the zygapophyses are inclined at about 20° from vertical. The middle caudal vertebrae are represented by a single neural arch (text-fig. 4j). This differs from the neural arches of the anterior tail vertebrae in lacking any trace of the transverse processes. The distal parts of the Fabrosaurus tail are represented by a single vertebra (text-fig. 4k). Its slender and constricted centrum terminates in fiat circular surfaces and bears distinct facets for the attachment of chevron bones. The neural arch consists of little more than a small pyramidal eminence. The slender and finger-like prezygapophyses are situated close to the mid-fine; the postzygapophyses appear to have been very weakly developed or absent. The ribs (text-fig. 5) are represented by numerous fragments. One rib appears to have come from the posterior cervical region (text-fig. 5e). The proximal part of this rib is flattened and rather plate-like. Capitulum and tuberculum are both well defined (the latter being distinctly the longer) and enclose an angle approaching 90°. More distally the antero-lateral edge of the rib tends to a definite sharp- ness whilst the postero-medial margin remains thicker and well rounded. The dorsal ribs are also two-headed (dichocephalous), though the hindmost ones show a tendency to the single-headed (holo- cephalous) state. The posterior dorsal region is, however, rather poorly known and there is no incon- trovertible evidence that any of the ribs ever fully attained the holocephalous condition. In the larger ribs from the front of the thorax (text-figs. 5a-c) capitulum and tuberculum are both well developed and diverge at somewhat less than a right angle. The expanded proximal part of each rib passes distally into a long, slender, and rod-like portion. The entire rib is arched to the exterior (the greater part of this flexure occurring in the proximal one-third of the bone) and the antero-lateral edge is noticeably thinner and sharper than the postero-medial edge. In the posterior dorsal ribs (text-fig. 5d) the capitu- lum and tuberculum are situated closer together. These ribs are distinguished from those at the front of the thorax by being shorter, thicker, and more obviously arched to the exterior. The delicate trans- verse processes of the anterior tail vertebrae (text-fig. 4h) probably represent caudal ribs which are fused on to the vertebrae. Eragments of ossified tendons (text-fig. 5f-h) are preserved alongside the neural spines of the dorsal and caudal regions. It is probable that the tendons originally extended to cover much of the tail in Fabrosaurus. Each slender, compressed, and rod-like tendon is applied to the flanks of up to five successive neural spines. At one end (anterior or posterior) the tendon tapers to a point; towards the other end it gradually widens and splays out into several narrow rays. Each tendon is about a milli- metre wide and is marked with fine longitudinal striae. The tendons are grouped in definite bundles and in lateral view (text-fig. 5f) there is a slight suggestion of these bundles being disposed in a lattice- like pattern with diamond-shaped interstices. No chevron bones are preserved in assemblage B. 17. But this is not surprising in view of the paucity of tail bones in general. Chevron bones were clearly present since the caudal centra bear prominent facets for their attachment. 36 PALAEONTOLOGY, VOLUME 15 -tub Hralis. Ribs and ossified tendons, X 1-2 (except figure H). a-b, anterior thoracic rib in anterior and medial views, c, middle thoracic rib in anterior view, d, posterior thoracic rib in medial view, e, posterior cervical rib in posterior view, f, ossified tendons associated with neural spines from three dorsal vertebrae, g, anterior view of a neural spme (from dorsal region) to show arrangement of the ossified tendons, h, detail of ossified tendons, x 2. Pectoral girdle (text-fig. 6) The scapula (text-fig. 6) is a tall, blade-like bone which is roughly triangular in lateral profile. The widely expanded dorsal margin is less solidly constructed than the rest of the bone and has a distinctly porous texture. This porous zone (text-fig. 6e) represents a region of transition between the scapula proper and a cartilaginous supra-scapula. At its postero-dorsal corner the bone is extended into a short tongue-like process; the antero-dorsal corner is obtusely angular. Vertical striae on the dorsal and central parts of the lateral scapular surface doubtless mark the origin of a broad sheet of muscle (the scapular deltoid) running down to insert at the proximal end of the humerus. The ventral part of the scapula is rather ‘foot-like’ in profile due to the presence of a salient and forwardly projecting ‘acro- mial’ process. In this region the depressed lateral face of the scapula probably bore the origin of a second shoulder muscle (scapulo-humeraUs anterior) which inserted, like the deltoid, on the proximal part of the humerus. The posterior view (text-fig. 6b) demonstrates the strong latero-medial compres- sion affecting the dorsal half of the scapula and also shows that the bone is elegantly curved so as to follow, in life, the convexity of the underlying rib cage. The glenoid cavity is roughly oval in plan, higher than wide, and opens postero-ventrally ; it is confluent antero-ventraUy with a shallow trough which received the dorsal margin of the coracoid. This trough is not as broad as the glenoid but is con- siderably longer owing to its anterior prolongation beneath the ‘acromial’ process. No coracoid has been recovered from the material. Since the scapula bears a salient ‘acromial’ process (which lengthens the region for coracoid attachment) it is reasonable to infer that the coracoid was of considerable size. A distinct notch in the ventro-medial margin of the scapula (text-fig. 6c) indicates that the coracoid was perforate. In related genera (such as Hypsilophodon) this scapular notch is continuous with a coracoidal foramen which served to transmit the supracoracoid nerve and small blood vessels. Fore limb (text-fig. 7) The slender and columnar humerus (text-fig. 7a-e) is expanded at each end and is almost imper- ceptibly arched to the front. In anterior view (text-fig. 7a) it may be seen that the proximal end is THULBORN: POST-CRANIAL SKELETON OF FABROSAURUS 37 a little wider than the distal end and that the humeral shaft is narrowest at a point slightly distal to its centre. Both proximal and distal expansions are directed principally to the medial side. The blunt and slightly projecting proximo-medial corner constitutes the head of the humerus; the proximo-lateral corner is obtusely angular in profile. The lateral edge of the bone is fairly straight and the erect TEXT-FIG. 6. Fabrosawus australis. Scapula, a-b, left scapula (from larger animal in assemblage B. 17) in lateral and posterior views, X 1 . c-d, ventral part of same scapula in medial and ventral views, X 1 - 5. E, dorsal part of left scapula (smaller animal) showing incompletely ossified marginal zone, x 2. F, ventral part of right scapula (smaller animal) in medial view, X 2. delto-pectoral crest, which afforded insertions for some of the principal shoulder muscles, accounts for some 27% of the total humeral length. The crest is situated very high up on the humerus and appears, in fact, to be more restricted in distal extent than in any other ornithischian dinosaur. The medial distal condyle is fractionally larger than its lateral counterpart. Though the condyles are slightly expanded from back to front they are not appreciably attenuated or up-curved behind. The radius (text-fig. 7f-k) is a slender rod-like bone, distinctly shorter than the humerus, which is expanded at both proximal and distal ends. It is quite straight and untwisted. Transverse sections near the middle of the shaft are of elliptical outline, widest antero-posteriorly. Similarly the convex and crescentic proximal surface is widest from front to back. Near the proximal end the anterior edge of TEXT-FIG. 7. Fabrosaunis australis. Fore limb bones, x 1 (except figures Lt o r). a-e, left humerus (from larger animal) in anterior, posterior, medial, proximal, and distal views, f-h, left radius (larger animal) in lateral, proximal, and anterior views, j-k, right radius and ulna (smaller animal) in antero-lateral and distal views, l, bones of right hand, as preserved, x2. m-o, right distal carpal (the second?) in proximal, palmar, and medial views, X 5. p-q, right distal carpal (the third?) in distal and proximal views, X 5. R, reconstruction of left hand in dorsal view (reconstructed portions shaded), x2. THULBORN; POST-CRANIAL SKELETON OF FABROSAURUS 39 the radius tends to a definite sharpness. In lateral view (text-fig. 7f) the almost straight anterior margin contrasts with the concave rear edge. The distal articular surface is oval in plan and rather flat, though a shallow depression at the postero-medial margin lends it a ‘saddle-shaped’ appearance. The sole example of the ulna (text-fig. 7j-k) is somewhat crushed and lacks the proximal end. At the middle of the bone, which is a little stouter than the radius, the shaft is elliptical in cross-section (widest from front to back). Anterior and posterior margins of the shaft are both quite thin, though the latter is distinctly the sharper. The distal articular surface has the outline of a narrow triangle with a width (latero-medial) of barely 2-5 mm. This incomplete ulna seems to be in natural relationship with the associated radius (text-fig. 7j); the ulna is situated lateral to the radius and slightly behind it, its concave medial face accommodating the rounded flank of the radius. The carpus is represented by two distal carpal elements, both from the right fore limb of the smaller individual in assemblage B. 17. One distal carpal (text-fig. 7m-o) was found at the proxunal end of the second metacarpal. This carpal bone is a flattened irregular quadrilateral measuring some 3 mm (latero- medial) by 4-5 mm. It is nearly 2 mm thick. All of its edges are thickened and rounded and its proximal surface is shghtly depressed. The other distal carpal (text-fig. 7p-q) was located at the proximal end of metacarpal III. This small and rectangular carpal bone measures some 4 mm (latero-medial) by 2-5 mm and is compressed to a thickness of about 1-5 mm. The bones of the manus (text-fig. 7l) are described from the right fore limb of the smaller individual in assemblage B. 17. This partial right hand comprises metacarpals I to IV together with five phalanges. Metacarpal I is a slender rod-like bone nearly 6-5 mm long. It terminates proximally in a wide and slightly inflated articular surface of elliptical outline. Distally the metacarpal is expanded into a pair of small condyles. These condyles are about equally developed and each bears a faint circular pit on its flank. Metacarpal II is decidedly narrower than metacarpal 1 and is much longer (11 mm). Meta- carpal 111 is even larger, attaining a length (estimated) of 12-5 mm. Metacarpal IV is narrower than any of the others and has a length of 8-5 mm. The fifth metacarpal has not been recovered. The other bones of the hand are identified as the first phalanges in digits 1 to IV and the second phalanx in digit II (text-fig. 7r). The proximal phalanx of digit I is represented by a fragment close to the distal end of metacarpal I. The first phalanx in digit II hes at the distal end of metacarpal 11; this short (5-5 mm) and stout phalanx has a maximum width of almost 4 mm and bears two sub-equal condyles at the distal end. The proximal phalanx of digit 111 is fractionally shorter than that of digit II. The first phalanx in digit IV is the smallest of the proximal phalanges ; it is 3-5 mm long and has a maxi- mum width of barely 2 mm. The remaining phalanx is, to judge from its position (text-fig. 7l), the second in digit 11. This bone resembles the other hand phalanges and is 4-5 mm long. The Fabrosaurus hand is shown reconstructed with a phalangeal formula of 2 : 3 : 4 : 3 : 0 (text-fig. 7r) ; this reconstruction is based upon the hand of the related Hypsilopbodon. Pelvic girdle (text-figs. 8 and 9) The ilium (text-fig. 8) is a blade-hke bone roughly twice as long as it is high. The anterior iliac pro- cess is long, slender, slightly deflexed, and acutely pointed; the posterior process seems to have been considerably shorter and broader. The pubic peduncle extends antero-ventrally to articulate with the acetabular part of the pubis (text-fig. 9f-g). Striations on the pubic peduncle (sp) mark the former presence of cartilaginous tissues serving to bind the ilium to the pubis. The ischiadic peduncle is directed straight downwards ; its swollen ventral tip met the iliac process from the ischium (text-fig. 9a-c) so as to define the rear margin of the open acetabulum. Immediately above the acetabulum the lateral surface of the ihum is strongly inflated (principally to the exterior, but also shghtly in a dorsal direction). This supra-acetabular swelling isaf), which serves to deepen the acetabulum, contrasts with the generally flat remainder of the lateral surface. The rear margin of the ischiadic peduncle is extended into a thin and sharp-edged plate of bone. Behind the peduncle this bony sheet merges with the posterior iliac process and assumes the form of a horizontal shelf, its free edge being directed medially (text-fig. 8d). The ventral surface of this shelf carried the origin of the coccygeo-femoralis brevis, an important thigh muscle which inserted on the fourth trochanter of the femur (text-fig. 10) and functioned in drawing back the hind limb during locomotion. The lateral surface of the ilium bears a number of easily dis- cerned markings (text-fig. 8b). A narrow striated zone at the dorsal margin id fib) probably defines the origin of the posterior ilio-tibialis muscle; this muscle inserted on the front of the tibia and served to extend the knee joint. Directly beneath this striated zone, and immediately over the acetabulum, there 40 PALAEONTOLOGY, VOLUME 15 TEXT-FIG. 8. Fabrosaurus australis. Right ilium, X 1 . A, lateral view, b, lateral view with surface markings shown diagrammatically. c, medial view, d, dorsal view with transverse sections at the points indicated. THULBORN: POST-CRANIAL SKELETON OF FABROSAURUS 41 lies a long, shallow, and roughened groove {il tr)\ this doubtless represents the origin of the ilio- trochantericus muscle (which inserted on the greater trochanter of the femur and functioned in femoral protraction). The striated lateral face of the anterior process {sar) presumably bore the origin of the anterior ilio-tibial is muscle (or ‘sartorius’) ; this would have assisted the posterior ilio-tibialis in extending the knee joint. The medial surface of the ilium (text-fig. 8c) resembles its lateral surface in that the ventral parts are somewhat inflated. The dorsal half of the medial surface is ornamented with vertical striae. These markings indicate the attachment of dorsal axial muscles which would, in life, have run antero- posteriorly between the ilia. These striae (// c and lev) are most deeply impressed on the anterior half of the iUum — suggesting that the dorsal axial muscles may have been divided into anterior (ilio-costalis) and posterior (levator coccygis) groups. The medial surface of the anterior process bears two prominent and nearly horizontal ridges. At the top of the pubic peduncle there is a shallow and ill-defined depres- sion in the medial iliac surface. Behind this, and at a slightly higher level, there extends a series of four similar depressions. The first of these four lies mid-way over the acetabulum, the second over the ischiadic peduncle, the third (and largest) at the base of the posterior process, the fourth (and faintest) on the posterior iliac shelf. These five excavations (srl-srS), representing attachment areas for the sacral vertebrae, are separated by smooth and convex surfaces. The dorsal view of the ilium (text-fig. 8d) not only illustrates the extent of the supra-acetabular swelling but also demonstrates that the thick and flat dorsal margin is not everted above the acetabulum (i.e. there is no ‘antitrochanter’). The dorsal margin is thickest over the acetabulum and has a sinuous course; it curves slightly outwards over the rear part of the acetabulum, slightly inwards over the anterior part. The anterior process is deflected to the exterior. The ischium (text-fig. 9a-c) comprises a blade-like distal portion separated from the expanded proximal end by a long and weakly constricted ‘neck’. Pronounced torsion of this ‘neck’ region causes the proximo-lateral face to turn forwards as it is traced distally. The proximal end is composed of two stout processes separated by a shallow embayment representing the ventral border of the acetabulum. The dorsal (iliac) process tapers slightly to end in a convex surface for articulation with the ischiadic peduncle from the ilium. The broader and longer anterior (pubic) process terminates in a flat face which meets the pubis {is /, text-fig. 9f-g). The rear margin of the ischium forms a sweeping curve (concave posteriorly); the anterior margin forms a corresponding curve, though this is interrupted by the pro- jecting obturator process. This process, a thin and sheet-like extension of the anterior margin, curves forwards and outwards to form a distinct hollow on the lateral face of the bone. Below the twisted ‘neck’ the posterior margin is very thick, being composed of two roughly parallel ridges separated by a deep and narrow groove. This groove seems to have borne the origin of the ischio-trochantericus muscle (dinosaurian equivalent of the avian ischio-femoralis). Such a muscle would have extended up and forwards to insert near the head of the femur; it doubtless served to prevent femoral dislocation during locomotion. The grooved rear margin of the ischium bears a shallow pit, a few millimetres long, just below the level of the obturator process. This pit, which is marked with a feather-like pattern of divergent striae, probably accommodated the origin of the flexor tibialis muscle (equivalent of the ischio-flexorius in birds). The small and relatively weak flexor tibialis ran forwards and down to insert on the rear face of the tibia; it would have functioned in flexing the knee and in drawing back the hind limb. At the distal end of the ischium much of the lateral surface is ornamented with fine longitudinal striae. When ischium and pubis are placed together in natural articulation it is evident that this striated face lies directly opposite the similarly marked dorsal surface of the postpubis. The groove between the two bones was probably floored in life with ligamentous tissues serving to bind the two bones together. It is from both walls of this pubo-ischiadic groove that a muscle termed the pubo- ischio-femoralis externus is presumed to have originated. Such a muscle (equivalent of the avian obturator) inserted close to the head of the femur and assisted in femoral retraction. Striations on the medial surface of the ischium define the origin of some of the ventral axial musculature (probably the ischio-caudalis, which ran back to insert upon the centra of the foremost tail vertebrae). The blade- like distal part of the ischium is slightly arched in a medial direction, presumably to allow clearance for the femur during locomotion. The pubis (text-fig. 9d-e) exhibits comparable flexure, apparently with the same functional basis. The pubis (text-fig. 9d-g) may be divided, for convenient description, into an expanded acetabular portion and a rod-like distal portion (postpubis). The proximal part of the better preserved (left) pubis ac ilp THULBORN; POST-CRANIAL SKELETON OF FABROSAURUS 43 is damaged anteriorly (i.e. the prepubis is ineomplete). The prepubis is twisted so that its lateral face is directed somewhat ventrally. A stout posterior process from the acetabular part of the pubis curves down towards the dorsal surface of the postpubis and defines the uppermost limit of the large obturator foramen (text-fig. 9f-g). The flattened dorsal surface of this process represents the pubic portion of the acetabular margin; anteriorly this same surface is modified into a facet (// /) to receive the pubic peduncle from the ilium. The deflexed tip of this sub-acetabular process lies some 2 mm away from the dorsal surface of the postpubis and defines the incomplete posterior margin of the elliptical obturator foramen. The postpubis is a long and slender bony rod, directed postero-ventrally away from the acetabulum. Its dorsal surface is slightly flattened, so that cross-sections are elliptical or oval. In lateral view (text-fig. 9d) the postpubis shows very slight ventral ‘bowing’ which is interrupted by a distinct dorsal kink about 25 mm behind the obturator foramen. Immediately behind the obturator foramen the dorsal surface of the postpubis bears a short and deep groove {g is, text-fig. 9f) which accommodated the ventral edge of the pubic process from the ischium. In its central and distal regions the postpubis is drawn out medially into a thin and sharp-edged flange nearly 2 nmi wide. The striated dorsal face of the postpubis forms one side of the pubo-ischiadic groove and carried the origin (together with the adjacent part of the ischium) of the previously considered pubo-ischio-femoralis externus muscle. Striations on the ventral face of the postpubis indicate the former attachment of part of the ventral axial musculature (running forwards to the trunk region internal to the thigh). Hind limb (text-figs. 10, 11, and 12) The femur (text-figs. 10, 11h-m) is a stout columnar bone which is expanded both proximally (to form the head and the proximal trochanters) and distally (to form the condylar region). The femoral shaft is not perfectly straight but is slightly arched to the front. In its central regions the latero-medially compressed shaft is elliptical in cross-section. A faint vertical ridge down the front of the shaft probably marks the line of division of the femoro-tibialis musculature into lateral and medial portions. These muscles, extending over the front of the knee to insert upon the tibia, served to open the knee. The femoral head is not demarcated by any constriction or ‘neck’ and is a simple bulb-hke process which is directed medially away from the shaft at an angle approaching 90°. The depressed rear face of the head probably accommodated the ischiadic peduncle from the ilium when the femur was drawn up and back during locomotion. Fine vertical striae on the posterior face of the head doubtless mark the attachment of ligaments which held the head in place within the acetabulum. The greater trochanter is a blade-like process, directed dorsally, which is applied to the lateral face of the head. This trochanter is somewhat shorter than the head but is noticeably taller than the adjacent lesser trochanter. The striated lateral face of the greater trochanter (text-fig. 11h) probably represents the insertion area of the ilio-femoralis internus muscle. This muscle originated from the posterior thoracic region, and possibly from the prepubis (Galton 1969), and served to extend the femur. The roughened upper surface of the greater trochanter represents the insertion area of the ilio-trochantericus muscle (see description of ilium for details). The lesser trochanter is an erect finger-like process which diverges antero-laterally from the region where the head and the greater trochanter meet anteriorly (text-fig. 11h-j). The lesser trochanter lies antero-medial to the greater trochanter and is separated from it by a deep vertical cleft. Just below this cleft, on the lateral surface of the femoral shaft, there lies a small, rounded, and conspieuously pitted eminence (text-fig. 10b). This pitted area, together with the striated lateral face of the lesser trochanter, seems to have borne the insertion of the ilio-femoralis externus muscle (see deseription of ilium for details). The fourth trochanter arises from the rear face of the shaft and is entirely confined to the proximal half of the femur. This trochanter is a triangular and blade-like structure with an acute and declined tip (i.e. it is of ‘pendent’ type). The surface of the fourth trochanter bore the insertion of the large eoccygeo-femoralis brevis muscle (see account of ilium for details). Medial to the fourth trochanter there lies a prominent roughened depression (text-fig. IOd). This excavation doubtless marks the TEXT-FIG. 9. Fabrosaunis australis. Ischium and pubis, X 1 (except figures f and g). a-c, left ischium in antero-lateral, postero-medial, and posterior views, d-e, left pubis in lateral and ventral views. F-G, acetabular portion of left pubis (reconstructed) in lateral and medial views, x3. The arrow indicates the probable course of the obturator nerve and associated blood vessels. 44 PALAEONTOLOGY, VOLUME 15 insertion of the occygeo-femoralis longus (which originated from the anterior tail vertebrae and served to retract the femur). The shaft is widest just above the distal end. The lateral distal condyle is fractionally larger than its medial counterpart; these condyles are not appreciably attenuated behind and are separated by the wide and deep posterior intercondylar fossa. There is no trace of any anterior intercondylar fossa. TEXT-FIG. 10. Fabrosaurus australis. Right femur, xl. Posterior (a), lateral (b), anterior (c), and medial (d) views. The tibia (text-fig. 11a-e) is considerably longer than the femur. Its proximal end is widest from front to back whilst its distal end is expanded latero-medially. These differing directions of expansion lend the tibia a decidedly twisted appearance, the proximal view of the bone (text-fig. 1 1e) showing that this torsion ranges through some 70°. The anterior view (text-fig. 11b) shows that the bone is also affected by a weak sinuous flexure, the proximal half being arched medially whilst the distal half is arched to the exterior. The convex and roughened proximal surface is crescentic in outline. At the proximal end of the tibia the antero-medial surface is transversely convex whilst the postero-lateral TEXT-FIG. 11. Fabrosaurus australis. Tibia, fibula, and femur, X 1. a-b, left tibia in lateral and anterior views, c, distal part of same tibia in posterior view, d, distal parts of right tibia and fibula in natural juxtaposition (anterior view), e, proximal outline of left tibia (thick line) superimposed upon distal outline (shaded) to illustrate torsion affecting the bone, f-g, right fibula in lateral and anterior views. H-J, proximal part of left femur in lateral and anterior views, k, proximal view of right femur, l, plan of head and proximal trochanters in the left femur, m, distal view of right femur. 46 PALAEONTOLOGY, VOLUME 15 face is generally depressed. This postero-lateral concavity is interrupted near the middle by a blunt triangular projection (the ‘lateral condyle’) which extends down the tibial shaft as a thick and well rounded rib. Anterior to this there Ues a similar, though rather smaller, ‘accessory condyle' (text-fig. 1 1a). The ‘inner condyle’ is a blunt projection forming the posterior corner of the tibia at its proximal end. In consequence of the torsion affecting the tibia the cnemial crest (the thickly rounded anterior margin of the bone) shifts over to the medial side as it is traced distally. The lateral malleolus is a little broader and longer than its medial counterpart. The sharpened margins of the malleoli extend for a short distance up the tibial shaft as weak ridges. The anterior faces of the malleoU are almost flat. There are few obvious surface markings on the tibia. Indistinct striae on the cnemial crest probably mark the insertion of part of the extensor musculature (the femoro-tibialis and the ilio-tibiaUs or parts thereof). The slender fibula (text-fig. 11f-g) resembles the tibia in displaying pronounced torsion. The proximal tip is latero-medially compressed and has its posterior corner extended into a short process. From the depressed proximo-medial surface a shallow groove runs down the fibular shaft for about a quarter of its length. Below this the medial surface is nearly fiat. In its central regions the lateral face of the bone bears a prominent vertical ridge (which accounts for the almost triangular cross- sections of the shaft). As it is traced proximally this lateral ridge shifts over to the posterior margin. Distal parts of the right tibia and fibula are preserved in natural relationship (text-fig. 1 Id); the tip of the fibula lies on the flat anterior face of the outer tibial malleolus. The tarsus (text-fig. 12c-e) is represented by two poorly preserved distal tarsals, both from the left side. One of these is a small, flattened, and disc-like bone (text-fig. 12c-d); its depressed distal surface accommodates the raised proximal end of metatarsal 111. When these bones are articulated in this fashion the overhanging medial edge of the tarsal meets the lateral half of the proximal surface of metatarsal II. The other tarsal bone (text-fig. 12e) is less well preserved; this is slightly thicker than the other tarsal and seems to have articulated with the proximal end of metatarsal IV. The pes (text-fig. 12a-b, f-e) is represented by numerous scattered phalanges (including three unguals), a well preserved left metatarsus (text-fig. 12a-b) and fragments of the right metatarsus. Metatarsal I is a thin, sharp-edged, and splint-like bone about half as long as the adjacent second metatarsal. Its swollen distal tip is widest transversely and bears a shallow median furrow. Metatarsal I differs from the other metatarsals in its orientation; instead of running straight downwards it is directed down and back so that its distal tip lies well behind the other bones of the foot (text-fig. 12b). Metatarsal II is a thick and rod-like bone, 58 mm long, which is slightly arched to the front. Its flat proximal surface is roughly triangular in outline owing to the narrowness of the posterior margin. Its convex and sub-rectangular distal surface is developed into two small condyles; the slightly smaller medial condyle is extended up the rear face of the bone as a sharp ridge. Metatarsal 111 is the longest of the hind limb metapodials, attaining a length of 67 mm (i.e. more than half the length of the tibia). It is basically similar to, but a little stouter than, metatarsal II. Metatarsal IV is fractionally shorter than metatarsal II (56 mm as opposed to 58 mm) and is perfectly straight. A thin and sharp ridge per- sists along the entire lateral margin of this metatarsal. Metatarsal V has not been recovered. Fifteen phalanges of the foot are preserved in assemblage B. 17. Eight of these are assigned to the right foot, seven to the left. In the left foot the first phalanx in digit I was found in natural articulation with metatarsal I. This slender phalanx is 17 mm long (text-fig. 12h). Cross-sections of the bone are triangular in consequence of its compressed medial edge. The proximal surface is nearly flat whilst TEXT-FIG. 12. Fabrosaiirus australis. Ankle and foot bones, X 1 (except figures c, d, e, and q). a-b, left metatarsus in anterior and medial views, c, distal tarsal bone in distal view, x 2. d, cross-section of same tarsal bone to show surfaces for articulation with metatarsals II and III, X 2. e, proximal view of a second distal tarsal bone, X 2. E, first phalanx of digit 3 (right foot) in dorsal, medial, and ventral views. G, diagrams to show structure of same phalanx, h, first phalanx of digit 1 (left foot) in dorsal and lateral views. J, first phalanx of digit 4 (left foot) in dorsal and medial views, k, first phalanx of digit 2 (right foot) in dorsal and lateral views, l, second phalanx of digit 2 (right foot) in dorsal and medial views, m, third phalanx of digit 4 (left foot) in dorsal and lateral views, n, second phalanx of digit 3 (left foot) in dorsal and lateral views, o, third phalanx of digit 3 (right foot) in dorsal and medial views, v, dorsal and medial views of an ungual phalanx (probably from digit 1 of the right foot). Q, diagrams to show structure of same ungual phalanx, X 2. r, reconstruction of left foot in dorsal view (reconstructed portions shaded). THULBORN: POST-CRANIAL SKELETON OF FABROSAURUS 47 48 PALAEONTOLOGY, VOLUME 15 the distal end is elaborated into a pair of small condyles. Each condyle bears a shallow circular pit on its flank; similar pits, marking the attachment of digital extensor muscles, are evident in the other foot phalanges. The proximal phalanges are distinguished from the more distal phalanges of the foot through the structure of the proximal surface; in the proximal phalanges the proximal face is almost flat whilst in the distal phalanges this surface is deeply excavated (compare text-figs. 12f and 12l). This criterion serves to distinguish five more proximal phalanges within the material. Two of these are merely fragments; the remaining three all differ in their proportions. The stoutest of these phalanges (text-fig. 12f) would seem, from its size, to be the first one in digit III. A second, rather narrower and longer phalanx (text-fig. 12k) is regarded as the proximal one in digit II. The remaining proximal phalanx (text-fig. 12j) is shorter than the other two but is intermediate in stoutness. This represents, by elimination (and assuming that metatarsal V bore no phalanges), the first phalanx in digit IV. The distal phalanges, forming the foot digits between the proximal row of phalanges and the unguals, are represented by six examples. A pair of these are left and right counterparts and there are, in effect, only five examples to be considered. The stoutest of the five (text-fig. 12n) is assumed to be the second phalanx in digit III since it articulates quite agreeably with the first phalanx in this digit. Its proximal surface is divided by a vertical ridge into two concavities which receive the distal condyles of the pre- ceding phalanx. A somewhat narrower and longer phalanx (text-fig. 1 2l) is presumed to be the second in digit II. A third example (text-fig. 12o) is tentatively identified as the third in digit III. A rather short (11 mm) phalanx is probably the second in digit IV. The smallest example (text-fig. 12m) is doubtless the third phalanx in digit IV. Of the three ungual phalanges recovered from assemblage B. 17 only one, the smallest, is at aU well preserved (text-fig. 12p-q). This phalanx has the form of a curved cone with a transversely flattened ventral (palmar) surface. The slightly excavated proximal surface is nearly circular in outline. Half way up each side of the phalanx there lies a narrow and deeply incised claw groove; these grooves are about equally developed on each side of the phalanx and extend nearly half way along the bone from its bluntly rounded distal apex. It is assumed that the largest ungual (13-5 mm long) comes from digit III. The smallest (8-5 mm long) is assigned to digit I. The third example (10 mm in length) is assigned to digit II, though it might possibly have come from digit IV. The foot of Fabrosaurus is shown reconstructed (text-fig. 12r) with a phalangeal formula of 2: 3:4: 5:0. Measurements in mm. Main measurements of the two individuals of Fabrosaurus australis in assemblage B. 17. *Indicates estimated figure. Larger Individual Smaller Individual (cont.) scapula height 75 postpubis length *100 humerus length 68 femur length 104 radius length 43 tibia length 129 fibula length *123 Smaller Individual metatarsal I length *30 scapula height 66 metatarsal 11 length 58 humerus length 58 metatarsal III length 67 ulna length *40 metatarsal IV length 56 radius length 37 lengths of foot phalanges: metacarpal I length 6-5 proximal phalanx, digit I 17 metacarpal II length 11 proximal phalanx, digit II 22 metacarpal III length *12-5 proximal phalanx, digit III 20 metacarpal IV length 8-5 proximal phalanx, digit IV 14 lengths of hand phalanges : second phalanx, digit II 18-5 proximal phalanx, digit I *4 second phalanx, digit III 15-5 proximal phalanx, digit II 5-5 second phalanx, digit IV 11 proximal phalanx, digit III 5 third phalanx, digit III 14 proximal phalanx, digit IV *3-5 third phalanx, digit IV 10-5 second phalanx, digit II 4-5 ungual phalanx, digit I 8-5 ilium length *85 ungual phalanx, digit II (IV ?) 10 ilium height 31 ungual phalanx, digit III 13-5 ischium length *95 THULBORN: POST-CRANIAL SKELETON OF FABROSAURUS 49 DISCUSSION Systematic position of Fabrosaurus In his original account of the genus, based upon a jaw fragment, Ginsburg (1964) recognized the ornithischian status of Fabrosaurus and suggested that it might be closely related to the Liassic Scelidosaurus. In a subsequent description of the skull (Thulborn 1970a) this alliance with the armoured and somewhat problematical Scelido- saurus has been refuted and Fabrosaurus has been referred to the family Hypsilopho- dontidae of the suborder Ornithopoda. The structure of the post-cranial skeleton endorses this concept of Fabrosaurus as a hypsilophodont. The Fabrosaurus skeleton is very like that of Hypsilophodon itself, though it is distinguished through its noticeably more delicate construction. The vertebral column of Fabrosaurus, though it remains poorly known, matches that of Hypsilophodon in most essentials. The main point of difference concerns the number of sacral vertebrae; Fabrosaurus has 5 whilst Hypsilo- phodon typically has 6 (Galton in press). But since the number of sacral vertebrae is slightly variable within the ornithopods {Hypsilophodon, for example, sometimes has 5) this distinction does not seem excessively important. The limb girdles of the two animals are remarkably similar. The Fabrosaurus scapula is distinguished from that of Hypsilophodon through its projecting postero-dorsal corner and through its prominent ‘acromial’ process. In possessing this salient ‘acromial’ pro- cess Fabrosaurus is somewhat unusual amongst ornithischians (with the exception of the stegosaurs) and resembles some of the theropod saurischians (e.g. Gorgosaurus). The most obvious difference in iliac structure concerns the immediate supra-acetabular region; in Hypsilophodon this part of the ilium is almost flat whilst in Fabrosaurus it is strongly inflated and flared out to the exterior. The Fabrosaurus ischium is not quite as straight as that of Hypsilophodon and has the obturator process situated rather nearer the acetabulum. The Fabrosaurus pubis is very similar to that of Hypsilophodon ; the postpubis demonstrates none of the shortening seen in later and larger ornithopods. The humerus is remarkably like that figured for Hypsilophodon by Swinton (1936); in both cases the free edge of the delto-pectoral crest accounts for roughly one third of the total humeral length. The fore arm bones and the diminutive manus of Fabrosaurus are quite comparable with those of Hypsilophodon. The femora of the two animals are both characterized by a large fourth trochanter of ‘pendent’ type which is located unusually high up on the shaft. In both cases there is no anterior intercondylar fossa and the proximal trochanters are divided by a deep cleft. Within the Fabrosaurus hind limb, the tibia is considerably longer than the femur; this unusual tibio-femoral ratio is quite typical of members of the family Hypsilophodontidae. The Fabrosaurus meta- tarsus is equally as long and as narrow as that of Hypsilophodon. In both animals the phalangeal formula for the foot appears to be 2: 3:4: 5:0 and the digits terminate in slender claws. Finally Fabrosaurus resembles Hypsilophodon in possessing a system of ossified tendons along the rear parts of the vertebral column and in having hollow and thin-walled limb bones. There can be no doubt, in view of this evidence, that Fabrosaurus is a genuine orni- thischian dinosaur of Triassic age. This is amply demonstrated by its possession of a predentary bone at the mandibular symphysis (Thulborn 1970a) and by the tetra- radiate plan of its pelvic girdle. Certain structural peculiarities, such as the toothed C 8472 E 50 PALAEONTOLOGY, VOLUME 15 premaxilla (Thulborn op. cit.) and the unusual tibio-femoral ratio, indicate that this genus should be included within the family Hypsilophodontidae. It is proposed, in view of these findings, to remove Fabrosaurus australis from the Scelidosaurinae (Gins- berg’s assignment, 1964) and to place it within the family Hypsilophodontidae of the suborder Ornithopoda. Ginsburg’s original diagnosis is greatly amplified. TEXT-FIG. 13. Fabrosaurus australis. Restoration of skeleton. Approximately J natural size. Class REPTILIA Order ornithischia Suborder ornithopoda Family hypsilophodontidae Genus fabrosaurus Ginsburg 1964 Monotypic species F. australis Ginsburg 1964 Diagnosis (for genus and sole known species): unarmoured ornithischian, about 1 metre long, with slender and hollow limb bones. Skull* about 10 cm long, triangular, diapsid, with extensive circular orbits at sides. Antorbital vacuity triangular, widely open. Premaxilla extended behind naris but does not reach lacrimal. Maxilla flat above tooth row; jugal slender, without ventral flange. Parietals separate, forming broad and flat zone between upper temporal openings. Frontal with transverse crescentic depres- sion marking front limit of upper temporal opening. Quadrate tall, extended anteriorly, with front edge overlain by slender descending process from squamosal. Mandible slender, with salient finger-like retroarticular process and weak coronoid apophysis. Small median edentulous predentary at mandibular symphysis. Dentition heterodont; implantation thecodont; teeth in simple marginal row. Premaxilla with up to 6 acute. * Details of skull construction from Thulborn 1970a. THULBORN: POST-CRANIAL SKELETON OF FABROSAURUS 51 smooth, recurved teeth, last 2 bearing minute marginal denticles. About 14 teeth in maxilla; equivalent number in dentary. Crowns of cheek teeth squat, triangular, inflated bucally, flattened lingually; mesial and distal edges of crowns with small erect denticles of unvarying size. Replacement from lingual side, alternate; wear affects mesial and distal edges of cheek teeth separately.* About 15 dorsal vertebrae; sacrum of 5 vertebrae, with neural canal expanded ventrally within centra. Scapula tall, with projecting postero- dorsal corner and prominent ‘acromial’ process. Fore limb much smaller than hind limb. Humerus slightly shorter than scapula, with delto-pectoral crest confined to upper third. Radius and ulna slender, roughly equal in length, shorter than humerus. Manus diminutive, with probable formula of 2: 3:4: 3:0. Pelvis tetra-radiate ; ilium long, low, with pointed and deflexed anterior process, without ‘antitrochanter’. Postpubis long, narrow, rod-like, fairly straight; prepubis short, blade-like, twisted. Obturator process very high up on ischium. Acetabulum open, roofed above by lateral extension of ilium. Femur twice as long as humerus, with pendent fourth trochanter confined to proximal half; greater and lesser trochanters divided by deep cleft; distal condyles sub equal, not drawn out behind. Tibia stout, twisted, longer than femur; fibula slender, rod-like, slightly shorter than tibia but longer than femur. Metatarsus long and narrow; meta- tarsal I reduced, splintlike; metatarsal III equivalent to 55% of tibia length. Phalangeal formula of foot 2: 3:4: 5:0; digits clawed. Size It seems likely that Fabrosaurus australis is a dinosaur which did not attain any great size (rather than a foimi represented by immature specimens). All known specimens are of much the same size; the list includes the holotype (Ginsburg 1964), a nearly complete skull (Thulborn 1970n), the two individuals in assemblage B. 17 and parts of two undescribed individuals in the British Museum (Natural History). In his discussion of Hypsilophodon, Swinton (1936) implied that the length of the humerus, relative to that of the scapula, might indicate the maturity of individual hypsilophodonts: ‘. . . scapula and humerus ... are almost equal in length in the new young specimen, but the former is definitely shorter than the latter in the adult, so that generally it may be said that this somewhat unusual condition in dinosaurian osteology is common to Thescelosaums neglectiis and Hypsilophodon.^ If scapula and humerus lengths really are equal in immature hypsilophodonts, whilst the humerus is longer in adults, comparisons of these bones should provide a rough working guide to the maturity of individual specimens. Table 1 shows that in Fabrosaurus the scapula is longer than the humerus, an arrangement which is totally irreconcilable with Swinton’s hypothesis. The scapula-humerus ratio in Fabrosaurus is comparable with that in the Upper Cretaceous hypsilophodont Parksosaurus (Sternberg 1940) and in the iguanodont Camptosaurus (Gilmore 1909). It is clear that this skeletal ratio is no sound criterion upon which to establish the relative maturity of hypsilophodont speci- mens. This ratio is rendered even more suspect when one considers that the dorsal margin of the scapula may, since it passes into the supra-scapula, be ossified to very different degrees in diflerent individuals. * Details of tooth wear and replacement from Thulborn 1971. 52 PALAEONTOLOGY, VOLUME 15 Gallon (in press) maintains that in Hypsilophodon the humerus displays greater tor- sion with greater maturity of the individual. This seems to imply that the straight and untwisted humerus of Fabrosaurus signifies immaturity. Alternatively the lack of torsion affecting the Fabrosaurus humerus might well be interpreted as a primitive character, especially since this bone is only slightly twisted in pseudosuchians such as Euparkeria. Since all the known specimens are of roughly similar size it seems reasonable to assume that Fabrosaurus was, in fact, a rather small ornithischian dinosaur. It is esti- mated that the smaller (more complete) individual in assemblage B. 17 had a maximum length (from snout to tail tip) of slightly less than one metre. The hind limb is com- parable in size with that of a living chicken {Gallus). The fore limb is very much shorter than the hind limb whilst the neck, which was relatively short, carried a quite large skull (perhaps 10 cm long). The tail is not well represented in the material but is shown in the reconstruction (text-fig. 13) as roughly equivalent in length to head, neck, and trunk combined (i.e. much as in other hypsilophodont ornithopods). Locomotion It is important to recognize that there are no specific features of skeletal construction which might serve as absolutely reliable criteria in distinguishing between bipedal and quadrupedal dinosaurs. A comparable situation exists in living lizards, where bipeds are indistinguishable from quadrupeds through examination of the skeleton alone. There are, however, numerous osteological characters in Fabrosaurus which are dis- tinctly suggestive of bipedalism and which, in conjunction, render the concept of Fabro- saurus as a biped quite acceptable. These adaptations for bipedalism are evident in almost every part of the skeleton. The entire skeleton is very lightly built. The slender, hollow and thin-walled limb bones resemble those of birds and of pterosaurs, where weight reduction would have been of critical importance. Lightening of the skeleton is most marked in advance of the hips — in the fenestrated skull (Thulborn 1970a), in the relatively short neck, in the small fore limbs and in the rather delicate construction of the presacral vertebrae. Such weight reduction in front of the hips is explicable when one considers that in a biped the whole body must be pivoted over the hips and that, in consequence, the tail alone must counter-balance the weight of the trunk, fore limbs, neck, and head. Further, the lack of dermal armour in Fabrosaurus would have con- tributed to the reduction of total body weight. The almost horizontal zygapophysial faces of the vertebrae immediately preceding the sacrum would have prevented undue sagging of the vertebral column whilst the animal was in a bipedal pose. The ‘lumbar’ vertebrae of large and undoubtedly bipedal theropods {Tyrannosaurus, AUosaurus, and the like) frequently show traces of fusion, presumably with a similar functional basis. The lattice of ossified tendons, attached to the neural spines in front of and behind the sacrum, seems to have a similar purpose. Ostrom (1964) suggests that such a tendon system would have effected resistance to any sagging of the vertebral column. The zygapophysial faces of the caudal vertebrae are practically vertical, indicating that flexures of the tail took place mainly within a vertical plane. Snyder (1949) has emphasized the importance of the tail in the bipedal locomotion of lizards such as Basiliscus and has shown that their bipedal faculties are seriously impaired when the tail is even partially amputated. This author points out that the tail is held clear of the THULBORN: POST-CRANIAL SKELETON OF FABROSAURUS 53 ground (i.e. elevated in a vertical plane) during bipedal running. Snyder (1962) further makes it clear that such tail movements serve to counter-balance the weight of those parts of the body in advance of the hips. Vertical tail movements, in every way com- parable to those of bipedal lizards, would seem to have been of fundamental importance in Fabrosaurus. These tail flexures would not have been impaired by the ossified tendons since individual bundles of tendons would have ‘slipped’ relative to those crossing above and below. The five centra of the Fabrosaurus sacrum are distinguished through the great enlarge- ment of the neural canal within them. Ewer (1965) noted similar inflation of the neural canal in the whole ‘lumbar’ region of the pseudosuchian Euparkeria (from the 13th dorsal vertebra to the 1st caudal). It is evident that this peculiarity affects similar zones in Euparkeria and Fabrosaurus but that owing to the shortness of the sacrum in the former (only two vertebrae) it extends to include both posterior dorsal and anterior caudal vertebrae. The functional significance of the dilated neural canal is debatable. Ewer (op. cit.) maintains that these dilations in the centra might have been filled with non-nervous tissue intimately associated with the nerve cord (rather than with any expansion of the spinal cord itself). Such an arrangement might be paralleled in birds, where the sinus lumbosacralis is the associated tissue (Terni 1924). This hypothesis suffers, however, from some difficulties. Firstly, the avian sinus lumbosacralis lies dorsal to the nerve cord whilst the excavations in the Fabrosaurus vertebrae (and those of Euparkeria) are situated ventrally. Secondly, the function of the glycogen-filled sinus lumbosacralis is not readily apparent. It is unlikely that such glycogen-rich tissues could have provided fuel for muscular energy since (in birds at least) the main locomotor muscles derive fuel from deposits of fat, which provides twice the energy that glycogen does (George and Berger 1966). It is suggested here, in contrast, that the inflated neural canal in the sacral region did in fact accommodate nervous tissue— a genuine ganglionic expansion of the nerve cord. Dilations of the spinal cord have long been quoted in a variety of dinosaur sacra (e.g. see Marsh 1881; Seeley 1882) and Romer (1956) sug- gests that this local refinement of the central nervous system is to be related directly to the size of the hind limbs. In both Euparkeria and Eabrosaurus the hind limbs are considerably larger than the fore limbs. Yet sheer relative size of the hind limbs alone would not seem to account for any local expansion of the nerve cord in these animals, particularly when their over-all small size is recalled. It is important to recognize, how- ever, that Eabrosaurus is presumed to have been an habitual (if not obligatory) biped. When not running this animal must have walked slowly on the hind limbs alone. In such slow bipedal progression there regularly comes a point when contact with the ground is maintained by one foot alone (assuming that the tail would have been nearly clear of the ground). Thus for short periods, perhaps a second or so in duration, the animal must be poised on one foot and must, as a result, be prone to simply topple over. The only way in which this tendency can be counteracted is through delicate shifts of body weight so as to maintain equilibrium. This, in turn, demands perfect muscular control within and between the hind limbs and the major organ of balance, the tail. Such sophisticated muscular control might well have been governed by a local dilation of the nerve cord which, logically, would have been situated close to both hind limbs and the base of the tail (i.e. in the sacrum). The proximal end of the humerus bears an extensive articular surface but lacks any 54 PALAEONTOLOGY, VOLUME 15 salient ‘head’. This indicates that the humerus had significant freedom of movement within the glenoid cavity. Many earlier dinosaur reconstructions have the proximal end of the humerus set firmly in the glenoid; in consequence the humerus is directed horizontally at right angles to the line of the vertebral column (see Casier 1960, for restorations of Hypsilophodon and Megalosaurus). Whilst this attitude was undoubtedly possible it seems more likely that in normal circumstances the humerus would have been closely applied to the side of the thorax and directed down and forwards. In this position the projecting proximo-medial corner of the humerus would have served as the functional ‘head’. Such humeral mobility suggests that the fore limb had no very great positive locomotor function; the humerus would surely have been too prone to dis- location for the fore limb to have sustained any sizeable proportion of the body-weight. This, once again, is indirectly suggestive of habitual bipedalism. The Fabrosaurus hand, in relation to the foot in the same animal, is diminutive (com- pare text-figs. 7r and 12r). None of the bones of the hand shows the elongation which characterizes the foot bones. It is clear that this delicate hand could have had no sig- nificant locomotor function. In quadrupedal archosaurs (e.g. Alligator, Stegosaurus) the hand is generally only slightly smaller than the foot, despite a startling size-difference between the entire fore and hind limbs. It appears that the span of the hand relative to that of the foot (rather than the length of the fore limb against that of the hind limb) is of some use in deducing the probable mode of locomotion. Strong pelvic and thigh muscles have been inferred for Fabrosaurus on the evidence of muscle scars on the femora and pelvic girdle bones. These muscles are matched in the related dinosaurs Thescelosaurus (Romer 1927) and Hypsilophodon (Galton 1969) and are comparable, in general terms, with those of birds and lizards. The principal locomotor agent in Fabrosaurus was doubtless a strong backwards thrust of the hind limb, generated by contraction of the powerful femoral adductor muscles. These adductor muscles (the coccygeo-femorales) extended from the fourth trochanter of the femur to areas of origin on the rear part of the ilium and the anterior tail vertebrae. During femoral adduction there would necessarily have been some tendency for the base of the tail to bend into a kink towards the approaching femur. This is admirably shown by Snyder (1962) in a figure of the lizard Crotaphytus. Such tail fiexure would have affected the efficiency of the adductor muscles to a considerable degree. It is likely that the vertical zygapophysial faces of the caudal vertebrae served to brace the tail in order to resist such lateral flexure. The Fabrosaurus ilium is distinguished by its swollen and flared out acetabular mar- gin. This forms, in effect, an overhanging roof above the acetabulum. In other hypsilo- phodonts the supra-acetabular part of the ilium is flat or only very slightly inflated. Fabrosaurus seems, in fact, to be unique amongst ornithischians in this portion of its iliac morphology. Such roofing-over of the acetabulum may be matched only in the coelurosaur Coelophysis and in the problematical reptile Poposaurus (Colbert 1961). These three reptiles have, moreover, certain other features in common; they are all of late Triassic age and they all appear (with the possible exception of Poposaurus) to have been habitual bipeds. The supra-acetabular expansion is probably a specialization related to bipedalism. In a biped much of the mechanical thrust affecting the femur is directed upwards; hence a deepened and partially roofed-over acetabulum would have assisted in retaining the ‘head’ of the femur in place during locomotion. This arrange- THULBORN: POST-CRANIAL SKELETON OF FABROSAURUS 55 ment may, in turn, be correlated with the rather weak development of the femoral ‘head’ in these forms. The dorsal margin of the ilium is not at all everted or extended laterally and there is no trace of the ‘antitrochanter’ which occurs in larger ornithopods and in quadrupedal ornithischians. The functional significance of the ‘antitrochanter’ is obscure, though Romer (1927) suggests that its presence reflects some elaboration of the ilio-femoralis musculature. Lack of this structure from the Fabrosaunis ilium presumably points to an unspecialized arrangement of the ilio-femoralis (which holds the femoral ‘head’ in place and assists in elevating the thigh). The anterior process of the ilium is only slightly deflexed and has an acutely pointed tip (in contrast to the broadly spatulate tip observed in many iguanodonts). Most importantly the anterior process exhibits none of the arching seen in the ilia of hadrosaurs (e.g. Hypacrosaunis). Romer (op. cit.) relates such arching with reversion to quadrupedalism, suggesting that this flexure of the anterior process permitted passage for the ilio-femoralis internus muscle from the femur to the posterior thoracic region. Two ridges on the medial face of the anterior process (text-fig. 8c) seem to have strengthened this rather delicate structure. It may be noted, in this context, that the anterior process would have been subject to some lateral ‘pull’ through contraction of the attached ‘sartorius’ muscle. The postpubis rivals the ischium in length and is also fairly straight; it lacks any of the downwards curvature which Romer correlates with quadrupedalism (1927). The large obturator foramen (text-fig. 9f-g) probably served as an exit for the obturator nerve and associated blood vessels. The foramen is very nearly encircled by bone and the small gap at the rear margin was doubtless filled with cartilage during life. This near- complete enclosure of the obturator foramen is characteristic of hypsilophodonts ; in many other ornithopods the foramen is widely open at the back and is little more than a notch. The prepubis is so poorly known (text-fig. 9d) that it cannot be discussed in detail. Hence it is impossible to reconsider Romer’s hypothesis (1927) that the prepubis served principally as an abdominal support structure and that no musculature of any conse- quence was attached to it. Recently Gallon (1969) has suggested that the prepubis did not provide the main support for the abdomen and that some muscle (the pubo-tibialis or part of the pubo-ischio-femoralis internus) originated from its lateral surface. The elongated and thin-walled bones of the Fabrosaurus hind limb are not unlike those of birds in general appearance and are distinctly suggestive of bipedal potential. The hind limb is somewhat unusual in that the tibia is considerably longer than the femur. Comparable predominance of tibia over femur is seen in related hypsilophodonts, in some pseudosuchians (e.g. Saltoposuchus) and in many coelurosaurs (e.g. CoeJophysis, Ornithomimus). The metatarsus of Fabrosaunis is similarly attenuated, the longest (third) metatarsal being equivalent to some 55 % of the tibia length. Such elongation of the hind limb is almost certainly indicative of habitual bipedalism, though this does not imply that forms with a relatively short tibia and metatarsus (e.g. Thescelosaurus, Euparkeria) were precluded from a similar mode of locomotion. Lengthening of the hind limb probably served to increase potential for rapid acceleration. Hildebrand (1959, 1961) has shown that acceleration is achieved, in cursorial mammals at least, by lengthening of the stride rather than by any increase in the number of limb strokes per minute. This suggests that the long hind limbs of Fabrosaurus increased this animal’s 56 PALAEONTOLOGY, VOLUME 15 ability to lengthen the stride and, in consequence, its capacity to achieve acceleration. It is probable that a dinosaur as small as Fabrosaurus could take off" into rapid bipedal flight from a stationary position, much as the lizard Basiliscus (Snyder 1962) or the domestic chicken. There is no trace of the fifth digit in the Fabrosaurus foot. In all probability digit V was represented only by a splint-like vestige of the fifth metatarsal (i.e. as in Hypsilo- phodon and Thescelosaiirus). Digits II, III, and IV are the longest and stoutest and the Fabrosaurus foot may be considered as functionally tridactyl and rather bird-like (text-fig. 12r). The tridactyl foot would seem to have been a specialization related to bipedalism since it is encountered in other hypsilophodonts, in the pseudosuchian thecodonts (though digits I and V are not excessively reduced here) and in saurischian bipeds (e.g. Allosaurus, Ornithomimus). The second, third, and fourth digits of the Fabrosaurus foot were directed forwards and were somewhat splayed out whilst the shorter first digit was probably directed back and down as a heel-like ‘prop’. This interpretation is borne out by the orientation of the first metatarsal when the metatarsus is preserved in an undisturbed state (text-fig. 12b). In the saurischian dinosaurs Colbert (1964) has indicated some relationships between certain skeletal proportions and the presumed mode of locomotion. Some of the con- clusions attained by this author may be extended to cover the early ornithischian now imder consideration. Colbert correlates a ‘dolichoiliac’ type of pelvis (i.e. one with a long, low ilium) with the development of ‘complete bipedalism’, citing Coelophysis, Compsognathus, and Ornithomimus as examples. This author suggests that ‘. . . the dolichoiliac pelvis . . . would furnish the muscular base for an efficient bipedalism’. A similar argument might be applied to Fabrosaurus: a powerful pelvic musculature, well-suited for bipedal locomotion, has been inferred from the evidence of muscle scars whilst the long and blade-like ilium could be accommodated without difficulty in Colbert’s ‘dolichoiliac’ category. Colbert (op. cit.) also attempts to establish some line of distinction between saurischian bipeds and quadrupeds on the basis of disparity in size between the fore and hind limbs. Such an approach cannot, however, be utilized in the ornithischian dinosaurs; there are several cases where a limb ratio of bipedal aspect (with the fore limb very much shorter than the hind limb) is encountered within undoubted quadrupeds (e.g. Stegosaurus, Nodosaurus). Despite this difficulty it is still possible to distinguish purely bipedal ornithopods from those with a tendency to quadrupedalism — through comparisons of limb bone lengths within the hind limbs. In habitually bipedal types, such as the hypsilo- phodonts, the tibia is considerably longer than the femur and the metatarsus is equiva- lent to a significant proportion of the femoral length (66% in Fabrosaurus). In those ornithopods tending to quadrupedalism (notably iguanodonts and hadrosaurs) the tibia is not as long as the femur and the short, stout metatarsals constitute a foot of graviportal aspect. It seems reasonable, in view of all this evidence, to envisage Fabrosaurus as a small and agile biped with distinct cursorial ability. In conclusion it may be pointed out that Fabrosaurus compares favourably with cursorial bipeds from elsewhere within the Reptilia — with Basiliscus and Chlamydosaurus (Snyder 1949, 1952, 1954, 1962), with Coelophysis (Colbert 1964), with Euparkeria (Ewer 1965) and with Velocipes (von Huene 1932). THULBORN: POST-CRANIAL SKELETON OF FABROSAURUS 57 Ornithischian origins Since all known Triassic ornithischians may be referred to the family Hypsilopho- dontidae it is clear that the whole question of ornithischian ancestry is bound up with the origin of this family in particular. This inferred monophyletic origin for the order Ornithischia is sustained by a remarkable homogeneity of structure throughout the group; important diagnostic features, such as the predentary bone and the biramous pubis, are encountered in even the most aberrant ornithischians. The presence of ornithischians in the Upper Trias certainly implies that the group came into existence at some considerably earlier date. This concept of an extremely early start to orni- thischian history, though unsupported by fossil evidence, is reinforced by the geographic and structural diversity of the known Triassic forms {Fabrosaurus, Lycorhinus, and Geranosaurus from southern Africa, Tatisaurus from China, Pisanosanrus from Argen- tina). Such diversity points, in turn, to some pre-Upper Triassic episode of adaptive radiation and dispersal. Ornithischian origins are probably to be sought within the order Thecodontia. Romer (1966) distinguishes four suborders of thecodonts; Proterosuchia, Phytosauria, Aeto- sauria, and Pseudosuchia. Of these the proterosuchians and the phytosaurs may at once be discounted as possible near-ancestors of the Ornithischia on account of their re- markably specialized construction. The phytosaurs may also be rejected in view of their stratigraphic location (being mainly of late Triassic date these are contemporary with early ornithischians). The aetosaurs (including Stagonolepis and its allies) have recently been studied by Walker (1961). In some respects these reptiles are very similar to ornithischians; Walker (op. cit.) mentions especially the elongate external naris, loss of teeth from the front of the premaxilla, the generally reduced number of teeth, the forwardly inclined quadrate and the well developed dermal armour. Further, the existence in Stagonolepis of a horny sheath at the mandibular symphysis immediately calls to mind the ornithischian predentary bone. But the possibility that the aetosaurs might represent ornithischian ancestry must be discounted for two important reasons. Firstly, certain features of aetosaur construction are totally irreconcilable with orni- thischian conditions — principally the extremely specialized armour (whilst Triassic ornithischians are unarmoured), the very marked reduction of the lower temporal opening, the lateral situation of the upper temporal opening, and the typically thecodont pelvic girdle. Secondly, the aetosaurs are mainly of late Triassic age (i.e. contemporary with early ornithischians). It seems rather improbable, in view of these facts, that the aetosaurs could be involved in ornithischian history. This leaves only the pseudosuchian thecodonts to be considered as possible orni- thischian ancestors. In discussing the Lower Triassic pseudosuchian Euparkeria Ewer (1965) supports the suggestion, advanced by Broom (1913), that the family Euparkeriidae probably represents the ancestry of all the major groups of later archosaurs, including the Ornithischia. It is, however, rather difficult to imagine the derivation of orni- thischians from hypothetical Euparkeria-like ancestors. This difficulty springs from fundamental differences in structure; Ewer (op. cit.) concludes that the Ornithischia arose ‘. . . from some form other than Euparkeria, differing from the latter in the struc- ture of both pelvis and ankle . . .’. Whilst it may be inferred that ornithischian ancestry extends back ultimately into the Euparkeriidae this still does not clarify the problem of ornithischian history between Lower and Upper Trias. Euparkeria and its allies display 58 PALAEONTOLOGY, VOLUME 15 no obvious tendency towards the ornithischian state of organization whilst the earliest known ornithischians exhibit relatively few primitive characters and might be regarded as ‘fully-fledged’ members of the Ornithischia. There are, in consequence, no apparent ‘intermediates’ between the Lower Triassic Euparkeria and the Upper Triassic Fabro- saurus. TRIAS JURASSIC CRETACEOUS ® hypsilophodont genera. STEGOSAUF IS cO^> 1 ^ ^O^’^ IGUANC HADROSAURS )DONTS ^ I ^ / / / /'I thecodont / / | / / ^ ancestors \ CERATOPSIANS ANKYLOSAURS TEXT-no. 14. Outline of ornithischian phytogeny. It has already been suggested that Fabrosaurus is a fairly direct antecedent of the hypsilophodonts of the Jurassic and Cretaceous (Thulborn 1970a). The structure of the post-cranial skeleton fully substantiates this assertion. So it is clear that Fabrosaurus represents the earliest known portion of a hypsilophodont stock which persisted through the greater part of the Mesozoic era. These hypsilophodonts appear to lie at the core of ornithischian history; they represent the ancestry, ultimately at least, of such groups as the iguanodonts, hadrosaurs, and ceratopsians (text-fig. 14). Hence there is some justification for regarding Fabrosaurus as a genuine ‘archetypal’ ornithischian. Amongst other Triassic ornithischians the Chinese Tatisaurus and the South American Pisano- saurus seem to be fairly close relatives of Fabrosaurus. The coeval Lycorhinus (Hetero- dontosaurus), from southern Africa, has a peculiar dentition which includes large ‘canine’ teeth (Crompton and Charig 1962; Thulborn 1970Z7, 1971). This genus appears to THULBORN: POST-CRANIAL SKELETON OE FABROSAURUS 59 represent an extremely early and rather specialized hypsilophodont divergence which failed to survive the changes concomitant with the close of the Triassic period. Acknowledgements. It is a pleasure to express my thanks to Dr. K. A. Kermack, of University College, London, who provided the material for this paper and offered many helpful suggestions. Mrs. F. Mussett has given me much useful advice on preparation techniques. This work has also received the benefit of discussions with Dr. A. J. Charig (British Museum, Natural History), Dr. P. M. Galton (Peabody Museum, Yale University) and Dr. P. L. Robinson (University College, London). Financial support came from the Natural Environment Research Council and, subsequently, from a research fellowship at the Department of Geology, University of Birmingham. REFERENCES BROOM, R. 1913. On the South African pseudosuchian Euparkeria and allied genera. Froc. Zool. Soc. Lond. 1913, 619-633. CASAMIQUELA, R. M. 1967. Un nucvo dinosaurio ornitisquio triasico {Pisanosaums mertii; Ornithopoda) de la formacion Ischigualasto, Argentina. Ameghiniana, Rev. Asoc. Pal. Argent. 5, 47-64. CASiER, E. 1960. Les Iguanodons de Bernissart. L’inst. roy. Sci. nat. Belg, Brussels, 134 pp. COLBERT, E. H. 1961. The Triassic reptile, Poposaiims. Fieldiana (Geol.), 14, 59-78. 1964. Relationships of the saurischian dinosaurs. Amer. Mas. Novit. No. 2181, 1-24. CROMPTON, A. w. and CHARIG, A. J. 1962. A new Ornithischian from the Upper Triassic of South Africa. Nature, 196, 1074-1077. EWER, R. F. 1965. The anatomy of the Thecodont reptile Euparkeria capensis Broom. Phil. Trans. R. Soc. B248, 379-435. GALTON, p. M. 1969. The pelvic musculature of the dinosaur Hypsilophodon (ReptUia: Ornithischia). Postilla, No. 131, 1-64. (in press). On the anatomy of the ornithischian dinosaur Hypsilophodon foxii. Bull. Brit. Mus. {Nat. Hist.) Geol. GEORGE, J. c. and berger, a. j. 1966. Avian myology. Academic Press, New York and London, 500 pp. GILMORE, c. w. 1909. Osteology of the Jurassic reptile Camptosaurus, with a revision of the species of the genus, and descriptions of two new species. Proc. U.S. Nat. Mus. 36, 197-332. GiNSBURG, L. 1964. Decouvcrtc d’un Scelidosaurien (Dinosaure ornithischien) dans le Trias superieur du Basutoland. C.r. hebd. Seanc. Acad. Sci. Paris, 258, 2366-2368. HILDEBRAND, M. 1959. Motions of the running cheetah and horse. J. Mammal. 40, 481-495. 1961. Further studies on locomotion of the cheetah. Ibid. 42, 84-91. HUENE, F. VON. 1932. Die fossile Reptil-Ordnung Saurischia, ihre Entwicklung und Geschichte. Monogr. Geol. Paldont. 4, 1-361. MARSH, o. c. 1881. Principal characters of American Jurassic dinosaurs; Part iv: Spinal cord, pelvis and limbs of Stegosaurus. Amer. J. Sci. (3) 21, 167-170. OSTROM, J. H. 1964. A reconsideration of the paleoecology of hadrosaurian dinosaurs. Ibid. 262, 975-997. ROMER, A. s. 1927. The pelvic musculature of ornithischian dinosaurs. Acta Zool. Stockholm, 8, 225-275. 1956. Osteology of the Reptiles. Chicago, 111 pp. 1966. Vertebrate paleontology. 3rd edn. Chicago, 468 pp. SEELEY, H. G. 1882. On Thecospondylus Horneri, a new Dinosaur from the Hastings Sand, indicated by the Sacrum and the Neural Canal of the Sacral Region. Q.J. Geol. Soc. 38, 457-460. SIMMONS, D. J. 1965. The non-Therapsid reptiles of the Lufeng Basin, Yunnan, China. Fieldiana {Geol.), 15, 1-93. SNYDER, R. c. 1949. Bipedal locomotion of the Lizard Basiliscus basiliscus. Copeia, 1949 (2), 129-137. 1952. Quadrupedal and bipedal locomotion of lizards. Ibid. 1952 (2), 64-70. 1954. The anatomy and function of the pelvic girdle and hindUmb in lizard locomotion. Amer. J. Anat. 95, 1-46. 1962. Adaptations for bipedal locomotion of lizards. Amer. Zool. 2, 191-203. 60 PALAEONTOLOGY, VOLUME 15 STERNBERG, c. M. 1940. Thescelosaunis edmontonensis, n.sp., and classification of the Hypsilophodon- tidae. J. Paleont. 14, 481-494. (Abstract for this paper published separately in 1937; Geol. Soc. Amer. Proceedings for 1936, p. 375.) swiNTON, w. E. 1936. Notes on the osteology of Hypsilophodon and on the family Hypsilophodontidae. Froc. Zool. Soc. Lond. 1936, 555-578. TERNi, T. 1924. Ricerche sulla cosidetta sostanza gelatinosa (corpo glicogenico) del midollo lombo- sacrale degli Uccelli. Arch. ital. Anat. Embriol. 21, 55-86. THULBORN, R. A. 1970fl. The skull of Fabrosaurus australis, a Triassic ornithischian dinosaur. Palaeon- tology, 13, 414-432. 19706. The systematic position of the Triassic ornithischian dinosaur Lycorhmus angustidens. Zool. J. Linn. Soc. 49, 235-245. 1971. Tooth wear and jaw action in the Triassic ornithischian dinosaur Fabrosaurus. J. Zool. 164, 165-179. WALKER, A. D. 1961. Triassic reptiles from the Elgin area: Stagonolepis, Dasygnathus and their allies. Phil. Trans. R. Soc. B244, 103-204. R. A. THULBORN Department of Geology University of Birmingham Birmingham, 15 Revised typescript received 18 June 1971 PERIODICITY STRUCTURES IN THE BIVALVE SHELL: ANALYSIS OF STUNTING IN CERASTODERMA EDULE FROM THE BURRY INLET (SOUTH WALES) by G. E. FARROW Abstract. Individuals of Cerastoderma edule from the Burry Inlet are smaller than those from any other British cockle population. This stunting results from the situation of the cockle flats near neap high water mark, and is due to arrested growth during periods in the tidal cycle when the shells were exposed to the air. This, together with the longer winter stoppages, leaves cockles from high water neap level some two-thirds of the size of their contemporaries from low water spring level. The external width of a winter ring and the sharpness of its incision into the shell profile become more acute higher up the shore. Greater prominence of the crossed-lamellar structure in the outer shell layer is associated with winter reduction in growth rate, the lamellae become markedly deflected if an actual stoppage, marked by a dark periostracal band, takes place. Application of these results to the geological record would lead to a precise differentiation of littoral environments and enable the recog- nition of stunting in fossils. The Burry Inlet, like the Thames whose cockle populations have already been described (Farrow 1971), is an estuarine area and one of the three most important commercial sites in the country (Hancock and Urquhart 1966, fig. 1). Its environment is, however, different in several important respects : {a) The unusually high situation of the cockle flats, caused by the marked silting up of the Inlet. {b) The large tidal range (10 m at major spring tides). (c) Greater instability of the substratum, caused by migration of the river channel and exposure to gales. In this stringent habitat fully grown cockles rarely exceed 30 mm in length, compared with over 50 mm for examples from Barra in the Hebrides. The present work owes much to the co-operation of the Burnham-on-Crouch Fisheries Laboratory whose staff have been engaged since 1958 in a study of the population dynamics of the Cerastoderma edule (L.) community. The present experiments on daily growth patterns thus effectively supplement a sound framework of macroshell growth analyses (Hancock and Simpson 1962; Hancock 1965, 1967). ‘Transect F’ of Hancock and Urquhart (1966, figs. 4-6) was levelled accurately and living cockles collected from stations 40 m apart. Specimens from this transect, preserved immediately after collec- tion and subsequently oven dried, were supplied by Dr. D. A. Hancock and these form the main basis of this paper. The location of the transect within the estuary is shown in text-fig. 1. TRANSECT DATA Abundance and distribution of age-groups. Text-fig. 2 shows the abundance of the various year-groups present along the sand-flat in February 1969. Cockles in their first, second, and sixth winters are most abundant; in the intervening years spatfalls [Palaeontology, Vol. 15, Part 1, 1972, pp. 61-72, pis. 8-10.] 62 PALAEONTOLOGY, VOLUME 15 TEXT-FIG. 1. Map showing the distribution of Recent sediments and the location of Transect F within the Burry Inlet, based on Admiralty Chart no. 1167. All cockles described in the text are from this transect. FARROW: PERIODICITY STRUCTURES IN CERASTODERMA 63 were insignificant. Densities of up to 7000/m^ are recorded for the 1967 year-group and this spatfall was selected for study since it was the most widely distributed along the transect. The density distribution of the other year-groups is broadly similar. Size-frequency distribution of cockles with two winter rings. Text-fig. 3 shows the varia- tion in shell length of the 1967 year-group along the transect, sampled on 14 May 1969. Modal specimens from stations 250 m apart are illustrated for comparison on text-fig. 4. Densest settlement occurred just below neap high water mark where three stations yielded more than 5000/m^ Both higher than this, and below it where the steeper flank of the flat is reached, densities are much lower. 6 4 Winter Ring 3 TEXT-FIG. 2. Curves of density distribution of the various age-groups of cockles collected from the transect in February 1969; maximum density shown = 7000/m^. Plots based on OT m^ quadrats at 40 m intervals. ANALYSIS OF RESULTS Two sets of samples were used in studying internal details of shell growth by means of acetate peels of radial valve sections: the first a random series of shells from the February survey; the second a complete series of shells, one being selected from a sample of six modal individuals sent from Burnham for each station (text-fig. 3), obtained on 14 May 1969. Since chance preservation of shells in the fossil record does not usually permit large numbers to be examined it is of some value to compare the 64 PALAEONTOLOGY, VOLUME 15 F21 15 20 25 30 I ► F8 ) FO 15 Shell Length (mm) TEXT-FIG. 3. Curve showing the size-frequency distribution of two-year-old cockles along the transect on 14 May 1969; greatest width corresponds to 1400 of one particular centimetre group/m^; highest density shown = 5500/m^ TEXT-FIG. 4. Diagram showing the shore profile of Transect F (from Hancock and Urquhart 1966, fig. 6). Cockles selected from the mode at four stations each separated by about 250 m demonstrate the striking reduction in shell length on the higher parts of the flats (which is also apparent in their relative size at the first winter ring). Black dots indicate the location of specimens illustrated on PI. 9; stipple density is proportional to density of cockle settlement. FARROW: PERIODICITY STRUCTURES IN CERASTODERMA 65 results obtained. External measurements of shell length were carried out by the staff at Burnham on all shells collected during the May survey. Relationship of shell length to position on tidal flat. The striking visual correlation may be seen on text-fig. 4; this is also apparent in the cockle’s relative size at the first winter ring. Text-fig. 5a shows that when plotted out arithmetically the rate of reduction in TEXT-FIG. 5. Graphs illustrating the relationship between modal shell length and tidal height: a, plotted arithmetically; b, plotted logarithmically from the curve fitted to a. Chart Datum (C^) = —14 ft O.D. (Newlyn). total growth increases sharply on the higher parts of the flats. Plotting points from the fitted curve of text-fig. 5a on a logarithmic scale resolves growth characteristics into two groups, both of which are related logarithmically to tidal height. The bulk of the population may be fitted to the curve : y = 0T9+0-087X, where y = log(20— tidal height in feet+Q), X = shell length in mm; Q = Chart Datum. F C 8472 66 PALAEONTOLOGY, VOLUME 15 This relationship seems to hold on the flats down to a point (text-fig. 5b) corresponding to a tidal height of about 1 1 feet, after which a second function is operative. However, text-fig. 3 indicates that values of modal shell length on the lower part of the transect may be in error owing to sparsity of individuals, so that it would be unwise to attach undue significance to these two categories. Nevertheless it seems unlikely that tidal cover per se can explain the observed variation completely. The fact that the rate of reduction in growth increases on the most level part of the flats may imply that friction causes a decrease in tidal current velocity here, and hence also in suspended matter on which the cockles feed. Greater turbidity in this region may also be important. The theoretical limit of cockle growth may be determined from the above relation- ship at the point where x = 0. The resulting tidal height of 18-5 feet is only inches above the highest level at which cockles are recorded; which proves that the higher Burry cockles must be ‘stunted’ to a degree which approaches the maximum theo- retically possible. Winter rings. The internal form of a cockle’s first winter ring is governed strongly by its position on the shore; this is seen in both the random (PI. 8) and modal (PI. 9) samples. Because of poor growth during the initial months the high shore shell F. 0 is still very thin during its first winter (PI. 8a) and may already truly be referred to as ‘stunted’ by reference to the longer, much thicker shells from lower on the shore ; the inner complex crossed-lamellar layer is particularly thin compared with F. 14 for example (PI. 8b). The most striking difference, however, is seen in the external width of the winter ring and in the sharpness of its incision into the generally smooth outer shell profile. Shells from the vicinity of low water springs show a relatively shallow trough beneath which growth appears to have been continuous (Pis. 8c, 9e). Moving up the shore this trough becomes more acute, its base being marked by a dark periostracal band extending back into the shell structure. This marks a stoppage of growth when the mantle was strongly retracted. Because of this stoppage, growth before and after is relatively rapid and produces a sharp nick in the highest shore shells (Pis. 8a, 9a), but the lower shore examples show a gradual diminution followed by a gradual increase which produces only a shallow indentation (PI. 9d, e). These wider areas are often more noticeable externally (e.g. F. 21, text-fig. 4) and create an illusion of greater winter susceptibility, in complete contradiction to the internal evidence. One particular aspect of the shell structure is associated with any interruption of the normal pattern of calcification, being especially apparent during the winter. The crossed EXPLANATION OF PLATE 8 Acetate peels showing daily increments during the first autumn and winter in three specimens of Cerastodenna edide selected at random from different stations along Transect F, Burry Inlet : A. High-shore specimen (F. 0) showing disturbance ring and sharp winter ring: shell mueh thinner than lower shore individuals, especially the inner complex crossed-lamellar layer. B. Mid-shore specimen (F. 14) showing markedly cyclical growth pattern, broader winter ring and thicker shell. c. Low-shore specimen (F. 21) showing continuous, uniform growth and very broad winter ring; because of the mueh greater thickness of this shell only part of the outer shell layer can be illustrated. Dark lines in a and b extending baek from the winter rings into the shell structure mark a cessation of growth. Palaeontology, Vol. 15 PLATE 8 FARROW, Periodicity structures in Cerastodenna FARROW: PERIODICITY STRUCTURES IN CERASTODERMA 67 lamellae become extremely prominent, appearing to transgress the growth lines; immediately before the stoppage they extend strongly outwards (PI. 9a) ; after it they appear inconspicuous. Marked deflections in the orientation of the lamellae take place across the dark periostracal band. Disturbance rings. The problem of separating disturbance rings from those of annual origin can be tackled statistically by external growth-ring analysis (Craig and Hallam 1963), though this is a somewhat lengthy procedure. Preparation of an acetate peel of a shell takes only five minutes, and from it the two can be distinguished at a glance even at low magnification. PI. 8a shows an autumnal disturbance ring in the first year of growth; PI. 10a an autumnal disturbance during the second year on the same specimen. Although the interruptions may produce dark bands extending back into the shell structure in the same fashion as truly annual rings, albeit fainter, the disturbance rings are readily diagnosed by their suddenness; revealed by deep, narrow slots in the outer shell profile (rather than the gentle trough-like depressions associated with annual rings) ; and revealed by a stable background of high daily increments on either side of the disturbance (well seen in PI. 10a). Thus, in contrast to the pattern of daily growth preceding winter stoppages, there is no hint in the micro structure of the disturbance to come. Subsequent growth is at a rate identical to that prior to the stoppage, and this is a reflection of some kind of physical rather than biological disturbance, for with a spawning ring, for example, resumption of growth is gradual and background values may not be attained for some weeks (Pannella and MacClintock 1968, PI. 6, fig. 2). Comparison of high and low shore cockles shows that physical disturbances are commonest on the higher parts of the flats; the external expression of an autumn disturbance ring in the first year can be seen on F. 8, text-fig. 4. PI. 10 shows growth during the second autumn for shells from three stations along the transect: F. 0 has a pronounced disturbance ring, but the indentation of the outer shell profile of F. 14 at the same period is scarcely perceptible; F. 21 from low water springs exhibits very uniform growth throughout the period. Physically induced disturbances are severe only during the autumn (Flouse and Farrow 1968; also for cockles inhabiting sand in the Thames, Farrow 1971). The reason for this is to be sought in the equinoctial tides, as is explained in the following section. Cyclicity in the pattern of daily growth. Study of microstructural periodicities demon- strates the close control of tidal cyclicity on the growth of cockles from different transect stations. Again this is shown as well by random samples (text-fig. 6) as by individuals carefully selected from the mode at each station (text-fig. 7). On text-fig. 6 are plotted second year summer and autumn daily increments for the random series of cockles. A 29-day tidally controlled cyclicity can be identified, even in the low shore F. 17, but this becomes attenuated during the autumn with growth stoppages occurring at the beginning and end of each cycle in the high shore F. 0. The modal specimens (text-fig. 7) show that the severity of such stoppages decreases as low water mark is approached; further, it shows that this effect is pronounced only around the time of the equinoctial tides. The probable reason for this is illustrated on text-fig. 8 and outlined briefly below. The higher shore cockles are situated very close to mean high water of neap tides (text-fig. 4), which means that at certain seasons when the tidal range is small the flowing 68 PALAEONTOLOGY, VOLUME 15 tide never reaches them and they may be left high and dry for days on end. The degree to which observed disturbances correlate with predicted occurrences of very low high water is shown on text-fig. 8. Even at other periods some individuals may be covered by only a few inches of water, and during the summer this evidently leads to a dis- turbance of growth (text-figs. 6, 7). Throughout the year it is the resumption of vigorous growth following neap-tide deceleration which produces the marked cyclicity. The reduced effect nearer low water springs enables more continuous growth to take place, •’T V- "n- •’U- TEXT-FIG. 6. Daily increment plots for three shells selected at random from different transect stations, showing summer and autumn growth in the second year. The amplitude of the cyclical growth pattern is considerably greater in the higher shore specunen F. 0 than in F. 17; in the autumn the pattern becomes attenuated as a result of periodic growth disturbances. Shells collected in February 1969; maximum increment = 1 50 /xm. though in the second year individual daily increments are not necessarily greater here than higher on the shore, for shells like F. 21 have already reached a comparatively large size as a consequence of much more prolonged growth during their first autumn than higher shore shells (text-fig. 7) which are still quite small. It is thus possible to relate the amplitude of the cyclicity to position on the shore, values for each lunar cycle being tabulated in Table 1. Variation in the amplitude and attenuation of the cyclicity is thus the key to understanding why the higher shore specimens are stunted. PALAEOECOLOGICAL IMPLICATIONS Two aspects of the Burry Inlet experiment are of especial value to the palaeontologist. First, all specimens studied were collected in life position and the results obtained can thus be applied readily to in situ infaunal fossils. Second, two series of shells were analysed side by side; a random collection of single cockles from unselected transect stations and shells from a quantitative survey which were statistically selected from the modal shell length value for regularly spaced stations. The fact that the results could be EXPLANATION OF PLATE 9 Acetate peels showing cross sections of the first winter ring in modal specimens of Cerastoderma edule from successively lower along Transect F: (a) F. 0 (b) F. 8 (c) F. 12 (d) F. 17 (e) F. 21. Trans- gressive crossed-lamellar structure is particularly evident in the higher shore individuals immediately prior to the winter stoppage. Progressive increase in width of the winter ring with increasing depth is well shown: in the lowest example growth appears to have been continuous, but dark periostracal bands indicating stoppage seem to be present in the remainder. Position of the stations is indicated on text-fig. 4 : Scale bar = 200 ixm. Palaeontology, Vol. 15 PLATE 9 F12 FI 7 FARROW, Periodicity structures in Cerastoderma H H 70 PALAEONTOLOGY, VOLUME 15 compared closely is encouraging for the extrapolation into the fossil record where numbers sufficient for statistical work are but rarely found. The palaeoecological implications of the work are best assessed on two levels. First, that of the individual mollusc. Five minutes spent preparing an acetate peel for the internal analysis of any one shell enables many incidents in the life of that shell to be recognized. Winter rings can be distinguished readily from disturbance rings by their external profile and transgressive crossed-lamellar structure, thus enabling the true life span to be calculated : the season of greatest disturbance may be compared with the season of death : the month with lowest winter water temperature can be obtained from the correlation of pronounced autumnal growth cyclicity with the equinoctial tides. Tidal Range Daily Growth Increments number per cycle days stoppage days HW below critical level (18') TEXT-FIG. 8. Diagram illustrating the probable correlation between the occurrence of very low high tides and the incidence of growth disturbances in cockles from the higher parts of the flats during late summer and autumn of the second year. Daily increments = F. 0 (modal) : tidal values for each spring and neap tide from Whitaker's Almanac (1968) corrected according to Hancock and Urquhart (1966, p. 15). Secondly, implications may be considered at the community level. Here it should prove possible to assess the degree of mixing which has taken place between different faunal elements in dead shell accumulations by utilizing discrepancies in, for example, winter ring characteristics or in the amplitude of growth cycles. In considerations of possible EXPLANATION OF PLATE 10 Acetate peels showing daily growth increments during the second autumn for the three shells illustrated on Plate 8 ; A. High-shore specimen (F. 0) showing cyclical growth pattern and a pronounced disturbance ring, before and after which growth increments are large (cf. winter rings). B. Mid-shore specimen (F. 14) showing cyclical growth but with only a slight indentation in the smooth outer shell profile. c. Low-shore specimen (F. 21) showing the uniform thickness of the growth increments: a cyclicity in the type rather than the thickness of the diurnal bands is apparent if the plate is viewed from the side at a low angle. Palaeontology, Vol. 15 PLATE 10 FARROW, Periodicity structures in Cerastodenna F21 FARROW: PERIODICITY STRUCTURES IN CERASTODERMA 71 Stunting in any fauna internal analysis of periodicity structures may reveal its cause, whether it be a prolonged winter cessation of growth or repeated physical disturbance caused by periodic subaerial exposure. The most novel application of this experiment to the fossil record would undoubtedly lie in palaeotidal analysis. It would be most exciting to extend the semi-quantitative assessment of intertidal environments using amplitude measurements, of the type pre- sented in Table 1, in conjunction with the equation formulated from text-fig. 5. Even extending the use of periodicity structures into sub-tidal regimes is likely to prove TABLE 1 . Variation in amplitude of tidally controlled growth cycles in Cerastodenna edule from stations at different heights along Transect F, Burry Inlet, S. Wales Transect Tidal height number 20 June 19 July 18 Aug. 16 Sept. 15 Oct. Mean of Stations amplitude (inftA- Upper shore {May-Sept.) MLWS) F. 0 10 19 11 13 8 8 13-3 18-8 F. 8* 13 15 8 14 10 7 12-5 18-7 F. 11/12 5 7 8 10 4 5 7-5 17-5 F. 17 5 5 6 7 4 5 5-7 160 Lower shore Amplitude = maximum daily increment— minimum daily increment per lunar monthly cycle (mm x 160); all values represent the average of measurements from text-figs. 6 and 7 except F. 8 * which was obtained from text-fig. 7 only. MEWS (Mean low water spring tide) = —15 ft O.D. (Newlyn). rewarding to judge from the work of Rhoads and Pannella (1970, p. 158, fig. 9) who have illustrated the extremely uniform growth of deep-water molluscs, where spawning dis- turbances replace winter temperature and physical disturbance rings as the most conspicuous interruptions of the normal calcification process. Periodicity in the type rather than the thickness of diurnal increments seems to characterize the growth of those molluscs living in sublittoral habitats which are nevertheless influenced by tidal flux: compare Cerastodenna edule from extreme low water springs (PI. 10c, viewing at a low angle) with Tridacna squamosa (Pannella and MacClintock 1968, pi. 7) and Nucula proxima from —6m (Rhoads and Pannella 1970, fig. 9b). With further examples to act as standards molluscan growth characteristics could become most useful indicators of contemporary water depth in ancient seas. Before having confidence in such esti- mates, however, additional experiments on living molluses must be undertaken. First, there is the question of how widespread is the tidally controlled cyclicity characteristic of the Burry Inlet cockles; it is certainly dilficult to perceive in the Thames fauna where it is swamped by other ecological variables (Farrow 1971). Future studies should be undertaken not only on a wider range of cockle habitats but on a wider spectrum of organisms, for there is no reason to suppose that Cerastodenna should be more prone to physical growth controls than any other carbonate-secreting animal. Acknowledgements. This work forms part of a project financed by the Natural Envffonment Research Council which was carried out under the general direction of Professor M. R. House. Without the generous co-operation of Dr. D. A. Hancock and Mr. A. C. Simpson of the Fisheries Research Laboratory, Burnham-on-Crouch, this paper could not have been written. Mr. K. G. Walker prepared and photographed the acetate peels. An early version of the manuscript was read by Dr. L. F. Penny, whose suggestion of additional mathematical treatment has resulted in major improvement. 72 PALAEONTOLOGY, VOLUME 15 REFERENCES CRAIG, G. Y. and HALLAM, A. 1963. Size-frcqucncy and growth-ring analyses of Mytilus edulis and Cardiurn edide and their palaeoecological significance. Palaeontology, 6, 731-750. FARROW, G. E. 1971. Periodicity structures in the bivalve shell: experiments to estabhsh growth controls in Cerastoderma edide from the Thames Estuary. Ibid. 14, 571-588. HANCOCK, D. A. 1965. Graphical estimation of growth parameters. J. Cons. perm. int. Explor. Mer. 22, 77-90. 1967. Growth and mesh selection in the edible cockle {Cardiurn edule L.) J. Appl. Ecol. 4, 137- 157. and SIMPSON, a. c. 1962. Parameters of marine invertebrate populations. In The Exploitation of Natural Animal Populations. Ed. E. D. le gren and m. w. holdgate, Oxford, 29-50. and URQUHART, A. E. 1966. The fishery for cockles {Cardiurn edule L.) in the Burry Inlet, South Wales. Fishery Investigations, ser. ii, 25, 1-32. HOUSE, M. R. and farrow, g. e. 1968. Daily growth banding in the shell of the cockle, Cardiurn edule. Nature, 219, 1384-1386. PANNELLA, G. and MACLiNTOCK, c. 1968. Biological and environmental rhythms reflected in moUuscan shell growth. In Palaeontological Society Memoir 2, 64-79. RHOADS, D. c. and PANNELLA, G. 1970. The use of molluscan shell growth patterns in ecology and palaeoecology. Lethaia, 3, 143-161. G. E. FARROW Department of Geology The University Typescript received 3 March 1971 Hull THE MECHANICAL PROPERTIES OF BIVALVE (MOLLUSCA) SHELL STRUCTURES by JOHN D. TAYLOR and MARTIN LAYMAN Abstract. Bivalve shells are composed of a two phased composite material consisting of calcium carbonate and a largely protein matrix. The two phases are arranged into a number of distinct shell structures; these occur in discrete layers and their occurrence appears to be correlated with mode of life. Some mechanical properties of individual shell structures were tested; these included compression, bending, impact, and microhardness tests. Density and matrix content were also determined. Some structures were nearly twice as strong as bone. The relative strength is apparently related to the size of the microstructural units rather than to the matrix content, which is low. The possible functional significance of the various shell structures is discussed but it is difficult to see why any structure apart from nacre, which is both the strongest and the phylogenetically oldest, has been evolved. Recently much attention has been given to the mechanical properties of bone (Evans 1957; Currey 1964 and, with a good review, 1970; Bell 1969; and many others) but little attention has as yet been paid to other calcified tissues such as mollusc shells. In spite of the recent aetivity in the study of shell structures the only worker to have con- sidered the microstructure of mollusc shells from a mechanical functional point of view is Wainwright (1969). Having studied the microstructure of molluscan shell materials for some years (Taylor et al. 1969; Kennedy et al. 1969) we were impressed by an apparent correlation between the type of shell structure and the mode of life of the animal concerned. We thus decided to investigate the mechanical properties of these materials in relation to their possible functional significance. The limitations imposed by the mechanical properties of the shell materials may have influenced the course of molluscan evolution; for instance this study might help to explain why certain possible shell coiling forms have never been utilized in nature. The bivalve shell has obviously important functions in the protection of the animal, the maintenance of the mantle cavity and the support of the organs within it. In addition the shell plays an important part in the burrowing and boring processes (Trueman 1968). The shell is as functional as the more widely studied structures such as gills, siphons, stomachs, etc. Wainwright (1969) has stated that the meehanical function of the shell depends upon its ability to resist deformation and failure under environmental stresses; and that two main factors in shell architecture, shape, and construction materials, are involved in determining shell strength. SHELL STRUCTURES The bivalve shell, like bone (Currey 1964), may be considered as a material consisting of two phases retaining their separate identities (Wainwright 1969). The phases are crystalline calcium carbonate in the form of ealcite or aragonite, and an organic matrix consisting largely of fibrous protein. The phases are arranged into various distinct fabrics which are recurrent throughout the Bivalvia and other molluscan classes. The mineralogy and micromorphology of these shell structures have been described in some [Palaeontology, Vol. 15, Part 1, 1972, pp. 73-87.] 74 PALAEONTOLOGY, VOLUME 15 detail by Schmidt (1924), B0ggild (1930), Wada (1961), Wilbur (1964), Wilbur and Simkiss (1967), and Taylor et al. (1969 and in press). The shell structures found in the Bivalvia belong to six main arrangements briefly described below and illustrated diagrammatically in fig. \a-h. Further details can be found in the references cited; the nomenclature is largely retained from Boggild (1930). Simple prismatic structure consists of columnar crystals, polygonal in section, up to 200 ^tm in length and 9-80 /xm in width, but the size is very variable. Each prism is sur- rounded by a sheath of matrix. The prisms are aligned normal to the shell exterior and are usually found as an outer shell layer. Composite prismatic structure consists of very small needle-like crystals 2 /xm in width and up to 10 /xm in length radiating from a central axis which is aligned parallel to the shell exterior. This structure is found only as an outer shell layer. Nacreous structure consists of tablet-like crystallites 2-10 /xm in length and 0-4-3 /xm in thickness, which are arranged in sheets and in section have the appearance of a brick wall. Another variety of nacre has the crystallites arranged into columns (lenticular nacre). Nacreous structures are usually found in the middle and inner layers of shells. In foliated structure the crystalline units are lath-like crystallites 2-4 /xm in width, 0-2-0- 5 /xm in thickness and up to at least 20 /xm in length, and are arranged in side to side contact into irregular sheets which have the same general orientation towards the shell margin and lie subparallel to the inner shell surface. Crossed-lamellar structure consists of lath-like crystals 5 /xm in width and up to 20 /xm in length arranged into lamellae. The lamellae are of variable size but some can be seen with the naked eye ; in adjacent lamellae the crystallites are aligned in opposing direc- tions. Complex crossed-lamellar structure is rather similar to crossed-lamellar, but con- sists of an intergrowth of blocks of crystallites arranged with four principal orientations. Homogeneous structure consists of small granular crystallites up to 5 /xm in diameter with no obvious crystal form. The shell material deposited beneath the muscle attachment areas, the myostracum, has an irregularly prismatic structure. The structures described above are found in discrete shell layers ; certain combinations of structures are recurrent and show a distribution related to the probable phylogenetic history of the class. The morphology of the organic matrix has been extensively studied by Gregoire (1967 with references), and in bivalves mostly consists of lace-like sheets which surround and in some cases are contained within the crystallites. The protein of the matrix resembles the keratin-myosin-epidermin-fibrin group of fibrous proteins (Degens et al. 1967; Wilbur and Simkiss 1968). The variation in amino-acid composition and amino sugars may be related to both phylogenetic and environmental effects. Proteins of the shell matrix group are characterized by a high degree of cross-linkage, a feature which will have an effect on mechanical properties and resistance to disaggregation. Variation in the amount and type of cross-linkage in the various shell structures has not yet been studied, and any possible effects upon shell strength are unknown. Sur- prisingly little is known of the total matrix content of the structural types. Hare and Abelson (1964) gave some general results which indicated a total protein content of 0-l%-5%, varying between various shell structures. The work of Hudson (1967), although based upon more exact layer separation and documentation, examined too few structural types to be of use in the present context. TAYLOR AND LAYMAN: MECHANICAL PROPERTIES OF BIVALVE SHELL 75 h TEXT-FIG. 1. Diagrammatic rep- resentation of the textures of bivalve microstructures as seen in sections normal to the shell surface. (a) Simple prismatic structure (b) Composite prismatic struc- ture (c) Sheet nacreous structure id) Lenticular nacreous struc- ture (e) Foliated structure (/) Crossed-lamellar structure (g) Complex crossed-lameUar structure (b) Homogeneous structure 76 PALAEONTOLOGY, VOLUME 15 METHODS AND MATERIALS The fresh specimens used in the tests were supplied from Plymouth and Millport marine laboratories, with the exception of Tridacna maxima which was collected at Malindi, Kenya. All dry and preserved specimens were from the collections of the British Museum (Natural History). Microhardness. Tests were made on shell layers from seventy species from a wide variety of habitats and geographical localities and exhibiting all the shell structural types. A list of species and localities is available on request. Specimens of separate shell layers were mounted in quick-setting resin, ground flat and polished to 3 ju.m. When the layer to be tested was very thin it was mounted on the surface of the resin and tested without further treatment. Indentations were made with an Akashi microhardometer, a standard Vickers diamond pyramid indenter, and a load of 500 g. Several tests were made for each specimen and the average taken. The material tested was at least five times thicker than the depth of indentation; tests were made at more than five times the indentation diagonal from another indentation or the edge of the specimen. Initially tests were made upon Mytilus edulis to determine the hardness variation within a layer and the effects of age and orientation upon hardness. Fresh, dry, and formalin-preserved specimens were tested in a preliminary survey. Little difference was found between wet and dry, so dry specimens were mostly used in the survey. Considerable variation was found in formalin-preserved specimens. Compression tests. Test specimens of dimensions 8 X T5 x 1 -5 mm were cut using a Capco Q. 35 cutting machine, which produces parallel cuts and ensures accuracy to 0 025 mm. The specimens were glued to a Sindyano base which was attached to a base allowing 90° rotation. The cutting machine was lubricated and cooled by mineral oil which might conceivably penetrate the specimens, but this was unavoidable. The specimens were carefully washed after cutting and fresh specimens kept under water until tested. The length to diameter ratio of the specimens was high, and this may have produced slight bowing which could reduce the values of compressive strengths obtained and also have some effect upon the modulus of elasticity. However, in producing longer specimens the stresses during cutting were reduced. There was little plastic deformation produced by the tests and as the specimen ends were cut parallel the tendency to bow was reduced. The convenience of the larger specimens outweighed the effect of buckling, which was considered to be small. The results are valid for comparative purposes even if the absolute values may have a small error. Testing was carried out using an Instron, an accurate machine with a high elastic stiffness, upon which a load versus compression graph is automatically plotted. A crosshead speed of 0 05 cm/minute was used throughout testing. Both fresh and dry specimens were tested to fracture and the results plotted on a stress/strain curve. Similar specimens were tested to a load below fracture and then the cross head velocity reversed and the load removed. Griffith’s cracks on the specimen surface may influence the fracture strength; although the specimens appeared satisfactory visually the cutting pro- cess may have caused some surface deformation. A sample of nacre without visible banding was there- fore polished on diamond paste to 1 jum, and tested for comparison with the unpolished specimens. Bend tests. Bivalve shells are brittle, and with the equipment available it was not possible to cut specimens in a suitable shape for direct tensile tests. Thus, as in ceramics, the modulus of rupture as determined through bend tests was used to give an indication of tensile properties. For bivalves a three point test was used for convenience, although the superiority of the four point test is recognized. The dimensions of the test specimens were 20 mm in length, 5 nun in width, and T5 mm in depth. The length between the lower knife edges was 16 mm. The cutting of the specimens was carried out on a Capco cutting machine similar to that used for compression tests. Dry and fresh wet specimens were tested. The bending was carried out on a three point test rig with an Instron testing machine. Displacement of the specimen at the load point was automatically plotted against load and the specimens tested until fracture. Impact tests. There was no standard impact testing machine suitable for the testing of bivalve shells. TAYLOR AND LAYMAN; MECHANICAL PROPERTIES OF BIVALVE SHELL 77 Either the machine was too large and lacking in sensitivity or the specimen size and shape were un- suitable. Consequently a simple test machine was constructed which, although unable to give absolute values of the energy absorbed, could give a comparison of the impact resistance of the various shell structures. The apparatus was modified from a crystal cleaver mounted in a wooden frame, with a hammer head replacing the cleaver blade and the specimens held against two blunt edges of metal. Portions of fresh shells containing one or more shell layers and periostracum were tested but as the shells were of different thickness, curvature, and ornamentation little direct information was obtained on shell structures. To obtain results for individual shell layers specimens of single structural types were cut to 5 X 1-5 X 1-5 mm on a Capco cutting machine and tested in both the fresh and dry states. Density. The densities of individual shell structures were measured in two ways; by a standard weighing method and by a titration method using heavy liquids (Embrey 1969). The results obtained were closely comparable. Total organic nitrogen content. A Kjeldahl digestion method was used, followed by steam distillation of the alkali treated digest. Initially this technique was applied on a semi-micro scale using up to 100 mg of shell. In view of the variability of the small quantities of nitrogen detected in some samples the amount of shell subsequently used was increased tenfold. Pieces of individual shell structures were separated out, care being taken to remove all the peri- ostracum. The shell was then digested over low heat with 6 ml of 50% sulphuric acid containing 1 % selenium dioxide plus a small crystal of cupric sulphate. Prior to steam distillation into OOIN sulphuric acid the digest was made alkaline by the addition of 14 ml of ION sodium hydroxide. The quantities involved were within the scope of Quickfit semi-micro apparatus, and although the variation between samples of the same piece of shell structure was still high the limits appeared to narrow with the increased quantity of shell used. Microstrnctiires. Microstructures were studied by acetate peels of polished and etched sections of shells and by reflected light microscopy of polished surfaces. Surfaces and sections were also examined by scanning electron microscopy. RESULTS Compression tests. A graph of load versus compressive strain was automatically plotted during compression testing and then replotted as a stress/strain diagram (text-figs. 2-6). After minor adjustments (bedding down) most specimens exhibited a virtually linear relationship (text-fig. 2). This signifies elastic behaviour with the material obeying Hooke’s law. The modulus of elasticity was obtained from the slope of the stress/strain curve. Deformation was elastic almost up to fracture, with possibly a small amount of ‘plastic’ deformation just before the point of fracture. Slight local deviations were observed in some curves ; these were small and made no difference to the over-all form of the plot but indicated that the mechan- isms of deformation, although apparently corresponding to Hookean elasticity, may be more complicated than for single phase materials. TEXT-FIG. 2. Stress/strain diagram for compres- sion tests on the outer crossed-lamellar layer and the inner complex crossed-lamellar layer of Tridacna maxima. A few specimens exhibited to a small degree behaviour which resembled that of an elastomeric material (text-figs. 3, 4). Materials showing this behaviour were of nacreous 78 PALAEONTOLOGY, VOLUME 15 and homogeneous structures. The elastomeric-like characteristics were exhibited in the homogeneous structure of Arctica islandica in both the wet and dry states, but only in wet specimens of nacre. The single specimen of lenticular nacre examined also showed elastomer-like properties. In these samples a constant value of modulus could not be calculated and the value quoted is an average. TEXT-FIG. 3. Stress/strain diagram for compres- text-fig. 4. Stress/strain diagram for compres- sion tests on sheet nacre of Modiolus modiolus. sion tests on the middle homogeneous layer of Arctica islandica. TABLE 1 . Compression test results Species Structure Condition No. of tests Stress c kg Mean It fracture Std. dev. Strain at fracture X 10-2 Modulus kg ,nm-2 Pinclada maxima Sheet nacre Dry 5 38-2 2-7 0045 0-85 Pinctada maxima Sheet nacre Polished 2 42-3 0044 1-0 Modiolus modiolus Sheet nacre Dry 4 39-3 4-8 0-050 0-80 Modiolus modiolus Sheet nacre Wet 4 33-4 6-8 0 050 0-62 Neotrigonia margarltacea Lenticular nacre Dry 1 30-6 0 036 0-89 Pinctada maxima Calcite prisms Dry 5 23-6 1-8 0-029 0-85 Codakia tigerina Composite prisms Dry 4 10-8 1-4 0-018 0-68 Mercenaria mercenaria Composite prisms/homogeneous Dry 3 23-8 4-6 0-024 0-99 Mercenaria mercenaria Composite prisms/homogeneous Wet 3 31-5 5-2 0-035 0-94 Glycymeris glycymeris Crossed-lamellar Dry 4 13-2 40 0-015 0-93 Glycymeris glycymeris Crossed-lamellar Wet 4 8-33 1-5 0-012 0-74 Tridacna maxima Crossed-lamellar Dry 5 14-5 1-6 0-019 0-78 Tridacna maxima Crossed-lamellar Wet 2 10-9 0-025 0-44 Tridacna maxima Complex crossed-lamellar Dry 6 24-4 5-4 0-032 0-78 Tridacna maxima Complex crossed-lamellar Wet 2 21-3 0-033 0-64 Arctica islandica Homogeneous Dry 6 37-4 5-8 0-043 0-93 Arctica islandica Homogeneous Wet 4 32-4 4-4 0-050 0-90 Pecten maximus Foliated Dry 3 20-3 4-4 0-029 0-74 Pecten maximus Foliated Wet 2 10-2 0-021 0-49 Crassostrea gigas Foliated Wet 3 0-64 0-i 0-005 1-34 The stress and strain at fracture and the modulus of elasticity of the various struc- tures are shown in Table 1 . Several tests were carried out for most structural types. The fracture strength of the various structural types in descending order is nacre, homo- geneous, composite prisms, homogeneous, complex crossed-lamellar, calcite prisms, foliated structure (Pecten), crossed-lamellar, composite prisms (Codakia), and the foliated structure of Ostrea. The two layers were tested together in Mercenaria because of cutting difficulties. A typical result for the specimens which were loaded to about half the fracture stress and then unloaded is shown in text-fig. 5. Only a small amount of ‘plastic’ deformation TAYLOR AND LAYMAN: MECHANICAL PROPERTIES OF BIVALVE SHELL 79 occurred and in all cases the plot for unloading did not correspond to a straight line but tended to follow the load curve, showing a decrease in modulus at low levels of loading. Wet fresh specimens (with one exception) displayed a slightly lower fracture strength than dry shells of the same species, and the modulus of elasticity was also lower. Mercenaria mercenaria showed a higher strength, but this may have been because different proportions of the two layers were tested in the two samples. Extension cms TEXT-FIG. 5. Load/unload diagram for com- pression tests on the sheet nacre layer of Pinctada maxima. TEXT-FIG. 6. Stress/strain diagram of the unpolished and polished specimens of sheet nacre from Pinctada maxima showing the effect of the removal of some surface imperfections. A statistical test for significant differences at the 5 % level between the samples in the wet and dry states (r-test, see Bailey 1959) showed that most structures are significantly different, although two pairs, calcite prisms and the foliate structure of Pecten, and homogeneous and nacreous structures, were similar in strength. The specimens of sheet nacre from Pinctada maxima which were polished to reduce surface cracks before testing showed slightly higher fracture stress and modulus of elasticity than the unpolished specimens (text-fig. 6). Bend tests. The data obtained from the automatically plotted load/displacement curve were used to calculate modulus and strain; these are shown in Table 2. Stress-strain curves are shown in text-figs. 7, 8. Because of the difficulties of cutting large enough test specimens of uniform structure, too few specimens were tested for statistical analysis. The fracture stress was lower for compression tests and the modulus higher. Although the stress-strain plots approximate to a straight line, elastomer-like properties are seen in most cases (text-figs. 7, 8). The nacreous structure in both Modiolus modiolus and Pinctada maxima exhibited a small ‘plastic’ deformation range just before fracture. Again nacre is by far the strongest structure, but homogeneous was much weaker than under compression, being less strong than the crossed-lamellar layer of Tridacna and not much stronger than the prismatic layer of Pinctada. Again by far the weakest was 80 PALAEONTOLOGY, VOLUME 15 the foliated structure of Crassostrea gigas. The fracture strengths of dry specimens were slightly higher than of wet ones. Impact tests. Tests on individual shell layers showed that nacre was again the strongest structure (Table 3). It was followed in decreasing strength by homogeneous, calcite TEXT-FIG. 7. Stress/strain diagram for bend text-fig. 8. Stress/strain diagram for bend tests on sheet nacre from Modiolus tests on the inner complex crossed-lamellar modiolus. layer of Tridacna maxima. TABLE 2. Bend test results Species Structure Condition Load at fracture kg Stress at fracture kg mm~^ Modulus kg mm~'^ Strain XlO-5 Pinctada maxima Sheet nacre Dry 17-6 3608 4-7 7-7 Modiolus modiolus Sheet nacre Dry 1L6 23-8 4-69 5-0 Modiolus modiolus Sheet nacre Wet 104 21-3 3-15 6-7 Pinctada maxima Calcite prisms Dry 4-85 9-94 1-98 5-0 Tridacna maxima Crossed-lamellar Dry 5-75 11-79 3-20 3-68 Tridacna maxima Crossed-lamellar Wet 4-2 8-5 2-1 4-0 Tridacna maxima Complex crossed-lamellar Dry 4-25 8-71 2-57 3-4 Tridacna maxima Complex crossed-lamellar Wet 3-75 7-5 1-9 3-9 Arctica islandica Homogeneous Dry 5-25 10-76 3-11 3-46 Arctica islandica Homogeneous Wet 70 14-35 4-46 3-22 Crassostrea gigas Foliated Wet 0-2 0-41 8-29 1-4 prisms, complex crossed-lamellar, and the very weak foliated of Crassostrea. The tests carried out on larger pieces of shell which had variable thickness and ornament are not listed here, but indicated the additional and maybe overriding effect of shape and ornament over shell structure as a factor controlling shell strength. The behaviour of the foliated structure in Ostrea edulis and PJacima placenta was interesting; in these specimens the cracks were not propagated through the whole structure but a localized hole was punched through the specimen by the test hammer. Microhardness. The results of the microhardness survey of the shell layers are listed under the various shell structure types in text-figs. 9a, b, together with a t-test for TAYLOR AND LAYMAN: MECHANICAL PROPERTIES OF BIVALVE SHELL 81 TABLE 3. Impact results (individual layers) Species Structure Impact number {N) Pinctada maxima Sheet nacre 69 Modiolus modiolus Sheet nacre 38 Tridacna maxima Crossed-lamellar 14 Tridacna maxima (wet) Crossed-lamellar 17 Tridacna maxima Complex crossed-lamellar 17 Arctica islandica Homogeneous 25 Arctica islandica (wet) Homogeneous 28 Pinctada maxima Calcite prisms 24 Crassostrea gigas Foliated 5-5 100 aragonite prisms calcite prisms composite prisms lenticular nacre sheet nacre foliated complex crossed-lamellar crossed-lamellar homogeneous myostraca micro-hardness 200 3Q0 ■- F ' 400 mean & standard error Central junction groove Primary layer approx. TEXT-FIG. 3. Simplified and generalized cross-section of a dissepiment in Cladocora. This is the most basic structural type of dissepiment noted among the Scleractinia to date. The dissepiments in Lophelia are flat and co-extensive, all joining together in the axial area of the corallite to form a flat floor to the calyx. These are the type labelled tabular by Wells (1956, p. F344). All dissepiments in the species studied have certain characteristics in common. The underside of all dissepiments have a central junction line and evidence that the basal, first-formed part of the structure grew centripetally from septa and theca. All dissepi- ments are characterized by an upper layer (extending to the upper surface) that is com- posed of an interferring mass of upward growing spherulites of aragonite needles. The schematic drawing (text-fig. 3) illustrates terminology used with respect to the cross- sectional structure of dissepiments, the primary layer, usually basal, and the upper spherulitic layer. In Manicina (PL 1 8, fig. 2) dissepiments that are ‘parathecal’ also have what has been termed the lower spherulitic layer in the upper portion of the dissepi- ment where it abuts against the theca. Lophelia does not have a primary layer thick Fig. 4 is photomicrograph. Figs. 1-4. Lophelia proUfera, Recent, Blake Plateau, Atlantic. 1, Transverse polished and etched section (same as PI. 1 1 , Fig. 3) with septum at right side of composite micrograph, showing remnant organic material along growth lines, x500. 2, Overview, polished and etched, of theca with stereome, composed of clusters of crystallites, and slightly more porous in the inner portion (ex- treme top of figure), X 50. 3, Portion of fig. 2, enlarged to show differing orientation of crystallites in darker area (above) and lighter area below, x 1000. 4, Photomicrograph (crossed nicols) of stereome (lower arrow), and septa (upper arrow) to illustrate retention of septal structure in secon- darily thickened skeleton, X 25. Figs. 1-6. Manicina areolata. Recent, Florida Keys. 1, External view of epitheca showing growth ridges, X 420. 2, Portion of fig. 1 with greater magnification to show weak expression of crystallites on growth ridges, x 8200. 3, Broken cross-section of epitheca showing algal borings and chevron- like arrangement of crystal clusters, X 1000. 4, View of interior surface of epitheca with subhori- zontal growth lines, and also broken edge at upper right, x 1000. 5, Enlarged portion of fig. 4, to show crystallite terminations on interior face of epithecal sheath, x 5000. 6, Broken cross-section of same specimen showing angularity between crystallite clusters 1, at base of micrograph, 2, in centre and 3, at top, x 2000. EXPLANATION OF PLATE 19 EXPLANATION OF PLATE 20 Palaeontology, Vol. 15 PLATE 19 SORAUF, Lophelia Palaeontology, Vol. 15 PLATE 20 SORAUF, Manicina SORAUF; SCLERACTINIAN MICROSTRUCTURE, ETC. 103 enough to show in etched cross sections, and may not have any at all. Nevertheless, as shown by the central junction groove (PI. 21, fig. 2) and faint growth lines, the method of formation in this genus is apparently the same as in the other genera examined. In genera such as Manicina (PI. 21, fig. 3) and Cladocora (PI. 21, figs. 4, 5), the under- side of the dissepiments show distinct cording of microcrystals, especially adjacent to irregularities or granulations on the septal flanks. Cladocora (PI. 22, fig. 1) shows very well-developed growth lines, with each growth increment considered to be a diurnal one. This would be the result of rapid growth of microcrystals in daylight under the dual influence of zooxanthellae and enzymes, with slower growth in darkness when only enzymal action would aid in the biocrystallization process (as noted by Goreau 1959, p. 72). The upper spherulitic layer is seen in Cladocora (PI. 22, fig. 2) to be composed of rather random, upward oriented spherulites of aragonite, except for a single row of large, very well-developed spherulites situated directly over the central junction groove. This row, called the keystone spherulites after their resemblance to the keystone of an arch (Sorauf 1970, p. 7), can be somewhat exaggerated in their growth and actually form a central ridge on the upper surface of the dissepiment (as in Trachyphyllia, PI. 22, figs. 3, 4). Generally, the upper surface of the dissepiments of shallow water corals are a series of spherulite clusters of aragonite needles which may or may not show a de- pressed centre to the cluster (see Manicina; PI. 22, fig. 5). The lower spherulitic layer noted in Manicina dissepiments (PI. 18, fig. 2) is regarded as the result of the manner of withdrawal of the polypal flesh from this parathecal area (see Sorauf 1970, p. 6). This lower layer decreases in thickness away from the theca, so that the central and lower portion of this steeply tilted dissepiment has the primary layer as its basal (or innermost) part of the plate. The external microarchitecture and internal structure of dissepiments in Lophelia differ from that in shallow water corals, in that growth lines are almost lacking; there is no cording of microcrystals; no visible primary layer can be noted; and the upper surface of the dissepiments are apparently contiguous with a spherulitic sheath covering the septa (PI. 23, fig. 2). The specimen is a deep-water dweller, lacking zooxanthellae. Whether depth of water, absence of symbionts, or genetic differences are most account- able for the marked difference in structure is not yet known. 9. Synapticulae Synapticulae are defined as bars positioned in the interseptal spaces connecting the septa. Their function is varied; they provide a strengthening of the septal blades, they provide a false wall between corallites, and they provide support for the base of the polyp. This last function is perhaps most marked in genera such as Fungia, where synapticulae are large and grow continuously upward as the polyp grows larger. The structure of synapticulae is either compound or simple. Fungia has compound synapticulae, composed of a number of trabeculae; it is thought likely that the com- pound nature of the synapticulae is related to the compound nature of septal trabeculae in this genus. A lateral outgrowth of a compound trabecular bundle would logically be compound itself. The microphotograph (PI. 23, fig. 1) shows more than ten trabecular centres in each synapticula. The ability of the basal flesh of the polyp to form compound centres of calcification has previously been discussed, and is here refleeted in 104 PALAEONTOLOGY, VOLUME 15 the synapticulae. However, each of these trabecular centres is identical in nature (although smaller in size) with the general model of trabecular crystallization centres. Simple synapticulae are well shown in Siderastrea (PI. 15, fig. 1). Rows of the bars are aligned along a single septal trabecula. They apparently result from the enlarge- ment and lateral growth of a trabecula (perhaps due to branching) and are not much different from septal granulations when small. However, they do grow out and join protrusions from the neighbouring septum. Since they are the result of the outgrowth of a single large, simple trabecula, they are simple synapticulae. From time to time, such a completed bar does show the secondary development of an extra trabecular centre. This led Ogilvie (1897, p. 180) to name those bars without any true development of separate trabeculae as pseudosynapticulae, reserving the term synapticula for the form possessing new trabecular centres. This is unnecessary, and I refer to all connecting bars as synapticulae, although recognizing a basic difference between those of the sort seen in Fimgia (compound, with a much greater role in skeletal formation and polypal support) and those in Siderastrea and Porites (simple, with or without great significance in polypal support). The formation of synapticulae in Siderastrea is well illustrated by the two sets of micrographs here presented. A majority of the bars are formed by the simple junction of laterally adjacent septal granulations (PI. 15, fig. 1). The other micrograph here pre- sented (PI. 23, fig. 4) shows a rather extraordinary growth of spherulitic clusters below the synapticular bar. Note also that along the top of the bar there is upward growth of spherulitic aragonite. No reason is apparent for the rather wild, disoriented growth of EXPLANATION OF PLATE 21 Fig. 1. Manicina areolata. Recent, Florida Keys, polished and etched section through epitheca to illustrate chevron-like arrangement of crystallite clusters. At left (outside of epitheca) are seen algal borings, filled by impregnating plastic and left in relief by etching, x 1000. Fig. 2. Lophelia prolifera. Recent, Blake Plateau, Atlantic, with tabular dissepiments, here seen from the underside, illustrating junction line in middle of each, and manner of merging to form a flat floor to the calyx, x 50. Fig. 3. Manicina areolata. Recent, Florida Keys, to show cording of microcrystals in the primary layer on underside of dissepiment, x 200. Figs. 4, 5. Cladocora caespitosa. Recent, Adriatic. 4, View of underside of dissepiment illustrating central junction and growth lines on the undersurface of the primary layer, X 85. 5, An enlarged view of the underside of a dissepiment to show the central junction and crystallites growing towards it, xlOOO. EXPLANATION OF PLATE 22 Figs. 1, 2. Cladocora caespitosa. Recent, Adriatic. 1, Underside, flank of dissepiment with luxuriant crystallite growth occurring with definite periodicity, most likely diurnal, X 4000. 2, Polished and etched transverse section of dissepiment (placed vertically to save space) illustrating primary layer and formation of central keystone spherulites and upper layer of dissepiment (see text-figure), X400. Figs. 3, 4. Trachyphyllia amarantiim. Recent, Borneo. 3, Upper surface of dissepiment illustrating rather smooth matte of crystallite tips and central spherulite ridge, x 50. 4, Enlarged portion of fig. 3 showing clustered crystallites of upper surface slightly tipped towards central ridge apparently composed of a single line of spherulites, x 1000. Fig. 5. Manicina areolata. Recent, Florida Keys, illustrating rather incompletely crystallized spheru- litic clusters, with central depression, that occur on the upper surface of some dissepiments, x 5500. Palaeontology, Vol. 15 PLATE 21 SORAUF, Scleractinia Palaeontology, Vol. 15 PLATE 22 SORAUF, Scleractinia SORAUF: SCLERACTINI AN MICROSTRUCTURE, ETC. 105 spherulites beneath the synapticula; and perhaps it simply represents formation of the structure during a period of extremely rapid growth. Such rapid crystallization could result in excess aragonite clustering in the void space beneath the synapticula. In transverse view (PI. 23, fig. 3), Porites has very simple, symmetrical synapticulae. These bars apparently function to form a porous, weak theca separating the neighbouring corallites. Their occurrence appears random. CONCLUSIONS 1. A workable model of biocrystallization has resulted from the studies of Goreau (1959, 1961), Bryan and Hill (1941), and Vahl (1965). Aragonite needles comprising the skeleton grow directly into neighbouring mucopolysaccharide-like material, most often in spherulitic clusters. The mucopolysaccharide may act as a template controlling the microarchitecture of the exoskeleton. Several problems exist in the blanket applica- tion of this model, particularly the presence of what are thought to be muscle scars on septa (Wise, 1970), and spatial problems that result wherever spherulites grow together to form a tight junction, as in septotheca. 2. The basic unit of septal construction is the trabecula, a modified spherulite, formed within an up-pocketing of the basal ectoderm of the coral polyp. Around the framework of trabeculae are formed clusters of spherulitic aragonite. Trabeculae generally are arranged in some modification of a fan shape. Trabeculae are either simple or compound and form, together with additional spherulitic aragonite, the larger ‘blades’ seen in several genera. 3. The microarchitecture of the septal flanks is apparently of considerable taxonomic use in the Recent Scleractinia. In Fungia clusters of aragonite microcrystals are arranged in an overlapping scale-like fashion, while most Faviids {Manicina, Trachyphyllia) generally show clusters of microcrystals (fasciculae. Wise 1970) but no easily recognized pattern to these clumps. In the Dendrophyllid Astroides caiycularis, no pattern was apparent. The Caryophyllid Lophelia prolifera is characterized by sheaths of spherulites coating the blade-like septal centre. 4. Pali and ribbon-like columellae can be regarded as extensions of the trabecula- forming processes into the axial part of the corallite. The former are composed of easily recognized trabeculae while the latter are ribbons of spherulitic aragonite in Astroides. 5. The theca (wall of the corallite) forms in the ways characterized by previous work (Wells 1956, p. F346). Septotheca is formed by spherulitic outgrowths from neighbour- ing septa and are thickened within a pocket formed by the internal and external basal flesh of the polyp. Synapticulotheca is porous when formed of rings of synapticulae, but where these elements are coalesced, as in Siderastrea, the resulting structure is indistinguishable from septotheca. Paratheca in Manicina is formed of a septothecate portion and accessory dissepiments which are subvertical and contain an extra, internal spherulitic layer when compared to subhorizontal dissepiments. 6. Coenosteum, as noted in Astroides is remarkably similar in configuration and structure to the ribbon-like columella in this genus. 7. Stereome, as seen in Lophelia is composed of transverse bundles of aragonite needles varying in orientation one bundle from another. The formation of this is 106 PALAEONTOLOGY, VOLUME 15 apparently due to action of the peripheral edge zone of the polyp, but is not well understood. 8. Epitheca, present only in Manicina among the species studied, is composed of sub-horizontal crystallites which have a chevron-like appearance in transverse section. The crystallites have grown from the outside in, although the apparent growth of the epitheca itself is upward. 9. Dissepiments are constructed of a first-formed primary layer with an overlying upper spherulitic layer. The primary layer grew centripetally from septa to a central junction line. The upper spherulitic layer is composed of vertically oriented aragonite spherulite clusters, with a keystone row of spherulites aligned over the central junction of the dissepiment. Growth lines are readily apparent on the undersurface of shallow water corals studied. Tabular dissepiments in Lophelia, a deep water coral, are markedly different from others in that no growth lines or primary layer can be observed, and the spherulitic layer is continuous with a spherulitic sheath coating the septa. Manicina, in its parathecal dissepiments, has a lower spherulitic layer below (inside of) the subvertical primary layer. This lower spherulitic layer is only present in the area near the theca and indicates a somewhat different mode of origin from that in other genera. 10. In their simplest form, synapticulae are the junction of gradulations on opposing septal flanks, as in Sidemstrea. In Fiingia, synapticulae are formed of a multiplicity of trabeculae and play a much more important role in polyp support and wall construction. Acknowledgements. The laboratory work and electron microscopy for this study was carried out at the Institute for Palaeontology in Bonn, Germany due to the kind hospitality and help of Dr. H. K. Erben. The writer is also grateful to Dr. Heinrich Ristedt who aided greatly with advice and helpful discussions regarding microscopy and biocrystallites, and to Miss Ch. Klatt who aided greatly in the technical and photographic aspects of the scanning electron microscope. Dr. Paul Enos of S.U.N.Y. at Binghamton provided editorial comment on the manuscript. The research in Bonn was carried out during a sabbatical leave from State University of New York at Binghamton, with financial aid of the Research Foundation of State University (Joint Awards Council, Grant no. 40-251-A) and the Alexander-von-Humboldt Foundation of Bad Godesburg, Germany (Research Fellowship). I am sincerely grateful to those who made this aid possible. REFERENCES ALLOiTEAU, J. 1957. Contribution d la Systematique des Madreporaires Fossiles. 462 pp. C.N.R.S., Paris. BARNES, D. J. 1970. Coral skeletons: an explanation of their growth and structure. Science, 170, 1305- 1308. EXPLANATION OF PLATE 23 Fig. 1 is photomicrograph. Fig. 1 . Fungia sciitarea. Recent, Pacific, photomicrograph (crossed nicols) illustrates compound nature of synapticulae (arrows), with upwards of 10 trabecular centres evident in each, x25. Fig. 2. Lophelia prolifera. Recent, Blake Plateau, Atlantic, polished and etched section to show sheath of crystallites (at right) coating septum (far right) and contiguous with dissepiment at left, x 500. Fig. 3. Porites porites. Recent, Florida Keys, polished and etched section of very simple, symmetrical synapticulae formed by junction of septal trabeculae outgrowths, x 850. Fig. 4. Siderastrea radians. Recent, Florida Keys, polished and etched section to illustrate continued and disoriented growth of spherulites under synapticula, x 450. Palaeontology, Vol. 15 PLATE 23 SORAUF, Scleractinia SORAUF: SCLERACTINIAN MICROSTRUCTURE, ETC. 107 BRYAN, w. H. and HILL, D. 1941. Spherulitic crystallization as a mechanism of skeletal growth in the hexacorals. Proc. R. Soc. Qd. 52, 78-91. GOREAU, T. F. 1959. The physiology of skeletal formation in corals. 1. A method for measuring the rate of calcium deposition by corals under different conditions. Biol. Bull. mar. biol. lab. Woods Hole, 116, 59-75. 1961. Problems of growth and calcium deposition in reef corals. Endeavour, 20, 32-39. KATO, M. 1963. Fine skeletal structures in Rugosa. /. Fac. Sci. Hokkaido Univ. ser. iv, 11, 571-630. 1968. Note on the fine skeletal structures in Scleractinia and Tabulata. Ibid. 14, 51-56. MA, T. Y. H. 1937. Growth rate of reef corals and its relation to sea water temperature. Pal. Sinica, B, 16, 1-226. OGiLviE, M. 1897. Microscopic and systematic study of madreporarian types of corals. Phil. Trans. R. Soc. B, 187, 83-345. SCRUTTON, c. T. 1965. Periodicity in Devonian coral growth. Palaeontology, 7, 552-558. SORAUF, J. E. 1970. Microstructure and formation of dissepiments in the skeleton of the recent Sclerac- tinia (hexacorals). Biomineralization, 2, 1-22. STETSON, T. R., SQUIRES, D. F., and PRATT, R. M. 1962. Coral banks occurring in deep water on the Blake Plateau. Am. Mus. Novit. 2114, 1-39. VAUGHAN, T. w. and WELLS, J. w. 1943. Revision of the suborders, families, and genera of the Sclerac- tinia. Spec. Pap. Geol. Soc. Amer. 44, 363 pp. VAHL, J. 1966. Sublichtmikroskopische Untersuchungen der Kristallinen Grundbauelemente und der Matrixbeziehung zwischen Weichkorper und Skelett von Caryophyllia lamarck 1801. Z. Morph. Okol. Tiere. 56, 21-38. WAiNWRiGHT, s. A. 1964. Studies of the mineral phase of coral skeleton. Expl. Cell Res. 34, 213-230. WELLS, J. w. 1956. Scleractinia. F328-F444. In moore, r. c. (ed.). Treatise on Invertebrate Palaeon- tology, Part F Coelenterata, Kansas, 498 pp. 1963. Coral growth and geochronology. Nature, Fond. 197, 948-950. 1969. The formation of dissepiments in Zoantharian Corals. In Campbell, k. s. w. (Ed.), Strati- graphy and Palaeontology: Essays in Honour of Dorothy Hill. Canberra. 1969, 17-26. WISE, s. w. JR. 1970. Scleractinian coral exoskeletons: Surface microarchitecture and attachment scar patterns. Science, 169, 978-980. J. E. SORAUF Department of Geology State University of New York Binghamton New York, 13901 U.S.A. Typescript received 25 March 1971 ON ARBERIA WHITE, AND SOME RELATED LOWER GONDWANA FEMALE FRUCTIFICATIONS by J. F. RIGBY Abstract. The genus Arberia White and its type species Arberia minasica White are redefined, and are shown to be female pteridospermous fructifications that bore large numbers of naked ovules on pinnate branchlets arranged laterally along a forked rachis. It forms the basis of the family Arberiaceae. Other similar fructifica- tions from Santa Catarina, Brazil, and New South Wales, Australia, are also mentioned, but are not named. The Lower Gondwana, or Glossopteris Flora is typified by an abundance of leaves belonging to the form genera Glossopteris and Gangamopteris. The original authors and many of their early successors considered these leaves to belong to ferns. White (1908) was the first to consider them to be the leaves of pteridosperms. With the description of attached fructifications by Plumstead (1952) and a large variety of non-pteridophytic cuticles by Srivastava (1956) their spermophytic affinity was confirmed. The fructifica- tions described here are, in my opinion, more closely related to the pteridosperms than to any other group of seed-bearing plants, and although isolated, I think they belong to plants bearing leaves of the Glossopteris-Gangamopteris alliance. I shall treat these fructifications as pteridospermous but I am aware that the discovery of more material may indicate some other affinity. LOCALITIES Specimens from localities in the State of Santa Catarina, Brazil, and New South Wales, Australia, are discussed. All localities are in rock units of Lower Gondwana age. The standard Lower Gondwana sequence in Santa Catarina (omitting some units) is; Passa Dois Group Estrada Nova Eormation Irati Eormation Tubarao Group Palermo Formation Rio Bonito Formation Treviso Coal Barro Branco Coal Camada Irapua Ponte Alta Coal Camada Joaquim Branco Orleaes Formation The corresponding sequence in the lower Flunter Valley of New South Wales is: Newcastle Coal Measures Tomago Coal Measures Maitland Group Greta Coal Measures Dalwood Group Information concerning the Brazilian localities is detailed, but for the Australian [Palaeontology, Vol. 15, Part 1, 1972, pp. 108-120, pis. 24-26.] RIGBY: ARBERIA WHITE 109 localities is based entirely on the museum card accompanying the specimen, which is the only information available. Description of the individual localities follows. Bainha. This locality is named after a suburb of the city of Criciuma, state of Santa Catarina, Brazil. The locality occurs in mudstones of the Camada Irapua, Rio Bonito Formation of the Tubarao Group, in a cutting on the western side of Rua Dr. Joao Pessoa approximately 1,150 metres from the corner of Pra?a Dr. Nereu Ramos. It was discovered by Sr. Aristides Nogueira da Cunha of the Divisao de Geologia e Minera- logia, Departamento Nacional da Produ9ao Mineral, Rio de Janeiro (Dolianiti 1946). Laiiro MiiUer. I. C. White (1908, p. 65) reported the discovery of a locality as ‘Joaquim Branco Plant Bed. Along the Estrada Nova, one-half kilometer north of the railway station at Minas . . .’ (Minas was the old name for the city now known as Lauro Muller). D. White (1908) reported many species in lots 3586 and 3921. Flis list of fossils agreed with the list given by I. C. White, although he (D. White, p. 357) described the locality in the English text as ‘Northeast of Minas; 55 meters above the granite, or 225 meters below the Iraty (Irati in modern orthography) black shale’. The Portuguese text uses ‘noroeste’ which is correct. Throughout the text ‘noroeste’ has been consistently trans- lated as ‘northeast’ hence discrepancies between the locality information given by I. C. White and D. White have never been apparent to Brazilian geologists. These papers are written in both English and Portuguese, with the English text compiled by I. C. White or D. White on the odd numbered pages and the Portuguese text compiled by E. P. de Oliveira on the facing, even numbered page. Oliveira has been credited as translator. Mendes (1952, text-fig. 2) has given a columnar section based on the data of I. C. White. In this section the Lauro Muller fossil locality is identified as ‘(I) Fossil Plants’. This locality was the source of all D. White’s specimens of Arberia minasica. My material is based on collections made over the last 25 years by staff members of the University of Sao Paulo. Barro Branco. Dr. Yoshida of the University of Sao Paulo, who collected the speci- mens, informed me that the locality is situated along the Lauro Muller to Barro Branco road, about two kilometres from Lauro Muller, and probably immediately underlying the Camada Bonito of the Rio Bonito Formation. Putzer (1955) has described the geology for the above parts of southern Santa Catarina. Adamstown. This is a suburb of Newcastle, New South Wales, Australia. East Maitland is approximately 16 miles to the west of Newcastle. No information con- cerning the location of the plant localities or the collectors is available. All rock out- crops at Adamstown are sediments of the Newcastle Coal Measures; those at East Maitland are of the underlying Tomago Coal Measures. The approximate geographical coordinates of these localities are: Bainha: W 49° 22', S 28° 4T; Lauro Muller: W 49° 24', S 28° 24'; Barro Branco: W 49° 24', S 28° 25'; Adamstown: E 151° 43', S 32° 57'; East Maitland: E 151° 36', S 32° 46'. Specimens prefixed by DGP 7/ are housed in the Cadeira de Paleontologia, Instituto de Geociencias e Astronomia, Univeridade de Sao Paulo, and by NSW are housed in the Mining Museum, Sydney, New South Wales. 110 PALAEONTOLOGY, VOLUME 15 PRESERVATION OF SPECIMENS The specimens described here are all preserved in rather soft rocks. Those from Bainha are in a pink to brown claystone, as are some of those from Lauro Muller and Barro Branco but others are in a yellow or orange argillaceous sandstone. The Australian specimens are in similar but slightly harder rocks. In every specimen the original organic or coaly substance has vanished entirely. In some it has left a cavity which is purely an impression but in others the substance has been replaced by a powdery pinkish mineral. The surface may show some fine features, but there is no possibility of preparing a cuticle or of demonstrating internal anatomy. DESCRIPTIVE TERMINOLOGY The fructifications are thought most likely to be pteridospermous. They are all described as megasporophylls consisting of a primary rachis, which may fork but may not. The rachis and its forks branch in an irregularly pinnate manner and the secondary branches may themselves bear a branch of considerable size. The rachis, its forks, and its branches all bear ultimate branchlets and those may end in an ovule or be sterile. They never have a lamina. The ovules are of various sizes and the small ones are con- sidered to be immature. It is impossible to say whether the large ones have been pol- linated or fertilized; if they were fertilized they would qualify for the description as seeds, but I disregard this possibility and call them all ovules. DESCRIPTION OF NEW MATERIAL FROM BRAZIL The specimens described here are in various stages of development, but as they appear to have been shed before growth was complete, they represent abortions. As is shown below they form a sequence grading from one form to another, hence they may be assumed to show various phases of normal development. 1. Specimens from Lauro Miiller The specimen DGP 7/1060 shown in PI. 24, fig. 1 is one of the best. Its thick rachis forks and bears small ultimate branchlets one of which shows a small ovule 2-5 mmx 2T mm near the top, and there seem to be several others but they are less clear and complete. All these ovules are small and are considered young. The rachis and its branches are longitudinally striate, the coarser striations being obvious, but there are also fine ones at 5 per mm. These striations have a wavy course and branch and fuse. The coarse and fine striations are useful in indicating the direction of a branch which might otherwise be doubtful as there is much overlap. PI. 24, fig. 7 (specimen DGP 7/1061) shows parts of two fructifications, one overlying the other. They are, like the one in fig. 1, mineral replacements. The main vertically orientated one bears a small ovule near its top; the fine striations of the branchlet bearing it indicate some twisting. This main specimen resembles Millan’s Dolianitia opposita (his 1967 pi. 1, fig. 4) and also his D. alternata. The fragment in PI. 26, fig. 3 (specimen DGP 7/1062) shows four of the ultimate branchlets which bear no other structures. This fragment is like that of D. White RIGBY: ARBERIA WHITE 111 (1908, pi. 8, fig, 8). There are also a number of poorly preserved specimens from this locality. 2. Two specimens from Barro Branco One of these is seen in PI. 24, fig. 2 (specimen DGP 7/1063); it is very unusual but linked with normal ones by intermediates. I take it to be the youngest specimen of all. The secondary branches (pinnae) are here very short and curve back over the main rachis with the undeveloped ultimate branches appearing as marginal lobes. The second specimen is a poorly preserved collection of branchlets and ovules. 3. Specimens from Bainha The specimen in PI. 24, fig. 3 (DGP 7/1064) is taken as slightly older than the previous specimen (DGP 7/1063). The rachis is wide but broken off at its top (by a fold towards the observer). Secondary branches along the margin are still very short. Over the sur- face of the rachis there are some tiny lumps which may be the rudiments of ultimate branchlets. They are in oblique rows which are consistent with a spiral arrangement; but since very similar oblique rows are to be seen in the other direction they are equally consistent with alternating rows, if indeed their arrangement is regular. The specimen in PI. 24, fig. 4 and also shown in text-fig. 1e (DGP 7/1065) has an un- forked rachis and has strongly striated secondary branches bearing rudimentary ultimate branchlets. The striations of certain branchlets (drawn in 1e) show a slight curve which perhaps recalls faintly that of a young fern pinna. The fine specimen in PI. 24, fig. 5 (DGP 7/1066) has an unforked rachis. The ultimate branchlets are borne both marginally and across the face of the rachis. If their arrange- ment is truly regular then perhaps they are in whorls with alternating members. The tips of the ultimate branchlets are folded, the folding is taken as an extension of the curving in the previous specimen. The specimen shown by Feistmantel (1881, pi. 28, fig. 5) is similar except that the ultimate branchlets are longer; this was renamed A. indica by D. White. Also White’s figure of A. minasica (reproduced here on PI. 25, fig. 3) is the lower part of a sporophyll with still longer lobes. Specimen DGP 7/1067 in PI. 24, fig. 6 is taken to be similar but with distinctly more developed pinnae. The lowest on the left terminates in a structure suggesting the upper part of an ovule which is not obvious in the figure; the other pinnae are folded. Some branchlets arise across the face of the unforked rachis. I suppose that the specimen in PI. 24, fig. 8 developed slightly differently. Here the main rachis forks and the pinnae are longer but the ultimate branchlets are very feebly developed. This specimen had been figured earlier by Rocha-Campos (1967, pi. 33, fig. 4), as Pluma sp., a determination made by Yoshida. Three of Millan’s (1967) speci- mens of D. opposita look to me very similar (Millan, pi. 1, figs. 1, \a, 5; pi. 2, fig. 1; the first is the type of the species and genus). Some of his other specimens look slightly different but in my judgement ought not to be separated as different species without much clearer evidence. For reasons that will be discussed in the systematic portion of this paper, specimens with a distinctly forked rachis and with pinnae arranged marginally are considered to be examples of Arberia, such as this specimen, whereas the few speci- mens lacking the forked rachis and having branchlets both along the margins and across the face of the rachis (e.g. PI. 24, figs. 3, 5, 6) are excluded. 112 PALAEONTOLOGY, VOLUME 15 TEXT-FIG. 1. Arberia minasica White, a-d, show interpretation of the function of growing points, natural size. The symbols indicate: A, developing non-ovulate pinna; o, developing ovulate pinna; •, ovule. A, Specimen DGP 7/1069, an expanded but immature example, b. Specimen DGP 7/1070, an expanded, mature specimen showing ovules in various stages of growth, c. Specimen forming the counterpart of DGP 7/1070, drawn as a mirror image; branching pinnae do not correspond entirely with those shown on b because branching in upper part of fructification is so complex, d. Specimen DGP 7/1077, showing complexity of branching. E-K show superficial features of growing points at various stages of development, x 2. e. Specimen DGP 7/1065, showing more closely spaced lineations at unexpanded tips, f. Specimen DGP 7/1069, showing a folded and an unfolded tip; most lineations connect base of fructification with growing points, but a few join one growing point with the lineations leading to higher growing points, g. Specimen DGP 7/1070, a folded pinna, h, Specimen DGP 7/1069, showing typical pinna forms before elongation becomes significant; the upper is considered to be a developing ovule, and the lower a sterile pinna, i, Specimen DGP 7/1076, showing elongated pinna lobes of smaller size than in the previous specimens, this may be of specific significance ; the slight lobe on right of lower pinna showing lineations is probably the beginnings of a branch. J, Specimen DGP 7/1070 (counterpart), where a definite boundary has developed between the pinna and the ovule, k. Specimen DGP 7/1070; lower ovule appears to be terminal on a pinna, whereas upper ovule is attached to lower side of a pinna. RIGBY: ARBERIA WHITE 113 The specimen in PI. 25, fig. 1 has both a more or less fully developed rachis and pinnae. The pinnae themselves fork or give off a strong branch, and the ultimate branchlets are expanded and many end in a swollen tip, a young ovule. Others end without a swelling and are evidently sterile. An analysis of this specimen is given in text-fig. 1a where young ovules and sterile branchlets are distinguished while text-fig. If shows two tips with their striations, one tip being folded, the other flat. The specimen in PL 25, fig. 2 is still older and is regarded as almost mature. Here some of the ovules are distinctly larger than others. The specimen is analysed in text- fig. 1b for developed ovules, small ovules, and sterile branchlets. It is possible that the larger ovules have already been pollinated and even fertilized in which case they would be seeds, but on analogy with what we know of certain other pteridosperms where fertilization occurred long after the ovules were shed, it is best to call them ovules. Two of the larger ovules are shown in detail in text-fig. Ik; the upper appears to be on the face of some sort of disc which is possibly a development from the smaller ovule shown by text-fig. 1j; but the effect may have been produced by folding. The lower ovule appears to be pendulous on the end of a short stalk. The counterpart of this specimen is represented in text-fig. Ic, but for convenience in comparison a mirror image has been made. Some of the ovules and branchlets are evidently the same but others are different because some of the crowded branchlets had lain in a different plane and so do not appear in text-fig. 1b. The specimen identified as Baiera from a Glossopteris- Vertebraria association in Queensland by White (1961, p. 1, figs. 5, 6) is closely similar to the right-hand upper branch of my specimen. Another specimen (DGP 7/1077; text-fig. Id) has nearly all its branches terminated by ovules, and 1 feel sure that all branches were at least potentially fertile. It is evident that there is not only variation in the stage of development, but the details of branching vary from specimen to specimen. Specimen DGP 7/1071 (PI. 25, fig. 4) has its secondary branches (pinnae) all emerging from the rachis in the same plane, but the ultimate branchlets are in different planes; for instance the lowest pinna on the right has one branchlet ending in a swelling but the other projects downwards and backwards into the rock. The rather large primary rachis (DGP 7/1072; PI. 25, fig. 5) has laterals on which no further branching can be recognized; probably it is a fragment of a large sporophyll apparently larger than the sporophyll DGP 7/1070 (PI. 25, fig. 2). Millan (1967, pi. 3, figs. 3, 3a; pi. 4, figs. 2, 2a) illustrated two rather similar specimens as D. crassa. A better specimen of similar appearance is shown in PI. 25, fig. 6 and to me resembles D. crassa of Millan (pi. 3, figs. 2, 2a). Another similar specimen (not figured) looks like that of Plumstead (1958, pi. 23, fig. 1) named Plimia longicaiilis male, but there is cer- tainly not enough evidence to identify Pluma with Arberia, and I do not do so. The speeimen in PI. 25, fig. 7 is, I presume, a detached pinna bearing several ovulate ultimate branchlets. The enlarged tips look as though folded, but after removal of a small fragment of a tip, it can be seen that this appearance is not caused by a fold but is merely a groove between the stalk and the rounded head. Lundqvist’s specimens (1919, pi. 1, figs. 25, 26, 29) have similar or slightly smaller ovules, but they differ in showing a broad border (sareotesta) not seen in any of mine. I think therefore that his specimens which he named 2 A. brasiliensis are most probably distinct. The fragment in PI. 26, fig. 1 has similar ovule-bearing branchlets. One on the right I C 8472 114 PALAEONTOLOGY, VOLUME 15 has a distinct rim where the ovule meets its branchlet and this clearly corresponds to the grooves in the previous specimen. There is apparently a differenee in the internal tissue at this point but the fine striations which I suppose are more superficial cross unbroken from the branehlet to the ovule (text-fig. li). I consider it unwise to suggest a determination for these ovules as features normally used for even generic identification of isolated seeds are not apparent. A wide variety of isolated seeds are known from these loealities (Millan 1965). D. White (1908, pp. 540- 541) thought the seeds he named Cardiocarpon {Samaropsis) Seixasi probably were derived from fructifieations of Arberia minasica. DEVELOPMENT OF THE MEGASPOROPHYLL AND OVULE I have interpreted the series of specimens that I determine as A. minasica as being’at various stages of growth and development. I suppose that the parent plant dropped many of its fruiting megasporophylls at early stages as do many modern trees. These are thus abortions whieh though reflecting normal development may not be exactly young stages of any normal and fully functional organ. After this warning I proceed to treat the specimens as a normal sequence, though being aware that certain deviations are caused by the earlier failure of nutrition of some parts before the whole organ fell and perished. The first part to develop is the broad raehis. We do not know how thick its substance becomes, but it was probably not cylindrical. The raehis presumably either forks (dichotomizes) or else remains simple when very young and of minute size. We have no specimen illustrating this. No doubt also the lateral branehes (pinnae) originate early, the first we see of them are short outgrowths which bend back over the sides of the raehis (PI. 24, fig. 2). These laterals may remain simple or may themselves branch by more or less equal forking (PI. 24, fig. 3). Still later little outgrowths develop on the pinnae (PI. 24, fig. 4) and sometimes on the face of the main raehis (PI. 24, fig. 5) and these are the ultimate branehlets. At first they are short and their ends bend back (PI. 24, figs. 5, 6), EXPLANATION OF PLATE 24 All figures twice natural size. Figs. 1, 2, 4, 7, 8. Arberia minasica White. 1, Expanded specimen with a few ovulate structures; fine lineations cover the entire organ, coarse lineations or sulci lead upwards to margins of pinnae; DGP 7/1060, Lauro Muller. 2, Juvenile form with folded marginal lobes along the broad raehis which are pinnae; apex broken along a fold coming towards the viewer; DGP 7/1063, Barro Branco. 4, Juvenile form in a more advanced stage than the previous specimen ; pinnae have commenced unfolding, the folded lobe always lying on the basal side of the pinna; DGP 7/1065, Bamha. 7, Upright specimen on the left is a raehis with the upper, forked portion missing, small ovules are developing; the broad axis lying diagonally in the upper right is a fragment of another fructification; DGP 7/1061, Lauro Muller. 8, Specimen showing a well developed fork in the raehis; pinnae are still unfolding; DGP 7/1068, Bainha. Figs. 3, 5, 6. Arberia-Yike fructifications. 3, Much larger specimen than in fig. 2 showing unfolding of the pinnae; upper part of the raehis is folded towards the viewer; tubercles present across the front of the raehis suggest that branches may have been present; DGP 7/1064, Bainha. 5, More elongated specimen than shown in fig. 4, but the base is not broken; pinnae arise both marginally and across the face of the raehis; DGP 7/1066. 6, Unusually elongated specimen; pinnae almost completely unfolded; DGP 7/1067. Palaeontology, Vol. 15 PLATE 24 RIGBY, Lower Gondwana fructifications RIGBY: ARBERIA WHITE 115 but later they elongate and also straighten (PI. 25, fig. 1). Many fail to develop further; this may be a common and normal feature of Arberia or may reflect the beginning of the failure of nutrition of that speci- men. If successful, however (PI. 25, fig. 2), the swelling enlarges and becomes an ovule and this it seems is not necessarily terminal but may be placed on the side of its branchlet just before its end (text-fig. Ik). At the base of the larger ovules a transverse groove forms marking it off from the branchlet, and this I imagine is caused by the development of a stone inside the ovule. There is no evidence to show at what stage of ovule growth pollination might occur, or fertilization, but if Arberia is like the better known pteridosperms fertilization would occur after the ovule had fallen off. The largest ovules are rounded, 6 mm wide, and 8 mm long, but unfortunately their form in section, round or flat, is unknown and the micropyle is not recog- mzable. They do not seem to have possessed any soft specimen oi Arberia minasica White, layer around their stone or this would have formed based largely on specimens DGP 7/ a rim of compression. We know nothing at all of the 1070 and DGP 7/1077. A number of further history of the fructification. branched pinnae in the background, near the top, have been omitted from the figure for clarity. Irregularities as SYSTEMATIC POSITION OF ARBERIA shown here departing from the pin- nate form have been caused by If the whole specimen is a megasporophyll, that is crowding from swollen ovules and an ovule-bearing leaf which branches in a pinnate hoiri much-branched pinnae, manner, it follows automatically that it is to be placed in or near the pteridosperms. There is no other class that could accommodate it. As first defined the class Pteridospermae had a fairly precise meaning but a considerable variety of fossils have been placed in it without its redefinition and its meaning has become unfortunately vague. Clearly my preserved specimens give me no basis for redefining it but I merely say that by pteridosperm I mean a plant bearing its gymnospermous ovules terminally on pinnately branching structures. Of course the other organs have characters too but the present work does not deal with them. The pteridosperms include many diverse genera which have been placed in a number of families which largely, no doubt because they are imperfectly known, have only obscure relationships. Arberia is a single organ. Relationships obviously pertain to whole plants and not to single organs. We do not even know its leaf. I think specially of Glossopteris and Gangamopteris which are both associated with it but have no proof of connection. Arberia does not resemble the better-known attached glossopterid fructifications such as Seutum, Lanceolatus, and Ottokaria. The fructification does not belong to the same plant as the cordaitalean leaves, Noeggerathiopsis, as it does not resemble known cordaitalean fructifications where megasporophylls occur on short shoots as in Cordaianthus pseudojiuitans (e.g. see Florin 1944, pi. 173/174, fig. 10 and text-fig. 45). 116 PALAEONTOLOGY, VOLUME 15 Arberia does not lie within established pteridosperm families as the fructification lacks any evidence of pinnules or cupulate structures. The ovules are not arranged on a peltate disc. Comparison with the family Medullosaceae is not possible as there single ovules replace occasional pinnae. Family arberiaceae fam. nov. Diagnosis. Female fructifications of branched or unbranched rachis bearing laterally inserted pinnae which are simple, bifid or multifid with terminal or laterally placed solitary ovules. Pinnules with a lamina, cupules and other sterile structures absent. Type genus. Arberia White. Genus arberia White, emend. 1908 Arberia White, pp. 536-539. Emended Diagnosis. Small megasporophyll having a relatively broad, longitudinally striated rachis, usually forking towards the apex. Rachis pinnate; pinnae commonly forked, and bearing ultimate branchlets along their margins, the lowest being lateral to the pinna, but terminally forming a group by frequent apical forking. Pinnae branch- lets simple, either sterile and forming short rods, or fertile and ending in a rounded ovule situated on its surface either terminally or just below its apex. Ovule with a hard layer but no wing or outer flesh, micropyle not observed. No lamina developed at all. (No microscopic details of sporophyll or ovule known.) Type species. Arberia minasica White. Arberia minasica White, emend. Plate 24, figs. 1, 2, 4, 7; Plate 25, figs. 1, 2, 4, 6, 7; Plate 26, figs. 1, 2, 4; Text-figs. 1a-1k 1908 Arberia minasica White, pp. 540-543, pi. 8, figs. 8-10. 1961 Frond of Baiera, in White, pp. 1-2, figs. 5, 6. 1965 Ottokaria-\ik.Q head; Pant and Nautiyal, pp. 623-624 (pars), figs. 5, 6. 1966 OttokariaAike head; Pant and Nautiyal, pp. 98-99, fig. 1 only. 1967 Dolianitia ahernata Millan, pp. 9-10, pi. 2, fig. 2. 1967 Dolianitia crassa Millan, pp. 10-12 (pars), pi. 3, fig. 2; pi. 4, fig. 1. Emended Diagnosis. Mature female fructification about 6 cm long, main rachis about 6 mm wide in the middle but narrower below, divides once in the upper half. Lateral . EXPLANATION OF PLATE 25 All figures twice natural size. Figs. 1-4, 6, 7. Arberia minasica White. 1, Fully expanded specimen with a monopodial branching of the rachis, showing branching in the pinnae ; ovules are developing as expanded terminal lobes of the pinnae; DGP 7/1069, Bainha. 2, Mature specimen bearing a few ripe ovules, and many developing ovules terminally on pinnae; branching in rachis monopodial, and within pinnae di- chotomous; DGP 7/1070, Bainha. 3, Photographic reproduction of plate 8, fig. 10 of White 1908. 4, A number of ovulate, branched pinnae attached to a rachis. 6, Forked rachis with only one of its upper branches retained; terminal ovule borne on a pinna; DGP 7/1073, Bainha. 7, A cluster of branchlets arising from a single pinna; branchlets each end in a folded lobe; DGP 7/1074, Bainha. Fig. 5. Arberia sp.; poorly preserved rachis bearing a number of recurved processes which have the dimensions of ovules; DGP 7/1072, Bainha. Palaeontology, Vol. 15 PLATE 25 RIGBY, Lower Gondwana fructifications RIGBY: ARBERIA WHITE 117 pinnae spaced 5 mm or more apart. Pinnae, particularly in the upper part of the fructification subdivided one or more times into two or many ultimate branchlets; each segment up to 10 mm long and 2 mm wide, these bearing a rounded ovule just below the apex or being sterile. Ovule 5-6 mm wide, 6-7 mm long, marked off from branchlets by a groove; ovule striated (but other details unknown). Discussion. White’s description of the species is very detailed, but is based on pinna fragments (1908, pi. 8, figs. 8, 9) or pinnate fragments of the rachis (1908, pi. 8, fig. 10). Some pinna fragments are too small to be included in this species with any degree of certainty, and are better referred to as examples of Arberia sp. Examples are ?v4. brasiliensis of Lundqvist (1919, pi. 1, figs. 27, 28), the ‘squamae’ of Kurtz (1921, pi. 7, figs. 68, 69), and the fragment shown here on PI. 26, fig. 3. Other specimens, sometimes well preserved, from the basal part of the rachis, and usually bearing a number of unbranched pinnae, cannot be placed in A. minasica with certainty are also named Arberia sp. The specimen figured here on PI. 25, fig. 5 appears to have belonged to a larger fructification than the specimen on PI. 25, fig. 2. Some of Millan’s examples named D. crassa by him are smaller basal fragments (1967, pi. 2, fig. 3; pi. 3, fig. 3; pi. 4, fig. 2). Millan’s specimens of D. opposita (1967, pi. 1, figs. 1-5; pi. 2, fig. 1) might very well prove to be distinct from A. minasica as they are more slender and less pinnatifid, and lack the much dissected ultimate branchlets so conspicuous in minasica although they belong to the same genus. I am calling them A. Iminasica, but am aware that if they belong to a separate species Millan’s species will stand. The specimen shown here as PI. 24, fig. 8 also lacks any evidence of branching pinnae, and is also included here. Other specimens have been identified with Arberia in the past. Three further speci- mens as well as the two mentioned above were given under “iA. brasiliensis by Lundqvist (1919, pi. 1, figs. 25, 26, 29). These may represent a different species as the ovules show a rim of compression. A. umbel lata of Surange and Lele (1957) appears to be a different species with a shortened, and more spreading apical portion. The preserved parts of D. karliarbarensis described by Pant and Nautiyal (1966) are significantly more robust than any of the Brazilian specimens of Arberia, but insufficient is known of karhar- barensis at the moment to distinguish it from some of the specimens of A. minasica described here. SOME OTHER FRUCTIFICATIONS POSSIBLY RELATED TO ARBERIA These are all so imperfectly known that it is not possible to propose either genera or species for their reception. They appear to show some degree of relationship to Arberia and to one another. Specimens from New South Wales in the Mining Museum, Sydney, and photographed by me in 1963, resemble the Brazilian Arberia fructifications; they were not available at the time of writing. These are the three specimens in PI. 26, figs. 5-7 and the first two are also shown as text-fig. 3c, d. They need not be described further since the features visible in the photographs are all we have. We do not of course know whether they represent whole organs. There is some resemblance between them and the specimen I identify as Arberia in PI. 26, fig. 3. The Antarctic specimen of Schopf 1967 (text-fig. on p. 114) resembles a pinna of the specimen shown here as PI. 26, fig. 6. 118 PALAEONTOLOGY, VOLUME 15 There are two other types of similar ovulate fructification occurring at Bainha. Both bear a striking resemblance to Arberia but differ sufficiently to be considered generically distinct. Problematicum sp. A Plate 26, figs. 8, 9 ; Text-fig. 3b This species is represented by a small megasporophyll or fragment of one, and a single isolated ovule or seed. The megasporophyll is branched in a manner that recalls some of the specimens of Arberia, though details are not clear. The ovule how- ever has a pointed end, no doubt the micropyle, and is clearly distinct; in my opinion the difference is great enough to warrant eventual generic separation. I strongly suspect that the specimen shown in PI. 24, fig. 5 represents an immature stage of this species but it is impossible to relate to sp. A without evidence from addi- tional specimens. Both PI. 26, fig. 8 and PI. 24, fig. 5 have branchlets arising across the face of the unforked axis (equivalent to the rachis in Arberia). The more robust speci- mens of PI. 24, figs. 3 and 6 appear to be closer to Problematicum sp. A than to Arberia-, they may represent stages of a species related to the former. In the figures these are referred to as ArberiaAiko, fructifications. Problematicum sp. B Plate 26, figs. 10, 11; Text-fig. 3a This is represented by three small fossils; two are figured. The unfigured specimen bears a terminal and five alternately inserted ovulate structures. Two specimens are EXPLANATION OF PLATE 26 All figures twice natural size unless otherwise stated. Figs. 1, 2, 4. Arberia minasica White. 1, A number of pinnae attached to a fragment of rachis; surface striations continue unbroken from branchlets to ovulate structures; DGP 7/1075, Bainha. 2, Elongated ovulate structures on pendulous branchlets arising from a slender rachis; DGP 7/1076, Bainha. 4, Photographic reproduction of White 1908, pi. 8, fig. 8. Fig. 3. Arberia sp., branchlets after unfolding but before expansion of the tips; appears to be similar to White’s specimen (fig. 4 herein); DGP 7/1062, Lauro Muller. Figs. 5-7. Specimens from New South Wales resembUng Arberia. 5, Lobate pinnae developed in a plane; NSW 3003, East Maitland. 6, Rachis bearing two fused, lobate pinnae; NSW 3004 A, Adamstown. 7, Fragment similar to specimen shown in fig. 5, but at a younger stage of develop- ment; NSW 3004 B, Adamstown. Figs. 8, 9. Problematicum sp. A, from Bainha. 8, Pendulous micropylar ovules in the lower part and expanding ovulate axes towards the apex, borne on an unforked rachis that broadens upwards as in Arberia-, DGP 7/1079. 9, Isolated ovule shown in position of growth with base towards top of figure ; line of abcission of ovule marked by irregularities in surface hneations ; line of attachment of micropyle to ovule not apparent, but a boundary occurs at conjugate point on outline in apical half of ovule; DGP 7/1080, x 3. Figs. 10, 11. Problematicum sp. B, from Bainha. 10, Three folded pinnae similar to the lobes in Arberia minasica are present, one is terminal to the rachis; the pinna on the right folds away from the viewer, whilst the apical and left pinnae fold towards the viewer; DGP 7/1081. 11, Two ovulate pinnae attached to slender rachis ; broken apex originally bore a pendulous ovule, now visible only on the counterpart; DGP 7/1082. Palaeontology, Vol. 15 PLATE 26 RIGBY, Lower Gondwana fructifications RIGBY: ARBERIA WHITE 119 immature and appear to represent a stage of growth as shown by specimens figured as PI. 24, figs. 5, 6, and 8; the specimen shown on PI. 26, fig. 11 may be ovulate. The figures show all details that can be recognized. These specimens look rather like the ends of pinnae of Arberia minasica (e.g. in PI. 25, figs. 1, 2). As details and dimensions are different I think it unlikely that sp. B belongs to minasica or even Arberia. TEXT-FIG. 3. Fructifications of problematical affinity, from Bainha. a, Problematicum sp. B, specimen DGP 7/1081, showing folded pinnae; x2. b. Ovule of Problematicum sp. A, specimen DGP 7/1080, showing the fine of abcission of the ovule near the top, and the line marking the base of the micropyle towards the bottom of the figure; x4. c, d. Specimens from New South Wales resembling Arberia-, X 2. c. Specimen NSW 3003, showing folded tips of pinnae branchlets. d. Specimen NSW 3004 a, showing fusion between branchlets of pinnae. Acknowledgements. This investigation was carried out during the tenure of a Visiting Professorship during 1968/1969 in the Cadeira de Paleontologia of the Departamento de Geologia e Paleontologia, Universidade de Sao Paulo, awarded by the Fundacao de Amparo a Pesquisa do Estado de Sao Paulo. Professor J. C. Mendes accompanied the author in the field. Dr. R. Yoshida provided locaUty informa- tion and collected specimens. Field work was supported by a grant from the Conselho Nacional de Pesquisas. White’s specimens have been reproduced photographically from the Relatorio Fmal of the Comissao de Estudos das Minas de Carvao de Pedra do Brasil, printed by Imprensa Nacional, Rio de Janeiro, 1908. REEERENCES DOLiANiTi, E. 1946. Noticia sobre novas formas na ‘Flora de Glossopteris’ do Brasil meridional. Notas Prelim. Estudos, Div. Geol. Mineral. Bras. 34, 1-6. FLORIN, R. 1944. Die Koniferen des Oberkarbons und des unteren Perms. Pt. 7. Palaeontographica 85B, 457-654. KURTZ, F. 1921. Atlas de plantas fosiles de la Republica Argentina. Actas Acad. Nac. Cienc. Cordoba 7, 125-139. LUNDQvisT, G. 1919. FossUe Pflanzen der Glossopteris Flora aus Brasilien. K. Svensk. VetenskAkad. Handl. 60 (3), 1-36. MENDES, J. c. 1952. The Gondwana formations of Southern Brazil; Some oftheir stratigraphic problems, with emphasis on the fossil flora. Palaeobotanist 1, 335-345. MiLLAN, J. H. 1965. Consideragoes sobre as sementes do carbonlfero do Brasil. Notas Prelim. Estudos, Div. Geol. Mineral. Bras. 123, 1-18. 120 PALAEONTOLOGY, VOLUME 15 MiLLAN, j. H. 1967. Novas frutifica9oes na flora Glossopteris do Gonduana Inferior do Brasil. Dolianitia gen. nov. Ibid. 140, 1-19. OLIVEIRA, E. p. DE 1908. See note following the citation of white, d. 1908, below. PANT, D. D. and NAUTiYAL, D. D. 1965. Seed-bearing Ottokaria-VikQ fructifications from India. Nature, 207, 623-624. 1966. On two peculiar fossils of Karharbari Stage, India. Symp. Florist ics Strut. Gondwana- land 1964, 98-101. PLUMSTEAD, EDNA p. 1952. Description of two new genera and six new species of fructification borne on Glossopteris leaves. Trans, geol. Soc. S. Afr. 55, 281-328. 1958. Further fructifications of the Glossopteridae and a provisional classification based on them. Ibid. 61, 51-76. PUTZER, H. 1955. Geologia de Folha de Tubarao, Estado de Santa Catarina. Bolm. Div. Forn. Prod. Mineral. Bras. 96, 1-94. ROCHA-CAMPOS, A. c. 1967. The Tubarao Group in the Brazilian portion of the Parana Basin. Problems in Brazilian Gondwana Geology. Brazilian contribution to I Internat. Symp. Gondwana Strat. Palaeont., Curitiba, 27-102. SCHOPF, j. M. 1967. Antarctic fossil plant collecting during the 1966-1967 season. Antarct. J.U.S. 2, 114-116. SRIVASTAVA, p. N. 1956. Studies in the Glossopteris flora of India, 4. Glossopteris, Gangamopteris and Palaeovittaria from the Raniganj Coalfield. Palaeobotanist 5, 1-45, SURANGE, K. R. and LELE, K. M. 1957. Studies in the Glossopteris flora of India. 6. Plant fossils from the Talchir Beds of South Rewa Gondwana Basin. Ibid. 5, 82-90. WHITE, D. 1908. Fossil floras of the coal measures of Brazil. Com. Estudos, Minas Carv. Pedra, Bras. 3, 337-617. (Note: the text of this paper is bilingual with Portuguese on the even numbered pages and English on the facing, odd numbered pages, e. p. de oliveira was responsible for the Portuguese text.) WHITE, I. c. 1908. Report on the coal measures and associated rocks of South Brazil. Com. Estudos, Minas Carv. Pedra, Bras. 1, 2-300. This is referred to as i. c. white in the text to distinguish it from the previous reference. Also see the note under white, d. 1908, above. white, MARY E. 1961 (unpubl.). Plant fossils in core samples from A. A. O. No. 5 Roma Bore, North Queensland. Rec. Bur. Min. Resour. Aust. 1961/18. Final typescript received 27 May 1971 J. F. RIGBY Geological Survey of Queensland, Brisbane, 4000, Australia COMPRESSION STRUCTURES IN THE LOWER CARBONIFEROUS MIOSPORE DICTYOTRILETES ADMIRABILIS PLAYFORD by G. CLAYTON Abstract. Specimens of the dispersed miospore species Dictyotriletes admirabilis Playford 1 963 are described from large spore masses obtained from the Lower Carboniferous of eastern Scotland. D. admirabilis is trans- ferred to the genus Piinctatisporites (Ibrahim) Potonie and Kremp 1954, and compression of sporangial masses is suggested as the mechanism by which the characteristic indentations in the exine were formed. Dictyotriletes admirabilis was first described by Playford in 1963 from the Horton Group (Mississippian) of eastern Canada. Subsequently a similar but smaller form was recorded by Butterworth and Spinner (1967) from the Lower Carboniferous of north- west England. Spore masses containing D. admirabilis were found in one coal sample by Dr. E. G. Spinner {pers. comm. 1970) during an investigation of the Visean megaspores of East Lothian, Scotland. The sample from which the spore masses were obtained was a thin coal from depth 32 ft 8 in in the Institute of Geological Sciences’ Skateraw (1969) bore- hole, East Lothian. This horizon is approximately two feet below the Mid Skateraw Limestone in the Lower Limestone Group, which in this area is considered to be Upper Visean in age (Wilson pers. comm, in Spinner 1969). Further investigation of the same sample has resulted in the isolation of several more spore masses of the same type, and the isolation of individual spores from some of these masses. The sample was also prepared by standard techniques for dispersed miospores. SAMPLE PREPARATION The coal was crushed into small pieces approximately 1 cm in diameter, treated with Schulze solution for 12 hours, washed until neutral, rinsed rapidly with 2% potassium hydroxide solution, and washed again until neutral. The residue was then sieved at 100 B.S. mesh size, and the spore masses picked from the remaining coarse fraction. The spore masses were broken down into small clusters or single spores by repeated treatment with fuming nitric acid for approximately 1 minute, washing until neutral, then application of ultrasonic vibration for approximately 5 seconds. Selected speci- mens were mounted for scanning electron microscope investigation, and the remaining spores were mounted in glycerine jelly. The same sample was also prepared by standard dispersed miospore techniques, and permanent scatter mounts using cellosize and Canada balsam were made. All figured specimens are housed in the Micropalaeontology Collection of the University of Shelfield Geology Department. Specimens mounted for scanning electron microscopy are denoted by ‘SEM’ after the collection reference number. Representative specimens are also deposited in the Institute of Geological Sciences, Leeds. [Palaeontology, Vol. 15, Part 1, 1972, pp. 121-124, pi. 27.] 122 PALAEONTOLOGY, VOLUME 15 SYSTEMATIC DESCRIPTIONS Spore masses containing D. admirabilis Plate 27, fig. 2 Description. Seven specimens were recorded ranging from 500 to 900 pm in longest dia- meter. All are irregular in shape and are flattened. The constituent miospores are well preserved, and are in close contact with each other. Tapetal material is irregularly distributed between the spores as small spheres up to 8 pm in diameter. The affinity of these spore masses is unknown. Anteturma sporites H. Potonie 1893 Turma triletes (Reinsch) Dettmann 1963 Suprasubturma acameratitriletes Neves and Owens 1966 Subturma azonotriletes (Tuber) Dettmann 1963 Infraturma laevigati (Bennie and Kidston) Potonie and Kremp 1954 Genus punctatisporites (Ibrahim) Potonie and Kremp 1954 Type species. Punctatisporites pimctatus Ibrahim 1933. Punctatisporites admirabilis (Playford) comb. nov. Plate 27, figs. 1, 3, 4, 6, 7 1963 Dictyotriletes admirabilis Playford p. 29, pi. viii, figs. 5-7. 71967 Dictyotriletes admirabilis Butterworth and Spinner, pi. 2, fig. 16. Holotype. Playford 1963, pi. viii, fig. 5; Horton Group, Nova Scotia (GSC loc. 6400). Dimensions. 64 (75) 91 pm, 61 specimens, spore mass B. Description. Spores radial, trilete. Amb circular to oval or rounded polygonal. Trilete mark often indistinct. Suturae straight, normally accompanied by low, membranous folds of the exine bordering the suturae, length one half to two thirds of spore radius. Exine approximately 3 /xm thick, finely scabrate. The spores are preserved in large masses, in polar, oblique and lateral compressions. The spore exine is affected by several large, shallow, partially superimposed depressions, which, in clusters of spores, can often be seen to affect two or more adjacent spores. In transmitted light individual depressions are normally seen as either relatively light or dark areas, depending on the focus, separated from each other and from non-depressed areas by well-defined arcuate boundaries. In the scanning electron microscope these arcuate markings, described by Playford (1963, p. 29) as ‘thread-like muri’ are seen to be low crests between adjacent depressions, or separating depressions from relatively high, non-depressed areas. The radius of curvature of the depressions is never greater than the maximum observed spore radius. Peripheral folding is common. EXPLANATION OF PLATE 27 Figs. 1-4, 6, 7. Punctatisporites admirabilis (Playford) comb. nov. 1, ML849 SEM, X 500. 2, ML850 SEM, spore mass; approx, x 100. 3, ML851, showing abortive spore, x400. 4, 6, 7, ML852-854, x400. Fig. 5. P. planus Hacquebard, ML 855; x400. Palaeontology, Vol. 15 PLATE 27 CLAYTON, Lower Carboniferous miospore - ' VA t' f \ i~ ■ . J CLAYTON: MIOSPORE COMPRESSION STRUCTURES 123 Remarks. D. admit' abilis was assigned by Playford (1963) to the genus Dictyotriletes (Naumova) Potonie and Kremp 1954 on the basis of the presence of muri forming a reticulum. This genus was later emended by Smith and Butterworth (1967). Examina- tion of Playford’s illustration of the holotype together with scanning electron micro- scope studies of the Scottish material have however clearly shown that the reticulate appearance of this species is formed by partially superimposed depressions in the spore exine, and not muri sensu Smith and Butterworth (1967, p. 116). This species is there- fore transferred to Pimctatisporites as it is a laevigate form, and does not possess muri in the accepted sense (Smith and Butterworth 1967, p. 116) as projecting thickenings of the exine. Comparison. P. admirabilis comb. nov. is very similar to P. planus Hacquebard 1957, except for the presence of the prominent arcuate markings in the former species. Pimctatisporites planus Hacquebard 1957 Plate 27, fig. 5 Dimensions. 58 (70) 89 p.m, 50 specimens, dispersed miospore preparation. Description. Radial trilete miospores. Amb circular to oval. Non-polar compressions common. Trilete mark often indistinct. Suturae straight, often accompanied by low, membranous folds of the exine bordering the suturae, length one half to two thirds of spore radius. Exine finely scabrate, approximately 3 ju-m thick. Folding rare. Previous records. Hacquebard 1957 (coal) and Playford 1963 from the Horton Group (Mississippian) of Nova Scotia. DISCUSSION In many clusters of P. admirabilis the arcuate markings can be traced across several spores, in some cases almost completing a full circle (PI. 27, fig. 6). The size and distri- bution of the depressions are consistent with their having been formed by compression against neighbouring spores, which may also have caused some separation of the spores from the tetrad state. The common peripheral folding in this species was probably caused by the spores ‘spreading’ against each other normal to the axis of compression. The presence of indentations on both surfaces of the flattened spores irrespective of their post-compressional orientation suggests that the depressions were formed during compaction of the enclosing sediment, rather than by growth of the spores in the restricted volume of the sporangium during maturation. If the latter mode of formation was the case, the depressions would be restricted to the distal surface of the spores, with the attendant development of such specialized proximal surface features as clearly defined contact areas, due to the close mutual contact of the spores within their tetrads. The spores would also be expected to be present in all cases in the dispersed miospore preparation. The presence of P. admirabilis in the dispersed miospore preparations described by Playford (1963), and Butterworth and Spinner (1967) may be accounted for by the break up of spore masses during oxidation, as Playford figures one cluster of specimens. 124 PALAEONTOLOGY, VOLUME 15 The similarity between P. admirabilis and P. planus in all aspects except the depres- sions in the former species is interpreted by the author as indicating the probable derivation of P. admirabilis from spores referable to the morphographic species P. planus by an unusual mode of fossilization. This interpretation is supported by the mutual exclusion of these species in the spore masses, and in the dispersed miospore preparation. The specimen of P. admirabilis figured by Butterworth and Spinner (1967, pi. 2, fig. 16) is somewhat smaller than the lower limit of either the size range recorded for this species by Playford, or that of the specimens from the Skateraw sample. P. debilis Hacquebard 1957, the only species of Punctatisporites recorded by Butterworth and Spinner from the sample containing P. admirabilis is proportionately smaller than P. planus, and its size range covers the diameter of the specimen figured by these workers. This provides some substantiation for the hypothesis that the characteristic exine de- formation of P. admirabilis is not a primary structure, but is produced during fossiliza- tion, and could therefore be duplicated in many other morphographic species under suitable conditions. The postulated criteria for the generation of P. admirabilis style of exine deformation in miospores can be summarized: 1 . Preservation of spores in clusters or perhaps even whole sporangia, rather than as dispersed individuals. 2. A thick exine relative to the spore diameter, which would be indented by the sur- rounding spores, rather than simply folded during compression. 3. A relatively smooth exine which would allow contact with the adjacent spores over a large surface area, unimpeded by projecting ornament. Acknowledgements. I thank Professor L. R. Moore for use of the facilities of the Geology Department, University of Sheffield, and Dr. R. Neves, Dr. E. G. Spinner, and Dr. K. J. Gueinn for their advice. Dr. R. B. Wilson of the Institute of Geological Sciences, Edinburgh, made samples from the Skateraw borehole available to Dr. R. Neves. REFERENCES BUTTERWORTH, M. A. and SPINNER, E. 1967. Lower Carboniferous spores from north-west England. Palaeontology, 10, 1-24, 11 pis. HACQUEBARD, p. A. 1957. Plant spores in coal from the Horton Group (Mississippian) of Nova Scotia. Micropaleontology, 3, 301-324, 3 pis. PLAYFORD, G. 1963. Miospores from the Mississippian Horton Group, Eastern Canada. Bull. geoL Surv. Can. 107, 47 pp., 11 pis. POTONiE, R. and kremp, g. 1954. Die Gattungen der palaozoischen Sporae dispersae und ihre Strati- graphie. Geol. Jb. 69, 111-194. SMITH, A. H. V. and butterworth, m. a. 1967. Miospores in the coal seams of the Carboniferous of Great Britain. Spec. Paper Palaeont. 1, 324 pp., 27 pis. SPINNER, E. 1969. Megaspore assemblages from Visean deposits at Dunbar, East Lothian, Scotland. Palaeontology, 12, 441^58, 3 pis. GEOFFREY CLAYTON Department of Geology The University Sheffield 1 Typescript received 13 April 1971 REGIONAL ENVIRONMENTAL CHANGES ACROSS A LOWER JURASSIC STAGE-BOUNDARY IN BRITAIN by B. W. SELLWOOD Abstract. In much of Northern Europe and in particular Britain, the end of the Sinemurian stage was marked by substantial environmental changes which caused numerous faunal changes. Lands bordering the Sinemurian sea (East Greenland, Southern Scandinavia, the London Platform) were transgressed as the Pliensbachian com- menced. In persistently marine areas the sediments became finer grained and less kaolinitic, representing deeper- water environments than those of the Sinemurian. Sedimentary cycles, reflected by the faunas and trace-fossils, resulted from small-scale changes of water-depth. Deeper-water environments represented by shales were characterized by low-diversity faunas of thin-shelled pectinids and protobranchs. Shallower-water bioturbated sandstones were typified by higher diversities with pholadomyoids, venerids, mytiloids, thick-shelled pectinids, and complex crustacean burrows. The substrates of marly sediments were too soft and unstable to allow the development of a diverse benthos, and argillaceous calcilutites were only slightly more stable. Condensed sequences occurred on swells and were either chamositic with shallow-water faunas and structures; or calcareous (calcarenites and micrites) with abundant shallow-water faunas, glauconite and phosphate. The latter formed away from the terrigenous iron sources. The epeiric sea of the Northern European Lias generally had gentle slopes and was profoundly affected by small-scale changes of water-depth which may have been eustatically controlled. There is little evidence of strong salinity controls to the fauna within the persistently marine areas. The presence of tidally influenced marginal sequences testify against salinity-controlled faunal regimes which would have required minimal current action for their development and maintenance. The zonal stratigraphy of the Lower Lias is well known but the depositional environ- ments are understood only in rather general terms. The existing stratigraphical frame- work forms a sound base upon which to construct a facies analysis because it allows the short time zones to be widely traced. Hallam (1961) suggested that the Sinemurian- Pliensbachian boundary represented a phase of major faunal and facies change. The aim of the present study is to test his proposals and to determine whether the changes were due to environmental or evolutionary factors. The results of this facies analysis also shed light on the nature of epeiric seas in general. During much of the Mesozoic Era, Northern Europe was covered by a shallow epicontinental sea which has no modern analogue (text-fig. 1). Lower Lias faunal assemblages can, however, be fairly closely compared with those of their modern descendants, and clay mineral distribu- tions, sedimentary structures, and geochemical variations can all be compared with information from modern seas. The less tangible concepts such as eustasy (Hallam 1969u), tidality (Klein 1970; Sellwood in press) and salinity (Hallam \969b) remain more open questions. Stratigraphy. The Raricostatum and Jamesoni Zones fall below and above the boun- dary separating the Sinemurian and Pliensbachian Stages (Table 1). In northern Britain the commencement of the Pliensbachian is generally marked by a loss of quartz sand, and in southern Britain by an increase in the carbonate content of the sediment. Hallam (1961) noted that whilst some invertebrate genera persisted beyond the Sinemurian, many more appear at about the base of the Pliensbachian; particularly brachiopods and belemnites. [Palaeontology, Vol. 15, Part 1, 1972, pp. 125-157, pis. 28-29.] 126 PALAEONTOLOGY, VOLUME 15 Table 1 gives the zonal scheme for the Lower Lias with the subzonal stratigraphy and ranges of the main ammonite genera. This zonal sequence (Dean et al. 1961) is applicable to most of the sections studied (text-fig. 2), but the lack of continuous and unmeta- morphosed exposure on Mull; and of ammonites in the Golspie and Lossiemouth TEXT-FIG. 1. Lithofacies reconstruction of the European region in Jamesoni Zone times. Carbonates extended south to North Africa. sections makes the application of their zonal scheme difficult in these areas. Correlation of the major British sections is given in text-fig. 3, while text-figs. 4 and 5 give the major lithofacies distributions during Raricostatum/Jamesoni times. Work in Britain was sup- plemented by visits to Scandinavia and Spain, thus permitting some of the broad interpretations presented below. Palaeoecological principles. The more important factors which control the distributions of marine faunal assemblages are temperature, salinity, water and substrate chemistry. SELLWOOD: LOWER JURASSIC STAGE-BOUNDARY 127 biological competition, and nutrient supply (Ellison 1955 gives an expanded list). Many of these factors are depth related. The proportion of suspended material in sea-water is broadly related to depth and environmental energy as well as to the availability of the material and its size; the distributions of suspension-feeding animals are coincident with this (Jorgensen 1966). Thus with large quantities of suspended material and rela- TABLE 1. Ranges of the characteristic ammonite genera (modified from Dean et al. 1961) tively low sedimentation rates in fairly high energy environments, suspension-feeders are dominant (Driscoll 1969), whereas detritus feeders dominate areas of high turbidity and more rapid sedimentation. Sanders (1958) found that suspension-feeders dominated the modern marine sands of Buzzards Bay, whilst the clay content (which is itself con- trolled by depth and geographical factors) controlled the distribution of deposit- feeders. Seilacher (1967) has clearly argued a case for regarding feeding-mode as an important clue in interpreting depositional environments and suggests a direct bathy- metric relationship between the predominance of either suspension- or deposit-feeders. The Lias fauna consists mainly of bivalves whose modes of life are readily inter- pretable, both from their attitudes within the sediment and in the light of much modern work on living communities (Allen 1953, 1958; Driscoll 1969; Kauffman 1967, 1969n; Parker 1956, 1964; Saleuddin 1965; Stanley 1968; Yonge 1923, 1939, 1953n, 1953Z?, 128 PALAEONTOLOGY, VOLUME 15 1957, 1960; and many others). Table 2 summarizes the modes of life of the faunal and trace-faunal elements and the general lithofacies relationships of the more important ones are given in text-figs. 6, 7. In general, shales are typified by thin-shelled pectinids and protobranchs. This fauna is similar to that of modern outer-shelf muds ; the pecti- nids were well adapted to a life in mud (because of their valve-clapping and swimming TEXT-FIG. 2. Lias outcrops in Britain and locality map of major sections mentioned in text. habits) while protobranch bivalves like Nuculana and Nucula were deposit-feeders and lived at shallow depths within the substrates. Rarer lucinoid bivalves also occur like Liicina and Mactromya and by comparison with modern Lucinoids, it seems that these were not strictly siphonate, but constructed mucus-lined tubes and were really sus- pension/deposit-feeders. At present, lucinoids burrow deeply in muddy substrates where adverse Eh or high turbidity prevents colonization by truly infaunal suspension-feeding bivalves (Allen 1958). The shales also contain a high proportion of bivalve juveniles indicating a high juvenile mortality. The bioturbated sandstones contain radically different body- and trace-faunas from those of the shales (Sellwood 1970, and text-figs. 6, 7). These are typified by suspension-feeders which indicate increased energy and probably lower turbidity conditions. TEXT-FIG. 3. Stratigraphic summary of major sections mentioned in text. 0 8472 K 130 PALAEONTOLOGY, VOLUME 15 TABLE 2. Table showing interpretation of feeding modes and modes of life for the more important faunal elements in Raricostatum-Jamesoni sediments Mode of Life Fauna Carnivore- scavenger Mode of life Suspension Deposit Suspension- deposit Nekton Echioceratidae X Polymorphitidae X Belemnites X Nekto-Benthos Apoderoceras sp. X Epifauna Antiqilhna X Camptonectes X Chlamys X Entolium X Gryphaea X Oxytoma X Plagiostoma X Pseudolimea X Pseiidopecten X Tetrarhynchia X ZeiUeria X Pentacrinus X Pleurotomaria X Infaunal Semi-Infaunal Pinna X Shallow As t arte X Grammatodon X Hippopodium X Niicida X Nucidana X Protocardia X Procerithiim X Rhizocorallium X Chondrites X Deep Pholadomya X Pleuromya X Mactromya X Lucina X Diplocraterion X Chondrites X Pyritic, tubular burrows X Thalassinoides X Tigillites X Compiled from references in text and Hudson and Palframan (1969) Clay mineral data. Clay mineral distributions may be important guides to depositional environments. Although most clay mineral groups are stable, certain ones (particularly the montmorillonite group) may be altered during diagenesis. However, the lack of montmorillonite in these Lias sediments indicates a depositional absence rather than its removal during diagenesis (Hallam and Sellwood 1968). The predominant clay minerals in Lias shales are illite and kaolinite and these minerals probably reflect the SELLWOOD: LOWER JURASSIC STAGE-BOUNDARY 131 TEXT-FIG. 4. Changing lithofacies distributions through the Raricostatum and Jamesoni Zones: (a) lower Raricostatum, (b) upper Raricostatum, (c) lower Jamesoni, (d) upper Jamesoni. 132 PALAEONTOLOGY, VOLUME 15 nature of the source areas (Weaver 1958; MacKenzie 1965; Gluskoter 1967; Griffin et al. 1968, and many others). Chlorite, montmorillonite, and mixed layer minerals have not been detected in any Lias clays analysed. There is a general tendency for kaolinite contents to decrease from north-east to the south and west with highest concentrations occurring at Lossiemouth (more than 60 %) and the lowest in the Somerset-Dorset area (5 % or less). In a given area the Jamesoni Zone is generally poorer in kaolinite than the Raricostatum Zone. Kaolinite in recent Marine sediments is generally restricted to the nearshore areas (Griffin and Goldberg TEXT-FIG. 5. Block diagram to illustrate lithofacies relationships and possible controls during late Jamesoni Zone times. 1963; Biscaye 1964; Griffin et al. 1968) and in the Lias decreasing kaolinite contents probably reflect greater distance from source area. The well-marked facies changes at the base of the Pliensbachian may well have resulted from increased water depths in the basins, and marine transgression of the Sinemurian shore-lines. Iron and calcium distributions. Many authors have considered that iron-rich concretions typify depositional environments closer to the source area than those in which iron- deficient calcareous concretions are dominant (Curtis 1967; Curtis and Spears 1968; Hallam 1967Z>; Cronan and Tooms 1969). In the Type 1 cycles (see below) the calcareous concretions at the cycle tops are iron-poor while in the shales they are strongly sideritic with iron concentrations of 9-8-12-6%. The calcareous concretions at the cycle tops represent phases of reduced terrigenous influence, possibly resulting from marine transgressive phases. Small-scale sedimentary-cycles. Parts of the Raricostatum-Jamesoni sequence are characterized by rhythmic units which are defined by variations in either the carbonate to clay content, or sand and silt to clay content. Some of these rhythms have been con- sidered in detail (Sellwood 1970; Sellwood et al. 1970). The major features of the two major types are summarized here. SELLWOOD: LOWER JURASSIC STAGE-BOUNDARY 133 Id I □. Calcarenite Calcilutitz Marl Bituminous shale ^ Clays Sandy and micaceous clays Argillaceous sand KEY Belemnites Apoderoceras ^ Other Ammonites i Pholadomyoids ^ Hippopodium Astorte and Cordin/a Nuculoids Oxtoma Inoceramus Protocardia Gryphaea Lucina and Moctromya Pinna P T Pleurotomaria Brachiopods Crinolds Oppelismilia Echinolds Serpulids Driftwood Procerithium TEXT-FIG. 6. Lithofacies/faunal relationships for the major faunal elements. KEY Diplocraterion y (large and small) Thalassinoides ^ Rhizocorallium (simple) Rhizocorallium (vertically ascending) .1 ^ Chondrites «> Siphonites Q Teichichnus tubular burrows (large and small) of deposit feeders storm scour . rippled surface with gastropod trails TEXT-FIG. 7. Lithofacies/trace faunal relationships. Key to lithofacies as in text-fig. 6. 134 PALAEONTOLOGY, VOLUME 15 Type 1 (of Sellwood 1970). Each cycle coarsens upward from shales at the base to a bioturbated argillaceous sandstone. Lenticular sandstones often occur in basin-shaped scours, sometimes with a lag-deposit of crinoid-debris at their base. These filled-scours are attributed to storm action. The shale interval in each cycle is typified by a fauna of thin-shelled pectinids, protobranchs, and a trace-fauna of small pyritic tubes produced by infaunal deposit-feeders. The bioturbated sandstones, however, contain a diverse body- and trace-fauna (pholyadomyoids, brachiopods, Diplocraterion, Rhizo cor allium and Thalassinoides) indicative of shallower water and higher energy conditions than those under which the shales accumulated. Cycle-tops may be cut by meandering shell- filled runnels up to 50 cm in diameter, similar to those described by Hantzschel et al. (1968). The sand fraction of the argillaceous sandstones is well sorted, but bioturbation of the sands with finer material has rendered the grain-size distributions bimodal. It is prob- able that the sands were introduced as discrete pulses of well-sorted sediment. Accumu- lations of ammonites (in calcareous nodules) occur on the tops of some sandstone units and the hummocky burrowed tops of the sandstones are draped by the basal shales of the next unit. These basal shales are often rich in the pyritic nuclei of ammonites. Each cycle represents a shallowing upward sequence with the subsequent deepening phase represented by the ammonitic nodules and shales at the bases of succeeding cycles. Type 2 (of Sellwood 1970 and PI. 22, fig. 3). Cycles of this type are the limestone-marl rhythms of previous authors. Bioturbation reveals the primary nature of the cyclicity and the vertical distribution of different ichnogenera displays the asymmetry in the cycles. The tops of limestone units define the tops of individual cycles. The coccolith Crepidolithusl (Defiandre) (PI. 28, fig. 1) is commonly present in the limestones. These organisms may have been the primary contributors of fine-grained carbonate but recrystallization generally obliterates much of the fine structure. Diplocra- terion burrows may descend from the tops of limestone units which were extensively bioturbated by Rhizocorallium, Thalassinoides, and small Chondrites. These burrows piped light-coloured calcareous material down into the underlying marls where a larger form of Chondrites is found (PI. 29, fig. 3). The limestone units may represent the accumulation of relatively undiluted calcareous skeletons during phases of clastic starvation. Storm scours with a bioclastic fill are often present, similar in their scale to those in Type 1 cycles, and these structures may indicate that both Types 1 and 2 were produced in comparable water depths. EXPLANATION OF PLATE 28 Fig. 1. CdCrepidolithus (Defiandre) from an argillaceous calcilutite unit in Bed 115 of Lang, upper Jamesoni Zone, Charmouth, Dorset. Electronmicrograph x 5000. Fig. 2. Schizosphaerella (Defiandre and Dangeard), Levesquei Zone, La Almunia, Spain, Electron- micrograph X 2000. For comparison with Fig. 4. Fig. 3. Pimm folium (Young and Bird) in life position. Sediment filling lower part of body-cavity cemented by siderite, uncemented upper portion compacted and surrounded by shell fragments. Hammer handle 28 cm. Fig. 4. Schizosphaerella (Defiandre and Dangeard), basal Jamesoni Zone, Charmouth, Dorset. Electronmicrograph x 1600. Fig. 5. Wavy- and llaser-bedded sands and clays, marginal facies, and possibly tidal-flat sediments. (?)Sinemurian, Bornholm, Denmark. Clinometer 12 cm in diameter. Palaeontology, Vo! 15 PI ATE 28 SELLWOOD, Lower Jurassic stage boundary SELLWOOD: LOWER JURASSIC STAGE-BOUNDARY 135 YORKSHIRE AND LINCOLNSHIRE The sections at Robin Hood’s Bay (text-fig. 8; National Grid Reference NZ 950055) and Roxby (text-fig. 9; SE 910170) are generally similar. Robin Hood's Bay (text-figs. 2, 3, 8). 21 m of Raricostatum Zone and 49-5 m of Jamesoni Zone occur in a predominantly shaley sequence; argillaceous sandstones occur in the seven Type 1 cycles composing the Raricostatum Zone. In general, the subzonal boundaries in this zone correspond with the tops of cycles but the top of the Aplanatum Sub Zone is an exception; persisting to a 6-cm-thick shell bed 3-7 m above unit 13 (text-fig. 8). This bed contains abundant overturned Gryphaea, aligned belemnites, and rarer ichthyosaur and bone fragments. This bed probably represents a winnowed deposit. Siderite nodules in the Raricostatum shales contain about 9-8-12-6% Fe and approxi- mately 1-2% Mn whereas the shales themselves contain around 3-5% Fe and OT % Mn. Calcareous nodules at the tops of cycles contain only 1 -4 % Fe and traces of manganese. Illite is the dominant clay mineral with subordinate kaolinite (10-30%). In the argillaceous sandstones, originally aragonitic infaunal bivalves occur as moulds (in life-positions). Epifaunal pectinids are usually disarticulated in both sand- stones and shales, and protobranchs may be either articulated or disarticulated. Rarely, Pentacrinus is preserved intact in the shales, but more often only disarticulated fragments occur. Ammonites in the shales and sandstones occur as pyritic nuclei whereas in cal- careous and sideritic nodules larger calcitized specimens occur. The Jamesoni Zone at Robin Hood’s Bay commences in silty shales containing numerous semicontinuous bands of siderite concretions. The more important bands may be traced to the south side of the Bay at Ravenscar, some 3 km away, where they are useful datum bands (ja-jo in text-fig. 8). The siderite cement in these bands probably reflects a selective secondary cementation of a primary sedimentary difference between the nodule bands and the intervening shales. Within and just below some sideritic beds, Gryphaea and Pleuromya (in life-position) may be found associated with Rhizocorallium, Thalassinoides, and Chondrites. This association is distinct from that which occurs in the intervening shales and supports the idea that the siderite is exaggerating some non- or slow-depositional phases which occurred at these levels (Sellwood 1971). Belemnites, Phrieodoceras and the thicker-shelled nodose ammonite Apoderoceras are present in the silty shales. From about 3 m above the base of the zone, the shales become more uniform and less silty, they also contain a more restricted and less abundant fauna of protobranchs and thin-shelled pectinids (text-fig. 8). Pyritic moulds of the deposit- feeder Proeerithium are sometimes abundant. Above these basal shales, the remainder of the Taylori Subzone contains a very restricted fauna charaeterized by protobranchs and thin shelled pectinids. Phrieodoceras occurs, but Apoderoceras does not. This sequence of uniform shales probably represents the deepest water conditions which existed during Jamesoni Zone times in Yorkshire; the fauna is a typical outer muddy- shelf assemblage (by comparison with modern examples). Toward the top of the Taylori Subzone, silt and fine sand were again introduced. This sedimentary change was accompanied by a faunal change, with the introduction of Pleuromya, Pholadomya, Gryphaea, Pinna, thick-shelled peetinids, Rhizocorallium, and rarer Diplocraterion (text-fig. 8). The whole fauna takes on a more inner-shelf aspect and the abundance of infaunal and semi-infaunal suspension-feeders, and thicker shelled SELLWOOD: LOWER JURASSIC STAGE-BOUNDARY 137 pectinids suggests a return to shallower agitated waters with high food contents (text- figs. 6, 7). Apoderoceras also returns with this change of facies and because this ammonite is strongly controlled by facies it may well have lived in a semi-benthonic manner as a scavenger (text-fig. 6). Certainly the shape of the animal would have prevented it from being an efficient swimmer. Storm-scours are present, as are shell bands rich in exhumed Pinna lying flat to the bedding. Bands of Pinna alternate with shales which contain Pinna in their life positions (PI. 28, fig. 3). Silty shales containing a rich fauna and occasional beds of sideritic mudstone continue through the remainder of the zone. Illite is the dominant clay mineral and the remainder of the clay fraction is composed of kaolinite which constitutes from 5% to 20% usually averaging about 10%. The top of the zone is marked by a highly bioturbated sandy clay which contains abundant Rhizocorallium burrows. Above this unit (jo of text-fig. 8) a number of coarsening-upward sequences containing Chondrites occur before the commencement of very fine grained sedimentation in Ibex Zone times (with shales containing Inoceranms and protobranchs). Sedimentological and faunal data suggest that the over-all environment in Rari- costatum times was shallow neritic with alternating shallowing and deepening phases reflected in the cyclicity. The Jamesoni Zone commenced with a deepening phase which continued through the Taylori Subzone producing the muds with their restricted faunas. Shallower-water conditions returned and persisted through the remainder of Jamesoni times with renewed deepening occurring in the Ibex Zone. Roxby (text-figs. 2, 3, 9). 15-0 m of Raricostatum Zone and 19-0 m of Jamesoni Zone are exposed in a predominantly shaly and clay succession which rests upon a winnowed shell bed at the top of the Frodingham ironstone. This shell bed marks the probable omission of the upper part of the Oxynotum Zone. The Raricostatum Zone displays seven Type 1 cycles, similar to those at Robin Hood’s Bay but the clays contain far less mica and silt. Illite is the dominant clay and the kaolinite content ranges from 10-15%. Subzonal boundaries occur at the tops of the cycles except for that of the Aplanatum subzone which continues to a shell-bed in the shales above the cyclic sequence (text- fig. 9). This bed contains overturned Gryphaea, thick-shelled Pseudopecten, cidarid spines, fish scales, and abundant foraminifera. The material is broken and encrusted with bryozoans and foraminifera such as Ammovertella. The bed represents a winnowed deposit like its counterpart at Robin Hood’s Bay. Facies in the Jamesoni Zone are similar to those at Robin Hood’s Bay. Pinna is com- mon in the clays, often in life-position, but more abundantly as exhumed shells. Illite is the dominant clay with kaolinite contents being usually 10-15%. Toward the top of the zone, the facies ehanges suddenly to the chamosite limonite oolite known as the Pecten Bed (text-fig. 9). This bed is stratigraphically condensed and within its 1-8 m thickness is probably included the bulk of the Ibex Zone. Trough cross- bedding is present, as are storm scours, and the abundant Pseudopecten which occur at several horizons within the bed are thick shelled and always in their current stable positions. Thus there is evidence of at least periodic current action. Infaunal suspension- feeders like Cardinia, Phoiadomya, and Pleuromya replace Pinna as the dominant faunal elements and moulds of the gastropods Procerithium and Amberleya are common in some shell beds. The whole assemblage clearly represents shallower and more turbulent 138 PALAEONTOLOGY, VOLUME 15 TEXT-FIG. 9. Stratigraphic section and faunal distributions at Roxby Mine, Lincolnshire. SELLWOOD: LOWER JURASSIC STAGE-BOUNDARY 139 water conditions than those under whieh the bulk of the zone were deposited. The fauna in the chamositic Pecten Bed is not stunted and depositional conditions appear to have been normal. The problems concerning the origin of chamosite have been discussed by many authors (Hallam 1966; James 1966). In the light of recent papers by Rohrlich et al. (1969), and Porrenga (1965) it is probable that the chamosite formed diagenetically in faecal pellets, and in this condensed bed, where much of the sediment was reworked and digested many times by burrowers, the formation of the mineral may well have been facilitated by chemical processes within the guts of deposit-feeding organisms. Fossil biofabrics are generally similar to those at Robin Hood’s Bay, but in the shales aragonitic shells are often preserved in their original state. This may be a funetion of the lower sediment porosity preventing post-depositional dissolution of aragonite. The sequence of environments represented compares with that in Yorkshire. Lower silt, mica, and kaolinite contents suggest that the area was slightly further from the sediment-source. The major difference between the two successions is the development of a chamosite oolite facies. The condensed nature of the succession and diverse shallow- water fauna support Hallam’s (1966) hypothesis that these sequences formed on ‘Swells’. A minor ‘Swell’ developed in this area during late Jamesoni times (text-fig. 5). THE MIDLANDS AND THE LONDON PLATFORM Cheltenham (text-fig. 2) (SO 947238). A temporary seetion at Folly Lane exposed between 5 m and 7 m of Densinodulum to Raricostatum Subzone clays with little mica. Many thin (15 cm) beds of bioturbated silty clay alternated with the clays which are predominantly illitic, containing less than 10% kaolinite. The fauna of the clays is typified by thin-shelled, free-living pectinids such as ChJamys securis (Dumortier), Entolium sp., Camptonectes nnmdus (Melville) ; the byssally attached pterioid Oxytoma inaequivalvis (J. Sowerby); Gryphaea sp.; Grammatodon sp.; Proto- cardia sp.; and Nuculana sp. Ammonites occur throughout and Cruci/obiceras are abundant, often preserved in their original aragonite. By comparison with modern communities, this assemblage represents a middle to outer shelf-mud environment. Stowed Park Borehole, Gloucestershire (SP 084118) (text-figs. 2 and 3). This hole was drilled for the Geological Survey in 1949 and as only small fragments of core are now available, the published data of Green and Melville (1956), Melville (1956), and Spath (1956) are reproduced here. In the section (text-fig. 5), subzonal boundaries have been redrawn to conform with the stratigraphy proposed by Dean et al. (1961). The Raricostatum Zone consists of two main parts, the lower (Densinodulum and Raricostatum Subzones) composed essentially of dark laminated shales and mudstones, and the upper (Macdonnelli and Aplanatum Subzones) of shelly ironstone mudstones, muddy limestones, and black shales. Lingula oecurs in the lower Raricostatum Zone, associated with a fauna containing Nucula, Parallelodon, Grammatodon, Oxytoma, Gryphea, Modiolus, Antiquilima, and Mactromya. The presence of Lingula and lucinoids and the absence of pholadomyoids suggests a highly turbid environment with little current action except for periodic scouring by storms. In the upper Raricostatum Zone the fauna is more diverse with the introduction of Tropiorhynchia, and more infaunal suspension-feeding bivalves (e.g. Astarte and Phola- domya) indicating increased current activity and improved substrate conditions. 140 PALAEONTOLOGY, VOLUME 15 The Jamesoni Zone consists of mudstones with some burrowed limestones (‘fucoid’ beds of Green and Melville 1956) containing a diverse fauna of epifaunal suspension- feeders (mostly pectinids) but lacking a suspension-feeding infauna. These conditions persisted to the top of the Brevispina Subzone where, apart from the brachiopods Cincta and Tropiorhynchia, the fauna becomes restricted to infaunal deposit-feeders. This assemblage compares with a modern outer shelf mud environment and the ‘fucoid beds’ contain burrows which may represent periods of reduced sedimentation. TEXT-FIG. 10. Transgression of the London Platform. Explanation : . X X X X X X X Shore-line in Raricostatum times. Shore-line in late Jamesoni times. Sites of boreholes which provided data for the diagram: A Ashdown B Brabourne Br Brightling Bt Betteshanger C Cambridge Cf Cliffe Ci Canvey Island Cl Calvert Cu Culford D Dover E El ham Eb Ebbsfleet F Folkestone H Henfield Compiled from the data of: Davies and Pringle (1913), Lamplugh and Kitchin (1911), Lamplugh et al. (1923), Taitt and Kent (1958). London Platform. Jamesoni Zone sediments overstep Raricostatum Zone sediments, and are themselves overstepped by sediments of later zones (text-fig. 10). At Calvert (Buckinghamshire, SP 680257, text -fig. 10), a fragment of derived Echio- ceras was found in the 1 m thick ironshot limestone of the Jamesoni Zone (Davies and Pringle 1913). This fragment shows that Raricostatum Zone sediments were deposited K Kingsclere L Little Missenden Ln London Lw Lowestoft Nc North Creake P Penshurst Pt Portsdown S Shalford Su Sutton W Warlingham We Ware Wee Weeley Wy Wyboston EXPLANATION OF PLATE 29 Fig. 1. Polished section through upper part of Watch Ammonite Stone. The less argillaceous portion (hght coloured) contains abundant randomly disposed ammonites. Light material was piped down into the darker by Chondrites burrows. X 1. Fig. 2. PoUshed section through upper portion of Hummocky Limestone showing part of a Diplo- craterion burrow (arrowed a) and limestone clasts (arrowed b). The black specks in the lower part of the picture are small Chondrites in section. X |. Fig. 3. Limestone/marl relationship, Belemnite Maris. Chondrites, Thalassinoides, and Rliizocorallium are conspicuous in section below the limestone. Burrows are filled with light coloured calcareous sediment from the bed above. Hammer handle 8 cm. The top of each specimen is to the left. Palaeontology, Vol. 15 PLATE 29 SELLWOOD, Lower Jurassic stage boundary SELLWOOD: LOWER JURASSIC STAGE-BOUNDARY 141 there, but later reworked. The Jamesoni Zone rests upon an erosion surface cutting reddened and weathered Tremadocian rocks. Thus, temporary transgression occurred in the Raricostatum Zone, followed by an extensive transgression in Jamesoni to Davoei Zone times. On the margins of the London Platform (text-fig. 10), if Rari- costatum and Jamesoni sediments are preserved at all, they tend to be condensed and are often ironshot. Beneath Kent, the Jamesoni zone rests upon Palaeozoic basement in bore-holes at Dover, Folkestone, Brabourne, and Elham; and Raricostatum Zone sediments are TEXT-FIG. 11. Stratigraphic sections in the Radstock Area. Modified from Tutcher and Trueman (1925). overstepped (text-fig. 10) (Lamplugh et al. 1923). In the Dover bore-hole plant debris was found in the basal ironshot sands (Lamplugh and Kitchin 1911). In a number of other boreholes such as Kingsclere, North Creake, Shalford, Warlingham, and Pens- hurst (text-fig. 10) the facies in the Jamesoni Zone change to sediments with a deeper water aspect and a finer grain size. These facies changes, and the overstep by the zone on to older rocks, suggest that partial transgression of the Platform occurred during the zone. There are enough facies changes in the neighbourhood of the London Plat- form to show that the absence of both Raricostatum and Jamesoni strata over most of the region is due to the area having been a source of sediment at the time and not simply to their removal during later phases of erosion. Wales. The Raricostatum and Jamesoni Zones are not represented in the main Lias out- crop of Glamorgan, but the recent Institute of Geological Sciences bore-hole at Mochras (text-fig. 2) passed through a ‘great thickness of silty-clay sediments representing these zones’ (Dr. A. W. Woodland pers. comm.). There is little coarse material to suggest a local source-area and Wales was probably totally submerged in this part of the Lias. 142 PALAEONTOLOGY, VOLUME 15 SOUTH WEST ENGLAND: SOMERSET AND DORSET Somerset {The Mendip Region). The Lias is very condensed in this area with the suc- cession from upper Rhaetic to Jamesoni Zone being less than 5 m thick. Three quarries near Radstock still expose the Raricostatum and Jamesoni Zones (Kilmarston Road ST 687545 and 689541 ; and Vobster ST 705498) (text-figs. 2 and 11). Many quarries were available to Tutcher and Trueman (1925) but most of these have been filled subsequently. The Raricostatum Zone is represented by a few centimetres of brown clays containing derived (phosphatized) and in situ Echioceras, Lepteehioceras, Procerithium, and belemnites. The Jamesoni Zone commences as the rather variable Armatum Bed which is never more than 1 m thick and contains abundant derived and phosphatized specimens of Echioeeras, Paltechioceras and calcareous mudstone frag- ments. This bed sometimes rests unconformably upon Carboniferous Limestone (e.g. at Vobster, text-fig. 11). The remainder of the zone is represented by a 1-1-5 m-thick bioclastic limestone, termed the Jamesoni Limestone by Tutcher and Trueman (1925). This limestone is composed of shell material, particularly echinoid debris. It also con- tains numerous limonite ooliths giving the rock its ironshot appearance. Pellets of glauconite and phosphate may compose 1-2% of the rock, and although the Jamesoni Limestone is thin, its composition ranges from biomicrite to biosparite. The biosparites contain up to 10% quartz grains which are often corroded at their margins. Reaction rims to these grains show that two phases of cement are present, the first phase involved the formation and early recrystallization of non-ferroan calcite which replaced the outer portions of quartz grains and the original aragonite, the second involved the partial replacement of the earlier cement and renewed replacement of the quartz grains by ferroan-calcite (calcite with a small quantity of ferrous iron in the lattice). These limestones contain abundant infaunal and epifaunal suspension-feeders both as fossils and trace-fossils; Astarte, Cardinia, Pleuromya, Pholadomya, Pseudolimea, and Gryphaea are abundant at certain levels along with Thalassinoides and Diplocraterion burrows. The bed is condensed stratigraphically and the majority of the shells have been winnowed from their life-positions, but sufficient remain to show that the fauna is representative of the area and not derived from elsewhere. The fauna also indicates soft-sediment conditions beneath agitated and probably shallow water. According to Tutcher and Trueman, northward from Radstock, the limestone facies passes into clays but no exposures exist now. The Radstock-Mendip area acted as a swell, starved of elastics, upon which bioclastic material slowly accumulated. Raricostatum Zone sediments were probably more thickly developed there originally, but the bulk of this material was removed before Jamesoni times. This was probably during the same phase of erosion which produced the win- nowed shell beds at the top of the Raricostatum Zone in Yorkshire and Lincolnshire and also the major non-sequence below the Jamesoni Zone on the Dorset coast. Dorset. Between Charmouth (SY 368930) and Seatown (SY 420917) 13-5 m of Rari- costatum Zone and 23-7 m of Jamesoni Zone are exposed (text-figs. 2, 3, 12). The Raricostatum Zone composes the uppermost part of the Black Ven Marls, whilst the Jamesoni and Ibex Zones together form the Belemnite Marls. Much of the detailed stratigraphic work was done by Lang (in Lang et ol. 1926, 1928) and although this zonal OS ov SELLWOOD: LOWER JURASSIC STAGE-BOUNDARY ^ ^ . /' t 7 " '^y ^ 1 V \r . / II . , ,N,/ ^>■5 -5-^-i «T O O ® O 001 I II O V\^VVAa;. V. A/v'^' vv;\ ^ y V * • ^ aA 'v . A A /' /• .;\/\/ A ;\/\/ \a V M V MM^ ^iriririB^iirTiiiirwTr i ' / \ / I V V' ^ I J3 I A. / S' 1 {rt ^ z\Y i ^ 1 1 1^ \ \ 1 §• ' /' h'\] / \/ V TEXT-FIG. 12. Stratigraphic sequence in the Belemnite Marls with insoluble residue data for each bed. 144 PALAEONTOLOGY, VOLUME 15 scheme is now obsolete his sequence can be easily fitted into the scheme of Dean et al. (1961). The base of the Raricostatum zone is marked by the Coinstone (Bed 89 of Lang) which is a discontinuous line of calcareous nodules. The upper surfaces of these nodules are bored and sometimes encrusted by Gryphaea. Rarely, the undersurfaces are encrusted by serpulids. This band of ‘Hiatus concretions’ (Voigt 1968), which marks the omission of the Oxynotum Zone and part of the Obtusum Zone represents a band of septaria which, when already hard, was exhumed and exposed on the sea floor (Hallam 1969c). The marls immediately below the Coinstone are penetrated by the trace fossils Chondrites, Rhizocorallium, and Thalassinoides: immediately above is a continuous, 2-cm-thick shell bed with broken Inoceramus, Plagiostoma, Oxytoma, Chlamys, and protobranchs, fish scales and abundant pyrite. This is the basal bed of the Raricostatum Zone which continues in laminated bituminous marls. There is a return to more massive and less calcareous clays in the highest part of the Raricostatum Subzone. Kaolinite occurs in only small quantities, never exceeding 10%, and the remaining clay is illite. Iron and manganese occur in only trace amounts and the rare concretions are entirely calcareous. The monotony of the laminated marls with their restricted fauna of byssate epifaunal and free-living bivalves {Oxytoma, Inoceramus, Pseudopecten, and Chlamys) is broken by the Watch Ammonite Stone, a discontinuous band of cementstone lenses rich in echioceratids (Bed 99 of Lang). It occurs 9-3 m above the Coinstone and upper surfaces of individual Watch Stone lenses were eroded and encrusted by Gryphaea before the succeeding beds were deposited. A thin winnowed shell bed rich in Pentacrinus frag- ments occurs immediately above the Stone and marks a phase of increased turbulence within the sequence. As well as containing abundant uncrushed echioceratids, the Watch Stone commonly contains Pseudopecten, Pseudolimea, Plicatula, and rarer Pleurotomaria and Tetra- rhynchia. Most of the fossils are concentrated in the topmost 9 cm of each lens, this uppermost portion of the Stone having a lighter colour than the rest, and abundant small Chondrites and Thalassinoides burrows piped this lighter material down into the darker mudstone below (PI. 29, fig. 1). Laterally, between the individual lenses, a sur- face occurs from which these same types of burrows descended. The upper surfaces of the lenses are sharp and overlain by the intensely bioturbated shell-hash (3-5 cm thick), rich in Pentacrinus debris, crushed ammonites, and Gryphaea. Apart from this bed, and rarely on Coinstone nodules, Gryphaea is absent. This absence is unusual because else- where in Britain the bivalve is present in a variety of diflbrent facies. The spat of Gry- phaea required some kind of hard substrate upon which to settle and the tops of Watch Stone Lenses had been planed-off and hardened, serving then as sites for attachment. Shell debris (in the shell-hash) also facilitated attachment by Gryphaea. This bed and the succeeding darker clays show a diversification of the benthos which is reflected by the foraminifera. A maximum of seven foraminifera species (but generally only two species) are present in the Densinodulum Subzone; the beds just above the Watch Stone, however, contain up to fourteen species (Barnard 1948). The Watch Stone possibly formed a minor ‘hardground’ and the associated accumula- tions of ammonites and other shells, along with the bioturbation, suggests a phase of slow sedimentation. The top of the Stone also marks the top of the Densinodulum Sub- SELLWOOD: LOWER JURASSIC STAGE-BOUNDARY 145 zone and it is probable that the slow or non-sedimentation phase exaggerated the change from the one subzone to the next. The Stone represents an extreme example of a Type 2 cycle (Sellwood 1970). Above, the facies returns to laminated marl and still the fauna continues to have a relatively low diversity, consisting of occasional ammonites, Anti- quilima, Inoceramus, and bivalve juveniles. The sharp lithological change which occurs about 1-6 m below the Hummocky Limestone, from laminated to homogeneous marls, is accompanied by a slight diversification in the fauna. Protobranch bivalves and rare Grammatodon occur, while Pseudolimea, Plagiostoma, and other pectinids become more common. The Raricostatum Zone ends just above an irregular limestone bed containing the coccolith Crepidolithus (?) (PI. 28, fig. 1), the bed was termed the Hummocky Lime- stone (Bed 103 of Lang 1928). Echioceratids are abundant on the undersurface of the bed, where Chondrites, Thalassinoides, and Rhizocorallium burrows also occur. Apart from the Watch Stone, the ‘Hummocky’ is the only other hardened bed within the zone; these are the only beds which contain more than 80 % CaCOg. The top of the Hummocky is penetrated by abundant small Chondrites burrows (OT to 1-0 mm in diameter) and rarer small Diplocraterion tubes (0-7 cm in diameter and 4-0 cm in length), which are filled with marl from the overlying bed (PI. 29, fig. 2). Rhizocorallium burrows also penetrate the topmost 1 cm of the bed, and their sediment-fillings, along with those of the Diplocraterion, have been reworked by larger Chondrites (which are otherwise absent). The small Chondrites and Diplocraterion which penetrate the lowest 9 cm of the limestone are totally uncompacted, whereas in the topmost 1 cm of this 10 cm thick bed the burrows are compacted by more than 50 %. The absence of Rhizocorallium and large Chondrites from the uncompacted and hardened portion of the bed may indicate that some hardening of the unit occurred at an early stage at a shallow depth below the sea bed. Intraformational clasts of limestone up to 1 -0 cm in diameter are present towards the top of the Hummocky Limestone (PI. 29, fig. 2) and these clasts contain dark specks of phosphate. Irregularly shaped clasts like these persist for 2-3 cm up into the overlying marls. Two cm above the top of Hummocky, a discontinuous band of nodular limestone 1 cm thick occurs and above, the rhythmic Belemnite Marls commence. This band of nodular limestone marks the omission of the top two subzones of the Raricostatum Zone and this erosive episode is indicated by the reworked clasts of limestone. Apart from a few calcilutite/marl rhythms at the base of the Taylori Subzone, this subzone is predominantly composed of marls and bituminous shales. As explained earlier (Sellwood 1970; and Sellwood et al. 1970), there is good evidence to suggest that the light to dark rhythms in the Belemnite Marls have a primary origin. It is likely that the development here of more uniform marls and shales in the Taylori Subzone parallels the development of uniform shales during the same subzone in Yorkshire. Light to dark alternations (PI. 29, fig. 3) can still be recognized even when the dif- ference in carbonate content between adjacent beds is only 5% and a similar record was reported by Kennedy (1967) from sedimentary rhythms in the Lower Chalk. The car- bonate component in the argillaceous calcilutites (light beds) consists of echinoid spines, crinoidal fragments, foraminifera, and ostracod shells in the microscopic fraction, and these components often represent micro-lag deposits at the bases of burrow-fills and in storm-scours. The storm-scours are similar to those described earlier, but are filled with bioclastic material, particularly belemnites and crinoid debris. L C 8472 146 PALAEONTOLOGY, VOLUME 15 The presence of scour structures of similar scale to those from the more clastic sequences suggests that the calcareous sediments accumulated under water that might have been no deeper than in northern Britain. The differences in sediment type are attributed to the greater distance of Dorset from the sediment source area. The fine- grained ‘lutite’ matrix composing some 60% or more of the rock consists of micro- crystalline calcite growing on clay flakes (PI. 28, figs. 1, 4). But a contribution is also made by numerous coccoliths and ISchizosphaerella (PI. 28, figs. 2, 4). The latter may be the outer cell- wall layers of calciodinellid dinoflagellates similar and possibly ancestral to those described by Wall and Dale (1968). The clay mineral and iron composition is not detectably different in the calcilutites and marls and only trace quantities of both kaolinite and iron are present in the sequence. The Belemnite Marls contain a poor benthonic assemblage; belemnites are the most common fossils, and ammonites are usually poorly preserved. Bivalves are limited to Inoceramns, Plagiostoma, and thin-shelled pectinids. Protobranchs do not occur, nor do infaunal and semi-infaunal bivalves like Pholadomya and Pinna which are so charac- teristic of the other areas. Even Gryphaea is absent. It is obvious from the poor state of preservation of the ammonites that some aragonitic shell material has been lost during diagenesis. Ammonites are mostly preserved as moulds, but not even the moulds of aragonitic burrowing bivalves occur, and certainly the absence of such bivalves as Gryphaea, with strong calcitic shells, cannot be explained simply in terms of their diagenetic loss. Barnard (1948) also noted the extreme paucity of foraminifera compared with equivalent beds in Germany. Brachiopods are only abundant at two horizons in the Jamesoni Zone, firstly at the top of the Polymorphus Subzone and secondly toward the top of the zone in beds 118-119 of Lang (in Lang et aJ. 1928). Brachiopods occur sporadically throughout the Belemnite Marls and are mostly represented by Cincta and Piarorhynchia. Crinoid debris is sometimes common in the storm scours and it is probable that eddying occurred around small assemblages of crinoids causing their collapse and disintegration (Sellwood 1970). Echinoids are represented by cidarid and diadematid spines, particularly in the calcilutite units. The burrows of suspension-feeders like Diplocraterion, RhizocoraUium, and ThaJassinoides are present. Chondrites is prominent but the burrow walls of these systems are not as distinct as they are in other areas, suggesting that the sediments were poorly con- solidated (Rhoads 1967, 1970). Sediment instability may have been one of the reasons for the restricted benthos, with the sediments having an oozy consistency similar to that envisaged by Kauffman (1967) for some Cretaceous chalks dominated by Inoceramus. Inoeeramus ventricosus (J. de C. Sowerby) from the Belemnite Marls is a relatively large flattened form and by comparison with some Cretaceous Inoeeramus described by Kauffman (1967) may have been adapted to a life on a soft substrate. The smaller 7. dubius usually occurs as disarticulated valves and this species may well have been pseudoplanktonic, attached to floating material like the Inoceramus figured by Hauff (1953) from the Posidonienschiefer. In summary, the high energy and shallow-water conditions represented by the Coin- stone were succeeded by a phase of deepening. Through much of the Raricostatum Zone, the lime-mud and low clay content produced unstable substrates and it was only during times of substrate stabilization in phases of winnowing and shallowing when a more normal benthos became established (Watch Stone). Toward the top of the zone SELLWOOD: LOWER JURASSIC STAGE-BOUNDARY 147 shallowing occurred allowing winnowing and substrate stabilization with a higher diversity benthos. This phase of shallowing culminated in scouring to produce intraclasts of limestone within the ‘Hummocky’ and an extensive non-sequence above it. Deepen- ing occurred in basal Jamesoni times succeeded by the alternating deeper- to shallower- water limestone/marl rhythms of the remaining Belemnite Marls whose impoverished benthos primarily reflects unstable soft substrate conditions. THE INNER HEBRIDES In Scotland, sediments ranging from the Raricostatum to Ibex Zones are included in the Pabba Shales (Judd 1878). The sequence is never continuously exposed and text- fig. 3 is based on a tentative correlation from Loch Slapin, Skye (text-fig. 13,NG 588175), to Pabba (text-fig. 14, NG 673264). The thickness of the Raricostatum Zone (82-6 m) and Jamesoni Zone (111 m) in the Hebridean Area is only exceeded by their thickness at Mochras, Wales. The Hebridean-Irish Sea region may have been one basin with rather more rapid sedimentation and subsidence than other areas. The Raricostatum Zone is not exposed on the Isle of Pabba, but an almost complete sequence, representing the lower portion of the Pabba Shales, is exposed on the eastern shores of Loch Slapin on Skye (NG 588175 to NG 587165). At Carsaig Bay on Mull (NM 535215) and at Hallaig on Raasay (NG 592391) exposures are also available, but the sections on Skye and Raasay are close enough and similar enough to be considered together whilst that at Carsaig shows a number of interesting features which will be mentioned separately. In the Hebrides the underlying Broadford Beds are terminated everywhere by a non- sequence marking the omission of the Oxynotum Zone (Richey 1961), and the absence of this Zone in parts of Dorset, Somerset, and Lincolnshire suggests widespread erosion at about this time. The Pabba Shales continue in silty micaceous shales containing up to 20 % kaolinite. The shales are typified by thin-shelled pectinids {Camptonectes, Chlamys, Entolium, Pseudolimea, Pseudopecten) and protobranchs. The shells commonly occur as fillings to sideritized burrow systems. In the Raricostatum Zone at Slapin (Skye) and Carsaig (Mull) numerous Type 1 upward coarsening cycles occur (text-fig. 13). Bioturbated sandstones at the tops of these cycles contain infaunal and semi-infaunal suspension-feeding bivalves {Pleiiromya, Pholadomya, and Pinna) in their life-positions as well as epifaunal Gryphaea. These introductions of infaunal suspension-feeders were probably related to phases of shallow- ing and increased turbulence. Primary sedimentary structures are limited to the fillings of storm-scours and, for the most part, bioturbation has obliterated any original lamination. At Slapin, Paltechioceras continues to the top of Unit 10 (in text-fig. 13) where the sequence ends with the massive bioturbated sandstone of Unit 1 1 in which no ammonites have been found. On the Isle of Pabba, the section commences with a massive sandstone of Unit 1 1 type and this sandstone is overlain by shales containing Apoderoceras and Phricodoceras (typical of the basal Jamesoni Zone (Table 1)). At Carsaig Bay, faulting and dyke injection make some of the sediments difficult to study, but the characteristic ammonites can be collected and a number of Type 1 coarsening-upward cycles can be seen (Sellwood 1970). The cyclic sediments which 148 PALAEONTOLOGY, VOLUME 15 TEXT-FIG. 13. Stratigraphic section and faunal distributions at Loch Slapin, Skye. SELLWOOD: LOWER JURASSIC STAGE-BOUNDARY 149 contain Paltechioceras rest upon a yellow-green coarse-medium grained sandstone which is devoid of fossils, but which contains numerous levels of interference and symmetrical ripples. Sometimes the ripples bear the trails of organisms (?gastropods) and the openings of vertical (?escape) burrows. Above the basal sands, the beds become more argillaceous and bioturbated, and take on their typical cyclic nature. Some of the sand- stones at the tops of these coarsening-upward cycles contain well-rounded granule- grade clasts of quartz and devitrified volcanic glass. These may have been derived from a local source area exposing the Old Red Sandstone (text-fig. 4). The Jamesoni Zone is best exposed on Pabba where it is mostly represented by extremely micaceous shales, with rare silt and fine sandy laminations (text-fig. 14). The shales are predominantly composed of illite (90%) with subordinate kaolinite. Toward the top of the zone, a number of Type 1 coarsening-upward sequences occur (Sellwood 1970). The shales contain an abundant fauna of thick-shelled and strongly ribbed Pseudopecten and Pseudolimaea; Spiriferina and Cincla are also common at certain horizons in the Taylori Subzone (text-fig. 14). The protobranch Nucula is present throughout the sequence, while bivalve juveniles and Apoderoceras also occur in the basal subzone. The coarsening-upward units toward the top of the zone contain the fauna described above in their shale portions, but in the bioturbated sandstones at the top of each unit infaunal and semi-infaunal bivalves are found, accompanied by adult Gryphaea. Gryphaea is usually only represented by juveniles in the preceding shales. Some sandstone units are capped by surfaces crowded with serpulids and Pentacrinus debris representing phases of winnowing and increased current action at the tops of the units. Coarsening-upward sequences are also present at Carsaig Bay where similar sequences of faunal and trace-faunal changes can be observed. The complete sequence may not be represented on Mull, but in general similar faunas occur as on Pabba, but with probably a greater abundance of infaunal suspension-feeders. NORTH-EAST SCOTLAND Below Dunrobin Castle near Golspie (text-fig. 2, ND 854007) more than 23 m of Raricostatum Zone and more than 5 m of Jamesoni Zone are preserved in a series of sandstones and micaceous shales (text-fig. 3). The stratigraphy of Lee (in Read et al. 1925) can still be applied. The oldest Lias consists of very coarse-grained trough cross- bedded sandstones with cosets up to 1 m thick, containing abundant comminuted plant debris. The sandstones contain well rounded and angular clasts ranging up to granule- grade in size. Quartz is dominant, but a variety of clasts are also present including silicified oolite and laminite, psammite, schist, driftwood, and rounded granules of microsparitic calcite. Sometimes the limestone fragments contain the ‘ghosts’ of pellets and such fragments cannot have been transported far. The clasts are likely to have been derived from either the Durness Limestone or the Old Red Sandstone to the north and north-west (cf the Great Estuarine Series described by Hudson 1964). 40 to 50% of the clay is kaolinite with illite as the remainder. Such a high kaolinite content indi- cates deposition near to the source area. Fossils and burrows are absent from the unit and exposures are poor but the trough cross bedding indicates that the currents which deposited the sandstone moved in a southerly or south-easterly direction. Upward 150 PALAEONTOLOGY, VOLUME 15 TEXT-FIG. 14. Stratigraphic section and faunal distributions on the Isle of Pabba. SELLWOOD: LOWER JURASSIC STAGE-BOUNDARY 151 through the unit (Bed 1 of Lee) there is a general decrease in grain-size, and fine-grained plant debris forms carbonaceous drapes on the toesets of cross-bedded units. These sands may have been deposited under a strong fluvial influence. Above the sandstone, the marine sequence of Raricostatum Zone sediments com- mences (text-fig. 3). A number of Type 1 coarsening-upward cycles are present and the silty clay portions of each cycle contain abundant muscovite. Some of the sandstones contain rounded, granule-grade quartz clasts (Bed 16 of Lee) and the majority of the sediments have been strongly bioturbated. Kaolinite to illite ratios are lower than in the basal sandstone with illite resuming its dominance of the clay fraction (kaolinite 20-30%). Rhizocorallium, Thalassinoides, and Tigillites (probably the burrows of suspension- feeders) are present in the sandy tops of coarsening-upward units, but in general, the fauna of these beds is poor; rare Astarte, Myochoncha, Modiolus, and Gryphaea occur but are not abundant. Mactromya and other lucinoids are also present in the shales. Two shale beds (Beds 8 and 9 of Lee) are, however, highly fossiliferous. Bed 8 contains abundant disarticulated Pseudolimea (with their original colour-banding still preserved) and abundant juvenile Gryphaea. Specimens of the latter are usually disarticulated, but the bed preserves both right and left valves which are often preserved in their life- orientations. Paltechioceras occurs in this and the succeeding bed (Bed 9 of Lee) which also contains abundant bivalves; juvenile Gryphaea are particularly common, accom- panied by Astarte, Cardinia, Pleuromya, Mytilus, and Nuculana. Pseudolimaea and Chlamys are present as disarticulated valves, and fish-scales are sometimes abundant. The whole assemblage is reasonably diverse and comparable to a modern muddy marine shelf assemblage. The Gryphaea represent a life-assemblage but their smallness may indicate adverse conditions (e.g. turbidity). The size-sorted nature of the uncemented shells suggests that some degree of winnowing has affected the bed, and Thalassinoides burrows present in Beds 8 and 9 are often filled with the minute disarticulated valves of bivalve-juveniles representing the smaller shells which are absent from the rest of the bed. These open burrows were probably filled as a result of weak current action. The shell-beds occur at the base of a coarsening-upward unit and three more cycles follow before the Raricostatum Zone ends at the top of Lee’s Bed 16. The ammonites collected by Lee from Beds 7 to 15 indicate the Aplanatum Subzone (Donovan in Berridge and Ivimey-Cook 1967). The Jamesoni Zone continues in fossiliferous shales (Beds 17-21) with much less mica than those in the preceding zone. They contain no obvious structures and are domi- nantly illitic (80%). Both the exposure and the fossil preservation are poor, but the moulds of small, thick-shelled Pseudopecten, Pseudolimea, and thinner-shelled Cardinia are common; accompanied by Gryphaea, Chlamys, Inoceramus, Astarte, Grammatodon, and Proto- cardia. Protobranchs are also common, but the absence of the larger infaunal suspension- feeders probably indicates a low environmental energy. Thus fluvial sandstones derived from the north-west were replaced during Rari- costatum times by a shallow-marine cyclic sequence showing alternating deeper- and shallower-water phases. The poor fauna in most of the Raricostatum succession was probably due to relatively high sedimentation rates and lower than normal salinities. Phases of reduced sedimentation rates, higher salinities, and substrate stabilization 152 PALAEONTOLOGY, VOLUME 15 (possibly during transgressive periods) were marked by diversification in the faunas (Beds 8 and 9 of Lee). In Jamesoni times, a deepening occurred which resulted from a transgressive phase. This lessened the influx of kaolinite, mica, and coarser clastic materials and produced the deeper-water aspect of the Jamesoni sediments. Lossiemouth (text-figs. 2, 3). Berridge and Ivimey-Cook (1967) described 69-5 m of Lower Lias, in an I.G.S. borehole near Lossiemouth (NJ 21586986). Part of this sequence contained Paltechioceras (between 46-47*9 m) and is of unquestioned Rari- costatum Zone age. Berridge and Ivimey-Cook suggested that the oldest sediments penetrated were lagoonal with a passage upwards into more marine beds containing Lingula. These pass upwards into the fully marine sediments containing the ammonites and bivalves. The sediments which occur above the highest Paltechioceras continue as sandstones, siltstones, and shales containing occasional Protocardia, Ceratomya, and Pholadomya. These sediments presumably represent part of the Jamesoni Zone and in view of their coarse-grained and highly kaolinitic nature, were probably deposited in a nearer shore situation than their equivalents at Golspie. Berridge and Ivimey-Cook commented on the ‘small scale oscillatory tendencies’ shown by much of the sequence and from their figure it seems that their oscillations are coarsening-upward sequences. The highest beds are extremely rich in kaolinite (60%-f-) which becomes the dominant clay. The sediments become much more sandy and fossils are not present, suggesting a reversion to fresh water conditions possibly late in Rari- costatum and (?) through lower Jamesoni times. Lossiemouth was marginal to the Lower Lias sea for some of the time and was periodically inundated by transgressive events. The persistence of coarse sediments at Lossiemouth opposes the general trend of a fining in grain which occurred in the rest of Britain from the Raricostatum to the Jamesoni Zone, and this suggests that in the vicinity of Lossiemouth, and probably to the south, a positive area existed which resisted subsidence and continued to supply sandy kaolinitic material (text-fig. 4). FACIES INTERPRETATION In Britain, the only truly marginal facies are the basal sands at Golspie, possible lagoonal sequences in the Lossiemouth borehole, and possible littoral sediments in some of the boreholes on the margins of the London Platform. Marginal sequences outcrop in Scandinavia, Greenland, and Poland. In Sweden and on the Danish island of Bornholm, Rhaetian to Sinemurian sediments are represented by fluvial and coal- measure facies (Troedsson 1951; Gry 1969). Accompanying these sequences are mar- ginal marine inter-tidal and sub-tidal sequences (Sellwood in press) exhibiting many of the features typical of modern tidal-flat and sub-tidal deposits (Reineck 1960, 1967; Reineck and Wunderlich 1968; Reineck et al. 1968; Van Straaten 1954). Wavy and tidal bedding (pi. 28, fig. 5) accompany many other features considered by Klein (1970) to characterize tidal conditions. The first beds containing abundant marine faunas are of Jamesoni Zone age consisting of ferruginous sands and clays with siderite nodules. In Sweden, paralic facies of Rhaetian and Hettangian age are succeeded by a marine sequence of Jamesoni age and a similar situation also occurs in East Greenland (Rosen- krantz 1934). In Britain the commencement of Jamesoni times is marked by renewed sedimentation SELLWOOD: LOWER JURASSIC STAGE-BOUNDARY 153 in Dorset and Somerset (regions of reduced or non-sedimentation during late Rari- costatum Zone times); by the deposition of marine sediments on some parts of the London Platform; and in Yorkshire, Lincolnshire, the Inner Hebrides, and Golspie, the zone is marked by a considerable reduction in grain-size with the loss of most sand- grade material. The exception to this pattern is Lossiemouth, where coarse-grained kaolinitic sandstones may represent a part of the zone. None of the sediments exposed in Britain take on a truly deep water facies and most of the sediments display some evidence of at least periodic disturbance by storm or wave generated currents. The lack of faunal mixing and the lack of turbidite-type sedi- ments argues against the presence of steep gradients upon the bed of this epicontinental sea, and in most localities the faunas which occur in shell beds consist of the forms which can be found in or close to their life-positions in the surrounding sediment. This is in marked contrast to the observations of Parker (1956, 1964) who found that on modern slopes downslope movement occurred to produce considerable faunal mixing. Generally, thicker sequences tend to occur toward the margins of the basin in sandy and silty shale facies and where subsidence was greatest. Condensed deposits are of two main types: ferruginous, like the Pecten Bed (with chamosite), and calcareous as at Radstock (calcarenites with glauconite and phosphate). Calcilutite/shale rhythms are really intermediate in character between the condensed calcarenites and uncondensed shales. In Dorset, the slight positive nature of the region is revealed by a number of non-sequences (Coinstone, Watch Stone, Hummocky Lime- stone) and the thinness of the beds in this section compared with those in other sections (except Somerset). Both the Dorset and Somerset areas were evidently swell regions starved of clastic sediments. The situation was analogous to that proposed by Kauffman (1969h) for the con- figuration of the Cretaceous epicontinental basin of the United States Mid West. The Lias sea of northern Europe was of course open southwards to the Tethys and possibly westwards to a proto-Atlantic trough (Smith 1971), whereas the Cretaceous basin of the United States was partially enclosed. In the Lias, the north European basin was punctuated by a number of small positive swells such as the London Platform, the Mendips-Dorset-Normandy Swell, and numerous others. Small swells of this type have not yet been recognized from the North American Cretaceous (Kauffman pers. comm.). Limestone/shale rhythms were developed on broad sediment-starved swells and silty and sandy clays accumulated in more rapidly subsiding nearshore belts, passing in their turn into thinner marginal and paralic sequences. Hallam (1967u) suggested a facies model for the Lias which has been tested in this work and the results presented here, although differing in detail, are broadly comparable and the present model (which is only applicable to the area of northern Europe) is given as text-fig. 5. The faunal changes which occur from the Raricostatum to the Jamesoni Zone in Britain are subtle and related to the decreased grain size and changes of facies which in most places reflect a slight increase in water depth. This was accompanied by marine transgression of the Scandinavian and Greenland shorelines in Jamesoni times. Eustasy. Hallam (1969a) suggested that some of the extensive marine transgressions in the Jurassic were caused by eustatic changes because of their synchroneity on a global scale. The basal Pliensbachian transgression occurred in regions bordering the North 154 PALAEONTOLOGY, VOLUME 15 Atlantic (Hallam 1969a) where the Jamesoni Zone marks a phase of either marine inundation or a change from shallow to deeper marine sedimentation. Smith (1971) suggests that the present phase of Atlantic ocean-floor spreading commenced in Pliens- bachian times, and if this is so, oceanic ridges must have been constructed, displacing sea-water. From the studies of Fowler and Kulm (1970), Van Andel (1969), and Van Andel and Heath (1970) it is known that large-scale vertical movements on ridges can occur. Smaller-scale oscillations could also be envisaged, sufficient to produce the small- scale cycles which are so typical of Lias epeiric sea sedimentation (Sellwood 1970). Ridge construction may also coincide with subsidence on continental margins. Tidality. On theoretical grounds, broad shallow epeiric seas should have had reduced tidal circulations (Shaw 1964). Direct evidence of tidality in shallow neritic sediments is equivocal but may be better in marginal and littoral sequences. The Lower Lias sediments from Bornholm strongly suggest a tidal origin, and facies regulation by tides (Johnson and Belderson 1969) in epicontinental seas may have been underestimated by many authors. Tidal regimes on the margins of the Lias epeiric sea indicate that tidal- current activity within the basin occurred. Tidal-current mixing of Tethyan and boreal waters would not have permitted the development of the salinity-controlled faunal realms envisaged by Hallam (19696). Salinity. The salinity-control of faunal realms and faunal gradients proposed by Hallam (19696) is not supported by observations on faunal distributions within the boreal reahn during Raricostatum and Jamesoni times. The Hallam hypothesis required the subtle control of faunas by minor salinity reductions over wide areas in the Boreal Realm, If minor reductions of salinity could cause such marked faunal changes in the major part of the European epicontinental basin one might expect even more drastic famial reductions in the marginal areas where salinities should be even lower because of river influences. However, faunas at Golspie (nearer the sediment-source) are more diverse in some beds than those of the same age in Dorset, and normal, diverse, shallow-marine faunas (including ammonites) occur in the basal Pliensbachian arkoses of East Green- land (Rosenkrantz 1934). 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VAN STRAATEN, L. M. J. u. 1954. SeduHcntology of recent tidal flat deposits and the Psammites du Condroz (Devonian), Geologie Mijnb. 16, 25-M. VOIGT, E. 1968. liber Hiatus-Konkretionen (dargestellt an Beispielen aus dem Lias). Geol. Rdsch. 58, 281-296. WALL, D. and DALE, B. 1968. Quaternary Calcareous Dinoflagellates (Calciodinellideae) and their natural affinities. J. Paleont. 42, 1395-1408. WEAVER, c. E. 1958. Geological interpretation of Argillaceous sediments. Bull. Am. Ass. Petrol. Geol. 42, 252-309. YONGE, c. M. 1923. Studies on the comparative physiology of digestion. 1. The Mechanisms of Feeding, Digestion and Assimilation in the Lamellibranch Mya. Brit. J. exp. Biol. 1, 15-63. 1939. The Protobranchiate Mollusca: a functional interpretation of their structure and evolution. Phil. Trans. R. Soc. B. 230, 79-147. 1953fl. Form and habit in Pinna carnea Gmelin. Phil. Trans. R. Soc. B. 237, 335-374. \952>b. The monomyarian condition in the Lamellibranchia. Trans. R. Soc. Edinb. 62, 443^78. 1957. Mantle fusion in the Lamellibranchia. Publ. Staz. Napoli, 29, 25-31. 1960. Oysters. Collins, London. B. W. SELLWOOD Department of Geology and Mineralogy Parks Road, Oxford Typescript received 27 April 1971 MORPHOLOGY AND TAXONOMIC STATUS OF THE JURASSIC BELEMNITE ^RHOPALOTEUTHIS' SOMALIENSIS SPATH 1935 by J. A. JELETZKY Abstract. The new genus Somalibelus is erected, type species Rhopaloteiithis somaliensis Spath 1935. The external and internal morphology of the species is described in detail using material from the type locality in the Kimmeridgian of Somalia, Africa. All the material studied is regarded as belonging to a single, highly variable species. The ontogeny and limits of variation of the species are discussed. The original diagnosis of Rhopaloteuthis somaliensis (Spath 1935, p. 223) points out the ventral position of the median alveolar groove (canal) which extends on its alveolar part. This statement is incompatible with the reference of this species to the genus Rhopaloteuthis and family Duvaliidae Pavlow 1914, which are characterized by the dorsal position of this groove. This had induced the writer (Jeletzky 1966, pp. 123, 124, 128) to place ‘i?.’ somaliensis into the belemnopseid genus Curtohibolites Stoyanova- Vergilova 1963. A subsequent, more detailed study of the original material of ‘i?.’ somaliensis including its type specimens necessitated a reappraisal of this assignment, the results of which are presented below. Acknowledgements. Dr. C. L. Forbes, Curator of the Sedgwick Museum, University of Cambridge, England, has made available a representative suite of the topotypes of ‘A.’ somaliensis and permitted the indispensable sectioning of several of these specimens. Drs. H. W. Ball and M. K. Howarth, Department of Palaeontology, British Museum (Natural History), London, England, have loaned figured and unfigured type specimens of ‘A.’ somaliensis. The writer expresses his sincere thanks to these colleagues. The writer expresses sincere thanks to his assistant Mrs. J. Danis who has prepared most of the thin sections and supervised the preparation of all photographs used in the paper. Thanks are also due to Miss Jeanne White and Mr. Frederick Cooke, Geological Survey of Canada, who prepared the photographs and photo-micrographs respectively, reproduced in this paper. Abbreviations. Repositories of specimens are indicated as follows; S.M.C., Sedgwick Museum, Cam- bridge; B.M.N.H., British Museum (Natural History). SYSTEMATIC DESCRIPTION Family belemnopseid ae Naef, 1921 emend. Jeletzky, 1946 Genus somalibelus nov. Type species. Rhopaloteuthis somaliensis Spath 1935 Diagnosis. A Curtohibolites-\ikQ guard characterized by a distinctly addorsally dis- placed, more or less distinctly oval to egg-shaped, dorso-ventrally elongated alveolus, absence of double lateral furrows, and the presence of single mediolateral longitudinal ridges flanked by flattened to slightly depressed, narrow longitudinal zones on one or [Palaeontology, Vol. 15, Part 1, 1972, pp. 158-83, pis. 30-38.] JELETZKY: ^RHOPALOTEUTHIS' SOMALIENSIS 159 two sides; splitting surface even but more or less rough-surfaced except in a narrow zone adjoining the ventral side of the alveolus and in the adoralmost part of the guard. Geographical range. Somalia, formerly Somaliland Protectorate (British Somaliland), Africa. Stratigraphic range. Kimmeridgian (lower?; or middle?; compare Spath 1935, pp. 219, 223). Historical remarks. The original placement of SomaUbeJus somaUensis in the duvaliid genus Rhopaloteuthis was caused by the long-standing controversy about the taxonomic status of this genus recently reviewed by Pugaczewska (1957, pp. 385-386) and Gusto- messov and Uspenskaya (1968, pp. 65-67). Spath (1933, pp. 664, 665; 1935, p. 219) was fully aware of the fact that the siphuncle of the S. somaUensis is situated on the same side of the guard as the medioalveolar groove. He nevertheless placed it in the genus Rhopaloteuthis Lissajous 1915 believing Lissajous’s (1915, 1925, pp. 41-42, text-fig. 23) conclusions about the dorsal position of the alveolar canal in its genotype R. sauvanaui (d’Orbigny) to be in error. Spath (loc. cit.) believed that Rhopaloteuthis is characterized by the ventral position of alveolar canal in contrast to Conobelus Stolley 1919 which is characterized by its mediodorsal position. These conclusions were subsequently discredited by work of Pugaczewska (1957, pp. 385-386), Jeletzky (1966, p. 144 and unpublished observations on original material of R. sauvanaui) and Gustomessov and Uspenskaya (1968, pp. 65-67). ‘i?.’ somaUensis Spath 1935 is extremely similar to representatives of the recently erected mid-Lower Cretaceous genus Curtohibolites Stoyanova-Vergilova 1963 in the external morphology of its guard. Like ‘7?.’ somaUensis, all Curtohibolites species are characterized by the presence of a medioventral canal on the alveolar part of the guard. For these reasons ‘7?.’ somaUensis was transferred into Curtohibolites by Jeletzky (1966, pp. 123, 124, 128) following the recognition of the duvaliid nature of Rhopaloteuthis, in spite of its considerably older (lower or middle Kimmeridgian) age. A subsequent, more detailed study of external and internal morphology of a representative sample of ‘7?.’ somaUensis, including its type specimens, revealed a number of important morpho- logical distinctions from Curtohibolites and all other genera of Belemnopseidae. These morphological distinctions necessitate the erection of a new genus for ‘7?.’ somaUensis and suggest its being an older, more primitive homoeomorph of Curtohibolites (see below). Affinities and differences. As already mentioned, the external morphology of Somali- belus resembles closely that of the genus Curtohibolites as interpreted by the type species C. trubatchensis Stoyanova-Vergilova 1963. However, it differs from Curtohibolites in the following taxonomically important morphological characters : 1. The guard of C. trubatchensis is characteristically feebly compressed in the anterior part but feebly depressed in its apical part. 2. The splitting surface of C. trubatchensis is smooth throughout and has a different shape. Its bottom runs in a straight line obliquely adapically in the inner half of the guard’s cross-section (Stoyanova-Vergilova 1963, p. 213, text-fig. 2). Then it turns abruptly and runs obliquely adorally in a straight line until it reaches the ventral sur- face of the guard a few mm adorally of the protoconch’s level. 3. Double lateral lines are characteristically present in C. trubatchensis. They are well developed to incised, closely spaced, subparallel and strongly displaced adventrally in the alveolar part of the guard. 160 PALAEONTOLOGY, VOLUME 15 4. The position of the alveolus in relation to the guard’s axis is not mentioned either in the description of C. trubatchensis or in that of any other species placed in Curto- hibolites by Stoyanova-Vergilova (1963). However, the poor figures provided by her (Stoyanova-Vergilova 1963, pi. II, figs. Ic, d, e, 2c, 5c, d, e, 6, Ic, d) are enough to attest its central position at least in C. trubatchensis and C. wernsdorfensis. The same appears to be true of the alveolus of the still less satisfactorily reproduced C. rasgradensis and C. orbignyamis Stoyanova-Vergilova 1963 non Duval-Jouve 1841 (see Stoyanova- Vergilova 1963, pi. I, figs. \d, 2c, d, 3c, 4c, d, e). These morphological distinctions appear to be ample for the recognition of generic independence of Somalibehis somaiiensis (Spath 1935) from Curtohibolites. 5. somaiiensis (Spath 1935) resembles representatives of Parahibolites Stolley 1919 in the characteristic feeble to marked compression of its guard. It differs markedly from all representatives of Parahibolites, however, in the addorsal displacement of the alveo- lus, an entirely different character and outline of the splitting surface, absence of double lateral furrows, presence of single lateral ridges, and the compressed cross-section of the phragmocone. The compression of the guards of Somalibelus and Parahibolites must, therefore, be the result of homoeomorphy rather than of a direct genetic link between these other- wise dissimilar Belemnopseidae genera. From all representatives of genera Belenmopsis Bayle 1878, Hibolithes Montford 1808, Mesohibolites Stolley 1919, and Neohibolites Stolley 1919, S. somaiiensis (Spath 1935) differs in the same morphological features as from the representatives of Parahibolites. The guards of the former four genera are, besides, characteristically depressed in their postalveolar parts at least, which contrasts with the more or less compressed cross- section of the corresponding part of the S. somaiiensis guard. Even the exceptional representatives of Belenmopsis (e.g. B. angusta Stolley 1919, B. rnackayi Stevens 1963, B. ex gr. uhligi Stevens 1963) and Hibolithes {H. beyrichi Oppel) characterized by equi- dimensional to somewhat compressed cross-sections of the posterior parts of their guards differ sharply from S. somaiiensis in all other above-mentioned features. This leaves no doubt about generic independence of S. somaiiensis from the four above- mentioned belemnopseid genera. All known representatives of Pseiidohibolites Bliithgen 1936 differ sharply from S. somaiiensis in the complete absence of medioventral canal and splitting surface on the preserved alveolar parts of their guards (Bluthgen 1936, p. 40). Furthermore, they possess strongly developed single lateral furrows on the anterior parts of the flanks which may merge into double lateral furrows on the posterior parts of the ffanks. At the same time they lack the characteristic single longitudinal ridges of S. somaiiensis. These morphological distinctions are of a familial rather than generic rank in the writer’s opinion. Genetic ties of Somalibelus. Among the Belemnopseidae Somalibelus resembles most closely the unusually short, sturdy, and laterally compressed representatives of Belem- nopsis (e.g. B. ex gr. angusta-apiciconus) occurring in the late early Bajocian and middle Bajocian of Normandy (Stolley 1927, p. 123, pi. 24, fig. 9; Eudes-Deslongchamps, 1878, pp. 69-73, pi. VII, figs. 1-4). In addition to the general similarity of the cross-section, shape, and proportions of the guard, Belenmopsis angusta Stolley resembles S. somali- JELETZKY: ^RHO PALOTEUTHIS' SOMALIENSIS 161 ensis in the indistinctness or complete absence of double lateral furrows. In spite of these points of similarity and suitable stratigraphic relationships, it is impossible to interpret S. somaUensis as a direct descendant of B. ex gr. angusta-apiciconus. All known repre- sentatives of this species group possess a differently shaped, completely smooth splitting surface closely resembling that of Hibolithes jaculum Phillips or H. inflexus Stolley (Krymgolts 1939, p. 12, pi. I, fig. 26; text-figs. 1, 5). This splitting surface begins slightly adapically of the protoconch and its bottom extends obliquely apically and ventrally until it reaches the ventral surface of the guard somewhat below its middle. The pre- sence of a considerably more advanced, completely smooth splitting surface already in the oldest known Bajocian Belemnopsis forms suggests that Somalibehis evolved directly out of some still unknown morphologically similar but older and morphologically more primitive belemnopseids transitional between Hastiles ex gr. clavatus lanceolatus Hart- mann 1830 on the one hand (Jeletzky 1966, pp. 143, 144), and Belemnopsis ex gr. angusta-apiciconus on the other. This hypothesis agrees well with the distinctly primitive Hastites-\\kQ ontogenetic development of the guard of S. somaUensis discussed below. It seems probable that the main stem of Belemnopseidae represented by the Hibo- lithes- and BeIemnopsis-\\k& forms repeatedly produced more or less short-lived, specialized offshoots characterized by unusually sturdy guards (e.g. Belemnopsis ex gr. angusta-apiciconus, Somalibelus, Curtohibolites). These offshoots may have been adap- tations to a less active, nektobentonic mode of life in closer proximity to the shoreline in comparison with the more typical, slender, and subfusiform representatives of the family. Somalibelus somaUensis (Spath 1935) Plates 30-38 1929 Beleimiites {Belemnopsis) sauvanaiii d’Orbigny; Weir, p. 18, pi. Ill, fig. 5. 1933 Rhopaloteiithis {Belemnopsis) sauvanaui (d’Orbigny); Spath, p. 665. 1935 Rhopaloteiithis somaUensis Spath, pp. 223-224, pi. XXV, figs. Aa, b. Type specimens. Spath (1935, p. 223) has expressly designated the only figured, frag- mentary specimen of R. somaUensis as its holotype. This choice is most unfortunate on two counts. Firstly, the selected holotype (C. 42147; Spath 1935, pi. Ill, fig. 5) consists of one half of the guard only and even this fragment lacks a few mm at the apical end. It is, therefore, impossible to observe a number of taxonomically important morpho- logical features in the holotype (e.g. the medioventral canal, character of the apical end, shape of the guard in ventral aspect). Secondly, the holotype does not represent the average form of the species but one of its extreme variants ; namely the extremely sturdy and apically obtuse form with an extremely deep alveolus. Such forms are by no means common in the population sample studied and the unfigured paratype II of Spath (1935, p. 223; this paper, PI. 31, fig. 2) is undoubtedly much more representative of S. somaU- ensis. The unfigured paratype I of Spath (1935, p. 223; this paper PI. 31, fig. 3) appears to be extremely close to the holotype in all taxonomically important features including the depth of its alveolus. The unfigured holotype of R. somaUensis var. attenuata (Spath 1935, p. 223) is repro- duced in PI. 31, fig. 1 of this paper. This reasonably complete and satisfactorily preserved guard is morphologically representative of another extreme variant of the species C 8472 M 162 PALAEONTOLOGY, VOLUME 15 characterized by relatively slender, markedly laterally compressed guard with a shallow alveolus (PI. 30, fig. 6; PI. 32, fig. 3). Material studied. This revision of somaliensis is based on a detailed study of about 85 satisfactorily to well preserved, fragmentary to almost complete guards from the type locality preserved in collections of the Sedgwick Museum, University of Cambridge, England. The holotype of the species, that of "R.’’ s. var. atteuuata, and two unfigured paratypes (Spath 1935, p. 223), preserved in collections of the British Museum (Natural History) were also restudied. A considerable number of other topotypes of 'R.’ somaliensis preserved in these collections were not studied in any detail as they did not seem to be any different from the Sedgwick Museum material. External morphology. The guard is small, short to very short and sturdy. The estimated length of the largest known representative (C. 45936; PI. 31, fig. 3) is about 33 mm. The estimated elongation of the guard (i.e. the ratio of estimated length to the maximum dorso-ventral diameter) fluctuates between 3 and 4-5 in the best preserved specimens. The critical measurements and ratios of best preserved and most complete guards are summarized in Table 1. As a rule, the guard is more or less distinctly subclavate, more markedly so in ventral than in lateral aspect. In ventral aspect, the shape of undistorted guards varies from slightly (PI. 30, fig. 5a) to markedly (PI. 32, fig. 2a, d) subclavate. The maximum lateral diameter is mostly situated within the apical half of the guard closely above or closely below the apex of the alveolus. This applies to sturdy individuals similar to the holotype of the species (PI. 30, figs. 3a, 5a; PI. 31, figs. 3a, 4a) and to slender forms similar to its var. attenuata (PI. 31, fig. la, PI. 32, figs. 2a, d, 3a, d). Some exceptional guards are, however, almost cylindrical in ventral aspect (PI. 30, figs. 6a, c, la, c). In these aberrant specimens the almost unnoticeable maximum swelling of the guard occurs either in its middle or slightly adorally therefrom. EXPLANATION OF PLATE 30 Sotnalibelus somaliensis (Spath 1935). Kimimeridgian (?lower or ?middle), near Bihendula, Somalia, Africa. Exact horizon and location unknown; the specimens may have been collected at different spots near Bihendula (Spath 1935, pp. 219, 224). Letter V marks the position of ventral side of guard. Figs. \a-e. SMC F. 13456/9. a. Ventral view, xl; b. Left lateral view, X 1 ; c. Right lateral view, X 1 ; d. Same view as in Ic, x4; e. Alveolar view, x 10 showing addorsal displacement of the alveolus and the siphuncle (marked s). Figs. 2a, b. SMC F. 13456/20. Fragment of the alveolar part of the guard, polished at both ends. a, Adapical cross-section, xA\b, Adoral cross-section, x4. Figs. 3a-c. SMC F. 1690. a. Ventral view, x\ \ b. Right lateral view, X 1 ; c. Left lateral view of phragmocone and splitting surface (marked sps), with left half of guard removed, x 4. Figs. Aa-d. SMC F. 13456/12. Fragment of the alveolar part of the guard, polished at the adoral end. a. Ventral view, X 1 ; Zj, Right lateral view, X 1 ; c, Adoral cross-section (polished), xA\ d, Adapical cross-section, X 1 . Figs. 5a-e. SMC 297. a. Ventral view, x\\ b. Left lateral view, X 1 ; c. Right lateral view with oral half of right side of guard (broken piece) removed, X\ \ d. Right lateral view of phragmocone and splitting surface, same view as in 5c, X 4. Note contrast between the almost to quite level and partly smooth appearance of splitting surface (marked sps) and the rough surfaced appearance of the dorsal part of the guard, c. Alveolar view, X 1. Figs. 6o-e. SMC F. 13456/21. a. Ventral view, X\\b, Left lateral view, X 1 ; c. Same view as 6a, X 3; d. Right lateral view, X 3 ; c. Alveolar view, X 3; /, Apical view, X 3. Figs. la-f. SMC F. 13456/15. a. Ventral view, x\\ b. Right lateral view, X 1 ; c. Same view as in la, X 2-5 ; d. Same view as in lb, X 2-5 ; e. Alveolar view, X 2-5 ; /, Apical view, x 2-5. Palaeontology, Vol. 15 PLATE 30 JELETZKY, Somalibelus somaliensis JELETZKY: ^RHOPALOTEUTHIS' SOMALIENSIS 163 In most undistorted specimens the guard contracts slightly and more or less evenly all the way adorally from the level of its maximum lateral diameter. In a few specimens (e.g. PI. 32, fig. la, d) this even and regular adoral tapering is interrupted by a feeble constriction of the guard restricted to the lower part of the alveolar region. This results in a feebly concave ventral outline of the alveolar parts of such specimens which is unlike the essentially straight ventral outlines of the majority of specimens. Adapically of the level of maximum lateral diameter most guards contract con- siderably faster in the ventral aspect than they do adorally therefrom. In many guards morphologically similar to the holotype of the species the contraction increases pro- gressively to the apex (PI. 30, figs, la, 5a; PI. 31, figs. 3a, 4a; PI. 32, fig. 4a). This results in a pronouncedly convex and obtuse (apical angle from 90 to 120°) apical end of the guard in ventral aspect. A small, mostly poorly defined, mucro may be superimposed on the broadly rounded base of the apical end in some of these specimens (PI. 31, fig. 3a). In a considerable number of other specimens either similar to 5. 5. var. attemiaia (PI. 31, fig. \a, c; PI. 32, figs, la, d, 3a, d) in the degree of their slenderness or approach- ing the holotype of the species in their sturdy proportions (PI. 30, fig. \a; PI. 31, fig. la, d) the initially slight and gradual adapical tapering of the guard increases more or less abruptly within its apical quarter. Further adapically the flanks of such guards converge at angles ranging from about 30° (PI. 32, fig. 3a, d) to about 60° (PI. 31, fig. la, d) to the apex which results in an essentially straight, conical ventral outline of the apical quarters. Some of the previously mentioned slender guards (PI. 30, figs. 6n, c, la, c), in which the maximum lateral diameter is situated either in the middle of the guard or slightly higher, contract gradually and increasingly right through the lower two-thirds of their length. This results in the obtusely rounded, distinctly mucronate appearance of the apex in some of these slender (laterally subconical; see below) guards (PI. 30, fig. 6a-d). Numerous transitional forms (e.g. PI. 32, fig. la, d) connect the above described extreme forms with one another. The lateral outline of many undistorted specimens is shaped similarly to their ventral outline except for a lesser degree of adapical and adoral contraction. This is true of most of the slender specimens approaching var. attenuata (PI. 31, fig. \b, e; PI. 32, fig. 3b, c) but also applies to a number of sturdy guards including the holotype (e.g. PI. 31, fig. lb, c, e, f; PI. 32, fig. 5a-d). However, a considerable number of sturdy specimens approaching the holotype (e.g. PI. 30, figs. \b, c, d, 3b, 5b; PI. 31, fig. 4b, c) are almost cylindrical in lateral aspect, except for their obtusely rounded (and sometimes mucro- nated) to conical apical quarters, the outlines of which remain entirely similar to the already discussed ventral outlines of the apical quarters of the same specimens. The lateral outlines of some of the previously mentioned ventrally subcylindrical guards (e.g. PI. 30, fig. lb, d) are entirely similar to their ventral outlines. Those of some other ventrally subcylindrical guards (e.g. PI. 30, fig. 6b, d) taper adapically throughout their length. This results in the high conical lateral outline of such guards. The lateral outlines of their apical quarters may either be obtusely rounded and mucronate because of a progressive increase of contraction in this direction (PI. 30, fig. 6b, d) or acute and wedge-shaped (PI. 30, fig. lb, d). The alveolar cross-sections of all undeformed guards vary from feebly to markedly 164 PALAEONTOLOGY, VOLUME 15 compressed and from more or less regularly elliptical to distinctly laterally flattened (PI. 30, figs, le, 2a, b, Ac, 5e, 6e, le\ PI. 31, figs. 1/, Ig, 4e; PI. 32, fig. Ad). Among these alveolar cross-sections, those of the sturdiest guards approaching the holotype of the species (e.g. PI. 30, fig. \e\ PI. 31, figs. 2g, Ae) are characterized by the least amount of compression (ratio lateral diameter/dorso-ventral diameter from 0-86 to 0-88) and almost regularly rounded flanks, while those of the relatively slender guards approaching var. attenuata in this respect (e.g. PI. 30, fig. 7e; PI. 31, fig. 1/) are the most compressed (the ratio lateral diameter/dorso-ventral diameter fluctuates from 0-84 to 0-86) and possess distinctly to markedly flattened flanks. Most of the slender forms approaching var. attenuata (PI. 30, figs. 2a, 6f, If-, PI. 31, fig. \g; PI. 32, fig. 3/) remain feebly laterally compressed all the way adapically and retain the above described elliptical but more or less laterally flattened cross-section throughout the posterior two-thirds of the guard. However, in a few slender guards like that reproduced in PI. 32, fig. 2, the compression decreases adapically and finally disappears at the level about 11-5 mm above apex where the dorso-ventral and lateral diameters are about 5-9 mm each. Further adapically the cross-sections of this guard remain about equidimensional in spite of the ventral surface becoming somewhat flattened in the middle (PI. 32, fig. 2g). The shape and proportions of cross-sections within the posterior half to one-third of the guard vary ordinarily from distinctly compressed and feebly laterally flattened cross-sections (PI. 31, fig. Ig; PI. 32, fig. Ae) to either slightly compressed (e.g. the unfigured specimen F 1689 with the compression ratio of maximum lateral diameter/ maximum dorso-ventral diameter of 8-0/8-4 = 0-95) or more or less equidimensional and regularly rounded cross-sections (PI. 31, fig. 3g); PI. 32, fig. 2g). The posterior cross- sections of another fairly numerous group of specimens are more or less equidimensional but rounded-subtrapezoidal with the maximum lateral diameter displaced adventrally (PI. 31, figs. 2h, Af). The about equidimensional regularly rounded and rounded- subtrapezoidal cross-sections are prevalent among the sturdy representatives of S. somaliensis. They appear to be about equally common in this form group. However, there are some sturdy representatives of S. somaliensis the cross-sections of which remain EXPLANATION OF PLATE 31 Somalibelus somaliensis (Spath 1935). Horizon and locality as for Plate 30. V marks the position of the ventral side of the guard. Figs. la-g. BMNH C. 42146. Holotype of Rhopaloteuthis somaliensis var. attenuata Spath 1935. a, Ventral view, x3; b. Right lateral view, x 3; c. Same view as in lu, X 1 ; r/. Dorsal view, X 1 ; e. Left lateral view, X 1 ;/, Alveolar view, X 1 ; Apical view, X 1. Figs. 2a-h. BMNH C. 45937. Unfigured paratype 11 of R. somaliensis Spath 1935, No. 253. a. Ventral view, X 1 ; Z), Left lateral view, X 1 ; c. Right lateral view, :< 1 ; d. Same view as in la, X 3 ; e. Same view as in 2c, X 3 ; /, Same view as in 2^, X 3 ; g. Alveolar view, X 1 ; Apical view, X 1 . Figs. 3a-g. BMNH C. 45936. Unfigured paratype of R. somaliensis Spath 1935, No. 251. a. Ventral view, X 3; 6, Right lateral view, X 3. Note the longitudinal lateral ridge which is exceptionally well developed in this specimen ; c. Same view as in 3a, x 1 ; d. Left lateral view, X 1 ; c. Same view as in 3b, X 1 ;/, Alveolar view, X 1 ; .g. Apical view, X 1. Figs. 4a-/. SMC F. 1691 (293). a. Ventral view, xl; b. Left lateral view, X 1. Note the well developed longitudinal lateral ridge; c. Right lateral view, X 1 ; <7, Dorsal view, x 1 ; c. Alveolar view, x 1 ; /, Apical view, x 1. Palaeontology, Vol. 15 PLATE 31 JELETZKY, Somalibelus somaliensis JELETZKY: ‘RHOPALOTEUTHIS^ SOMALIENSIS 165 compressed and somewhat laterally flattened throughout the apical parts of their guards much like those of the slender representatives of the species (PI. 32, fig. 4c). Finally, in a few extreme cases, apparently restricted to extremely sturdy guards with obtusely rounded apical ends, the cross-seetion of the apical half of the guard is slightly depressed. For example, specimen F. 1687 (PI. 32, fig. 6/) has a depression ratio maxi- mum lateral diameter/maximum dorso-ventral diameter of 9-2/9-0, or about 1-02. The medioventral groove restricted to the anterior half to three-fifths of the guard in most studied representatives of Somalibehis somaliensis (Table 1) is a true ventral canal (Jeletzky 1966, pp. 147, 148) as it is accompanied by an admittedly imperfectly developed splitting surface (see below) and the underlying layers of the guard exhibit distinct to pronounced inward bends throughout its alveolar part (PI. 30, figs. \e, 2a, b, 4c; PI. 32, fig. Ad). The conotheca is likewise bent inward (PL 32, fig. Ad) which results in its inner surface forming a sharp longitudinal ridge underneath the medioventral canal. As pointed out by Spath (1935, p. 223), the strength and length of the medioventral canal varies rather strongly. It is usually restricted to the anterior half (PI. 30, figs. 3u, 5a; PI. 31, fig. la, c) to three-fifths of the guard but may extend over most (PI. 30, fig. la, c; PI. 32, figs. 2a, d, 3a, d) or even all (PI. 30, fig. 6a, c) of its length. The adoral part of the ventral canal which is mostly limited to the adoral two-fifths to one-half of the guard’s length in the most complete specimens, is considerably deeper incised and more narrow than its adapical part. It has a narrowly V-shaped to narrowly U-shaped cross-section. Further adapically the ventral canal rapidly shallows, widens to at least twice its former width and is transformed into a broad, only slightly deepened, poorly delimited furrow. In the majority of specimens studied this furrow rapidly shallows and becomes less and less clearly defined adapically until it disappears com- pletely somewhere before the adapical quarter of the guard. However, in a few aberrant specimens exemplified by specimen F. 13456/21 shown in PI. 30, fig. 6 this shallow and wide, poorly delimited furrow continues without any weakening right to the apical end of the guard. As noted by Spath (1935, p. 223) the strong development and greater length of the posterior furrow-like part of the ventral canal is characteristic of the more conically shaped representatives of S. somaliensis. However, it also occurs in some sturdy specimens (PI. 30, fig. la) transitional between the typical form and var. attenuata and may be absent in other subconically shaped guards of the species. All extremes are con- nected by transitions, which indicates a low taxonomic value of the variations in length and strength of the ventral canal on the subspecific, let alone specific, level. Double lateral furrows were not observed in any of the investigated specimens. Their absence is believed to be an original morphological character of S. somaliensis rather than the result of weathering or abrasion, in view of the excellent preservation of the surface of some of the guards (PI. 31, figs. 3b, Ab, c). The flanks of all better preserved guards, including the holotypes of the species and S. s. var. attenuata, are ornamented by single, well-defined to barely perceptible longi- tudinal ridges (PI. 30, figs. \b, 5b; PI. 31, figs. \b, e, 2b, e, f, 3b, d, e, Ab, c; PI. 32, figs. 2b, c, e, 3b, c, 5d, 6b, c). These 0-8 to 2 mm wide ridges are invariably wider than high, very low in relief (their height is always considerably less than 1 mm), round- topped and poorly delimited from the adjacent parts of the guard’s surface. They begin at the oral rim of the guard and extend over the anterior three-quarters to four-fifths 166 PALAEONTOLOGY, VOLUME 15 of the flanks in all better preserved specimens, gradually weakening adapically and finally fading out before the end of this interval. In no instance were these ridges observed in the immediate proximity of the apex. Their frequent restriction to the oral half of the flanks (PI. 32, fig. 2b, c, e) appears to be caused by poor preservation of the adapical portions of the guards concerned. The single longitudinal ridges are situated either in the middle of the flanks or closely adventrally therefrom and are characteristically straight to nearly straight (PI. 31, fig. 3b). However, they may extend slightly obliquely across the flanks, their lower parts gradually shifting adventrally (PI. 31, fig. 2c,/) or be gently bent in the middle (PI. 31, fig. Ab). A flattened, or sometimes slightly depressed 2 to 3 mm wide longitudinal zone is commonly situated immediately adventrally of the above described ridges on the adoral half to three-quarters of the guard. This zone gradually narrows and then dis- appears adapically (PL 31, figs. \b, 3b, Ab; PI. 32, figs. 3b, c, 5d). It is believed to be the rudiment of the double lateral furrows, especially as it may occasionally (PI. 32, fig. 2c, e) be limited by a second longitudinal ridge on the ventral side. Another similarly flattened to slightly depressed longitudinal zone often occurs immediately addorsally of the single longitudinal ridge. Some specimens exhibit only one of these two zones, which may be a matter of preservation only. The surface of most guards is quite smooth, except for the above described ventro- alveolar canal, longitudinal single ridges, and accompanying flattened to slightly de- pressed longitudinal zones. However, the well preserved surface of the lower flanks of specimen C-45936 (251) below the apical ends of the longitudinal ridges is locally EXPLANATION OF PLATE 32 Somalibelus somaliensis (Spath 1935). Horizon and locality as for Plate 30. V marks the position of the ventral side of the guard. Fig. 1. SMC F. 1700, polished cross-section, x4. Figs. 2a-g. SMC F. 1708 (355). a. Ventral view, y.l;b. Right lateral view, X 2; c. Left lateral view, X 2; d. Same view as in la, X 1 . The apparent extension of the medioventral canal onto the apieal half of the guard is an optical illusion (compare fig. 2o); e. Same view as in 2c, x 1 ;/, Alveolar view, x 2; g. Apical view, x 2. Figs. 3a-/. SMC F. 1709 (350). o. Ventral view, X 1 ; Zj, Left lateral view, X 1 ; c, Same view as in 3b, x2; d. Same view as in 3a, x2; e. Alveolar view, x2;/. Apical view, x2. Note closely spaced adapical furrows in figs. 3c, d, and /. Figs. Aa-e. SMC F. 13456/10. a. Ventral view, x\;b. Left lateral view, X 1 ; c. Right lateral view, X 1 ; d. Polished cross-section of the alveolar end, X 4. Note the V-shaped inward bending of all layers of the guard and of the white conotheca underneath the medioventral canal. The plane of splitting surface is marked by a light grey weathering ; e. Apical view, X 1 . Figs. Sa-d. BMNH C. 42147. Holotype of Rhopaloteuthis somaliensis Spath 1935. a. Lateral view of the inside of the guard containing most of phragmocone, x\;b. Right lateral view of the outside of the guard, x 1 ; c. Same view as in 5a, X 4, to show morphological detail of phragmocone and splitting surface (marked sps) in proximity of alveolar end of the guard and along the ventral surface of the phragmocone. Its contrast with the rough surfaced break on the dorsal and adapical parts of the guard is quite apparent ; d. Same view as in 5b, X 3, to show the presence of a typically developed mediolateral longitudinal ridge. Figs. 6a-/. SMC F. 1687. a. Ventral view, x\; b. Left lateral view, X 1; c. Right lateral view, X 1; d. Dorsal view, xl; e. Alveolar view, x 1 ; / Apical view, X 1 . Figs. la-f. SMC F. 13456/11, a halfgrown guard, a. Ventral view, X 1 ; Z>, Left lateral view, xl; c, Right lateral view, x\; d. Dorsal view, xl; e. Alveolar view, X 1 ; / Apical view, X 1 . Palaeontology, Vol. 15 PLATE 32 JELETZKY, Somalibelus somaliensis JELETZKY: ‘RHOPALOTEUTHIS' SOMALIENSIS 167 covered by faint, ramifying, and irregularly wavering striae. These striae are too feeble to be visible even in the enlarged photographs of this specimen (PI. 31, fig. 3b). Two or three equally faint oblique to subtransversal striae were, furthermore, seen in the proximity of longitudinal depressions and ridges on the flanks of the guard C-45937 (253). There is no assurance that any of these striae are true vascular imprints similar to those observed on the guards of Belemnitellidae ; they could be the result of weathering. The surface of the apex appears to be quite smooth in most of the specimens including all typical representatives of the sturdy variant approaching the holotype and the para- type C-45936 (PI. 31, fig. 3). However, the apex of some representatives of var. attenuata (PI. 30, fig. la-d,f\ PI. 32, fig. 3a-d, f) is ornamented by a variable number of faint to well-marked, short, longitudinal furrows separated from each other by similarly de- veloped longitudinal ridges. These apical furrows and ridges also occur in some guards (PI. 30, fig. la-6?) morphologically transitional between the sturdy variant and var. attenuata and possibly in some representatives of the subconical variant (PI. 30, fig. 6a, c). The length of these apical furrows and ridges is not known to exceed 4 mm and usually is less than 3 mm. The number of furrows and ridges varies from a few each, restricted to one or both flanks of the apex (PI. 30, fig. Id) to at least fifteen each (PI. 32, fig. 3/) evenly spaced all around the apex. The medioventral apical furrows and ridges may sometimes be concentrated either exactly adapically of the apical end of medioventral canal (PI. 31, fig. 7c) or inside of its apicalmost part (PI. 30, fig. 6c). No connection between the lateral apical furrows and ridges and the previously described single lateral ridges was observed in any of the investigated guards. The apex is situated exactly to almost exactly centrally in most of the investigated guards, including all slender specimens characterized by a relatively long and pointed adapical part of the guard. It can, however, be markedly displaced adventrally in some of the sturdy guards characterized by the rounded-subtrapezoidal cross-section of the apical part of the guard (PI. 30, figs. 2b, c, e,f, h, 4b, c, f). Internal morphology. The axial line is subcentral (PL 32, fig. 1) to more or less markedly displaced addorsally (PI. 30, figs. 3c, 5c; PI. 32, fig. 5c). It is either slightly convex adventrally (PI. 32, fig. 1) or quite straight throughout its length in sectioned specimens. The depth of the alveolus fluctuates between about one-half (PI. 32, fig. 1) and about three-quarters (in paratype II of Spath 1935, p. 223 or C. 45936 of this paper) of the estimated length of the guard (see Table 1) in the most complete specimens studied. It is about 68 % of the estimated length of the guard in the holotype of the species (PL 32, fig. 5a, c). In lateral aspect the ventral side of the alveolus is distinctly concave while its dorsal side is feebly to distinctly convex. The dorso-ventral alveolar angle fluctuates from 23 to 25° in the sectioned specimens (see PL 30, figs. 3c, 5<7; PL 32, figs. 1, 5a, c, and Table 1). The alveolus is pronouncedly to feebly displaced addorsally throughout its length as is clearly visible in all longitudinally split (PL 30, figs. Ic, d, 3c, 5d\ PL 32, figs. 1, 5a, c) and transversely sectioned (PL 30, figs. Ic, 2a, b, 4c, 5c, 6c, 7c; PL 31, figs. 1/, 2g, 3f, 4c; PL 32, fig. 4d) guards. The addorsal displacement of the alveolus is, as a rule, most pronounced at the early and intermediate growth stages and becomes weak to barely perceptible in the latest growth stages of the largest (i.e. adult) guards (e.g. PL 31, figs, 2^, 3/). 168 PALAEONTOLOGY, VOLUME 15 Like the cross-sections of the alveolar part of the guard (see in previous section), those of the alveolus are invariably compressed. These cross-sections vary from regu- larly oval ones with more or less regularly rounded (PI. 30, figs. 2b, 4c; PI. 32, fig. Ad) to more or less pronouncedly flattened (PI. 30, figs. 6c, 7c) flanks to somewhat egg- shaped ones with the maximum lateral diameter displaced toward the venter (PL 30, fig. Ic; PI. 31, fig. 2g). The splitting surface (Jeletzky 1946, pp. 93, 94) of S. somaliensis differs from that of all other Belemnopseidae in its perfectly to reasonably smooth part being strongly spatially restricted, and in the rest being more or less level but somewhat to markedly rough-surfaced. The bottom of the splitting surface begins a few mm adapically of the protoconch and extends subtransversally to the ventral surface of the guard (PI. 30, fig. 5d\ PI. 32, fig. 5c). Throughout this interval the almost straight to somewhat adapically convex bottom of the splitting surface deflects slightly adapically forming an angle of about 1 10 to 120° with the alveolar extension of the guard’s axis. The boundary between the somewhat to markedly rough but almost level surface of the splitting surface and the irregularly rugged surface of more adapical parts of the guard is somewhat poorly defined. An almost to quite smooth area can be distinguished within the above defined splitting surface. It begins either a few mm below the protoconch or approximately at its level. At this level it is restricted to the inner one-quarter to one-third of the space between the ventral surface of the phragmocone and that of the guard. The outer three-quarters to two-thirds of this space are, as already mentioned, rough-surfaced but more or less even. From its starting-point at or near the protoconch, the boundary between the smooth EXPLANATION OF PLATE 33 Somalibehis somaliensis (Spath 1935) Kimmeridgian (?lower or ?middle), near Bihendula, Somalia, Africa; SMC F. 13456/2. Longitudinal, dorsoventral thin section of well-preserved early part of phragmocone, including protoconch, the first 14 septa, primordial guard, and adjacent parts of conotheca and guard. Fig. \a. Over-all view of preserved portion of the phragmocone and adjacent guard, x 15. b. Ventral parts of 7th to 10th septa (marked s) with adjacent parts of conotheca (marked con), and guard (marked g); septal necks of septa 8 to 10 (marked sn) are sharply delimited from adjacent parts of connecting rings (marked erg to ern); mural parts of aU septa torn off the conothecal bulges and displaced adapically. The four-layered structure of the conotheca described in text (see p. 171) is visible, however the thicknesses of individual layers are irregularly changed due to tectonic pressure ; individual layers are designated 1 to 4 from the innermost (or first) to outermost (or fourth) in- clusive, x250. c. Mural end of ventral part of the first septum (marked s) abutting the adapical surface of a tri- angular bulge of conotheca (marked con); the abrupt contact of the two is clearly visible; septal and conothecal layers obliterated by recrystallization; parts of ventral waist of phragmocone and the adjacent part of proseptum (marked ps) are visible near the lower edge of the photograph, x 750. d. Ventral parts of 1 1th and 12th septa (marked s) with adjacent parts of connecting rings (marked cr), conotheca (marked con) and guard (marked g); note the change of orientation of septa as com- pared with the earlier septa shown in fig. \b and the slit-like appearance of residual ventral parts of camerae (vs), x 250. e. Ventral parts of 12th and 13th septa with adjacent parts of connecting rings, conotheca and guard; the 13th central camera is even more slit-like than the 12th camera; the same abbreviations as in fig. \d, x 250. Palaeontology, Vol. 15 PLATE 33 JELETZKY, Somalibelus somaliensis e best-preserved guard Ratio Ratio diameter C/A C/B pex in Sturdy forms approaching 0-28 100 0-33 0-97 0-26 0-97 0-31 0-99 1 above) 0-21 0-95 above) 0-31 0-97 above) 0-34 0-88 iransitional between the sti 0-27 0-88 0-29 0-92 0-26 0-91 0-27 0-95 0-27 0-97 0-40 0-98 us approaching Somalibeliis 0-23 0-92 0-21 0-94 018 0-87 0-22 100 Slender, subcylindrica 0-25 0-94 0-31 0-94 V:<.;; ■■ ■ ■• yr.^'r;(i:fn.< ■,,?T’ ■ B . . , , M: A i. iUh i<- 1 ,uh't £f {htiv^hi . .C- *1S iW imf-Ui-t \ Alj , ' > ' ':•’■! « 2 vrff (jn] L-.-d, I'pbr, .SJl-'I.SOFUr.V":.'.:. cructwd;- . .' ■ • 0 ^>' % ■■ ^14*), ■{-■■; ■ *v. - ri 0'4;- ;.vj'5 y-^aiw ■•■'. J {*>2 0.-5r «'2t ^ V ; ij ■- «i'- ■ .,-3'-*V:iK'. ■ 033 < ' .-; .'4*; 2i~-2 ■ ■ ijv' '-ii-’V' 0-29 rc O .V2 ' (y-2 m'ns »•. •'■•;} ■ tv -4 6 t (7 (l-fufr' - 8 0' iio ;vi2;_. . P-'-l ;,.ri 9.5 (14 ^: •m H-6 U 2 0) « nu5 -r^ ,- l ;. .)■? (No. >-i ’ ■ 74 - . V'f f 1 ;■ 0.3 ?'0 030) ' 6-S <.S-0) : r' iV-.-. - ' 0 •' '. -.•H ; iW;J . ? nQH'^ SlCfttSST^W . V. , ! r-; -fo(;'v>e >..» - . ..1 •JVS:,;.- Cr.V ; . 0-.'3 ■ o'sic ,, V, i - 0 2.. ^ ^ 02 2) ;. , ' i' V, ■ ,.,; ' }a . ■ i‘ 2) ■ ■ ' “ k V-;; • ; o:?. ‘ ‘ '!'0J ' :2 y- • ‘t2 I-i', v;|;^' . ‘ 020^ '5Sm :/4 , ^ t' (:;i \0'' .) , ■ ' JELETZKY: ^RHO PALOTEUTHIS’ SOMALIENSIS 169 and rough-surfaced parts of the splitting surface extends sub-transversally and adapically convex for a few mm adventrally, and then turns obliquely adorally. Then it runs in a more or less straight line subparallel to the ventral surface of the phragmocone, gradually approaching the ventral surface of the guard to the point 4 to 5 mm below the oral rim of the alveolus. At the latter point (PI. 30, figs. 3c, 5; PI. 35, fig. 2b, c\ PI. 37, fig. \b, d\ PI. 38, fig. Ic) the conotheca appears to consist of four well- defined layers which are believed to be homologous to the four layers observed in the conotheca of Austroteuthis kuehni by Jeletzky and Zapfe (1967, p. 91, pi. Ill, fig. 1a, b) and in that of Megateuthis gigantea (Schlotheim) by Mutvei (1964, p. 97, fig. 8b). The best preserved specimens F. 13456/5 (PI. 35, fig. 2b, c), F. 13456/1 (PI. 37, fig. \b, d) and F. 1693 (PI. 38, fig. Ic) were studied in ordinary light at magnifications ranging from 250 to 650. The innermost (or first) conothecal layer is of variable thick- ness, dull brown to bluish grey, transparent to clouded, apparently well calcified and mostly distinctly to strongly and finely laminated throughout. This layer is commonly much darker and more distinctly laminated near its margins than in the middle prob- ably because of the weathering. The innermost layer is very sharply delimited from the mural parts of the septa which discordantly abut against its inner surface. It is less sharply but nevertheless clearly delimited from the second layer of conotheca, except where the two are strongly altered. The innermost layer is about as thick as the second layer between the septa. However, its thickness gradually increases within the conothecal bulges, which consist of this layer alone, until it at least doubles in their middle parts. In the places of its maximum development the innermost layer is two to two and a half times thicker than the second layer and comprises from one-third to about one-half of the total thickness of the conotheca. The second layer of conotheca is dirty white, cream, or buff coloured, transparent to 172 PALAEONTOLOGY, VOLUME 15 somewhat clouded and obviously well calcified. It has mostly an almost homogeneous to coarsely and irregularly crystalline appearance in the middle part but may either become replete with vermiform inclusions or show an irregular mesh-like structure elsewhere, especially near the margins. These variations of structure of the second layer appear to be caused by the weathering. The second layer maintains about the same thickness right across the camerae and opposite the mural ends of the septa. Its boundary with the third layer is abrupt and even where the conotheca is best preserved. Elsewhere the two layers may be indistinctly and unevenly delimited (e.g. PI. 35, fig. 2c), which is probably caused by weathering and micro-faulting. The third conothecal layer is either about as thick as the second or somewhat thinner, where it is best preserved (PI. 37, fig. Id). It is honey-yellow, light brown, or dark brown EXPLANATION OF PLATE 35 SomaUbelus somaliensis (Spath 1935) Kimmeridgian (?lower or ?middle), near Bihendula, Somalia, Africa. Fig. 1. SMC F. 13456/5. Longitudinal, dorsoventral thin section of well preserved early part of phrag- mocone including the first 20 septa, protoconch, most of primordial guard and adjacent portions of conotheca and guard. a. Over-all view of the preserved portion of thin section; pr = protoconch; pg = primordial guard; g = guard proper; siph = siphuncle, x 15. b. Ventral side of the waist of protoconch and of the first siphonal segment with dorsal and ventral septal necks, x 360. adn = adnation surface; vsi = ventral part of first septum; note the apparent continuity of proseptum and conotheca; psv = ventral part of proseptum (grading into conotheca) ; psd = dorsal part of proseptum ; crjV = ventral part of first connecting ring ; cm = closing membrane (torn oft' the conotheca on the ventral side) ; con = conotheca ; gi = innermost layers of guard filling out the waist of protoconch ; craV = ventral part of second connecting ring ; crid = dorsal part of first connecting ring; dsi = dorsal part of first septum; crjd = dorsal part of second connecting ring; siph = siphuncle. c. Lower part of protoconch (pr) and the saucer-like earliest part of primordial guard (pgi) surrounded by the wedge-shaped latter part of primordial guard (pg,) and the guard proper (g) ; X 130. d. Strongly enlarged view of the ventral part of closing membrane, proseptum and the ventral parts of first connecting ring and first septum shown in Fig. \b. adn = adnation surface of first septum and first connecting ring; f = foot of siphuncle; sni = ventral part of first septal neck; other symbols as in Fig. 1(>; x 650. Fig. 2. SMC F. 18361 (a, b). Longitudinal, dorsoventral thin section of well preserved middle portion of the phragmocone and adjacent parts of the conotheca and guard. a. Over-all view of portion of phragmocone consisting of approximately (estimated) 12th to 24th septa inclusive with adjacent parts of conotheca and guard, x 10. b. Mural end of dorsal part of 16th septum with adjacent portions of conotheca and guard, x500. s = septum; con = conotheca; b = bulge of conotheca; ca = Canada balsam exposed in the crack separating conotheca from the mural end of septum; component layers of conotheca marked 1 to 4 inclusive; g = guard. c. Mural end of the dorsal part of 18th septum with adjacent portions of conotheca and guard, X 500. All symbols the same as in Fig. 2b. d. Dorsal part of 16th septal neck with parts of adjacent connecting rings displaying structural relationships of these elements of phragmocone. s = septum; suie = septal neck; crie = 16th connecting ring; crj, = 17th connecting ring; adn = adnation surface of the neck with 16th con- necting ring. The gradually tapering adapical part of the 17th connecting ring overlaps the apical end of 16th septal neck and the adoralmost part of the 16th connecting ring. A sharp delimitation of these three elements of phragmocone from each other is quite evident; x275. Palaeontology, Vol. 15 PLATE 35 JELETZKY, Somalibelus somaliensis JELETZKY: ^RHO PALOTEUTHIS” SOMALIENSIS 173 in ordinary light and appears to be less thoroughly calcified than the other conothecal layers. The structure of this somewhat clouded layer varies from relatively coarsely laminated to irregularly meshed and charged with numerous, closely spaced black particles. In black and white photographs, where it is marked by number 3 (PI. 35, fig. 2b, c; PI. 37, fig. Id), the third layer appears to be considerably darker than the adjacent second and fourth layers. The fourth (or outermost) layer (marked 4 on PI. 35, fig. 2b, c and PI. 37, fig. Id) is mostly similar to the second layer in its colour, structure and inferred degree of calcifi- cation. However, it may be dark brown and charged with numerous dark grey to black particles in some specimens (e.g. F. 1693; PI. 38, fig. Ic). The boundary with adjacent dark brown and intensively transversely fibrose innermost layers of the guard is very sharp and discordant (PI. 38, fig. Ib-d). The boundary with the adjacent third layer is somewhat hazy. The specimen F. 13456/1 (PI. 37, fig. lb, d) shows that the above discussed conothecal layers extend into the earliest segments of the phragmocone and at least into the adoral- most parts of the protoconch. The gradual decrease of the conothecal bulges in the earliest two septa appears to be caused by an equally gradual decrease of the swelling of the first conothecal layer within them. None of the thin-sections permits definitive conclusions about the presence or absence of above described conothecal layers in the lateral and adapical parts of the proto- conch’s walls. However, specimen F. 13456/3 (PI. 36, fig. Id) may be interpreted as suggestive of the presence of more than one layer in the adapical part of these walls. All thin sections studied confirm Jeletzky’s (1966, p. 125) reinterpretation of velamen triplex of Miiller-Stoll (1936). The delimitation of conotheca (c or con.) and the inner- most layers of the guard (gi) is especially obvious in the thin section F. 13456/1 repro- duced in PI. 37, fig. lb, c, d. These photographs show clearly how the poorly layered, spongy-looking innermost layers of the guard (= stratum callosum of Miiller-Stoll, 1936, pp. 172-173) are superimposed on the conotheca and fill out the waist of the protoconch. The innermost layers of this ‘stratum callosum’ appear to pinch out completely adapically on the protoconch’s flanks but its outermost layers overlap discordantly the layers of primordial guard (PI. 37, fig. la, b). The same structural rela- tionships are less distinctly visible in PI. 35, fig. la, b and PI. 36, fig. la, d. Septal layers and their ontogeny. The component layers of septa are indistinguishable in most parts of the thin sections. The mostly crushed and deformed appearance of the septa (PI. 33, fig. In; PI. 35, fig. 2n; PI. 37, fig. la) and the pronounced changes of their thicknesses within shortest distances (PI. 37, fig. lb, c) suggest that the apparent absence of the component layers is the result of their deformation and concurrent recrystalliza- tion. The local presence of remnants of septal layers in better preserved septa (PI. 36, fig. lb, c) confirms this conclusion. Judging by the preserved remnants of septal layers, the septal structure of S. somali- ensis and its ontogenetic development were essentially similar to those of other Belem- nitida described and figured by Jeletzky (1966). The specimen F. 13456/1 shows the best preserved layering of the free parts of the earliest twenty septa in spite of their strong deformation and fragmentation (PI. 37, fig. In). In this specimen the central layer ‘c’ extends through about seven-eighths of the 174 PALAEONTOLOGY, VOLUME 15 ventral parts of the first (PL 37, fig. \b, d) and the third septa. The more or less homo- geneous and transparent layer ‘c’ comprises at least three-fifths of the thickness of the middle part of these septa. It gradually tapers to nothing shortly before the mural parts and the brims of these septa. The darker coloured upper (Ui) and lower (n,) outer layers surround the central (c) layer and merge into the undivided outer (n) layer where the central layer (c) pinches out (PI. 37, fig. \d). No traces of transitional layer ‘m’ were seen anywhere in these septa. The septal necks of the first and third ventral septa are built exclusively of undivided outer layer ‘n’. The same structural relationships seem to prevail in the less satisfactorily preserved dorsal parts of the earliest few septa of this and some other specimens of S. somaliensis (PI. 33, fig. \b, c; PI. 35, fig. \b, d). The central layer ‘c’ gradually approaches the brims of the dorsal parts of septal necks in the subsequent septa. It reaches the brims in the 17th to 22nd septa of speci- men F. 1693 (PI. 38, fig. \a, b). None of the available thin sections includes any later septa with clearly discernible septal layers. In the dorsal parts of 17th to 20th septa of the specimen F. 1693 (PI. 38, fig. \a, b) the almost transparent and homogeneous central layer ‘c’ occupies most of the septal cross-sections and the brownish-yellow, thinly laminated upper (n^) and lower (n,) outer layers are restricted to their fringes (PI. 38, fig. \b). The dark grey and locally black dotted transitional layer ‘m’ seems to be restricted to small spots at the rounded tips of the central layer ‘c’. The whole of the long, slender septal necks, the length of which comprises about one-sixth of that of the corresponding camerae, is built of the undivided outer layer ‘n’ (PI. 38, fig. 1^). The above described structure of the dorsal parts of the 17th to 22nd septa of S. somaliensis does not differ materially from that of the thirtieth to thirty-first septa of the Belemnitidae s. str. and Cylindroteuthididae (Jeletzky 1966, p. 116, pi. 7, fig. 1b; pi. 8, fig. 2Z>; PI. 9, fig. 2b). However, it appears to be considerably more advanced than that of the corresponding or even somewhat younger septa of these families (Jeletzky 1966, EXPLANATION OF PLATE 36 Somalibelns somaliensis (Spath 1935) Kimmeridgian (?lower or ?middle), near Bihendula, Somalia, Africa; SMC F. 13456/3. Longitudinal, dorsoventral thin section of well preserved early part of phragmocone, including protoconch, earliest nine septa, primordial guard and adjacent parts of the conotheca and guard. Fig. \a. Over-all view of preserved portion of phragmocone and adjacent parts of the conotheca and guard; x40. b. Mural part of 8th dorsal septum and adjacent parts of conotheca and guard; the septum dis- plays what appears to be a whitish coloured, thin central layer (designated c) flanked by considerably thicker upper and lower transitional zones designated mi and m,, and thin upper and lower outer layers designated ni and n,), X 650 (layer ni2 is designated mj in error). c. Mural ends of 4th and 5th dorsal septa and adjacent parts of conotheca, both septa display what appears to be the same component layers as in the septum shown in Fig. \b. Designations as in Fig. \b, X650. d. Protoconch with adjacent parts of the phragmocone and the guard, X 170. The ventral part of proseptum (designated pr.v) appears to merge imperceptibly in the completely recrystalhzed conotheca. The completely preserved closing membrane (designated cm) appears to be torn off the conotheca on the ventral side. This may be, however, the result of a recrystallization. Dorsal ends of proseptum and closing membrane obscured by nontransparent deposit. Palaeontology, Vol. 15 PLATE 36 JELETZKY, Somalihelus somaliensis JELETZKY: ^RHOPALOTEUTHIS' SOMALIENSIS 175 pp. 115-116; PI. 7, fig. 1e; pi. 9, fig. 2a; pi. 13, fig. Id). This ‘acceleration’ of the onto- genetic development of dorsal parts of S. somaliensis septa, as compared with those of all hitherto studied Belemnitida is believed to be taxonomically important at least on the generic level, as a similar ‘ontogenetic acceleration’ was also observed in the adventral migration of the ventral parts of 5. somaliensis septa. The apparent presence of similar ‘acceleration’ in Hibolithes hastatus and Belenmopsis ex gr. angusta-apiciconus (Jeletzky, unpublished) suggests that this morphological feature may be characteristic of the family Belemnopseidae as a whole. Free septum and septal neck of dorsal side. The generally poorly preserved free parts of dorsal septa do not seem to differ materially from those of other Belemnitida described by Jeletzky (1966, pp. 115, 116). The dorsal parts of the earliest seven to eight septal necks (PI. 33, fig. \a, b; PI. 35, fig. lb, d; PI. 36, fig. la, d; PI. 37, fig. la, b) are quite similar to those of Hibo- lithes hastatus (de Blainville) described and figured by Jeletzky (1966, pp. 115, 116; pl. 9, fig. 1a; pi. 10, fig. 1a, b; fig. 7) in their shape, relative length (about one-sixth of the length of corresponding camerae) and structural relationships with the adjacent connecting rings. The first dorsal septal neck is indistinguishable from the subsequent necks in its length and other features (PI. 35, fig. lb; PI. 36, fig. Id; PI. 37, fig. l^). This confirms Jeletzky’s (1966, p. 115) conclusion that the dorsal part of the first septal neck of Belemnopseidae is longer than that of Belemnitidae s. str. and about as long as the subsequent septal necks. In S. somaliensis the length and other morphological features of dorsal septal necks remain unchanged at least in the earliest twenty-five to thirty septa (PI. 33, fig. lb; PI. 35, figs, lb, 2d; PI. 36, fig. la; PI. 37, fig. lb; PI. 38, fig. la, b). All dorsal septal necks available represent the orthochoanitic growth stage (Jeletzky 1966, pp. 115, 116). No information about the half-grown and adult dorsal septal necks of S. somaliensis is available. The apparent presence of adorally directed prongs in some septal necks of S. somali- ensis (PI. 35, fig. lb; see first dorsal neck designated sn^) appears to be caused by the subsequent plastic deformation of relatively poorly calcified siphonal ends of the septa concerned. These rarely observed adoral prongs are quite irregularly distributed and shaped, occur only in strongly deformed and damaged septa, and alternate irregularly with the prevalent normally developed septal necks. Free septum and neck of ventral side. Like the dorsal free septa and necks, the ventral free septa and necks of S. somaliensis do not seem to differ materially from those of most other Belemnitida (except for Cylindroteuthididae) described by Jeletzky (1966, pp. 117-122). The ventral parts of septal necks of S. somaliensis are invariably longer than their corresponding dorsal parts (PI. 34, fig. lb, c; PI. 35, fig. lb; PI. 36, fig. Id; PI. 37, fig. lb; PI. 38, fig. lb). Like those of other Belemnitida the ventral parts of septal necks of S. somaliensis lengthen, become calcified, and transform from orthochoanitic to sub- orthochoanitic shape faster than their dorsal counterparts. Furthermore, they become situated adorally of the corresponding dorsal parts of the necks already in the eighth to tenth septum just like those of other Belemnitida (PI. 33, fig. lb; PI. 37, fig. la, b; PI. 38, fig. la, b). Finally, their structural relationships with the adjacent segments of the 176 PALAEONTOLOGY, VOLUME 15 connecting rings exactly duplicate those described and figured by Jeletzky (1966, pp. 117, 118, figs. 7, 8, 10, 12). The free parts of the first two to three ventral septa are straight to only slightly convex adapically and form angles from 40 to 50 degrees with the ventral wall of the conotheca. They bend more or less abruptly adapically at the brims so that the septal necks are oriented almost parallel to the ventral wall of the conotheca (PI. 35, fig. \b, d; PI. 36, fig. la, d; PI. 37, fig. la, b). The free parts of the next six to seven septa remain virtually straight and more or less abruptly bent at the brims (PI. 33, fig. \b; PI. 34, fig. Ic). How- ever, they become progressively shorter and shorter and more and more strongly deflected adapically until the angle between the free septum and the conotheca is reduced to only 10 to 12 degrees in the interval from eleventh to fifteenth septa (PI. 33, fig. lb, d; PI. 34, fig. lb; PI. 38, fig. Ic). This results first in a gradual decrease and then in an almost complete loss of the previously mentioned abrupt bends characteristic of the earliest few septa and in the gradual adventral migration of the successive septal necks. However, these septal necks are somewhat more strongly deflected adapically than the corresponding free septa proper and remain subparallel to the ventral wall of the conotheca throughout this interval. The ventral parts of camerae become correspondingly narrower but retain their trapezoidal shape (PI. 33, fig. lb, c; PI. 35, fig. lb; PI. 38, fig. Ic) because of the essentially straight (i.e. orthochoanitic) appearance of the ventral necks and connecting rings. The tempo of this ontogenetic change varies considerably from one specimen to another and the thirteenth ventral septum of some specimens (PI. 33, fig. Id, e) may be just as advanced ontogenetically as the fifteenth ventral septum of another (PI. 38, fig. Ic). EXPLANATION OF PLATE 37 Somalibelits somaliemis (Spath 1935) Kimmeridgian (?lower or ?middle), near Bihendula, Somalia, Africa; SMC F. 13456/1. Longitudinal, dorsoventral thin section of an early part of phragmocone including exceptionally well preserved proseptum (designated ps), adjacent parts of the conotheca (designated c or con) and the innermost parts of the guard (designated gi) ; the well preserved primordial guard (designated pg) is partly recrystallized. Fig. la. Over-all view of better preserved portion of the phragmocone, primordial guard and guard, x40. b. Ventral side of the waist of protoconch, 1st siphonal segment and remains of 2nd siphonal segment with dorsal and ventral septal necks. Proseptum (ps) merges imperceptibly into the cono- theca (c) while the latter is sharply delimited from the adjacent innermost layers of the guard (gi) filling the waist of the protoconch. Badly damaged closing membrane is pressed onto the adapical surface of proseptum, x 200. c. Dorsal side of the waist of protoconch, exhibiting the same morphological features as the ventral side shown in Fig. \b. The junction area of proseptum (ps) and conotheca (con) partly recrystallized and possibly fragmented; the mural parts of otherwise poorly preserved 1st and 2nd septa (s) have a typical appearance and are sharply delimited from the bulges of adjacent parts of conotheca (designated c), x 160. d. A much enlarged view of best preserved section of the ventral side of the waist of protoconch shown in \b. The four-layered structure of the conotheca described in text (see p. 171) is clearly visible: individual layers are designated 1 to 4 from the innermost (or first) to the outermost (or fourth) inclusive; these layers appear to persist across the waist of the protoconch into the adoral- most part of its wall at least. The structure of the 1st septum (see p. 174) is visible: the central layer (c) is surrounded by the darker coloured upper (nfl and lower (na) outer layers which merge into the undivided layer (n) where the central layer (c) pinches out; other designations as in other figures of this plate, X 450. Palaeontology, Vol. 15 PLATE 37 JELETZKY, Somalibelus somaliensis 34: % III JELETZKY: ^RHO PALOTEUTHIS' SOMALIENSIS 177 The gradual shortening and concurrent increase of adapical deflection of ventral septa continues until the apical ends of the still somewhat more strongly adapically deflected septal necks, and the whole lengths of the sublongitudinally oriented connecting rings, become contiguous with the surface of conotheca in the interval between the thirteenth and seventeenth camerae (PI. 33, fig. \e; PI. 38, fig. \b-d). This results in the almost complete disappearance of the adapical three-fifths of the ventral camerae and in their anterior parts becoming narrowly lens-like in cross-section between the conothecal sur- face and the adapical (now ventral) surface of only slightly addorsally arched septa (PI. 33, fig. Ic; PI. 38, fig. \b, d). The remaining feeble addorsal arching of ventral parts of the septa continues to decrease within the next few camerae until they become almost straight and contiguous with the surface of the conotheca in twentieth and twenty- second camerae. This results in the cross-sections of corresponding residual ventral camerae becoming slit-like, and in their splitting up into two disconnected sections (PI. 38, fig. \d, e). These residual ventral camerae seem to disappear completely in the twenty-third to twenty-fourth camerae but these and subsequent camerae are invariably poorly preserved. The younger ventral septa and necks are not preserved in any of the specimens. The observed ontogeny of the position, shape, and orientation of the ventral parts of free septa and necks of S. somaliensis differs from that of the representatives of the family Belemnitidae s. str. (Jeletzky 1966, pp. 115, 116; pi. 7, fig. 1a, c, d) and Cylindroteuthi- didae (Jeletzky 1966, pi. 13, fig. 1b, e) in a considerable ‘ontogenetic acceleration’. Namely, the apical ends of ventral necks of BeJemnites paxillosus Lamarck 1801 (Jeletzky 1966, pi. 7, fig. 1a and unfigured) do not become contiguous with the inner surface of conotheca until twenty-sixth or twenty-seventh septum and those of Mega- teulhis gigantea do not become contiguous until thirty-second or thirty-third septum (Jeletzky, unpublished). In Pachyteuthis densa (Meek 1865) this does not happen until thirtieth to thirty-second septum (Jeletzky, 1966, pi. 13, fig. 1e). In Gastrobelus urnbili- catus (de Blainville) this does not happen until thirty-fourth or thirty-fifth septum. The ontogenetic development of ventral necks of S. somaliensis is furthermore peculiar in their becoming almost straight and contiguous with the inner surface of the conotheca beginning with the twentieth to twenty-second septa. This is not the case in any of the Belemnitidae s. str. and Cylindroteuthididae studied (Jeletzky 1966, pi. 13, fig. 1b; pi. 15, fig. 1a; fig. 14). In these genera the middle parts of the ventral necks remain more or less strongly arched inward and separated from the inner surface of conotheca by the strongly reduced ventral parts of the camerae at least until maturity (till sixty-fifth septum in M. gigantea) and probably throughout their lifetime. It is not known whether the above described ontogenetic development of ventral parts of free septa and necks of S. somaliensis is characteristic of other Belemnopseidae genera. Only the earliest few septa of these genera (e.g. Hibolithes hastatus; Jeletzky 1966) have been studied so far. Mural ends of septa. Jeletzky (1966, pp. 123, 124) experienced considerable difficulties when trying to interpret definitively the structure of mural ends of the septa in the earliest thin sections of S. somaliensis phragmocones. The study of additional, better preserved thin sections (PI. 33, fig. Ic-c; PL 34, fig. Ic-g; PI. 35, figs, lb, 2b, c; PI. 36, fig. Ib-d; PI. 37, fig. Ic) indicates that even the mural ends of the earliest septa are C 8472 N 178 PALAEONTOLOGY, VOLUME 15 completely flangeless. The appreciably thickened, wedge-shaped (in cross-section) mural ends of all better preserved septa of S. somaliensis abut the adapical surface of pro- nounced bulges of the conotheca which are considerably longer than high and somewhat angular in cross-section. The mural ends of ventral septa are very sharply de- limited from these conothecal bulges. As already mentioned (see in the section on the conotheca and protoconch) these bulges are built exclusively of the innermost (or first) layer of conotheca, the individual laminae of which can sometimes (e.g. PI. 35, fig. 2b, c) be clearly traced within the bulges and directly underneath the contact of the mural ends of septa with the adapical surfaces of the corresponding bulges. The above observations indicate that the previously suggested (Jeletzky 1966, p. 123) presence of vestigial adoral flanges in the mural ends of the earliest septa of S. somali- ensis was simulated by their more or less complete recrystallization. This recrystalliza- tion resulted in the considerable weakening or complete disappearance of the originally sharp boundary between the septa and conotheca and in the loss of discordant cono- thecal layers underlying this boundary (e.g. PI. 34, fig. lb; PI. 37, fig. Id). On the dorsal side of the phragmocone the conothecal bulges become more and more prominent in the successive camerae of all thin sections. The same appears to be true EXPLANATION OF PLATE 38 Somalibelus somalietisis (Spath 1935) Kimmeridgian (?Iower or ?middle), near Bihendula, Somalia, Africa; SMC F. 1693. Longitudinal, dorsoventral thin section of well preserved middle portion of the phragmocone and adjacent parts of the conotheca and the guard. Fig. la. Over-all view of portion of phragmocone consisting of 13th to 19th septa inclusive with adjacent parts of conotheca and guard; the adventral part of 20th septum is visible in the left-upper corner of the photograph; x78. b. The eighteenth siphonal segment with the ventral part of 1 7th septum including adjacent parts of conotheca and guard and the dorsal septal necks of 17th and 18th septa. The structure of the dorsal septal necks (see p. 174) is clearly visible, the central layer (c) occupies most of the septal cross-sections, with the upper (nO and lower (n,) outer layers restricted to the fringes; the transitional layer (m) is limited to small spots at the tips of the central layer (c) and the undivided outer layer (n) makes up the entire septal neck; for details of morphology of ventral part of septum see Fig. Ic, x260. c. Ventral part of 1 5th septum with adjacent parts of conotheca (con) and guard (g), x 400. The adapical part of the septum (s) is not yet contiguous with the inner surface of the conotheca (con) but the ventral part of the camera (vc 15) is already sUt-like; the ill-defined (?strongly weathered) next adoral connecting ring (cr 16) is separated from the inner surface of the septum by the equally ill-defined (charged with dark grey particles) adapical part of the sixteenth camera (vc 16); the conotheca exhibits the usual four layers numbered 1 to 4 from the innermost to outermost respectively ; mural part of the septum strongly altered. d. Ventral part of 18th septum with adjacent parts of the conotheca and guard, x400; the adapical part of septum (i.e. septal neck; designated sn 18) is already contiguous with the surface of conotheca leaving only a residual ventral part of the camera (rvc) further adorally; other desig- nations as in Fig. Ic; conotheca is recrystaUized and does not show component layers. e. Ventral part of 20th septum with adjacent parts of conotheca and guard, x 400. The septum (Sao) is almost straightened with hardly any residual ventral camera (rvc) left between its outer surface and the adjacent part of inner surface of conotheca (con); this remnant of the camera is much smaller than the adjoining adapical remnant of the 21st ventral camera left between the inner surface of the septum and the apical part of next adoral connecting ring (crai) overlapping the latter; conotheca is completely recrystallized and does not exhibit any component layers but is sharply delimited from the adjacent innermost layers of the guard (g). Palaeontology, Vol. 15 PLATE 38 JELETZKY, Somalibelus somaliensis II I n ■ ■■ F'''' ' ''^f- *. :t ■ .■.;;;,i'’,|,;»:'' '■ ■■^^^ ■-'(ftf ■ ;,a!^k-:aa ■'M?» JELETZKY: 'RHO PALOTEUTHIS SOMALIENSIS’ 179 of the conothecal bulges of the ventral side where the bulges are less prominent than their equivalents on the dorsal side (compare PI. 33, fig. Ib-e and PI. 34, fig. \b-c with PI. 34, fig. Id-g). The above observations concerning the flangeless character of the mural ends of S. somaliensis septa are taxonomically important. A recent study of earliest septa of Neohibolites ewaldi (Jeletzky, unpublished) revealed their being completely flangeless and essentially similar to those of S. somaliensis. This suggests, in turn, that the somewhat unsatisfactorily preserved mural part of the septum of TV. miyakoensis Hanai (1953, pi. VI, fig. 1) is likewise flangeless and morphologically similar to those of TV. ewaldi Strombeck and S. somaliensis. The previously suggested presence of the Belemnitidae-like adoral flanges in the mural parts of TV. miyakoensis septa (Jeletzky 1966, p. 123) is probably erroneous. The more recent restudy of the somewhat poorly preserved mural ends of the septa of Hibolithes hastatus (de Blainville) previously described and figured by Jeletzky (1966, pi. 9, fig. 1a, b; pi. 10, fig. 1a, c) suggests their reinterpretation along the above men- tioned lines. These mural ends of the ventral septa may well be completely flangeless and only apparently continuous with the prominent bulges of the conotheca because of weathering and recrystallization of the specimen concerned. It seems possible that the complete absence of adoral flanges of mural parts of septa is diagnostic of all Belem- nopseidae. Proseptum and foot of the siphuncle. Structural relationships observed in thin sections of the specimens F. 13456/5 (PI. 35, fig. \b, d); F. 13456/3 (PL 36, fig. \d) and F. 13456/1 (PI. 37, fig. \b, c, d) apparently necessitate a revision of Jeletzky’s (1966, p. 126) tenta- tive conclusion about a sharp delimitation of the Belemnitida proseptum from the inner layer of conotheca. The well preserved and undamaged ventral part of this proseptum (PI. 37, fig. IZ), d) appears to be perfectly continuous with the conotheca and the same seems to be true of the somewhat less satisfactorily preserved and partly fractured dorsal part of this proseptum (PI. 37, fig. Ic). The dorsal part of the satisfactorily preserved proseptum of the specimen F. 13456/3 (PL 36, fig. \d) and the apparently undamaged ventral part of the specimen F. 13456/5 (PL 35, fig. \b, d) also support the idea of a con- tinuity of the proseptum and conotheca. The sharp boundaries observed near the mural ends of some of these prosepta have the appearance of accidental fractures. The same appears to be true of the previously observed (Jeletzky 1966, p. 126) sharp boundaries at the mural ends of other belemnitid genera. The evidence now available is insufficient for a definitive conclusion. However, it strongly favours the above suggestion concerning the continuity of the proseptum and conotheca in S. somaliensis and other Belemnitida. This interpretation is also more sensible because of the following general considerations. Both prosepta of the closely related Ammonitida are known to be the outgrowths of the conotheca in contrast to all their septa proper (Arkell et al. 1957, p. LI 7, fig. 4). Therefore the proposed continuity of the belemnitid proseptum and conotheca strengthens rather than weakens Jeletzky’s (1966, p. 126) suggestion that the belemnitid proseptum is homologous with the second ammonitid proseptum while the closing membrane is homologous with the first pro- septum and shell caecum of Ammonitida. The foot of the siphuncle of S. somaliensis (PL 35, fig. \b, d) does not seem to differ 180 PALAEONTOLOGY, VOLUME 15 significantly from those of other belemnitid genera described by Jeletzky (1966, p. 126, figs. 7, 9, 12, 13). Connecting ring. No component layers comparable to those recognized by Jeletzky (1966, pp. 127, 128, pi. 7, fig. 1b-e; fig. 6a, b) in the twenty-first to at least forty-fifth connecting rings of other belemnitid genera were recognized in S. somaliensis. However, only the earliest twenty-five connecting rings are present in thin sections available. Therefore it is uncertain whether the absence of layering is due to a generally unsatis- factory preservation of all connecting rings studied or to the somewhat delayed develop- ment of the component layer in S. somaliensis rings. The structural relationships of all better preserved connecting rings with adjacent septal necks (PI. 34, fig. \b, c\ PI. 35, fig. \h, d; PI. 38, fig. \c-d) appear to duplicate those observed by Jeletzky (1966, pp. 126-128) in other Belemnitida. As the ventral parts of S. somaliensis septa become more and more deflected adapically and nearly straightened (see section on the ventral part of free septum and neck), the ventral parts of the next adoral connecting rings approach the adoral surfaces of the septa more and more closely (PI. 33, fig. \b, d, c; PI. 34, fig. \b, c). Finally, these rings become almost contiguous with the adoral surfaces of the next adapical septa in the twelfth to fifteenth camerae (PL 33, fig. Id; PI. 38, fig. Ic), except for thin to barely perceptible dividing spaces or several lens-like dividing cavities. These structural relationships persist into the youngest well preserved (twentieth to twenty-second; see PI. 38, fig. In, b, d, e) ventral parts of the camerae observed. None of the thin sections studied permits a definitive conclusion as to whether or not the still younger connecting rings become completely contiguous with the almost straight ventral parts of their next adapical septa as happens in semiadult and adult (i.e. twenty-fifth to sixty-fifth) septa of all other Belemnitida studied by Jeletzky (1966, pi. 7, fig. 1a, c, d; pi. 1 1, fig. 2b, c; pi. 13, fig. 1b, e; pi. 15, fig. 1a; pi. 19, fig. 1a, c, f; fig. 10). Ontogeny of siphuncle and cameral deposits. The distance separating the base of the ventral wall of S. somaliensis siphuncle from the ventral surface of the conotheca in the first camera fluctuates between one-quarter of that separating it from the surface of the dorsal wall of the conotheca (PI. 33, fig. \a; PI. 34, fig. \a; PI. 36, fig. \a, d) and one-sixth of the latter distance (PI. 37, fig. la). The latter figure is believed to be more reliable because of a somewhat better preservation of the protoconch and proseptum in the specimen. The initial position of the siphuncle is, therefore, about the same as that observed by Jeletzky (1966, p. 129) in other Belemnitina and Belemnopseidae. However, it is considerably more adventrally situated than the first segment of siphuncle in Pseudobehis bipartitus (Kabanov, 1963, p. 123, fig. 1) and other Duvaliidae (Kabanov 1967, p. 45; figs. 18b, g, v) which was reported to be almost centrally situated. The general appearance and relative width of S. somaliensis siphuncle does not seem to differ materially from those of other Belemnitina and Belemnopseidae studied by Jeletzky (1966, p. 129). The same is true of the gradual adventral migration of S. somaliensis siphuncle (PI. 33, fig. la; PI. 34, fig. la; PI. 36, fig. la; PI. 37, fig. la). No traces of cameral deposits were observed in any of the early camerae of S. somali- ensis (PI. 35, fig. \b; PI. 36, fig. la, d; PI. 37, fig. \a-d). This confirms Jeletzky’s (1966, pp. 134-135) conclusion about the complete absence of cameral deposits in all Belem- nopseidae. JELETZKY: ‘RHOPALOTEUTHIS’ SOMALIENSIS 181 CONCEPT OF SPECIES AND INFRASPECIFIC VARIATION As clearly recognized by Spath (1935, p. 223), Somalibe/us somaliensis shows great variability and the example figured by Weir seems to have little resemblance to the holo- type (Plate XXV, fig. 4). In the latter, and still more so in the paratype II, as in Weir’s example, the point is sharp, while in the more elongated var. attenuata the shape is still more hastate and the apex long and pointed. There are also specimens (e.g. Nos. 350 and 357) with a more conical shape, and in one of them the ventral groove is unusually long and distinct. These, however, are all connected with the typical examples by passage-forms (if one can speak of passage-forms when dealing with belemnite guards), and it seems impossible to divide this apparently homogeneous assemblage up into a number of morphological ‘species’. Moreover, since they were purchased from the Arabs, and probably were collected at different spots near Bihendula, it would be inadvisable to increase the large number of belemnite species of doubtful horizon. The writer’s restudy of S. somaliensis has fully confirmed the above cited conclusions of Spath. All morphologically distinct guards described and figured (Pis. 30-32) in this paper are, therefore, treated as mere morphological variants of a single polytypic Somalibelus species. No new formal names were introduced for any of the extreme or intermediate morphological forms of the species. The grouping of the representatives of S. somaliensis according to the outline and proportions of the guard appears to be the best possible solution of the rather intricate problem of organization of numerous distinctive morphological forms included in this species. In distributing the guards among the morphological variants listed in Table 1, it was found necessary, however, to take into account the depth of the alveolus as well as the relative length and distinctiveness of the ventral canal, which show a distinct correlation with the shape and proportions of the guard. One morphological extreme is represented by the extremely sturdy, relatively less compressed, sybcylindrical guards with obtusely rounded, more or less distinctly mucronated apical end and unusually deep alveolus comprising between three-fifths and three-quarters of the guard’s length (PI. 30, figs. 3, 5; PI. 31, figs. 3, 4; PI. 32, figs. 4, 5). This extremely sturdy variant includes the holotype of the species (Spath 1935, pi. XXV, fig. 4; this paper PI. 32, fig. 5) and so must be treated as its typical variant in spite of its extreme character. Most of the representatives of the extremely sturdy variant are somewhat subclavate in ventral and lateral aspects. This subclavate shape may, however, be stressed or simulated by a commonly present lateral deformation of the alveolar part of the guard (e.g. PI. 31, fig. 3n). Another extreme variant is represented by much more slender, more or less markedly subfusiform and compressed guards with relatively long and acute apical ends (PI. 31, fig. 1; PI. 32, figs. 1, 2, 3). This variant is characterized by the most shallow alveolus which either does not or only slightly exceeds one-half the length of the guard (PL 32, fig. 1). The holotype of S. somaliensis var. attenuata Spath (1935, p. 223; this paper PI. 31, fig. 1) is a typical representative of this extremely slender variant which also includes more slender and compressed guards with somewhat attenuated adapical quarter (PI. 32, fig. 3) and much more subfusiform guards (PI. 32, fig. 2). The third extreme morphological variant is characterized by slender guards which are feebly to slightly subclavate ventrally and distinctly subconical laterally (PI. 30, fig. 6). They are strongly compressed throughout, possess an unusually long and 182 PALAEONTOLOGY, VOLUME 15 distinct medioalveolar canal extending over most or all of the ventral surface and have a characteristically shallow alveolus similar to that of S. s. var. attenuata. The shape of the apical end varies from the obtuse and distinctly mucronate to the long and acute. This extreme morphological variant is poorly understood, being only represented by about half a dozen fragmentary guards and recognizable fragments. The extremely sturdy variant of S. somaliensis is connected by numerous passage forms with S. s. var. attenuata. These forms exhibit various combinations of their diagnostic features (e.g. PI. 30, figs. 1, 7; PI. 31, fig. 2). Of these morphological forms those combining the more or less long and acute adapical part with the sturdy, more or less subcylindrical shape of the guard and a deep (60-75% of the guard’s length) alveolus are the most prominent in the material studied. They are recognized as the fourth morphological variant of S. somaliensis. Other transitional forms combine the slender subcylindrical shape of the guard with a distinctly mucronated apex and long, prominent ventral canal (PI. 30, fig. 7). REFERENCES ARKELL, w. J., et al. 1957. Cephalopoda, Ammonoidea. In moore, r. c. (Ed.). Treatise on Invertebrate Paleontology. Part L, MoUusca 4, xxii+490 pp., Univ. Kansas Press and Geol. Soc. Amer. BLUTHGEN, J. 1936. Die Fauna und Stratigraphie des Oberjura und der Unterkreide von Konig Karl Land. Geol.-Pal. Inst., Greifswakl Univ. Arb. 99, 92 pp., 8 pis. EUDES-DESLONGCHAMPS, M. E. 1878. Le Jura normand: Cephalopodes dibranches. Part 2, Mono- graph 6, 34-73, 7 pis. GUSTOMEssov, V. A. and USPENSKAYA, E. A. 1968. O rodc Rhopaloteuthis (Beleninitidae) i yego krymskich predstaviteliakh [On the genus Rhopaloteuthis (Beleninitidae) and its Crimean representatives.] Bull. Mosk. Ob-va Ispyt. Prir. (geol.) 43, 65-78. [In Russian.] HANAi, I. 1953. Lower Cretaceous belemnites from Miyako district, Japan. Trans. Jap. J. Geol. Geogr. 23, 63-80, pis. 5-7. JELETZKY, J. A. 1946. Zur Kenntnis der oberkretazischen Belemniten. I. Fdrhandl. Geol. Fbren. Stock- holm, 68, 87-105, figs. 1-4. 1966. Comparative morphology, phylogeny, and classification of fossil Coleoidea. MoUusca, Article 7, Pal. Contr., Univ. Kansas, 162 pp., 25 pis., 15 figs. and ZAPFE, H. 1967. Coleoid and Orthocerid Cephalopods of the Rhaetian Zlambach Marl from the Fischerwiese near Aussee, Styria (Austria). Ann. Naturhistor. Mus. Wien, 71, 69-109, 4 pis., 1 fig. KABANOV, G. K. 1963. Fragniokon Pseuciobelus bipartitus iz valanzhina Krima [The phragmocone of Pseudobelus bipartitus from the Valanginian of the Crimea]. Paleont. Zhurnal, 4, 121-123, figs. 1-2. [In Russian.] — — 1967. Skelet belemnitid; Morfologiia i biologicheskii analys [The skeleton of belemnitids; its morphology and biological analysis]. Akad. Nauk SSSR, Trudy Paleont. In-ta, 144, 100 pp., 16 pis., 45 figs. [In Russian.] KRYMGOLTS, G. 1939. The Mesozoic Belemnitidae of the USSR Fas. 1. The Lower Cretaceous Belmni- tidae of the Caucasus. Paleont. of USSR Monographs, 67, 1-54, 8 pis. LISSAJOUS, M. 1915. Quelques remarques sur les belemnites jurassiques. Bull. Soc. d'Histoire Nat. Macon, 125-154. 1925. Repertoire alphabetique des belemnites jurassiques precede d’un essai de classification. Travaux Mem. Fac. Sci. Lyon, Lab. Geol. 7, 175 pp., 23 figs. MULLER-STOLL, H. 1936. Beitrage zur Anatomic der Belemnoidea. Nova Acta Leopoldina, new ser., 4, 159-226, figs. 1-5, pis. 1-14. MUTVEi, H. 1964. Remarks on the anatomy of recent and fossil Cephalopoda; with description of the minute shell structure of belemnoids. Acta Univ. Stockholmiensis, Contrib. Geol. 11, 79-102, figs. 1-8. JELETZKY: ^RHO PALOTEUTHIS SOMALIENSIS' 183 PUGACZEWSKA, H. 1957. O dwoch gatunkach belemnitow rodzaju Rhopaloteuthis z jury Polski [Sur deux especes de belemnites du genre Rhopaloteuthis du Jurassique de Pologne]. Acta Palaeont. Polonica, 2, 383-404, 5 pis., 5 figs., 3 tables. [In Polish.'] SPATH, L. F. 1933. Revision of the Jurassic Cephalopod Fauna of Kachh (Cutch), Part VI. Mem. Geol. Surv. India, Palaeont. Indica, n.s. 9, Mem. 2, 659-945. 1935. Jurassic and Cretaceous Cephalopoda. In The Mesozoic Palaeontology of British Somali- land, Chapter 10, 205-228, pis. XXIV-XXV, 4 figs. STOLLEY, E. 1927. Zur Systematik und Stratigraphie mediangefurchter Belemniten. Jahresb. Niedersdchs. Geol. Verein. 20, 111-136, pi. 24. STOYANOVA-VERGiLOVA, M. 1963. CurtoMboUtes gen. nov. (Belemnitida) from the Lower Cretaceous sediments in Bulgaria. Travaux Geol. Bulgarie, Paleont. ser., Acad. Sci. Bidgarie, 5, 211-223, 2 pis., 3 figs. WEIR, J. 1929. Jurassic fossils from Jubaland, East Africa, collected by V. G. Glenday, and the Jurassic geology of Somaliland. Monogr. Geol. Dept. Hunterian Mas. Glasgow Univ. 3, 1-63, 5 pis. J. A. JELETZKY Geological Survey of Canada 601 Booth Street Ottawa Ontario KIA OE8 Typescript received 23 April 1971 Canada SHORT COMMUNICATION FOSSIL AND LIVING HEMICYPRIS (OSTRACODA) FROM LAKE RUDOLF, KENYA by RAYMOND HOLMES BATE Abstract. A comparison is made between the fossil Hemicypris postewtnmcata Bate 1970 and three living species of Hemicypris described from East Africa by Lindroth (1953). The possible ancestral position of H. posterotruncata to H. klei (Lindroth) is considered. Recently (Bate 1970) I described a new species of Hemicypris from sub-Recent beach sands discovered to the south-west of Lake Rudolf, Kenya. At that time I was unaware that Lindroth (1953) had described, in his paper on East African freshwater ostracods, three species of Cyprinotiis assignable to the genus Hemicypris. These are Cyprinotiis klei, C. intermedins, and C. nonstriatus. As all three species are similar in carapace outline to H. posterotruncata it was essential that a comparison of these ostracods be made. Through the kindness of Dr. A. Holm of the Uppsala Universitets Zoologiska Museum, I was able to borrow Lindroth’s original material thus making possible the following comments: Hemicypris intermedins (Lindroth). This species, although close to Hemicypris postero- trnncata in general outline, differs in the possession of a thickened anterior marginal TEXT-FIG. 1. {a) Left side, carapace, Hemicypris klei (Lindroth); No. 36a. {b) Right side of same, (c) Left side, carapace, Hemicypnis posterotruncata Bate; BMNHIo. 1410. {d) Right side of same. [Palaeontology, Vol. 15, Part 1, 1972, pp. 184-185.] BATE: HEMICYPRIS FROM LAKE RUDOLF 185 rim, a more broadly rounded posterior margin and a more strongly dentate left valve margin. Hemicypris nonstriatus (Lindroth). Although laterally similar to Hemicypris postero- truncata, the straight line dorsal valvular overlap as against the antero-dorsally sinuous overlap of H. poster otnmcata, readily serves to distinguish these two. Hemicypris klei (Lindroth). Inhabiting the same stretch of water (Lake Rudolf) as did H. posterotruncata, H. klei is also morphologically very close and a comparison of the lateral carapace outline of both species is given in text-fig. \a-d. From these illustra- tions it will be seen that H. klei differs in the following ways : the postero-dorsal slope is more steeply angled and the antero-dorsal angle less umbonate ; the ventral margin is more distinctly concave and the shell surface covered with broad, shallow pits. Hemicypris posterotruncata (sub-Recent or ?Pleistocene in age) not only occupies a position in time ancestral to H. klei, but geographically occupied the same spatial niche. Even without the soft part anatomy, the close similarity of carapace detail coupled with the stratigraphical position suggests that H. klei could have descended from H. posterotruncata. Whether this is also true of the other species of Hemicypris recorded from East Africa is a question which cannot as yet be answered. This note adds to the known geographical distribution (see Bate, 1970, p. 292) of the genus Hemicypris Sars. REFERENCES BATE, R. H. 1970. A new species of Hemicypris (Ostracoda) from ancient beach sediments of Lake Rudolf, Kenya. Palaeontology, 13, 289-296, pi. 52. LINDROTH, s. 1956 [printed 1953]. Taxonomic and Zoogeographical studies of the ostracod fauna in the inland waters of East Africa. Zool. Bidrag Uppsala, 30, 43-156. R. H. BATE Department of Palaeontology British Museum (Natural History) London S.W. 7 Typescript received 20 April 1971 •r ■ ■- - V *■•;■?=■ "kk. •: ■ . '"■ •' -■ .=,■- / - , 'i> f/iii ' ' ' .■■V V'»^ ,.r- ru\ ■■'.^:\% ^ • Oi . ’-- ‘ , |‘f* ' .. J“‘ ... ''*iJ>. V ivit;m5 r?*»- LORD: JURASSIC OSTRACODA 193 The genus oceurs in the Pliensbachian of north-western Europe, but present evidence suggests that G. tatei is restricted to Germany, whereas the type species, G. apostolesciii, occurs commonly in southern England, Erance, Germany, and north-east Spain. Gramannella is one of a number of Jurassic genera with somewhat similar muscle- scars and hingement which are distinguished by combinations of morphological features. Similarities exist between Gramannella and certain species of Aphelocythere (e.g. A. ramosa Fischer 1961) and the genus may prove to be ancestral to Aphelocythere, but such a lineage has yet to be demonstrated, and the differences in muscle-scars and overall morphology are adequate for distinction. The affinities of the genus are unknown, but it is readily recognizable and a good indicator of Pliensbachian deposits, occurring in the ibex, davoei and margaritatus zones. Gramannella apostolescui (Gramann 1962) Plate 39, figs. 14-23 1961 IProcytlieridea D, Cousin and Apostolescu, p. 429, fig. 2. 1961 Indet. gen. sp. 36, Oertli and Grosdidier, p. 460, table 6. 1961 tProcytlieridea sp. D, Apostolescu; Seronie-Vivien, Magne and Malmoustier, pp. 770, 781, table 2, pi. 4, figs, la-d. 1962 Procytlierideal apostulesciii\ Gramann, pp. 192-194, pi. 3, figs. 4-6. 1963 Indet. gen. sp. 36, Oertli, pi. 16 (1). Type specimens (Gramann (1962, p. 193)). Holotype, Tk. H. 3749; Paratypes, Tk. H. 3746-3748; material from Bohrung Burlo 1, 47*70-48'20 m. Material. 40 carapaces, 418 valves. Distribution. Dorset: Eype Clay, Down Cliff Sands and Margaritatus Clay (stokesi and basal subno- dosiis subzones, margaritatus zone). Robins Wood Hill, Gloucester: "’.margaritatus zone. Dimensions (in mm). Length Height Width Left valve, male, HU. 56.J.16 0-61 0-30 016 Left valve, male, HU. 56.J.16 (a) 0-67 0-31 016 Right valve, male, HU. 56.J. 17 0-67 0-31 017 Right valve, male, HU. 56.J.17 {a) 0-67 0-31 016 Left valve, female, HU. 56.J. 18 0-58 0-31 014 Left valve, female, HU. 56.J.19 0-58 0-29 013 Penultimate instar, left valve, HU. 56.J.20 0-57 0-27 Oil Antepenultimate instar, left valve, HU. 56.J.21 0-48 0-24 009 Antepenultimate instar —1, left valve, HU. 56.J.22 0-43 0-22 008 Antepenultimate instar —2, left valve, HU. 56.J.23 0-35 018 007 Carapace, male, HU. 56.J.24 0-69 0-31 0-28 Carapace, female, HU. 56.J.25 0-58 0-30 0-24 Description. Shape sub-rectangular. Dorsal margin straight or very slightly concave up to highest point at anterior cardinal angle; anterior round, normally with some asym- metry so that most distal part is in ventral half; ventral margin gently convex in lateral view but margin usually medianly or antero-medianly concave with distinct flange groove; posterior distally extended into an acuminate process, exact position of which may vary a little between mid-height and just ventral of mid-height; posterior may be somewhat ventrally inelined, especially in instars. Greatest length at mid-height, greatest 194 PALAEONTOLOGY, VOLUME 15 height usually at anterior cardinal angle, and greatest width posteriorly. Left valve larger than right. Valve surface ornamented with strong reticulate pattern; cells often deeply excavated, 6-sided or rounded, intercellular walls relatively thin; ornament absent on distal part of posterior, on ventral surface where valve is flattened beside margin, and along edge of dorsal margin. Notable smooth area close to anterior cardinal angle, sometimes slightly raised, but does not appear to have been a definite eye spot. Adductor muscle scar pattern a sub-vertical row of 4 rather flattened scars with rounded antennal scar anteriorly. Glou( Substage Zone tester Dor Paris set Basin N.W.G (Gramar 1 — Coupe ( (AQ ermany m 1962) Easte de Penne 20) Qu( ;rn Aquit Figea (Sondage a,ne 1 c Lot j DB240) G. tute Figeac Lot N.W.Gerrr (Sondage A68) (Gramann 1 1 lany 962) Upper Pliensbachian spinatum 1 ■ margaritatus 1 1 1 , . 1 1 1 1 1 Lower Pliensbachian davoei ? ? 1 M ibex 1 1 1 jamesoni TEXT-FIG. 3. Distribution of Gramaunella apostolesciii (Gramann 1962) and Graniannella tatei (Gramann 1962). Information from sources quoted in synonymy and from Viaud (1963). Hinge antimerodont, in left valve an anterior loculate groove with 7 small sockets, finely denticulate median ridge which frequently appears smooth, and posterior terminal groove with 6 or 7 sockets. Complementary structures present in right valve. Marginal zone of moderate width, widest anteriorly, inner margin and line of conscrescence coincident. Marginal pore canals simple, curved 8-10 anteriorly and 2 or 3 posteriorly. Sexual dimorphism evident, males relatively longer than females; females relatively short but not prominently inflated posteriorly. Adults and 4 juvenile moult stages recognized. Remarks. G. apostolesciii is distinguished from G. tatei, the only other species known to belong to the genus, by differences in ornamentation. In the former the surface is covered by a fairly strong, evenly developed, reticulation composed of similarly sized cells, whereas G. tatei possesses a far more irregular reticulate pattern, often with elongate cells, intercellular walls of dilferent strength, and smaller cells within larger. Gramann’s illustrations of G. tatei (1962, PI. 3, fig. 3) show 1 female right valve with much reduced reticulation. G. apostolesciii is a useful index for the middle of the Pliensbachian (see text-fig. 3). The range of the species in Dorset is not fully known; certainly it did not survive to the end of the subiwdosus subzone but its range down into the Lower Lias is unknown. A sample traverse through the Green Ammonite Beds {davoei zone) in order to prove the range yielded no ostracods at all. At Robins Wood Hill, Gloucester, the species is known from only 1 specimen. To the ranges shown on text-fig. 3 other, more general, records must be added: Domerien (Cousin and Apostolescu 1961), Pliensbachien LORD; JURASSIC OSTRACODA 195 (Seronie-Vivien et al. 1961), and base Domerien in the borehole Berneval 101 (Paris Basin) quoted in Oertli (1963). The geographic distribution of this species is of interest since it has been found in the Basins of Paris and Aquitaine, southern England, north-west Germany and north- east Spain (Arino, mid-Domerian). Viaud (unpublished thesis, 1963) specifically noted that this species, described under Oertli’s notation Tndet. gen. sp. 36’, is absent in south-west Germany and the Swiss Jura. When first described (Gramann 1962, p. 193) the name of the species was incorrectly spelt as ^apostulescui" instead of 'apostoIescuV , though named after the French micro- palaeontologist Vespasian Apostolescu. This would appear to constitute an ‘inadvertent error’ (Stoll 1961, I.C.Z.N. Article 32u (ii)) and is here corrected. Acknowledgements. The research work, of which this paper forms a part, was carried out during the tenure of a University of Hull Research Studentship, which is gratefully acknowledged. Dr. J. W. Neale and Dr. P. F. Rawson kindly read and commented upon the original manuscript, Mrs. L. Harvey prepared the manuscript, and the photographs were taken using the scanning electron microscope of the School of Environmental Sciences in the University of East Anglia. 1 wish to thank Dr. H. J. Oertli, and the Societe Nationale des Petroles d’Aquitaine, for their hospitality and permission to examine material collected during exploration work in Spain. REFERENCES ACER, D. V. 1955. Eield meeting in the Central Cotswolds. Proc. Geol. Ass. 66, 356-365. ANDERSON, F. w. 1964. Rhaetic Ostracoda. Bull. geol. Surv. Gt Br. 21, 133-174. BATE, R. H. 1963. Middle Jurassic Ostracoda from north Lincolnshire. Bull. Br. Mus. not. Hist. (Geol.), 8(4), 173-219. COUSIN, N. and apostolescu, v. in cousin, n., espitalier, j., sigal, j. and apostolescu, v. 1961. Ardennes, region de M&ieres (Departement des Ardennes). Colloque sur le Lias frangais. Mem. Bur. Recherches geol. min. no. 4, 423-43 1 . DEAN, w. T., DONOVAN, D. T., and HOWARTH, M. K. 1961. The Liassic ammonite zones and subzones of the North-West European Province. Bull. Br. Mus. nat. Hist. (Geol.), 4 (10), 435-505, pi. 63-75. FISCHER, w. 1961. Uber die Lias/Dogger-Grenze in Siiddeutschland. Neues Jb. Geol. Paldont. Mb. 8, 394^00. GRAMANN, F. 1962. Skulpticrtc Ostracoden aus dem niederrheinischen Lias. Fortschr. Geol. Rheinkl West/ 6, 185-198. HOWARTH, M. K. 1957. The Middle Lias of the Dorset Coast. Q. J! geol. Soc. Lond. 113, 185-203. 1958. The Ammonites of the Liassic Family Amaltheidae in Britain. Palaeontogr. Soc. (Monogr.), xxxvii + 53 pp. London. and RAWSON, p. f. 1965. The Liassic succession in a clay pit at Kirton-in-Lindsey, North Lincoln- shire. Geol. Mag. 102 (3), 261-266. KENT, p. E. 1949. A structure contour map of the surface of the buried pre-Permian rocks of England and Wales. Proc. Geol. 60, 87-104. KLINGLER, w. in SIMON, w. and BARTENSTEIN, H. (Eds.) 1962. LeitfossiUen der Mikropalciontologie. 1, viii+432 pp.; 2, 59 pi., 22 tab. Berlin. MOORE, R. c. (Ed.) 1961. Treatise on Invertebrate Paleontology, Part Q, Arthropoda 3, Crustacea, Ostracoda, xxiii + 442 pp. Lawrence, Kansas. OERTLI, H. J. 1963. Faunes d'ostracodes du Mesozoique de France! Mesozoic ostracod faunas of France. 57 pp., 90 pi. Leiden. and GROSDiDiER, E. 1961. Ostracodes de quelques sondages du Lias du Bassin de Paris. Colloque sur le Lias frangais. Mem. Bur. Recherches geol. min. no. 4, 459-461. PETERSON, J. A. 1954. Jurassic Ostracoda from the ‘Lower Sundance’ and Rierdon formations, western interior United States, J. Paleont. 28 (2), 153-176. 196 PALAEONTOLOGY, VOLUME 15 SERONIE-VIVIEN, R. M., MAGNE, J. and MALMOUSTiER, G. 1961. Le Lias des bordures septentrionale et orientale du Bassin d’Aquitaine. CoUoque sur le Lias frangais. Mem. Bur. Recherches geol. min. no. 4, 757-791. STOLL, N. R. 1961. (Chairman, ed. Committee) International Code of Zoological Nomenclature adopted by the XV International Congress of Zoology, xviii + 176 pp. London. SYLVESTER-BRADLEY, p. c. 1956. The Structure, evolution and nomenclature of the ostracod hinge. Bull. Br. Mus. nat. Hist. (Geol.), 3 (1), 1-21. viAUD, J. 1963. Les Ostracodes des principaux bassins liasiques frangais. Unpublished thesis. Univer- sity of Bordeaux. ALAN LORD School of Environmental Sciences University of East Anglia Revised typescript received 29 June 1971 Norwich nor 88c HYDROZOA AND SCYPHOZOA AND OTHER MEDUSOIDS FROM THE PRECAMBRIAN EDIACARA FAUNA, SOUTH AUSTRALIA by MARY WADE Abstract. Eoporpita medusa gen. et sp. nov., is a chondrophore with annular float chambers. Simple dactylo- zooids and details of its gonozooids differentiate it from modern Porpitidae but its affinities are closest to these. The enigmatic group Cyclomedusa Sprigg has characters in common with Eoporpita but typically lacks a float. They could represent a form close to the hydrozoan root stock from which chondrophores arose but no certainly-assignable oral side is known. Two species of Scyphozoa are recognized from positive composite moulds including internal structures. Brachiiia delicata gen. et sp. nov. is radial and annular in structure and Kimberella quadrata (Glaessner and Wade), new name, is tetramerous radial. Ediacaiia flindersi Sprigg and Rugoconites Glaessner and Wade are restored but it is still not certain what their structures mean in terms of coelenterate history. The study of ‘medusoids’ in the Ediacara fauna has lagged behind the study of more distinetive forms, both because of the great number of indifferently preserved specimens, and the morphologic intergrading of the simple outlines preserved. This paper is a progress report on forms that have become better known since their original description, and on new material. The greatest source of new knowledge comes from the discovery and study of com- posite moulds showing internal and external characters on the same specimen. Until they are found, any interpretation or restoration remains provisional. Composite moulds have been invaluable in linking the oral surface of a new chondrophore, Eoporpita, to its float and to its aboral side. Similar moulds allow description of Brachina delicata gen. et sp. nov. and its assignment to the Scyphozoa. Kimherella quadrata (Glaessner and Wade) (new name for Kimberia quadrata Glaessner and Wade) is also probably a Scyphozoan. Rugoconites enigmaticus Glaessner and Wade appears only as a composite mould; it has an unusual preservation in which ridges appear to have occupied the position of radial canals whether observed from the exumbrellar or subumbrellar side of the body. The necessity to explain this structure introduces a note of speculation into the restoration of this species and genus, of which a second species is described. The external morphology of Ediacaria flindersi Sprigg is now known in some detail but as none of its internal structures are known, it remains incertae sedis (Glaessner and Wade 1966). The lack of extensive composite moulding hinders our understanding of Cyclomedusa. From time to time medusoids are observed with one or more sharp re-entrants in the margin leading into deep creases across the body (pi. 42, fig. 1, centre right margin). These are reminiscent of the radial tears deep into the mesogloea which are often found in Recent medusae. Such tears appear to be the result of physical battering. T have mostly observed stranded Semaeostomatida and only noted tears on these but while battering during stranding is doubtless more severe than fully submarine battering, the structures in the fossils are closely similar to those in the Recent specimens. This [Palaeontology, Vol. 15, Part 2, 1972, pp. 197-225, pis. 40-43.] 198 PALAEONTOLOGY, VOLUME 15 re-entrant and furrow effect is not confined to any one form but is widespread in the Ediacara fauna; also, it occurs without regular spacing in an individual, or regular occurrence in a species. As such it cannot be satisfactorily considered an original structure but must be an artifact. Late in 1968 the Ediacara fauna was located in the main Flinders Ranges, 320 km north of Adelaide, a short distance above the base of the upper of two members which make up the Pound Quartzite. During the following year it was traced 140 km north and south from Mt. Scott Range, north of Ediacara Range, to Yappala, west of Hawker (text-fig. 1). All these occurrences proved to be at the same stratigraphic level and it was possible to show that the occurrences at Red Range (Beltana Station) and Ediacara Range also were deposited at this time (Wade 1970). Other workers are presently extending the discoveries to the east in the major syncline of which Mt. Scott is part, and to the southeast side of the central Flinders Ranges. Repositories. Specimens with numbers prefixed ‘F’ or ‘T’ or without prefix are deposited in the collections of the Geology Department, University of Adelaide. Those prefixed ‘P' are deposited in the South Australian Museum. SYSTEMATICS Class HYDROZOA Order chondrophorida Family porpitidae ? Genus eoporpita nov. Type species. Eoporpita medusa sp. nov. Diagnosis. As for type species. Eoporpita medusa sp. nov. Plate 40, figs. 1-6; Plate 41, fig. 6a, b; text-fig. 2 Material and occurrence. About 20 specimens from Ediacara Range. One from Mayo Gorge was shattered during collection. Holotype. T27; 2019, from Ediacara Range. Preservation. All of the fossils are preserved wholly or mainly in convex relief, on the depositionally lower surfaces of rock slabs. The actual preservation represents the complex interplay of a structure sometimes resistant enough to hold the sediment up until it had consolidated, forming an impression, with invariably non-resistant structures which disintegrated before the overlying sediment set and thus allowed the sediment to form casts. This combination of negative and positive preservations on one surface is a type of composite mould. The modes of preservation in these sediments have been discussed at length (Wade 1968). The fossils are circular and raised in the centre. They display several aspects which could not be combined without the presence of composite moulds, so they will be discussed under five preservational types and summarized in a diagram of the structure : 1. One, perhaps two specimens (PI. 40, fig. 4); almost flat cast with smooth, entire surfaces with a very faint radial structure, and a slight central dome. 2. Two specimens, almost flat positive composite moulds like (1) at the centre but WADE: AUSTRALIAN LATE PRECAMBRIAN ‘MEDUSOIDS’ 199 surrounded by flat, broad rings with depressed sutures between them. The whole annular structure is slightly depressed (see PI. 40, fig. 6). This is a composite mould dominated inwardly by a low, domed centre as in (1) and outwardly by a resistant, ringed structure, with ridged sutures between adjacent rings. Prior to fossilization this annular structure must have underlain a smooth outer surface such as that seen in PI. 40, fig. 4, because it was higher (depositionally) in the rock, than the centre it encircles. 3. Two specimens; casts of annulate discs made of rings of comparable size to those seen in (2). The smaller specimen is figured in PI. 40, fig. 2, and shows slightly depressed sutures. The larger specimen (PI 2720) has one end covered (on the depositionally lower side) by inwardly tapering strips of sand like those seen in (4). 4. Fifteen specimens; discoid bodies including those seen in PI. 40, figs. 1, 5. These are all casts. The specimen seen in fig. 5 has been sectioned and confirms the impression gained by viewing it entire, that the radially sculptured layers of sand are individually distinct to varying depths, but lose distinctness inwardly and merge in a structureless sand-mass. The chipping of layers from the specimen seen in fig. 1 and others shows that the normal preservation of these specimens is as layers of sand marked by furrows into irregularly disposed, inwardly tapering, rounded strips. Several specimens beside those in PL 40, figs. 1, 5 show 2 series of strips, several outer ones all approximately the same length and several inner ones of inwardly decreasing length. The greatest known length of strips is from the margin to the inner series of strips. On the evidence of the larger specimen (3) these layers or whorls of strips cover one side TEXT-FIG. 1. Locality plan showing the distribution of the Pound Quartzite in the central Flinders Ranges. Fossiliferous deposits are found along the strike of the beds in the named ranges, a short distance above the base of the upper, or white, member of the Pound Quartzite. Qnly the section in Brachina Gorge was as rich as any comparable area at Ediacara Range. Fossili- ferous sections recorded by Wade (1970) are indicated by asterisks if the fossils were found in situ or by crosses if only float is yet known. 200 PALAEONTOLOGY, VOLUME 15 TEXT-FIG. 2. Eoporpita medusa gen et sp. nov., natural size. The structures exhibited by the specimens shown in Plate 40, and additional specimens, have been scaled to one body-size and assembled in natural order without any further attempt to restore the original animal, or reconstruct the life position of the several structures illustrated. Upper surface: PI. 40, figs. 4, 6. Float: PI. 40, figs. 6, 2. Fig. 6 preserves the annules as a mould and the depressions between annules indicate original sutural ridges but the amount of distortion due to compression prior to moulding is unknown; the cast, PI. 40, fig. 2, shows depressed sutures between convex annules like a larger, unfigured, annular disc with tentacles attached to one end, and the lower surface of the float has therefore been shown with depressed sutures. Lower surface of body: based on 15 specimens including those illustrated in PI. 40, figs. 1, 5. Number of whorls and length of overlap: based mainly on the specimens seen in PI. 40, figs. 1, 5. Individual separation of "strips' marking the surfaces of whorls: small areas seen PI. 40, fig. 1, and on unfigured specimens, in which the outer strips or tentacles are few and sometimes very widely separated. Possible upper surface of mantle flap: PI. 40, fig. 4 ‘m’. Lower surface of mantle flap: PI. 40, 1 ‘m’. Association of upper and lower surfaces: PI. 40, fig. 3. TEXT-FIG. 3. Porpita porpita Linne, transverse section of a young specimen, after Mackie (1959). of the annulate disc. Necessarily, this is the opposite side from the smooth, centrally domed side. At the centre whorls of inwardly tapering strips cease against the base of a central mound. This mound can appear as a truncated cone (one specimen) or, because of eccentric wrinkling, as a rather flattened cone. It is always single. PI. 40, fig. 1, shows EXPLANATION OF PLATE 40 Figs. 1-6. Fojoo/yi/mmprfion gen. et.sp. nov., 1-3,6 Xl;4,5 xO-5. 1,T27;2019, holotype, oral surface; ‘m’ possible mantle flap; 1-3, tentacles of outer series (dactylozoids), 4-8, tentacles of inner series (gonozooids) and 9, incipient tentacles, surround a flattened centre. 2, FI 7453, paratype, float showing narrow annular chambers traversed by radial furrows which are irregular in position, length, and definition and thus do not appear to result from sulci. 3, FI 7454, paratype, aboral side, composite mould showing tentacles near four-fifths of margin. 4, P14283, paratype, aboral side showing central mound and faint, radial striae. 5, F17455, paratype, oral surface showing seven inner whorls of tentacles and (at edge) six outer whorls, gonozoids and dactylozooids respectively. 6, PI 4286, paratype, aboral side, composite mould showing central mound, faint radial striae, and impressions of annular chambers. Palaeontology, Vol. 15 PLATE 40 WADE, Eoporpita medusa WADE: AUSTRALIAN LATE PRECAMBRIAN ‘MEDUSOIDS’ 201 (at ‘m’) a relatively smooth area, depositionally above the radiating strips, marked off from the general rock surface by a shallow furrow. 5. One specimen fPl. 40, fig. 3), which appears to be partly equivalent to (1), and partly radiating strips which form a surface uniquely smooth for the strips. They are crossed (upper left side) by faint, equidistant annulations. This is a positive composite mould of upper and lower surfaces with some hint of an annulate disc between them. The smooth, centrally domed side had no hiding place for unobserved openings and is thus aboral ; from the fact that it was also a much thinner covering to the float than the ‘whorls of strips’ and conical centre, it was presumably the upper side in life. In compiling text-fig. 2, the structures observed are placed in order of superposition with the aboral surface at the top. This diagrammatic cross-section indicates what is actually seen rather than representing a restoration for (apart from the fact that the overall shape was lenticular) vertical control is lacking and there has been no attempt to restore original shape. This was done with the model in PI. 41, figs. 6a, b. The only ‘restoration’ in the diagram is the scaling of all structures to the same body size and the joining of the annulate structures mentioned under preservations (2), (3) and (5) as one, annular- chambered float. This structure must have been very lightly sclerotized as it was more prone to collapse under load than to form external moulds. Only its outer portion supported sediment (preservation 2) in two specimens: the inner portion gave way completely in these same specimens and allowed the centre of the specimen to be cast. In two other specimens the whole depositionally upper surface gave way while the lower surface still remained intact (preservation 3) and complete casts of the deposi- tionally lower surface resulted. At least one of these casts is of the side with whorls of strips, the lower side in life. Some of these strips have been separated from neigh- bours and reveal other strips in the gap between them, while neither side of the gap has lost the strip shape (PI. 40, fig. 1). This suggests that the strips had individual walls and were tentacle-like, like the internal mould figured as a possible Cyclomedusa (PI. 41, fig. 2-‘a’). On the other hand there is the tendency for the strips to merge into sheets or whorls of sand. Such a tendency would arise from very slight compaction during diagensis, if whorls of sand-casts overlay each other, but it is also possible that dragging of the body on the sea-floor caused sand to be caught between whorls of tentacles, and that the strips arise from external moulds of almost flattened tentacles. Whichever explanation of preservation is considered, only whorls of tentacles seem adequate to explain the behaviour of the numerous ‘strips’ ; up to 6 whorls are known in the outer series, while the inwardly-diminishing series had 6 or 7 more whorls. The whole layout is so like that of a porpitid chondrophore (text-fig. 3) that subjectively deciding to coin new terms to describe it ‘objectively’ seems unreasonable. P14289 is the second specimen referred to in preservation (1), it has a relatively broad ‘central dome’ which is slightly depressed in its centre ; this fragment is only questionably assigned to Eoporpita and not used in compiling the description. Diagnosis. A circular or elliptical chondrophore with radial symmetry. Two series of club-shaped ‘tentacles’ form several outer whorls (dactylozooids) of near constant length, and several inner whorls (gonozooids) of inwardly reducing size, encircling a single, large central cone (gastrozooid). Aboral surface smooth except for very fine radial striae; with a small, low, central dome. Float delicate, with numerous narrow. 202 PALAEONTOLOGY, VOLUME 15 annular chambers enclosing a small, circular, central chamber. Some radial creases reach from near centre to margin. Description. The average radius ranges from approximately 2 to over 8 cm. That of the smaller float (PI. 40, fig. 2) is about 2-5 cm and of the larger roughly 4-5 to 5 cm (the largest radius, probably about 6 cm., is obscured by a positive mould of some tentacles.) The holotype (PI. 40, fig. 1) shows the supposed tentacles most clearly. The central area is not very distinct but has overlapping ‘concentric’ folds, the outermost two of these are slightly corrugated (whorls 9 and 8) and (at maximum preserved radius) the distance from centre, across the corrugated folds or incipient tentacles to the base of the first well developed tentacles (whorl 7) is 1 -6 cm. From here to 3-7 cm the whole span of five whorls of tentacles, each whorl larger than the one before, is crossed. Roughly the same number of tentacles is present in equal sectors of each whorl. From 3-7 to 7 cm no further edges of whorls are observed though chipping shows that at least three whorls of tentacles are superposed at the outer edge. The thickness of the fossil suggests more than 3 layers here. The centre of the paratype in PI. 40, fig. 5 is not clear but at least seven whorls of tentacles are involved in the elongating series of tentacles and at least six whorls overlap at the outer edge. No differences except in relative length could be observed between the inner series of tentacles and the outer series. In both, the tentacles appear to have been club-shaped. Two or three other specimens also hint at this sort of tentacle-distribution. The largest, P 12753, has the best preserved centre. A small, trun- cated, inverted cone projects from among the inner tentacles. This has a fine, X-shaped furrow on its truncated end. The structure appears to be due to tiny creases radiating from the centre. In this speci- men well-developed tentacles approach closer to the central cone than in the holotype and they may have approached as closely in several of the specimens damaged predepositionally. Plate 40, fig. 3 shows a positive composite mould. It has a tilted, low, truncated mound of radius 7-8 mm at the centre, with two arcuate ridges on the more depressed side. Around four-fifths of the circumference rows of tentacles show in convex relief. A sharp crease separates them from the remainder of the disc. It extends from the margin, encircles the centre but not at a regular distance from it, and returns to the margin. The surface within this line is smooth except for the centre and except for extremely fine radial striae all over it. This specimen was buried to a maximum depth of 9 mm and the margin seen at the upper right side of PI. 40, fig. 3 is very smooth where it was most deeply impressed in the enclosing sediment; in fact, it is everywhere smoother than any other specimen. The remaining two aboral composite moulds are fragmental and show no margins. The larger fragment consists of a central dome 1-2 cm in radius and one quarter of the disc. About nine annuli show intermittently between 1-2 and 5 cm and remnants are seen on the poorly-preserved surface further out. The edge is vague but the complete radius was probably about 10 cm. Faint radial striae occur in small patches. The smaller fragment (PI. 40, fig. 6) is of little more than the central disc and parts of three annuli a short distance outside it. These are clearly defined by narrow grooves between flat surfaces. The fragmental cast of the aboral surface (PI. 40, fig. 4) is just over 8 cm at its greatest preserved radius. The centre is occupied by a low, rather flattened mound with a radius of just over 1 cm. The surface is partly smooth but mainly covered by numerous fine to very fine radiating striae. These can be traced across the main expanse of the disc and up the gentler slopes of the dome to its top (which is broken at the centre). As far as can be seen, striae are multiplied by the interpolation of extra furrows radially outward, and maintain a fairly constant spacing. A sharp groove (under 2 cm long, and at a slight angle to the striae) runs up the less steep side of the dome and disappears before the centre. It has no equivalent in the three composite moulds and is presumably accidental. A concentric groove (at bottom) may indicate the edge of the float. The smaller float (PI. 40, fig. 2) consists of a circular innermost chamber (2 mm in diameter) with at least 12 annular chambers (probably several more) around it. The centre of the innermost chamber is marked by a pinpoint depression. The float is dented at one side and asymmetric but there is no observable narrowing of individual, undistorted chambers as the shorter radius is approached: the shortening is possibly due to the denting. The larger specimen is also asymmetric but this has some of the soft parts preserved, overlapping the more elongate radius and projecting beyond its possible boundary. This elongation is also suspect but there is a possibility that the natural shape is elliptical, with the centre approximately at one pole of the ellipse. A third, almost round, float is now known. Restoration. The smooth, very finely striate surfaces of the four aboral (or partly aboral) WADE: AUSTRALIAN LATE PRECAMBRIAN ‘MEDUSOIDS’ 203 specimens are taken as representing the fleshy surface layer on the aboral side of the float. The central, truncate mound is a naturally domed centre slightly flatter than that of the preserved Porpita figured by Hyman (1940, fig. 154d). The striae appear to show more coarsely with compression. They can be equated to coenosarc between aboral, radiating, gastrodermal canals, which are very regular in young Porpita porpita Linne. The smoothness of the margin in the one composite mould which shows it, is attributed to the coenosarcal disc-edge or mantle flap, folding over the outer ends of the tentacles. The impressions of tentacles near four-ffihs of its outer edge would thus be due to composite moulding. The restoration of the oral surface is also securely based on numerous specimens. For simplicity PI. 41, fig. 6 has been restored as an adult considerably smaller than the holotype. It has only three whorls of 47 tentacles in the outer series and three well-developed and two incipient whorls in the inner series. In view of the similarity of arrangement to the Recent chondrophores, it seems reasonable to consider the outer series dactylozooids, the inner series gonozooids, and the larger central cone the gastrozooid. Remarks. The endoderm cells of the tentacles are vacuolated in Porpita and form a resilient ‘skeleton’ that returns them to the ‘resting’ position seen in text-fig. 3, whenever muscular control is relaxed (Mackie 1959). As musclature is virtually all radial (‘longitudinal’), movement is almost entirely in the vertical plane. It is interesting to note that there is remarkably little crossing-over of tentacles in Eoporpita, even though those of the outer series are long. Fossil chondrophores showing ‘tentacles’ are rare. The only form attributed to the Porpitidae is Paropsonema Clarke (Silurian to Devonian) but this form has apparently branched tentacles (Ruedemann, 1916; Chapman, 1926; Harrington and Moore, 1956). The vellelid Palaeonectris discoidea Rauff (1939) has dactylozooids of the simple, tapering broad- tipped form seen in E. medusa. One of Rauff ’s three specimens has a thick ridge across the body which has been interpreted as a sail and is the reason for the placement of this Lower Devonian form in the Vellelidae. Another specimen appears to be viewed from the dorsal side with the coenosarcal disc-edge folded upwards and inward, so that the inner edge of a hollow oval is formed of the mantle flap, showing concentric furrows due to muscular contraction, and the dactylozooids are attached to the body outside the mantle flap. It would be interesting to have this specimen X-rayed to find if the remainder of the body is still within the rock below the apparent ‘hole’ in the centre. The third specimen shows branched structures interpreted as gonozooids. The structure of the float in Eoporpita is strongly annular and bears no close resemblance to that in the Ediacaran bilateral chondrophores Ovatoscutum coucentricum Glaessner and Wade and Chondro- plon bilobatum (Wade 1971), which were resistant enough to form external moulds. The chamber sutures are much less sharply defined in most specimens of Eoporpita and this tends to substantiate the much softer material of the float suggested by the usual preservation as casts. The aboral views show the fleshy surface more than the floats. As the centres are quite clear it is certain that there was no sail or elongate crest but only a low, round mound in this region. The coarsest of the radial striae (explicable as due to relatively fine dorsal gastrodermal canals above) are as coarse as those of Cyclo- medusa plana Glaessner and Wade or C. gigantea Sprigg (1949); see also Harrington and Moore, 1956, fig. 122). In the centre of C. plana small, concentric furrows and ridges indicate no broad, low, central dome but a conical peak, which may be twinned (Glaessner and Wade, 1966, pi. 98, figs. 1-3). In C. gigantea the centre is preserved as a broad, low dome though it could have been conical before flattening as ring markings are not concentric, the mid- and out-fields of the disc being strongly corrugated concentrically. Though Palaeoscia floweri Caster (1942) is equally corrugated it is probably not a chondrophore (Osgood, 1970, p. 395-397). Though it is possible C. gigantea is a chondrophore there is no proof, and its strongly corrugated disc offers a substantial reason for regarding it as distinct from E. medusa, for it was either initially corrugated or much more convex than the aboral side of E. medusa. The shape of the float is a critical consideration in classifying chondrophores. E. medusa appears to have had narrow, circular chambers with a few radial creases and no definite bilateral symmetry. Not only does it differ from the other Ediacaran chondrophores, but it is morphologically closer to C 8908 P 204 PALAEONTOLOGY, VOLUME 15 the Recent Porpita than to Palaeozoic Porpitidae (Harrington and Moore, 1956). While it may seem unlikely that the same family could be present for over 600 m.y., only two positive characteristics distinguish Eoporpita from modern Porpitidae : (i) the tentacles or dactylozooids are invariably simple and club-shaped; shorter sizes have not been observed but this is to be expected for the growth of Porpita adds the younger whorls outside the older whorls (text-hg. 3, after Mackie 1959, fig. ID; Delsman 1922), (ii) Mackie showed that the whorls of gonozooids are also added to by outward growth in Porpita whereas the inner whorls of the inner series of tentacles are the smaller ones in Eoporpita. The inner series is also club-shaped except where very small (PI. 40, fig. 1 (4-9), 8 and 9 are incipient). No medusa-buds have been seen but these could have been lost or failed to be preserved. Whether the concensus of views ultimately places Eoporpita in the Porpitidae or not, it provides evidence of a long history of little change in the Chondrophorida which are much more conservative than the Scyphozoa. Indeed, Garstang (1946) and Mackie (1959) have shown how the modern members of this family can be compared to Recent Tubulariidae, Corymorpha in particular. The parallel is perhaps over- stressed in view of the great time gap between Corymorpha and the earliest known chondrophores, and the complete lack of reduction of stem in Corymorpha, which belongs to a group characterized by oral tentacles, unlike the chondrophores. Class HYDROZOA? Genus cyclomedusa Sprigg 1947 Plate 41, figs. 1-5; plate 42, figs. 1,2; text-fig. 4 Type species. Cyclomedusa davidi Sprigg 1947. A synonymy to the genus was given by Glaessner and Wade (1966). C. plana Glaessner and Wade is now known from the Ukraine and is thus the most widely distributed medusoid of the Ediacara fauna (Zaika-Novatskii et al. 1968; Glaessner 1971). Wade (1968, figs. 14, 15) figured specimens showing the flexibility of C. cf. davidi. After re-examining all the Cyclomedusa specimens in the South Australian Museum and the University of Adelaide in the course of this work, I now accept these forms as C. davidi. Material and occurrence. C. davidi is the commonest known. All species are known from Ediacara, C. radiata and C. davidi from Brachina Gorge and only C. davidi from Red Range. Preservation. On the bases of rock slabs; specimens always have some convex relief even in the flattest species, C. radiata. It is thought that all specimens showing radial structures are positive composite moulds of exumbrellar and internal structures ; some specimens are smooth except for concentric rugosities and these are casts of flattened exumbrellar sides (PI. 41, fig. 1). Only PI. 41, fig. 2 (right side — a) may represent Cyclo- medusa in subumbrellar view as an internal mould. Remarks on described species. C. davidi is usually concentrically rugose, as originally described. The central structure is very like that of C. radiata (below) but usually smaller and often more prominent. Its radial furrows are very variably developed ; as far as can be seen they never extend right to the central peak but may cross the entire body from the second ring furrow outside the central peak to the margin. No regularity in the addition of furrows has been observed but if well expressed, they tend to maintain EXPLANATION OF PLATE 41 Figs. 1, 2 (left side — b), 3-5. Cyclomedusa davidi Sprigg, X 1. Flattened casts of aboral sides. 1, PI 2775, 2, b, F16720B. Composite moulds showing zones or patches of radial furrows, fig. 4 (right) ap- parently where compressed; 3, T5, holotype; 4, P14176; 5, F17456. Fig. 2 (right side — a). Oral surface, possibly Cyclomedusa davidi, X 1 ; m, mantle flap, t, tentacles and bases of tentacles, g, gastrozooid. Fig. 6, a, b. Eoporpita medusa gen. et sp. nov., plasticene model of small adult, approximately X 1, viewed, respectively, from oral surface and, slightly obliquely from the side. Palaeontology, Vol. 15 PLATE 41 WADE, Cyclomedusa and Eoporpita medusa "■'m. '' k ’ ■ ] ■ i ■mj WADE: AUSTRALIAN LATE PRECAMBRIAN ‘MEDUSOIDS’ 205 a relatively constant spacing except on the outer ring or rings where new furrows are rarely inserted. These are interpolated between older furrows in forming the radial structure. On other specimens furrows may be few or none (PI. 41, figs. 1, 2 (left side), 4, 5). Fig. 4 shows a specimen with a patch where they occur quite close-spaced, though generally absent. Such patches may appear to have been at a lower level than the smooth surface of the body, e.g. on the holotype of Spriggia amndata and PI. 41, fig. 4. Furrows may be localized in zones as in PI. 41, fig. 5 and the holotype of C. davidi (PI. 41, fig. 3) where an inner annular zone shows more closely spaced radial furrows than are found in its outer zone. C. radiata contains several large specimens of which the best preserved is that shown in PI. 42, fig. 1, an oval specimen of maximum radius just over 7 cm and minimum a little under 6 cm. The best preserved centre is still that of the paratype illustrated by Sprigg (1949, pi. 14, fig. 3) (refigured here PI. 42, fig. 2). It has an oval, central, flat dome measuring 8-3 by 4-6 mm; this is surrounded by a deep, sharp furrow, marking the inner edge of a broad ridge. Its inner edge carries a slight ridge, and a fainter, slightly excentric furrow. The broad ridge is delimited on the outside by another sharp furrow and a narrow, rather smooth, zone. Radial furrows traverse the broad ridge in one place, and most of its outer margin is notched by the inner ends of the radial furrows which run to the margin of the fossil. Increase of furrows is by interpolation. They mostly commence outside the narrow, smooth zone. This specimen has been refigured and described in detail because its appearance seems to clearly represent the structure less well-preserved specimens appear to have had. The holotype (T23; 2037) deviates from this plan only in having a faint furrow nearer the outside than the inside of the broad ridge, in both specimens this faint furrow is probably due to flattening; several furrows are developed in some other specimens. Concentric folds can also be developed on the outer disc (PI. 42, fig. 1 ). Some developing near the margin of the holotype and a paratype were interpreted as ‘an epimarginal groove or (?) ring canal’ (Sprigg 1949; refigured Harrington and Moore, 1956, fig. 60 (4, 5)). C. gigantea has only one preserved radius, 6-7 cm. In general shape the centre is an oval platform about 20 by 22 mm radius, surrounded by a deep, wide, annular sulcus, and a concentrically ridged outer region. Radial striae show clearly in part of a zone from about 3-5 to 4-5 cm from the centre but can be traced more faintly to the margin and very faintly, almost to the centre of the bell. The centre of the bell is a flat oval 10 by 8 mm; not concentric with this is a circular, partly double ridged, furrow 31 to 32 mm across which is not concentric with the edge of the central platform either. There is no way of deciding how much elevation has been lost by flattening against the substrate, one side of the platform has a gently rounded surface but much is almost totally flat. No specimen duplicates the appearance of the holotype. In toto, its affinities are close to C. davidi with which it may be conspecific, as its radial striae are of similar dimensions at their coarsest. Cyclomedusa plana Glaessner and Wade is the only Cycloniedusa in which specimens with two centres exist without a furrow that completely traverses the bell from one side to the other passing between the centres (Glaessner and Wade 1966, pi. 98, fig. 3). Thus it is the only species of Cyclomedusa in which twinning appears a genuine possibility. Although a furrow has to completely divide two present-day medusae before they separate, it seems unlikely that medusae dying at such a moment would stay together and be deposited and fossilized together. Cyclomedusa must have been very supple (Wade 1968, figs. 14, 15) and any specimens with complete furrows between two centres could be two individuals juxtaposed in death. This must be suspected when, as in the C. davidi figured by Sprigg (1949, pi. 14, fig. 4, or text- fig. 8F), the centres are separated from the furrow by notably different distances, and the curvature of the concentric furrows suggests two complete bells with their adjacent free edges folded away from each other. The smaller specimen of these also bears a near-radial fortuitous crease which displaces structures that can still be matched across it, as tears in Recent medusae often do. Remarks on Cyclomedusa. The commonest medusoids in the whole fauna are those collectively referred to as ''Cyclomedusa'. They share the characteristics of a circular marginal outline and several to many near-concentric rugae which indicate, by their excentricity, a generally conical shape for the centre or even most of the body. Many but not all of these have radial structures of varying degrees of coarseness. Eoporpita was initially thought to belong in this plexus but was removed to the Chondrophora on the discovery of its float. 206 PALAEONTOLOGY, VOLUME 15 There remains one other specimen, F16720A (PI. 41, fig. 2 right side) giving evidence of ‘tentacles’ generally similar to those of Eoporpita. The specimen (as deposited) partly overlies a Cyclomedusa of the C. davidi kind (left side). Due partly to breakage and partly to compression against the Cyclomedusa, only about one third of the body is seen; it is generally flat, including the central region, though this is commonly high in Eoporpita. Its ‘tentacles’ are represented by a few, individual cones of sand regarded as fillings of rounded tubules. These occur in the mid-field of the disc, and the outlines of several more show toward the outside edge with the disc marginal zone ‘m’ exposed bare and smooth on each side of them. This marginal zone is apparently a mantle flap ; in natural section at the rock edge it is seen to extend inward, depositionally above the mid-field tentacles. All the inner tentacles have been infilled, as is shown by their individual, rounded bases, and fairly recently broken off during weathering, as differential staining shows. Only a few, doubled-over tentacles remain between the Cyclomedusa, the centre of F16720A and the broken edge. The many freshly-truncated, round bases are roughly arranged in concentric whorls around a larger, truncate, conical, central ‘zooid’. The specimen is thus the internal mould of a chondrophore-like animal. The mould is flatter, and its tentacles are less regularly placed than would be expected of an internal mould of Eoporpita (to judge from examination of the centre of its holotype). The alternative explanation is that the specimen may represent the oral surface of a Cyclo- medusa similar to the adjacent specimen of an exumbrellar side. These two specimens are so alike in proportions that it was at first thought that they were twinned, but on closer examination it is certain that one shows the subumbrellar and the other the exumbrellar side. They are not just different levels in bodies with similar orientation because the base of most and the full length of some of the tentacles is exposed. The central cones are respectively the gastrozooid of the right side ‘a’ and the aboral conical centre of the left side The outer edge of Cyclomedusa spp. is normally much more distorted than the remainder of the bodies (Wade 1968, fig. 14); the flexibility increases gradually and did not coincide with the development of ‘concentric’ rugae, as if rugae coincided with a change in structure like the difference between disc and outer ring in Ediacaria or Brachina. Rather, the flexibility lessens gradually toward the more elevated centre but text-fig. 4 shows that the whole bell may be compressed obliquely. One group of 'Cyclomedusa\ however, is not high in the centre but lower than the edge zone of the body. This is seen on many of 49 specimens on one bedding plane from Brachina Gorge, and several Ediacara specimens. The central two-thirds tends to hold a circular outline even when the edge zone is folded over it (two specimens). This evidence of an unusually resilient, though flattened, centre may also be evidence of a (collapsed) float in this group. The majority of once conical and wholly flexible forms, however, can scarcely be envisaged as possessing a float. Both dorsal and ventral gastrodermal canals of porpitid chondrophores are remark- ably strongly radial, as prepared specimens show. Similarly regular canals may cause TEXT-FIG. 4. Cyclomedusa davidi Sprigg. Tracing from photo- graph of a moderate-sized specimen which appears to have been steeply conical throughout. The apex was weathered and rather indis- tinct. WADE: AUSTRALIAN LATE PRECAMBRIAN ‘MEDUSOIDS’ 207 the ridges and furrows of Cyclomedusa, which may run from near their centres to their margins or be patchily distributed, or not occur at all, as though structures naturally at depth in the bodies are represented. Reconstruction of Cyclomedusa is not possible while the oral surface remains un- known. Its conical, rugose, flexible body indicates that it did not swim like a medusa, with the muscles reacting against a mesogloeal ‘skeleton’. On the contrary, the rugae suggest radial contractility, and it makes sense as a contractile animal only if attached in life by the apex which is truncate in all specimens where it can be observed (see PI. 41, figs. 1-5; PI. 42, fig. 2; Wade 1968, fig. 15). Thus the probability is that like the Aurelia scyphistoma, Stephanoscyplius and Comdaria described by Chapman (1966) Cyclomedusa developed (or retained, in a phyletic sense) chitin at the point of attach- ment. A broad, low conical form with a marginal zone of coenosarc continuous in structure with the aboral wall, with a strongly radial structure comparable to gastro- dermal canals and similarly at depth in the body, and probably secreting chitin at its apex, seems to have more adaptations leading toward chondrophores (and particularly porpitid chondrophores) than any better known form. Until the oral surface of Cyclo- medusa is definitely known, however, it will not be known whether it was allied to the chondrophores or merely a convergence. The larval stages of Recent chondrophores are so strongly modified as vehicles for the developing pneumatophore that their develop- ment does not cast light on their immediate ancestry (see Delsman, 1922; LeLoup, 1929) despite the similarities to Tubulariidae emphasized by Mackie (1959). The aboral truncate cone of C. plana is only a small portion of the whole animal, and the greater portion lacks the rugae that suggest contractility in the other species of Cyclomedusa. Taken together, these characters suggest that this species was not attached in adult life. Presumably swimming with the aid of the disc-edge (or mantle flap) was a possibility, or its near-flat shape may have enabled it to lie free on the sea floor as some modern medusae do. These two modes are not mutually exclusive. While it is possible to speculate that Cyclomedusa was a persistent ancestral type of the Chondrophora, a functional intermediate between normal, attached Hydrozoa and the pelagic forms with a float, it is necessary to remember that hydrozoan affinities for Cyclomedusa are not yet proved. Knowledge of this ‘genus’ is in such a primitive state that for the present suitable specimens can only be placed in the morphotypic species already described and, although these groups are reasonably clear, many Cyclomedusa remain outside them. Many of these are poorly preserved and may never be placed. Class SCYPHOZOA Order undescribed Genus brachina nov. Type species. Brachina delicata sp. nov. Diagnosis. As for type species. Brachina delicata sp. nov. Plate 42, figs. 3-5, text-figs. 5a-c Madigania annidata Sprigg (part), 1949, pi. 17, figs. 1, 2, possibly pi. 16, fig. 2. Ediacaria flindersi Sprigg. Glaessner and Wade (part), 1966, p. 602. 208 PALAEONTOLOGY, VOLUME !5 Material and occurrence. Six, possibly seven, large specimens and possibly one small specimen from Ediacara Range, two specimens from Brachina Gorge, South Australia. Holotype. FI 7343 (PI. 42, fig. 3) from Brachina Gorge. Preservation. The holotype is a fragment of maximum width 3 cm, maximum length 5-3 cm. The natural edge is somewhat crumpled but consists of small marginal lappets attached to a narrow, smooth band. Lappets and band are very faintly imprinted in the rock and form an external mould. The remainder of the fossil is preserved in convex relief and appears to be the mould of internal spaces in the original animal. To be, instead, the cast of the external (subumbrellar) surface, it would have had to be relatively deeply buried in the sediment. The adherent depositionally underlying matrix is a finely-laminated siltstone which was irregular enough to have caused distortion in the fossil of an elevation several times greater than the thickness of a lamina. The fossil clearly was not deeply buried in this siltstone as it did not penetrate even one lamina. Its margins were not buried at all in the siltstone as they formed an external mould in the overlying sand layer. The fossil as a whole is thus a composite mould (Wade, 1969; McAlester, 1962) dominated by the internal mould. The second specimen from Brachina Gorge is also dominated by the internal mould. Although this is a larger specimen it is very badly distorted by a contemporaneous lineation which penetrates the whole rock, and also weathered. The specimens from Ediacara Range are all dominantly casts of the exumbrellar sides but most show some degree of impression of the mouth-funnel through the disc, and less definite indications of other structures. These are positive composite moulds dominated by the exumbrella, in specimen T16; 2025 dominance is less than in the other three. Specimen T9 (Sprigg 1949, pi. 17, fig. 2; this paper PI. 42, fig. 5) is partly divided in two by a wedge of coarse sand and appears to show the centre of the stomach from the inside, folded depositionally upward at a steep angle to the cast of its external surface. The two surfaces merge on the lower bedding plane and the disc is thus largely a com- posite mould. (A second specimen ‘h’ which impinges on this individual is very badly preserved, it shows only the margin of the disc and the inside-top of the mouth-funnel.) Specimen T14 (Sprigg 1949, PI. 16, fig. 2) shows more complete composite moulding of the disc than any other individual discussed here, but is so badly preserved in other respects that it is not really generically identifiable. EXPLANATION OF PLATE 42 Figs. 1, 2. Cyclomediisa radiata Sprigg, F16729, X 0-5, largest specimen known. 2, T21 ; 2032, paratype, xl-3, small well-preserved specimen figured by Sprigg 1949, pi. 14, fig. 3. Figs. 3-5 Brachina delicata gen. et sp. nov. All positive composite moulds. 3, FI 7343, holotype, from Brachina Gorge, X 1-5, mainly internal mould (numbers 1-6, see text). 4, FI 7457, paratype from Ediacara, XO-5, mainly exumbrellar cast, markers indicate portion of margin shown as Ab, X 1-3, detail of marginal lappets. The inner edge of the annulus possibly shows mid-way across the outer ring and possibly both its edges can be seen near the markers. Within the ridge and double furrows of the disc margin the furrow attributed to the stomach "s' is not concentric with the ridge 7-’ attributed to surface ‘ornamentation’. 5, T9, paratype from Ediacara, xO-6, oblique view; the annulus occurs midway across the outer ring and disc markings resemble 4a except in the central region where a wedge of sand ‘vv’ separates the exumbrella from a portion curved depositionally upward through 90°. This shows the inside view of the mouth funnel. The three fragments "b' appear to be portions of a second specimen. Palaeontology, Vol. 15 PLATE 42 WADE, Cyclomedusa and Brachina WADE: AUSTRALIAN LATE PRECAMBRIAN ‘MEDUSOIDS’ 209 Diagnosis. A moderately large, discoid medusa with numerous, small, spatulate lappets attached to a broad outer ring of width about equal to the radius of the disc it encloses. On the exumbrella the outer ring joins the disc margin in a groove from which a rounded ridge arises abruptly. This is followed by a second groove which has a rounded bottom. Another rounded groove occurs about one third of the distance across the disc (this may represent the stomach margin). A sharp elevation of the surface occurs nearer the centre of the disc. The centre was occupied by a slight peak (except where compressed against the mouthparts). On the subumbrella the manubrium was small and conical. Radial passages (gastro vascular canals) within the subumbrellar wall reach almost to the outer edge of the outer ring and appear to have ended blindly. They increase in number outwardly by occasional dichotomous branching and anastomose inwardly forming a wide ring complex around the stomach. A large, pouched annulus occurs about midwidth of the outer ring on the subumbrellar side of the radial passages (it appears to have been an annular gonad within the subumbrellar wall). Description. The structures of the holotype may be described as six zones occupying concentric arcs. From the natural edge inward these zones 1-6 are numbered in PI. 42, fig. 3. 1. A line of small, spatulate impressions about 2 mm long and wide. Indications of these marginal lappets are seen at several places but they are complete only where numbered at the left side of the photograph. 2. A narrow, smooth zone just within the lappets. This sub-peripheral band was at least 1 mm wide. 3. The first zone of convex relief is about 8 mm wide and consists of radially arranged ridges and depressions, 10-11 pairs/cm. The ridges present blunt, roundish ends to zone 2 and become gradually less distinct toward zone 4 which cuts them off at right angles. 4. This is a raised annulus 1 cm across which shows occasional, shallow, dimpled depressions as if rather compressed. Its inner curve is smooth while its outer curve is cut by irregularly spaced, short, deep depressions which appear to have divided it into shallow pouches, unconstricted on their inner sides. The outer edge is more elevated above its surroundings than the inner. 5. This is again a zone of radial ridges and depressions; the ridges about the same size as in zone 3 but more closely packed. The ridges sometimes fuse inwardly. 6. Zone 5 grades irregularly into 6 by the breaking up of the radial depressions into pits and the anas- tomosing of the ridges which gradually lose their radial alignment and form a ring complex with a uniform, pitted surface. The second internal mould (from Brachina Gorge) clearly shows the junction of zones 5 and 6. Most of the surface is covered by zone 6 but a furrow, which distorts the whole thickness of the rock slab, and erosion have the effect of obscuring any central structures which might have been present. There is a hint of the annulus, zone 4, and slight indications of zone 3 and, in one spot, zone 1. The specimen confirms the supposition that zone 6 is relatively wide. Two of the four better-preserved positive composite moulds have small, spatulate marginal lappets. These are closely similar individuals about 9 cm in radius. The larger piece (PI. 42, fig. 4a, b) has part of its margin folded over towards the subumbrella but elsewhere has 12 or 13 lappets in 5-5 cm. Most are about 4 mm long and a little wider than long. One is slightly smaller and more tapered than most, and supported by a very small, elongate lobe at either side (PI. 42, fig. 4b). This structure is unique but the present material is not adequate to show occasional repetition. The structure may be fortuitous but may be sensory. The other, smaller piece, has a rather battered margin but its spatulate lappets are longer than wide at its maximum radius (10 cm) and a little shorter than wide in at least one of the places, on either side of the maximum, where the margin forms an arc of radius just under 9 cm. The largest specimen is T9 (Sprigg 1949, pi. 17, fig. 2; this paper, PI. 42, fig. 5). This is over 11 cm in radius from its mouth to the base of the lappets (if a slight crenulation of the margin is taken as evidence of these). Its margin is inturned and no lappets are seen. The fourth specimen (T16; 2025, Sprigg, 1949, pi. 17, fig. 1) is broken off short of its margin at maximum radius 10-6 cm. All four 210 PALAEONTOLOGY, VOLUME 15 specimens have a relatively flat outer ring ranging from 4 to at least 5-7 cm broad; on all except T16; 2025, this is ridged by very fine, discontinuous, concentric striae. In T9 and 379 these fine striae are interrupted across an annulus about 1-5 cm across. A similar structure exists on T16; 2025 where its outer edge appears to be broadly lobate; as it is clearer here, where there are no surface striae, it pre- sumably represents a subsurface structure. Its presence on FI 7457 (PI. 42, fig. 4a) is disputable; a faint, broad ridge is present in places, but does not interrupt the concentric striae. This annulus lies parallel to the edges of the outer ring at about the middle of its subumbrellar side in two specimens; and a little closer to the disc in the third specimen. The ring is of about the same width as the disc-radius or a little greater. It is thus possible to estimate the radius of the holotype fragment as 5-6 cm. An attempt to restore the size of the original by projecting the radial structures was not very satisfactory but sug- gested a circular body with radius 5-8 cm. The central structures of the original body are thus not observable on the fragmental internal mould of maximum radial width 3 cm. Erosion and the pleating of the thin rock-lamina have removed evidence of the central structures of the second internal mould. The margin of the disc is the most prominent feature of the exumbrella. The outer ring meets the disc in a groove (which is probably accentuated by flattening) and the disc edge rises sharply from the groove and forms a rounded ridge closely followed by a rounded groove which is often more distinct than that where disc and outer ring meet. The striae may continue on to the edge of the disc but the discs have more strongly marked concentric ‘ornamentation’ with considerable individual variation (see Table 1 ). On four specimens two concentric elements are present, a shallow, rounded groove about one third of the distance in from the margin, and a sharp elevation nearer the centre. The centre is expressed in a variety of ways: in T9 (pi. 42, fig. 5) it is likely to be viewed from inside (above). It consists of a narrow, annular furrow enclosing a rounded ridge which folds down into a shallow, central pit, irregularly closed at the base. Contrasting PI. 42, fig. 4a with fig. 5, the central depression is more arcuate, as if a slight mound occupied the side and centre of a pit. In T16; 2025 a depressed area is filled with coarse, arkosic sand which is in remarkable contrast to its fine-grained surround, but similar to the layer of sand depositionally just above the surface of the fossil. 379 is broken across its centre; it shows no evidence of a depression but only a slight mound, which appears to have been central. A comparison of all seven specimens is given in Table 1. Restoration. The characters in common between the largely internal composite moulds and the exumbrellar-dominated composite moulds are principally the small, spatulate lappets attached to an otherwise entire outer ring, and the broad annulus, pouched on its outer side, placed about midway across the outer ring, and towards the subumbrellar side. These characters define a group which is isolated from all other medusae so it is reasonable to combine both preservations in the one restoration. Text-fig. 5a-c is based on all 7 specimens, with the zones 1-6 numbered in the restored section 5c as in PI. 42, fig. 3. They are interpreted as: (1) a ring of small, marginal lappets, (2) the edge of the outer ring, (3) the internal moulds of radial passages which are traversed on the subumbrellar side by (4) a broad, inflated annulus with large pouches on its outer side, and re-emerge as (5) the internal moulds of radial passages sometimes showing fusion in an inward direction or dichotomous branching in an outward direction. These passages can be traced into (6) a ring complex of anastomosing spaces which, in its outer parts, shows remnant dichotomous branching. This ring complex presumably encloses (7) the stomach which is restored as if its outer edge is responsible (upon compression) for the shallow groove one third of the way across the disc. The small, conical manubrium (8) is most reliably shown by T9 (PI. 42. fig. 5) but is also shown by the very incomplete specimen that abuts it. The concentric rings around it are sometimes crossed by short radial markings interpreted as due to the musculature for operating it and (9) the mouth. The disc margin (10) is interpreted as a ridge separating a double groove in life as in the WADE: AUSTRALIAN LATE PRECAMBRIAN ‘MEDUSOIDS 211 PALAEONTOLOGY, VOLUME 15 TEXT-FIGS. 5-8. Restorations. 5 a-c, Brachina delicata gen. et sp. nov. Approximately xO-5, tentacles hypothetical, a. Moderately expanded small specimen in oblique, subumbrellar view showing the annular gonad and radial gastrovascular system through the wall. The manubrium was small and conical, b, Moderately contracted larger specimen viewed from side top of exumbrella, c, Restored section. For numbers see text. 6 a-c, Kimberellci quadrata (Glaessner and Wade), slightly enlarged, tentacles hypothetical, a. Side view, b, c. Cross-sections at the levels indicated by v-w and x-y. The gonads adhered to the radial canals and projected into the lumen of the bell. Gastric pouches alternating with the canals are hypothetical, as is the shape of the stomach at level v-w. Gastric filaments inside apex pass below puckering of bell wall. 7, Ediacaria flindersi Sprigg. Approximately xO-5. Oblique subumbrellar view of moderate-sized specimen. Tentacles observed on only one fragment. Radial striations believed to be a surface feature. 8 a, b. Rugoconites enigiuaticus Glaessner and Wade, canal system and tentacles based on specimen in PI. 43, fig. 3, x 0-57, outer flange and general shape based on both figured specimens, and others. WADE: AUSTRALIAN LATE PRECAMBRIAN ‘MEDUSOIDS’ 213 fossil. The sharp elevation toward the centre of the disc (11) is also interpreted as an external feature while the centre of the disc (12) is a low conical mound after specimens FI 7457 and 379. The presence of a central depression (hollow, ring or arc) is considered the effect of compression against the mouthparts. The tentacle (13) is the only structure for which there is no evidence. Text-fig. 5a shows a moderately expanded, small specimen obliquely from below while a moderately contracted larger specimen is seen from the side top in 5b. As in 5c, the tentacles are hypothetical, but the remainder of the structures have been restored by comparison of drawings from life of modern medusae with the structures of the fossils. The functional comparison of the new form with modern discoid Scyphozoa is very close but the detailed morphology shows significant differences. Although the marginal lappets have many parallels, the edge of the outer ring they attach to does not take part in the internal mould and so the radial passages appear to end blindly instead of being united by a ring canal, but as ring canals are lacking in many recent forms radial passages are still to be regarded as gastrovascular canals. They communicate with one another in the ring complex which presumably surrounded the stomach, and, as relict dichotomous branching is present in its outer parts (adjacent to zone 5, PI. 42, fig. 3; text-fig. 5) presumably represents phyletically increasing communication between the passages. The pouched annulus is a unique character. It is distorted in the same sense and places as the other zones of the body, and is constant in its spatial relationships with the other zones, and in its attitude. It thus appears to have been confined within the same body wall, a conclusion supported by its preservation in the holotype as an internal mould. Hence, its connection with the radial passages may be inferred from the fact that, like them, it was evenly filled with fine sand before the body decayed, though it shows no direct connection to the exterior. Admittedly, the holotype fragment is too small to prove that there were not rare external openings but the mould is evenly filled. In general appearance the pouched annulus is more like a simple gonad than any other medusa-structure. The four gonads of the recent Poralia rufescens Vanhoffen form an almost complete annulus but here, as in other Semaeostomatida, the gonads are posi- tioned at the junction of the gastrovascular canals and stomach. The pouched annulus, by comparison, is situated well away from the stomach toward the outer end of the gastrovascular canals. Its size and structure are radically different from any known gastrovascular canal and it is not on the same plane as the radial passages, as a ring canal should be. As the four factors of its size, pouched structure, level in the body, and position part way across the outer ring, militate against its interpretation as a ring canal, and only its unusual position (in comparison with modern medusae) is against its interpretation as a gonad, the latter interpretation is favoured. The annulus could have covered a ring canal of normal dimensions as it is several times wider (by modern standards) than a ring canal of width commensurate with the radial passages. Support for a hidden change of structure is weak, merely that the radial passages do not branch outside the annulus; this is an observable reduction in the frequency of branching, and does not prove the unbranched outer ends to be a structure like the unbranched canals external to the ring canal which serve large lappets in many Semaeostomatida (see, for example, Mayer, 1910, text-figs. 388, 392-396). Even if present, a ring canal hidden by the annulus could hardly be homologous with the structure in modern 214 PALAEONTOLOGY, VOLUME 15 Scyphozoa or Hydrozoa because that would require the annulus to be marginal and zones 1-3 to represent lappets — an inherently unlikely proposition. Ring canals are not present in HaUidaya hrueri or Skinnera brooksi Wade (1969) which are only slightly younger than Brachina (Wade, 1970). A ring canal or its morphologic substitute, a ring sinus, is not necessary to all kinds of water-vascular circulation, for numerous modern medusae have dispensed with it wholly or functionally, as many authors have noted since Browne (1904) d\?,cus,^Qd Proboscidactyla [as 'Willia']. Mayer (1910) described it as variable in Narcomedusae, and absent in Pelagiidae and Cyaneidae; Hyman (1940, p. 454) noted that in ‘Narcomedusae . . . the ring canal is often reduced to a solid strand or absent’ (see also further discussion in Hyman op. cit., pp. 508, 519, 521). Russell (1953, p. 6) gave a short general statement on its morphology in Hydromedusae. Gonads in modern medusae are sited in diverse well-oxygenated positions so it is necessary to consider possible water circulation through the annulus. As the smooth surface of the internal mould is not interrupted in about one fifth of its circumference, as seen from the subumbrellar side, or in two fifths of the exumbrellar side, the annulus can have had few or no external openings. The infilling with sand (in the holotype) could have taken place through connections to the similarly filled radial passages. In all, communication through the radial passages seems most likely from the preservation, and the undivided inner half of the broad annulus would allow considerable lateral water circulation. It may well have served both the functions of ring canal and gonad. Remarks. Brachina delicata is about the common size range of Ediacaria flindersi Sprigg but is differentiated from this species by its marginal lappets, its uniformly wide outer ring, its striking disc-margin with a circular ridge between double grooves, and more concentric grooves on the disc. Only one more groove is consistently present (see text-fig. 5b) but adventitious grooves are frequent. The concentric grooving caused Sprigg (1949) to place the first two specimens collected in "Madigania’ annul at a as neither showed the true margin with lappets. However, they both have the print of the annulus in the centre of the outer ring and all the disc grooves of Brachina; also, the strong conical projection in the centre of T9 (Sprigg, 1949, pi. 17, fig. 2; this paper, PI. 42, fig. 5) projects down from the subumbrella and not up from the exumbrella, as is shown by the oblique edge view which indicates a wedge-shaped layer of sand ‘w’ between the two surfaces. T9 and T16; 2025 were incorrectly transferred to E. flindersi when the holotype of "Madigania' anmdata [= Spriggia annulata (Sprigg) Southcott 1958] was transferred to Cyclomedusa Sprigg (Glaessner and Wade, 1966). A composite mould of a discoid medusa was described from the Nama System of Southwest Africa as Paramedusium africanum Giirich, 1933; re-illustrated in Harrington and Moore, 1956. This was about the same age as Brachina (Glaessner, 1963; Germs, 1968). W. Hantzschel infonned M. F. Glaessner that the specimen was lost during the war. No further specimens have been collected (pers. comm. Germs, dated 4 Feb. 1970). Its description was illustrated by an extremely unsatisfactory photo and a wash drawing which showed a half-specimen with a practically featureless centre and, in its outer one third, radial ridges (presumably gastrovascular canals) which occasionally branch dichotomously and are only slightly more widely separated than those of Brachina. They are connected to each other by narrow cross ridges, forming an irregular network. A patch of slight, fine radial markings is all the structure described for the central area. WADE: AUSTRALIAN LATE PRECAMBRIAN ‘MEDUSOIDS’ 215 The margin is not clearly described but two small portions of the figure show what might have been a smooth, natural margin with one niche. The specimen probably never was generically identifiable. Its resemblance to Brachiiia is only that its main radial passages run parallel, relatively close together, and maintain their spacing by occasional dicho- tomous branching. In Parameclusium they are united by cross-passages in the region where there are no cross-connections in Brachina. That Parameclusium certainly and Brachina probably lacked ring canals cannot be assumed to be significant as so many unrelated forms lack them too (above). In Brachina we have a medusa of the scyphozoan grade of complexity, like HaUidaya and Skinnera, which also does not fit a definition of Scyphozoa based solely on tetra- merous forms. Brachina is morphologically closer to Plallidaya than to Skinnera but they have little in common but dichotomous branching of the radial canals. Their gastrovascular systems are not similar for there is frequent dichotomous branching in HaUidaya and few canals extend from the stomach, in contrast to the ring complex and rare branching in Brachina. The annulus in Brachina has no parallel in HaUidaya and the nuclei of HaUidaya have no parallel in Brachina. Genus kimberella, nom. nov. = Kimberia Glaessner and Wade, 1966, non Kimberia Cotton and Woods, 1935. Type species. Kimberella qiiadrata (Glaessner and Wade). (= Kimberia qiiadrata Glaessner and Wade, 1966, pi. 97, figs. 6, 7). Dr. N. H. Ludbrook kindly drew attention to the fact that the name Kimberia is preoccupied by Kimberia Cotton and Woods, a subgenus of Tiirritella Lamarck. Accordingly the new name Kimberella is proposed. Diagnosis. As for type species. Kimberella quadrata (Glaessner and Wade) Plate 43, figs. 2a, b; text-fig. 6a-c 1959 ‘Problematic fossil, possibly belonging to the Siphonophora’ Glaessner, in Glaessner and Daily, p. 391, pi. 47, fig. 9. 1966 Kimberia quadrata Glaessner and Wade, pp. 611-612, pi. 97, figs. 6, 7. Material and occurrence. Four almost complete specimens and three fragments from Ediacara Range. All are positive composite moulds, laterally compressed. Preservation. All specimens appear in convex relief on the bottoms of rock slabs. Their preservation is not as simple, external moulds, for an elongate zone of transverse puckering of the surface may or may not traverse the edges of most obvious, radially elongate, convex structures. While the puckering can be viewed either as an exumbrellar or subumbrellar feature, the elongate convex structures were necessarily inside the puckered structure. Internal structures which also pass below the puckering occur inside the apex of the bell, these are filaments that occur in negative relief. These fila- ments must have been tougher than any other portion of the body, as they are the only structures in negative relief. On these two counts, then, the preservation is as positive composite moulds. Diagnosis. An elongate, slender, perhaps squarish, bell-shaped Scyphozoan with 4 216 PALAEONTOLOGY, VOLUME 15 pouched gonads attached to radial canals and projecting into the cavity of the bell and to each side of the canal. The centre of the area between the canals is often trans- versely puckered (probably by the contraction of 8 muscle zones on the subumbrella). Gastric filaments are present adapically. Tentacles possibly are few, and broad near the bell. Description. The elongate bodies appear to have been bluntly rounded at one end and reach their maximum diameter near this end; from there, they taper gradually for the remaining two-thirds or three-quarters of their length and are then truncated. The shape is best seen in PI 2739 (Glaessner and Wad;, 1966, pi. 97, hg. 7; this paper, PI. 43, fig. 2a, b). In the other specimen in which the truncate end is unbroken the positive mould fades out. No certain appendages to this body are preserved, though at least two broad tentacles could be present at the margin of PI 2739 (PI. 43, fig. 2a, marked as ‘?’). These structures are also open to interpretation as fortuitious markings, and no definite state- ment as to their organic or inorganic nature can be justified from this specimen. Within the body the most strongly-marked features are elongate, convex, segmented zones which run from the truncated margin up the sides of the body and converge near the apex. These present two aspects, either a slight, smoothly-rounded median keel which is not segmented, with a lobulate, less elevated portion on both sides, or a lateral smooth area (the keel) and one more deeply lobulated area on one or the other side of the smooth keel. Adjacent to the segmented zones is usually a narrow, elongate, smooth area; in one specimen (P13771) (unfigured) the smooth area extends right across the centre to the segmented zones on the other side but in the remainder it is followed by a puckered zone with transverse, narrow, ridges and furrows. In PI 2739 the puckered zone is interrupted by a fortuitous fold which distorts the specimen. In this specimen the inner curve of the segmented zones, where they come together adapically has sharp, deep furrows and ridges appended at right angles. Previously these were assumed to be part of the ‘frilled’ or puckered region although they are a little larger and at right angles to it except at the edges (PI. 43, fig. 2a, b ‘g’). Three or four of these adapical ridges and depressions are present on PI 3775, however, and here they pass below the puckered zone. Casts suggest they are, in fact, external moulds of tentacular structures inside the apical end of the bell. Specimen PI 3775 (unfigured) has the segmented zones of the left and right sides asymmetric in the opposite sense. Both have smooth keels facing in toward the puckered zone and deeply lobulate areas facing outwardly. In this the puckered zone is adjacent to the keel of the right segmented zone and near the apex reaches across to the keel of the left segmented zone. Lower down, this area is smooth on the left side, and still lower, it is deeply creased parallel to the puckers. It has a diagonally stretched appearance in this sector. Near the adapical end slight grooves on both sides extend obliquely up from EXPLANATION OF PLATE 43 Fig. 1. Subumbrella attributed to Ediacaria flindersi Sprigg, xO-8; specimens overlie each other on a crowded bedding plane. Structures thought to be the mouth are indicated by m and the possible stomach-edges by s. Fig. 2a, b. Kimberella quadrata (Glaessner and Wade), P12739, paratype. 2a, X 1, where marked with ‘?’ two structures delimited by faint double lines; these could represent tentacles. 2b, Apex X 1-8, gastric filaments, g. Figs. 3, 4. Rugoconites eniginaticus Glaessner and Wade, x 1 and xO-5 respectively. 3, latex cast from Brachina Gorge showing tentacles t and marginal flange /. The dichotomous ridges show more clearly in lighting unfavourable to the tentacles. This specimen is the main basis of text-fig. 5. 4, FI 7458. Shallow, conical depression with narrow, smooth, marginal flange and a weakly doubled marginal impression. Figs. 5-7. Rugoconites temiinigosus sp. nov. 5, F17461 holotype, X 1, Bunyeroo Gorge. The dichoto- mous furrows sometimes reticulate. They focus on a near-circular central furrow to weak depression thought to represent the stomach. The '?’ indicates a smaller circular furrow possibly due to the mouth. 6, FI 7460, paratype, xO-5, Brachina Gorge. Specimen showing little or no reticulation of its dichotomous furrows. Possible tentacles are seen at t, F17459, paratype, xO-7. Dichotomous furrows occasionally reticulate. Furrows near the centre form a coarse mesh which is partly circum- central. It is not known whether any of these furrows delimit the stomach. Palaeontology, Vol. 15 PLATE 43 WADE, Ediacaria, Kimberella, and Rugoconites WADE: AUSTRALIAN LATE PRECAMBRI AN ‘MEDUSOIDS’ 217 the respective creases at the edges of the segmented zones and are lost to view below the adapical ridges and furrows. As the puckered zone is also present here, the structure is obscure; it is seen in no other specimen. The width of featureless material between the outer membrane and the internal structures is always least near the truncated end and greatest toward the apical end, though not necessarily at the apex. Restoration. The reasons for believing there are four segmented zones present were advanced at the time the species was described. The structure of the segmented zones is now recognizable in the positive moulds as an individually variable number of discrete lobes with rather broad connections to radially arranged keels. These are interpreted in text-fig. 6 as deeply pouched gonads attached by their outer-central region to radial canals. The keel is interpreted as a radial canal rather than a septum because it presents a smooth curve to the outer wall and is itself convex like the gonad, which was pre- sumably hollow in life. As the gonads can be folded either to the left or right, showing the radial canal at either the right or left side, they must have projected into the cavity of the bell. They could be paired but this is not likely as the pouches are usually deeper if the keel is to one side than if it is centrally placed. The adapical ridges and furrows which appear to be tentacular are interpreted as gastric filaments which are described as having solid mesogloea inside an entodermal covering (Hyman 1940). These are a scyphozoan characteristic found in the Carybdeida which have similar overall shape. In the Carybdeida elongate gonads attached to the septa are paired, however, and though possible, this is not likely for Kimberella. Gonads in Carybdeida are also lamellar and confined in broad gastric pouches on either side of the interradial septa. Both cannot be folded to one side of the same septum as in Kimberella. There are now five specimens in which there are smooth areas adjacent to the radial canals and one fragment of one side; only in the specimen in which both gonads are folded outward (leaving the radial canals back to back) does the puckered zone give some evidence of extending from canal to canal. In this specimen the area between the radial canals appears stretched and the puckers are directed obliquely. Possibly they are creases on the subumbrellar wall due to the pull of muscles. No puckers are present in one of the seven specimens. The normal localization of the puckers in the centres of the sectors between the radial canals must be due to the placement of the radial muscles, but their abrupt line of commencement indicates a structural change as well. This could be produced by large gastric pouches in this position, as shown in the cross-sections, text-figs. 6b, c. The fact that the puckers are normally most strongly developed at one side or the other, suggests that they are an inert response of the subumbrellar surface to the contraction of muscle zones with a definite edge adjacent to the smooth zone between them and the adjacent radial canals, that is, they represent eight strips of muscle-fibres. This is a normal number for modern scyphozoan and hydrozoan medusae. Remarks. Glaessner and Wade (1966) pointed out that the positioning of the gonads suggested elongate gonads on radial septa or canals such as can be found in Carybdeida or Trachymedusina and Leptomedusina, and that the simplicity of the structure was more like the hydrozoans mentioned than the scyphozoan. On the other hand, the gastric filaments seem proven by position, dimensions and texture, i.e. they are a reliably established character considered strictly scyphozoan (Mayer, 1910; Hyman, 1940). Among structures found in Recent medusae, only gastric pouches seem to offer a ready explanation for the puckered zone. These are known in Carybdeida and 218 PALAEONTOLOGY, VOLUME 15 Narcomedusae (Mayer, 1910) in inter-radial and radial positions respectively. In Kim- berella the presumed gastric pouches alternate with the radial canals from which they are broadly separated. Though this cannot be used in defining radial and inter-radial in an unknown group, it indicates that, if present, gastric pouches are not of the narcomedusan type. It appears that Kiniberella is another primitive scyphozoan. Its tetramerous shape raises the question of whether it is an early member of the modern scyphozoan radiation. Kiniberella is not a member of the order Carybdeida but all its known characters are found in this group except that Kiniberella does not share the pair- ing, lamellar shape and placement of the gonads in the gastric pouches. This is the closest morphological similarity to modern forms found among the Precambrian Scyphozoa. All others, Brachina, Hallidaya and Skinnera, are more different from one another and from Kiniberella than Kiniberella is from the Carybdeida. It is possible that this form derives independently from the same root stock as modern Scyphozoa. It is coeval with Cononiednsites Glaessner and Wade, the earliest known member of the Conchopeltida. Glaessner (1971) has reviewed the modern views on the placement of the Conulata (= Conchopeltida +Conulariida) and regards them as polypoid animals, the earliest members of the group probably being ancestral to the polyps represented by the now reduced polypoid stages of modern Scyphozoa. He further drew attention to similarities between the chondrophore conaria larva and Cononiedusites, and to the advanced differentiation of the bilaterial chondrophores by the time of the Ediacara fauna. He thus inferred a considerable pre-Ediacaran evolution of this group, an inference that is borne out by the discovery of another kind, the circular chondrophore Eoporpita. The time involved in this much differentiation, at least, is by inference available for the differentiation of the early Conchopeltida. The original differentiation of the early Scyphozoa, as shown by the genera described here, had probably proceeded further by Ediacaran times than was previously known. Medusa incertae sedis Genus Ediacaria Sprigg 1947 Type species. Ediacaria flindersi Sprigg 1947. The genus is monotypic and the characters as diagnosed by Glaessner and Wade (1966, p. 603) except that the removal of several more extreme specimens to other genera (mostly to Brachina) has reduced the known variation in the proportionate width of the disc to the outer ring. The disc is usually about two-thirds to three-quarters of the total radius. Ediacaria flindersi Sprigg 1947 Plate 43, fig. 1 ; text-fig. 7 1947 Ediacaria flindersi Sprigg, p. 215, pi. 5, figs. 1, 2, text-fig. 3. 71947 Beltanella gilesi Sprigg, p. 218, pi. 6, fig. 1, text-fig. 4. 1949 Ediacaria flindersi Sprigg, p. 83, pi. 10, fig. 2, text-fig. 5. 1949 Protodipleiirosonia wardi Sprigg, p. 79, pi. 9, fig. 2, text-fig. 3E. 1956 Ediacaria flindersi Sprigg (partim); Protodipleurosoma wardi Sprigg; Harrington and Moore, in Moore, p. F47, fig. 60(1); p. F79, fig. 64. 71956 Beltanella gilesi Sprigg; Harrington and Moore, p. F70, fig. 56. 1959 Ediacaria flindersi Sprigg; Glaessner in Glaessner and Daily, p. 378. 71959 Beltanella gilesi Sprigg; Glaessner in Glaessner and Daily, p. 378. 1962 Ediacaria Sprigg; Glaessner, p. 483. WADE: AUSTRALIAN LATE PRECAMBRIAN ‘MEDUSOIDS’ 219 71962 Beltanella gilesi Sprigg; Glaessner, p. 483, pi. 1, fig. 3. 1966 Ediacaria flindersi Sprigg; Glaessner and Wade, p. 602, pi. 99, fig. 6. 71966 Beltanella gilesi Sprigg; Glaessner and Wade, p. 604. Preservation. Typical Ediacaria are low exumbrellar casts, and subumbrellar casts are now attributed to this specimen, but some specimens of either side show a furrow which is interpreted as the stomach margin, and these must be considered positive composite moulds, as must any in which the mouth shows through the disc on the exumbrellar side. Restoration. Sprigg (1947) associated an incomplete subumbrellar mould with Ediacaria flindersi (as Ediacaria cf. flindersi on the plate reference and as Ediacaria sp. in the text). This type of subumbrella is thought to be that of E. flindersi (Glaessner and Wade 1966, p. 602, 603). PL 43, fig. 1, shows parts of at least three subumbrellar impressions. All have a round to oval central mouth without any appendages or lips but in the most constricted, with a slight, circumoral furrow a short distance outside the mouth. Several other specimens beside these also show a similar mouth and a decided circular groove at about one third of the radius. Outside this groove, fine, radial striae extend to the margin. Sometimes they extend across this groove toward the mouth but very rarely reach to it. These radial striae increase in number outward by interpolation more often than by branching, and appear to be a surface structure. The size-range of these medusae coincides with the exumbrellar surfaces of E. flindersi and Brachina delicata. If the distinct groove at about one third width is taken as the edge of the disc, only B. delicata has the correct proportions, but this species has a small, funnel-shaped manubrium. Its annular gonad, also, though placed on the subumbrellar side of the gastrovascular canals shows on several of the exumbrella- dominated moulds. This kind of structure does not show on any of the subumbrellar surfaces here described nor do any have the regular lappets of B. delicata. It seems that comparison with B. delicata is not valid. There remains the comparison with E. flindersi. The groove at one third of the radius is about the right size to match the groove on the exumbrella-dominated composite moulds thought to represent the stomach. This inter- pretation would also explain the dying-out of the radial striae at, or soon after, this groove. The outer zone of radial striae is wider than the outer ring of E. flindersi but as it shows no internal structures it cannot be expected to show those of the opposite side. One specimen of an outer ring occurs on a very fine-grained sandstone slab which apparently broke off at the disc margin (though none of the disc is present). This has the dimensions of the outer ring of Ediacaria and appears to have had long, fine, numerous tentacles appended. All of these characteristics have been assembled in the reconstruction, text-fig. 7. A careful search was made for any trace of an annular gonad like that of B. delicata. The holotype of Ediacaria flindersi Sprigg has a number of partial concentric furrows and broad ridges on its outer ring but nothing delimiting a continuous band. The speci- men morphologically closest of all to the holotype similarly has an incomplete band. Other medium to small-sized specimens also show no annulus but both of the large specimens mentioned by Glaessner and Wade (1966) show an annular depression near the centre of the outer ring. In the low cast 21 cm in radius this is not sharply defined, though clearly continuous, and in the fragment of a much larger specimen, it is under C 8008 Q 220 PALAEONTOLOGY, VOLUME 15 1 cm wide and an observable maximum of 3 mm deep. As the outer edge of this depres- sion is not lobulate in either specimen, it is not suggested that this annular depression actually is an annular gonad. It may be present only by chance, or it may represent a real structure approximately the width of the annulus in specimens of Brachina of less than one third the radius of these Ediacaria. Genus Riigoconites Glaessner and Wade 1966 Type species. Riigoconites enigmaticus Glaessner and Wade, 1966, p. 611. New material has made the type species fairly well known, and enables description of a new species previously represented by inadequate material. Diagnosis. Moderate-sized medusa with a low, conical disc which often shows a double ring at the disc margin. Rarely, a narrow marginal flange is preserved and more rarely, very fine, numerous tentacles. Several to many furrows extend from the corners of a small, indistinct, polygonal to rounded centre (? stomach region) and repeatedly branch dichotomously. Mouth probably circular, apparently without appendages. Where furrows meet they anastomose. The furrows may be rather coarse and relatively few, to fine and numerous, depending on the species. Preservation. Save for one natural counterpart cast of R. enigmaticus on the top of a bed, all specimens are impressions on the bases of beds. R. tenuirugosus sp. nov. is always flat with fine, incised, branching furrows radiating from an indistinct centre, but the whole disc edge of R. enigmaticus is usually deeply incised and the impression of the fossil continues to deepen to its centre which may be severely distorted. Radiating, branched furrows run from near the centre to the margin. In latex casts they form ridges which indicate the sculpture of the bodies at the time of fossilization, which is not necessarily their life-shape. In R. enigmaticus they are clearest in a few, naturally rather flat specimens : small specimens are low conical and the ridges on them are very broad ; large specimens are often extremely confused in the centres as if a conical shape had collapsed, but their outer edges are undistorted. These are the only medusae in the Ediacara fauna which had sufficiently tough mesogloea to constantly form impressions in the overlying beds but they are not uniquely tough, for they show comparable resili- ence to Skinnera brooksi Wade (1969, p. 355, 361) from a slightly younger portion of the Central Mt. Stuart Beds, Northern Territory, Australia. As in this species, ‘ornamenta- tion’ may result from differential compression and the normal preservation also may be as negative composite moulds. This is emphasized by R. tenuirugosus which is more easily compressed, and yet shows a comparable pattern of furrows. This can only be regarded as a slightly negative composite mould. The presence of sharp furrows in this more compressible species shows that the resilience and resulting ‘ornamentation’ are not likely to be effects of an external cuticle. Riigoconites enigmaticus Glaessner and Wade Plate 43, figs. 3, 4; text-fig. 8a, b Riigoconites enigmaticus Glaessner and Wade, 1966, p. 611, pi. 100, figs. 2, 3. Material and occurrence. Twenty-one specimens from Ediacara Range and five fromiBrachina Gorge (the original of PI. 43, fig. 3 is still in situ). The Brachina Gorge specimens are extremely well preserved and most of the additional information comes from these. WADE; AUSTRALIAN LATE PRECAMBRI AN ‘MEDUSOIDS’ 221 Restoration. The new material of R. enigrnaticus allows the original animal to be re- constructed with a fair degree of confidence. Small specimens are the most conical and have a pattern of relatively coarse, dichotomously branched furrows radiating from a central area of obscure structure. Many larger specimens are greatly distorted in the centre, as if the original material was not strong enough to support sediment-load across the greater span. The deeply impressed edges of the disc indicate a truncate margin which probably sloped inward on the subumbrellar side. This truncate margin, rather than a marginal canal, is the probable cause of the double-ringed ‘disc’ margin seen in PI. 43, fig. 4 and in parts of several specimens; in this the radial structures cross the inner of these rings as they would if they were radial canals servicing the marginal flange among other portions of the body. The few larger specimens in which the furrows are relatively clear toward the centre are exceptionally flat. In the flattest specimen (PI. 43, fig. 3) they are only slightly de- pressed, but can be traced quite clearly (by lighting which does not favour the tentacles) and shown to anastomose, two giving rise to only one branch, where repeated dichoto- mous branching brings two furrows into contact. As this happens regularly, the branches were all in the one plane (text-fig. 8a). This one, undistorted specimen is two-thirds of quite a flat, depressed disc, and has a narrow, smooth zone with a slightly wavy edge encircling it. Very fine, unbranched striae radiate from the faint, inner ring of the disc margin and across the smooth area; in one place they extend beyond it. While four specimens show parts of such a smooth zone or marginal flange around the disc (e.g. PI. 43, fig. 4) only a fifth specimen shows similar striae. Here also the striae arise from the inner edge of the truncate margin (as can be seen in latex casts); they thus may be interpreted as very fine tentacles arising from the inner edge of the disc margin, while the outer flange arises from the outer edge (text-fig. 8a, b). Clearly the fossil is of a strongly medusiform animal but as its mouth has not yet been observed other structures must be invoked to decide its orientation. As seen in latex casts, it seems unlikely that the conical surface harboured a mouth, and its convex shape suggests it is the exumbrella. Of the flatter specimens only the two which have tentacles are well enough preserved to have shown a mouth and the larger of these is broken at the centre. The other shows very slight puckering at the centre but no definite mouth. Marginal flanges are associated with three conical sides and one flat surface with tentacles depositionally overlying the flange. In every example, marginal flanges seem to attach to the periphery as they have no inner structures of their own and do not obscure the outer ends of the radial ridges between the inner concentric ridge and the margin. Both specimens with tentacles have them attached in a ring that is about as far within the periphery as the inner ring seen in conical specimens. From these factors we can be sure that the tentacles are not marginal but slightly within the margin, while the flange is marginal. While the specimens are too few to be certain that the correlation of flat surface and tentacles is constant, all the evidence we have points this way. It seems most probable that conical surface and flat surface represent exumbrella and subumbrella respectively. The radial structures show equally clearly all over the flattish surfaces, but not equally clearly all over the conical surfaces. From this it is legitimate to assume that they lie in a plane (above) parallel to the flatter surface, equally close to both surfaces near 222 PALAEONTOLOGY, VOLUME 15 the margin, but at inwardly increasing depths below the conical surface. The radiating system thus occupies the position of gastrovascular canals. What is not explained by this comparison is the fact that the radiating system is clearly even more resilient than the tough mesogloea of this toughest medusa in the fauna. The idea that the impressions might be due to counterpart casting (Wade 1968) of (in this case) natural moulds of the subumbrella, formed in the underlying incompetent beds falls before the facts that (1) the fine ridges of R. tenuirugosiis are as clear or clearer than any of R. enigmaticus, and (2) the impression in the bottom of the upper bed is often deeper than the thickness of incompetent material that may be inferred from lithology as having been present below the fossiliferous surface. Another cause for the resilience should be sought. The filling of radial canals with frothy material that kept them distended while the remainder of the body shrank, has been described, but in stranded material. We have no reason for regarding any of the Ediacara fauna as stranded material (Goldring and Curnow 1967; Wade 1968). It is feasible, however, that the release of gaseous material within radial canals could have kept them distended without disruption for this medusa must have been exceptionally tough and slow to decay, as its preservation as imprints demon- strates. It seems quite likely that any food material would decay more rapidly than the medusa, particularly so if its canals contained symbiotic algae. Rugoconites tenuinigosus sp. nov. Plate 43, figs. 5-7 Material and occurrence. Three specimens are known from Ediacara Range, two from Brachina Gorge and one from Bunyeroo Gorge. Holotype. FI 7461, PI. 43, fig. 5, from Bunyeroo Gorge. Preservation. The holotype alone shows a composite of internal and external characters. The remainder consist of radial furrows incised like those of R. enigmatieus on the bases of rock slabs. Unlike R. enigmaticus every specimen is flat; though not so destruct- ible as to form casts like other medusae, they were not resilient enough to form impres- sions. Diagnosis. Rugoconites with very fine radial furrows which branch dichotomously about 3-5 times, diverging at a very low angle and tending to curve parallel; reticulation rare to common in different individuals; furrows reach smooth central area (? stomach). Description. The largest specimens known have discs just under 5 cm average radius. The holotype is just under 4 cm. It is broken across at one side of the probable stomach but presumably lost only radially repeated structures. The centre is occupied by a circle 4 mm across which is presumably the mouth as it is almost central in a smooth, oval to polygonal area about 15 by 12 mm. From the furrow delimiting this area, the probable stomach, radial furrows arise and repeatedly branch dichotomously, the branches diverging only slightly and rapidly curving to become almost parallel. In some individuals the outer branches may be reticulate but often their shape prevents them from meeting. The number of branches reaching the stomach cannot be clearly ascertained in any specimen but by extrapolation from the better preserved areas of several specimens it appears to have been about 10 to possibly 20. The specimen with least initial branches has the most divergent branching and branches four to five times, while on another specimen only 3 divisions could be seen. As a result, all specimens have terminal branches meeting the margin of the disc at right angles and less than 1 mm apart. Outside the disc margin even finer furrows, closer together, are seen on parts of two specimens (PI. 43, figs. 5, 6 7’). In fig. 6 they are seen to die out, but in the holotype fig. 5 they are present within a narrow area delimited WADE: AUSTRALIAN LATE PRECAMBRIAN ‘MEDUSOIDS’ 223 by an arcuate furrow here interpreted as a small portion of its outer flange which was mostly folded under the body. These fine and closely-spaced outer furrows are interpreted as tentacles. Remarks. The close resemblance of structure between R. temiirugosusdind R. enigmalicus, and the fact that both have a similar, exceptional preservation resulting from textures less destructible than the other medusae, are the basis for uniting them in one genus. They are differentiated principally by the finer, more numerous radial furrows in the new species, and the less divergent angles between their branches. Though forming shallow impressions unlike species of other genera, the disc is less resistant in the new form than R. enigmaticus, for all specimens are flat (apart from the furrows) and the margin is often indistinct. An initially more flat disc could not alone account for this. The orientation suggested here for the disc of the two best preserved R. enigmaticus — oral side to the rock — is not supported by a clear view of the orifice nor denied by its clear absence. If the surface of these two is a flat equivalent of the usually conical exumbrellar surface, the tentacles must arise on the exumbrellar side of the marginal flange which is thus comparable with the structures of some hydrozoans, Trachy- medusae in particular. On the other hand, if the orientation suggested here is correct, the tentacles will prove to be a subumbrellar feature on the oral side of the marginal flange, and the overall sum of characters tends to scyphozoan, as illustrated in the restoration, text-fig. 8. Among Recent medusae the morphologically closest form is, at first sight, Probo- scidactyla. This hydrozoan has both specifically and to some extent individually variable numbers of radial canals which branch and (in some) re-branch. Reticulation of canals is a rarely-seen teratologic phenomenon in the Recent species. It is not suggested that there is a close relationship between the two genera because, apart from the time factor, the anthomedusan type of velum is clearly not closely similar to the outer flange of Rugoconites. The mouth also is quite large and has angles and lips in Proboscidactyla. Another factor in which the two converge is that Proboscidactyla has no circular canal, no lumen in its circular endoderm strand. No detailed description is to hand of the circulation of water through the radial canals of medusae lacking circular canals but Browne (1904) described ‘active circulation’ in the radial canals and basal bulbs of tentacles in ‘ Willia' stellata (= Proboscidactyla stellata (Forbes)). This form has tentacles only opposite radial canals. It is hard to see how such a form could function without excretory pores but these were not mentioned by Browne, who noted them in Aequori- dae; or by Mayer (1910) or Russell (1953) who noted them in Aequoridae and some Eirinidae on papillae on the circular canals, opposite each tentacle or tentacular bulb. Hyman (1940, p. 396) did not specify which scyphomedusae have radial canals with pores opening near the tentacles. Clearly pores are usually far from obvious in Recent medusae, and the lack of evidence in fossil forms is less surprising than their presence would be. A Semaeostomatida without circular canals and with a dichotomously branched canal system similar in complexity to Rugoconites is Drymonema Haeckel (Mayer 1910) though in this also the canal system is not reticulated. The complexity of the canal system is not suflicient to place the genus in class or order, and gonad struc- tures are lacking. Ultimately the position of the mouth will probably reveal the orienta- tion, and the class and order may well be new. 224 PALAEONTOLOGY, VOLUME 15 CONCLUSIONS The Chondrophora are the only group among those discussed here which can be placed in taxonomic perspective. The floats of the circular and the bilateral Precambrian forms are more strongly differentiated than those of the modern forms Porpita and Vellela. The whole record consists of two widely differing bilateral forms which repre- sent the family Chondroplidae Wade (1971); Eoporpita gen. nov. which represents, or is closely allied to, the Porpitidae, several Palaeozoic Porpitidae (or close allies), Recent Porpitidae, and Palaeozoic and Recent Vellelidae which can be morphologically derived from porpitid ancestry. The concentric float of Archaeonectris Huckriede presumably could have derived from the partly embracing early chambers of either porpitids or vellelids. The Ediacara fauna is too young to cast light on whether the circular or bilateral floats are a primitive character but a single kind of chambered float is not the only possible derivative of a probably single chambered ancestral type. Taking the divergence of these early forms into account, a likely view is that the two bilateral forms and the circular form are two or three answers to the problem of how to increase the volume of a single float chamber without sacrificing overall strength or greatly increas- ing weight. Cyclomedusa may represent a hydrozoan form sharing common ancestry with the Chondrophora as its low conical form thins to an outer edge which is a prolongation of the coenosarcal disc-edge (i.e. a mantle flap) rather than a separate outer flange like the medusae possess: its internal radial structure resembles the radial gastrodermal canals of young Porpita in shape and position : the probability that it was adherent by the apex suggests the secretion of chitin in the place where the float rudiment appears in the development of Recent chondrophores. The small central cone of C. plana sug- gests the loss of attachment in the adult stages of this species. Scyphozoa are represented by Brachina deUcata and Kimberella qiiadrata, B. delicata is not close to any other known form unless Ediacaria jiindersi Sprigg belongs here; the gastrovascular and gonad systems of this form are still unknown. The tetramerous K. quadrata, which does not belong in any presently recognized order of Scyphozoa, is closer in morphology to the Carybdeida than Brachina delicata, Hallidaya brueri or Skinnera brooksi, the other early Scyphozoa, are to it, to one another or to any modern medusa. Kimberella was probably derived from the same line as the modern forms. The position of the other three is more obscure, but it is noteworthy that the oldest of the three has the structures most easily comparable to modern medusa. The diversification of Scyphozoa must have commenced prior to the Ediacaran. As yet the oral side of Rugoconites Glaessner and Wade has not been conclusively identified and its provisional restoration as scyphozoan rather than hydrozoan rests on the interpretation of two rather flat specimens with tentacles as representing oral sides. The peculiar ridged ‘ornamentation’ is interpreted as distended radial canals. Acknowledgements. The work on which this paper is based was carried out at the University of Adelaide. Mr. I. M. Thomas kindly provided comparative material of Porpita porpita Linne as microscopic preparations and preserved specimens. Field work was partly supported by an Australian Research Grant to Professor M. F. Glaessner who has also read the manuscript. I have benefited from discussions with him at various stages of the work. Miss A. M. C. Swan redrew most of the text-figures. WADE: AUSTRALIAN LATE PRECAMBRIAN ‘MEDUSOIDS’ 225 REFERENCES BROWNE, E. T. 1904. Hydromedusac, with a revision of the Williadae and Petasidae. In gardiner, j. s. (ed.) The fauna and geography of the Maidive and Laccadive Archipelagoes, 2 (3), 722-749, pi. 54-57. CASTER, K. E. 1942. Two siphonophores from the Palaeozoic. Palaeont. Amer. 3, 56-90, pi. 1, 2., CHAPMAN, D. M. 1966. Evolution of the scyphostoma. pp. 51-75. In rees, w. j. (ed.), 1966 (q.v.). CHAPMAN, F. 1926. New or little known fossils in the National Museum. Pt. 30; A Silurian jellyfish. Proc. R. Soc. Vic. 39, 13-17, pi. 1, 2. DELSMAN, H. c. 1922. Bcitragc ztir Entwicklungsgeschichte von Porpita. Treiibia, 3, 243-266. -GARSTANG, w. 1946. The morphology and relations of theSiphonophora. Quart. J. micr. Sci. 87, 103-193. GERMS, G. J. B. 1968. Preliminiary report on the Nama System, South West Africa. Sixth Ann. Rep., Precambrian Research Unit, Univ. Capetown, 14-22. GLAESSNER, M. F. 1971. The gcnus Conomedusites and the diversification of the Cnidaria. Palaeont. Z. 45, 7-17. and DAILY, B. 1 959. The geology and Late Precambrian fauna of the Ediacara fossil reserve. Rec. S. Aust. Mus. 13, 369-401, pi. 42-47. and WADE, M. 1966. The late Precambrian fossils from Ediacara, South Australia. Palaeontology, 9 (4), 599-628, pi. 97-103. GOLDRING, R. and cuRNOw, c. N. 1967. The stratigraphy and facies of the Late Precambrian at Ediacara, South Australia. Geol. Soc. Australia, Journ. 14(2), 195-214, pi. 10. GURiCH,G. 1933. Die Kuibis-FossilienderNama-Formation von Sudwestafrika.Pu/ueont. Z. 15,137-154, HARRINGTON, H. J. and MOORE, R. C. 1956. See MOORE, R. c. (ed.). HYMAN, L. H. 1940. The Invertebrates: Protozoa through Ctenophora. New York and London. LE LOUP, E. 1929. Recherches stir I’anatomie et le developpement de Velella spirans Forsk. Arch. Biol. 39. MACKIE, G. o. 1959. The evolution of the Chondrophora (Siphonophora-Disconanthe) : New evidence from behavioural studies. Trans. R. Soc. Canada, 53, (5), ser. 3, 7-20, pi. 1. MAYER, A. G. 1910. The medusae of the world. Pubis. Carnegie Instn, 109 (1-3), 1-735. MCALESTER, A. L. 1962. Modc of preservation in early Palaeozoic pelecypods and its morphologic and ecologic significance. J. Paleont. 36, 69-73. MOORE, R. c. (ed.), 1956. Treatise on invertebrate palaeontology. Part F, Coeienterata. Geol. Soc. Am. and Univ. Kansas Press. OSGOOD, R. G. 1970. Trace fossils of the Cincinnati area. Palaeont. Amer. 6 (41), 281-444, pi. 57-83. RAUFF, H. 1939. Palaeonectris discoidea Rauff, eine Siphonophoridae Medusae aus dem Rheinischen Unterdevon nebst Bemerkungen zur umstrittnen Brooksella rhenana Kink. Palaeont. Z. 21, 194-213. REES, w. J. ed., 1966. The Cnidaria and their evolution. Zool. Soc. London Symp. 16. RUEDEMANN, R. 1916. Note on Paropsonema cryptophya Clarke and Discophyllum peltatum Hall. N.Y. State Mus., Bull. 189, 22-27, pi. 1, 2. RUSSELL, F. s. 1953. The medusae of the British Isles. Cambridge. :souTHCOTT, R. V. 1958. South Australian jellyfish. S. Aust. Nat. 32, 53-61. SPRiGG, R. c. 1947. Early Cambrian (?) jellyfishes from the Flinders Ranges, South Australia. Trans. R. Soc. S. Aust. 71 (2), 212-224, pi. 5-8. 1949. Early Cambrian jellyfishes of Ediacara, South Australia, and Mt. John, Kimberley District, Western Australia. Ibid. 73, 72-99. pi. 9-21. WADE, M. 1968. Preservation of soft bodied animals in Precambrian sandstones at Ediacara, South Australia. Lethaia, 1 (3), 238-267. 1969. Medusae from uppermost Precambrian or Cambrian sandstones. Central Australia. Palaeontology, 12 (3), 351-365, pi. 68, 69. 1970. The stratigraphic distribution of the Ediacara fauna in Australia. Trans. R. Soc. S. Aust. 94, 87-104. 1971. Bilateral Precambrian Chondrophores from the Ediacara fauna, South Australia. Proc. R. Soc. Vic. 84 (1), 183-188, pi. 6. ZAiKA-NOVATSKiY, V. s., VELIKANOV, V. A. and KOVAL, A. p., 1968. First member of the Ediacara fauna in the Vendian of the Russian Platform (upper Precambrian). Palaeont. J. 2, 269-270. (In Russian.) MARY WADE Queensland Museum, Gregory Terrace, Fortitude Valley Queensland, Australia 4006 Typescript received 24 June 1971 TWO NEW CAMBRIAN TRILOBITES FROM TASMANIA by J. B. JAGO Abstract. The first published descriptions of Tasmanian Cambrian trilobites are given. Two new species, Opsidiscus argiisi and Scimialenseeia gostinensis, are described from a fauna, the age of which is probably either that of the latest Middle Cambrian Lejopyge laevigata 111 Zone or the Middle Cambrian/Upper Cambrian Passage Zone. Opsidiscus argiisi has well developed schizochroal eyes, recorded for the first time in this genus. The genera Opsidiscus and Scimialenseeia are reviewed. Opsidisus is placed in the Pagetiidae. Scimialenseeia acutangula Westergard is in need of revision and should be removed from Scimialenseeia. The presence of trilobites in the Middle and Upper Cambrian sediments of western and northern Tasmania has been recorded by various authors (Elliston 1954; Banks 1956, 1962; Blissett 1962; Burns 1964; Opik 1967; Gee et al. 1970; Jago and Buckley 1971). However, although many generic and some specific names have been listed, no descriptions of these trilobites have previously been published. Pike (1964) discovered a well preserved Cambrian trilobite fauna near the corner of the main Hampshire to Guildford road and Gin Creek road (41° 21-6' S, 145° 44-3' E), about 1-5 km south-west of St. Valentine’s Peak in north-west Tasmania. Unfortunately, the Cambrian sediments in the vicinity of the fossil locality are poorly exposed, and are probably separated by faulting from a better exposed Cambrian sequence about three kilometres to the north. Thus the exact stratigraphic position of the fauna con- cerned cannot be determined at present. Two of the trilobites from this locality are described below as Opsidiscus argiisi sp. nov., and Scimialenseeia gostinensis sp. nov. Other members of this fauna include Nepea, Aspidagnostus, Clavagnostus, Peronopsis, Agnostascus (?), and a species of a new genus, cf. Oidalagnostus. This faunal list indicates that the age of the fauna is either very late Middle Cambrian or very early Upper Cambrian. Nepea is not recorded above the Lejopyge laevigata Zone in Northern Australia (Opik 1970). The youngest recorded species of Opsidiscus is O. depolitus Romanenko from ‘layers transitional between the Middle and Upper Cambrian’ (Poletaeva and Romanenko 1970, p. 75). Clavagnostus is known from both Middle and Upper Cambrian rocks. However, as far as the author is aware, Aspidagnostus 2in6. Agnostascus are known only from the early Upper Cambrian. Other Tasmanian species of cf. Oidalagnostus are known only in late Middle Cambrian faunas. Although the question cannot be decided with certainty, it appears from this faunal list, and by comparison with other unpublished Tasmanian Cambrian faunas, that the age of this fauna is probably that of either the Lejopyge laevigata III Zone of Opik (1961), or the Middle Cambrian/Upper Cambrian Passage Zone of Opik (1967). The remaining trilobites from this and other Tasmanian localities will be described in later papers. Opsidiscus argusi and Scimialenseeia gostinensis are described separately in this paper because they are the only well-preserved representatives of their respective families in the Tasmanian Cambrian. A further reason for describing these is that both general are in need of review. [Palaeontology, Vol. 15, Part 2, 1972, pp. 226-237, pi. 44.] JAGO; TASMANIAN CAMBRIAN TRILOBITES 227 Almost all Tasmanian Cambrian trilobites have undergone some tectonic distortion. However, the trilobites from near St. Valentine’s Peak are among the least distorted of all Tasmanian Cambrian faunas. All trilobites from this locality are preserved as internal and external moulds in a weathered, buff-coloured siltstone. In order to prepare them for description, silicone rubber moulds of the external moulds were prepared. These rubber moulds were then photographed after being whitened with magnesium oxide. All specimens are housed in the collection of the Geology Department, Univer- sity of Tasmania. The catalogue numbers refer to this collection. Acknowledgements. The writer wishes to thank Dr. B. Daily (Geology Department, University of Adelaide) for much valuable advice and criticism, and also for making available rubber moulds of the type species of Opsidiscus and Schmalenseeia. These moulds were invaluable for comparative pur- poses. Dr. N. P. Lazarenko (Research Institute for Geology of the Arctic, Leningrad) kindly sent an excellent photograph of Schmalenseeia spiniilosa. Mr. P. Jell (Geology Department, Australian National University) offered valuable advice and criticism. Dr. V. Gostin (Geology Department, University of Adelaide) translated some of the Russian literature, and Mr. G. Pike originally showed the author the fossil locality. This work was done by the writer during the tenure of a Commonwealth Post-Graduate Award in the Geology Department, University of Adelaide. SYSTEMATIC DESCRIPTIONS Order agnostida Kobayashi 1935 Suborder eodiscina Kobayashi 1939 Family pagetiidae Kobayashi 1935 Genus opsidiscus Westergard 1949 Opsidiscus Westergard 1949, p. 606; Rasetti 1952, p. 436; Howell 1959, p. 181; Pokrovskaya 1960, p. 56; Kobayashi 1962, p. 21 ; Rushton 1966, p. 1 1 ; Rasetti 1967, p. 8; Palmer 1968, p. 38; Poletaeva and Romanenko 1970, p. 73. Aidacodisciis Westergard 1946, p. 26, Shaw 1950, p. 588; Hupe 1953, p. 59. Type Species. Aidacodisciis bilobatiis Westergard 1946, p. 26, pi. 1, figs. 16-22. Description. Pagetiid trilobite with two thoracic segments and closely spaced fine granulation (not visible on most photographs) on the dorsal surface. Cephalon moderately convex, wider than long (excluding the occipital spine). Rim moderately wide at the anterior, but narrowing posteriorly. Shallow marginal furrow with variable number of pits or transverse furrows in its anterior region, and small depressed area immediately in front of glabella. Glabella length about 0-75 cephalon length (excluding occipital spine) ; outlined by wide, deep furrows and tapering slightly anteriorly. Weak to well- developed anterior transverse glabellar furrow defines an anterior glabellar lobe. Eye ridges well defined to absent. Well defined sub-marginal schizochroal eyes, or large ‘eye tubercles’; no facial sutures. Pygidium moderately convex with narrow border; wider than long. Axis outlined by moderately deep furrows, which shallow posteriorly; does not quite reach posterior border. Large crescentic articulating half-ring. Axis consists of three to five segments plus a terminus. The two segments immediately in front of the terminus are fused and may bear a spine. The only sign of pleural segmentation is close to the axis. Discussion. The above description of Opsidiscus is based on a study of the figures of O. bilobatus (Westergard 1946, p. 26, pi. 1, figs. 16-22), O. altaicus Poletaeva 228 PALAEONTOLOGY, VOLUME 15 (Poletaeva and Romanenko 1970, p. 73, text-fig. 2, pi. 10, figs. 1-5) and O. depoJitus Romanenko (ibid., p. 74, text-fig, 3, pi. 10, figs. 6-9); two rubber moulds of O. bilobatus (a cephalon and pygidium, figured Westergard 1946, pi. 1, figs. 21, 20); and the new species described below. It differs in some respects from that given by Westergard (1946, p. 27) for the type species Opsidiscus bilobatus. The first difference is the very fine granulation of the test noted above. This feature is not noted by Westergard with respect to the type species, but an inspection of the rubber moulds of O. bilobatus reveals that a fine granulation is present. The pygidial axes of the other three species are better known than that of bilobatus and it is on these three species that the axial description is mostly based. The most important difference between the above description and that originally given for O. bilobatus is the mention of schizochroal eyes. These are known to date only in the new species, Opsidiscus argusi described below. Only large ‘tubercles’ are seen in the eye position of the other three species. The eye tubercles on the rubber mould of the holo- type cephalon of O. bilobatus were closely inspected. They are poorly preserved and as shown in Plate 44, fig. 7, they possess fine granules which could possibly be interpreted as eye lenses. However, they bear no resemblance to the well defined schizochroal eyes of O. argusi. It is possible that the eyes were present and have not been preserved. This suggestion is supported by the fact that in the more poorly preserved specimens of O. argusi no lenses are seen on the eye surfaces, which have a similar appearance to the ‘eye tubercles’ of O. bilobatus. Classification and Relationships of Opsidiscus. In discussing this subject a brief nomen- clatural observation must be made. The writer found that, in searching the literature on this and related topics, the term eodiscid is used to refer to either the suborder Eodiscina as a whole (i.e. including both the families Eodiscidae and Pagetiidae) or solely to members of the family Eodiscidae. This can be very confusing and in the following discussion the term eodiscid is restricted to members of the family Eodiscidae. Where reference is made to the suborder the term Eodiscina is used. Westergard (1946, p. 22) considered that Opsidiscus was the link between the pagetiids and the eodiscids in that it had a pair of tubercles (homologous with pagetiid eyes) and lacked facial sutures. However, this suggestion cannot be accepted because the first appearance of Opsidiscus is later than the last appearance of the eodiscids. Westergard (1946, p. 28) also noted the close similarity between Opsidiscus and Pagetia and con- sidered Opsidiscus to be a descendant of Pagetia. He included both the eodiscids and the pagetiids in the family Eodiscidae and suggested that a further breakdown into subfamilies, Pagetiinae and Eodiscinae, was unnecessary, partly due to the presence of the supposed intermediate form Opsidiscus. Westergard (1946) discussed Opsidiscus under his original generic designation, Aulacodiscus. However, Westergard (1949) realized that this name was preoccupied and replaced it with Opsidiscus. The classification of Hupe (1953) for the eodiscids and pagetiids is quite complicated. It includes the new family Aulacodiscidae, thus raising the preoccupied generic name to familial level. Howell (1959) proposed that the suborder Eodiscina be divided into two families, (1) the Eodiscidae, without facial sutures and usually without eyes, and, (2) the Pagetiidae, with eyes and facial sutures. He placed Opsidiscus in the Eodiscidae, presumably because of the lack of facial sutures. The classification of Pokrovskaya JAGO: TASMANIAN CAMBRIAN TRILOBITES 229 (1960) is basically the same as that of Howell, in that she recognizes the families Eodiscidae and Pagetiidae within the superfamily Eodiscoidea. However, she adds a third family, Opsidiscidae Hupe 1953, in which she places Opsidiscus. Prior to this Pokrovskaya (1959) included a new genus Tanmidiscus in the Opsidiscidae, a move followed by Kobayashi (1962) and Repina (1964). However, as pointed out by Rushton (1966, p. 22) and Rasetti (1966b, p. 10) Tanmidiscus is not related to Opsidiscus and belongs in the Eodiscidae. Rasetti (1967, p. 10) states that Opsidiscus could be referred to either the Pagetiidae or the Eodiscidae. Poletaeva and Romanenko (1970) retain Opsidiscus in the Opsidiscidae. Palmer (1968, p. 38) described a new genus, Yukonia from the Early Cambrian of Alaska. This genus has three thoracic segments, an unfurrowed glabella, prominent eyes and eye lines, fused facial sutures and a smooth test. As suggested by Palmer Opsidiscus and Yukonia are probably not closely related, although he tentatively in- cludes Yukonia in the Pagetiidae because of its well developed eyes and eye ridges. The discovery of well preserved eyes in Opsidiscus argusi sp. nov. indicates that Opsidiscus differs considerably from any known genus of the Eodiscidae, and cannot be included in that family as was done by Howell (1959). Opsidiscus argusi is very similar to some species of Paget ia as illustrated by Rasetti (1966a), and apart from the lack of facial sutures, it corresponds well to Pagetia as defined by him. This fact along with the reasonable presumption that Opsidiscus must have been able to moult quite easily without the presence of facial sutures, suggests to the writer that the absence of facial sutures in Opsidiscus is not sufficient to be the basis of a familial separation be- tween Opsidiscus and the Pagetiidae. This placing of Opsidiscus in the Pagetiidae dissolves the necessity for a separate family, the Opsidiscidae. Whether Opsidiscus evolved directly from Pagetia, as suggested by Westergard (1946, p. 22), cannot be determined from the Tasmanian faunas. However, Mr. P. Jell (personal communication, March 1971) considers that Opsidiscus is descended from the pagetiids in the Cambrian faunas of northern Australia. This suggestion is supported by the presence of schizochroal eyes in both Opsidiscus argusi, as described below, and Pagetia ocellata Jell 1970. Opsidiscus argusi sp. nov. Plate 44, figs. 1-6, 8-18 Holotype. The almost complete specimen on catalogue number UT 9201 1, figured Plate 44, fig. 1. Other material. One other well-preserved complete specimen; about ten cephala; and six pygidia, some of which are very well-preserved. Diagnosis. Opsidiscus species with numerous large pustules on the dorsal surface of both cephalon and pygidium. The pustules on the thoracic segments are smaller and much less numerous. Well defined palpebral lobes and schizochroal eyes of about seventeen lenses. Well developed, wide, shallow transverse glabellar furrow, and long occipital spine. Pygidial axis of five segments and a terminus; fourth and fifth segments fused and bear a spine. Description. Closely spaced, very small granules cover exoskeleton surface. Moderately convex cephalon distinctly wider than long; it has a semielliptical out- line; margins diverge slightly away from straight posterior margin and converge around 230 PALAEONTOLOGY, VOLUME 15 anterior margin. Shallow, wide anterior border furrow, narrows posteriorly. Anterior border of some specimens has six to eight pits or radial grooves. Convex, narrow, posterior border; narrow, shallow posterior border furrow; both fade adaxially. Border variable. Rim may be almost flat or markedly convex. Convexity of rim and development of pits and radial grooves show a continuous range of variation and is believed to reflect intraspeciflc variation rather than the existence of two or more species. Moderately convex glabella tapers very slightly to bluntly rounded anterior. It extends about 0-75 length of cephalon. Wide, deep axial furrows. Immediately in front of glabella is a deep pre-glabellar depression connected to border furrow. Cephalic margin slightly depressed and indented immediately in front of pre-glabellar depression. Towards glabellar anterior (about one-third of distance towards the posterior) is a well developed, wide, shallow, transverse glabellar furrow. Eye ridges meet glabellar furrows just anterior of transverse glabellar furrow. Occipital ring slightly wider than rest of axis. Occipital furrow has deep lateral notches and shallow midsection. These pronounced notches give lateral parts of occipital ring a rib-like appearance. Between occipital ring and transverse glabellar furrow are two glabellar segments, separated by faintly impressed lateral notches which are connected rarely by a very faint furrow. Long, strong, posteriorly directed occipital spine not usually preserved except for large spine base. Length of spine preserved in UT 92000 (PI. 44, fig. 18) indicates that spine extended over thorax and possibly over pygidial anterior. Pleural areas strongly convex. Eye ridges well developed in some specimens (e.g. UT 92009, PI. 44, fig. 12) but in others are either poorly developed or not developed at all (e.g. UT 92005, PI. 44, fig. 16). Prominent, convex, small palpebral lobes are slightly elevated above palpebral areas. Poorly developed palpebral furrows in some specimens, but usually palpebral lobe and palpebral area continuous. Ocular surface of each schizochroal eye is curved gently outwards. Each eye, when complete, possesses about 16 or 17 lenses. Facial sutures absent. As well as the very small granules scattered all over the surface, there are large pustules EXPLANATION OF PLATE 44 Figs. 1-6, 8-18. Opsidiscus argusi sp. nov. 1, UT 92011, a complete specimen, the holotype, x22. 2, 4, UT 92011 (separate cephalon); 2, cephalon, showing distinct eye ridges, Xl8; 4, right eye, x20. 3, 6, 9, 11, UT 92011 (the second complete specimen); 3, cephalon, showing fine granulation as well as coarse pustules, x 22; 6, right eye from the anterior, X 30; 9, right eye from the posterior, X 25; 11, thorax, x 22. 5, 15, UT 92006; 5, cephalon showing faint terrace lines on the edge of the doublure, X 19; 15, dorsal view, X 20. 8, UT 92004, pygidium showing fusion of fourth and fifth axial segments, x 16. 10, 14, UT 92003, pygidium; 10, side view showing spine base, X20 (the axial half-ring is not visible from the side); 14, dorsal view, X 20. 12, UT 92009, cephalon showing radial grooves in border, X 15. 13, UT 92001, pygidium, X 22. 16, 17, UT 92005, cephalon; 16, dorsal view, X22; 17, anterior view, x22. 18, UT 92000, poor cephalon showing long spine, x22. Fig. 7. Opsidiscus bilobatus (Westergard) (rubber mould of holotype figured by Westergard 1946, pi. 1, fig. 21), right eye region, x20. Figs. 19-22. Scluualenseeia gostineiisis sp. nov. 19, 20, UT 92012, the holotype partial cranidium; 19, external mould, X 10; 20, internal mould, X 13. 21, 22, UT 92013, pygidium and part of thorax; 21. internal mould showing full pygidium as well as an associated partial cranidium, x7; 22, external mould X 8-5. Palaeontology, Vol. 15 PLATE 44 JAGO, Cambrian trilobites JAGO; TASMANIAN CAMBRIAN TRILOBITES 231 scattered over the cephalon. On the glabella these are usually placed near the lateral margins, with a pair on first glabellar segment and three evenly spaced pairs on rest of glabella. Each well preserved cephalon has a row of about seven pustules on the pleural areas, close to, and parallel with the axial furrows. Other pustules tend to occur in irregular rows, parallel to either glabella or cephalic margins. Doublure partly exposed on one specimen (UT 92006 PI. 44, fig. 5). On edge of border of this specimen, where it starts to turn down to form the doublure, there are well preserved terrace lines, consisting of small rows of granules. These also occur on the doublure, the width of which cannot be determined. Neither rostral plate nor hypo- stome is known. The two thoracic segments are moderately well-preserved in only two specimens. Anterior segment is a little larger than posterior. Each pleura of anterior segment has two distinct areas; a small tumid antero-adaxially placed area with a distinct pustule, and a much larger adaxial area which includes the wide shallow pleural furrow (see PI. 44, fig. 11). Pleural furrow emerges from adaxial area; it deepens abaxially and runs outwards and slightly backwards. Anterior and posterior edges of outer area raised well above furrow, and possess small pustules. Pleural extremities of anterior segment directed outwards and backwards for anterior two-thirds of segment and inwards for the rest. Available posterior thoracic segments not as well preserved as anterior segments. Axial region of posterior segment bears median-sized spine base. Pleural furrows shallow adaxially; widen and deepen abaxially. Small pustules on raised areas on either side of furrow. Moderately convex pygidium with semicircular outline. At posterior, border is very narrow. Border furrow, shallow, moderately wide; edges of pleural regions very steep; posterior margin of pygidium is slightly indented immediately behind axis. Anterior border, convex, moderately wide, widest near centro-adaxially placed fulcral points. Anterior border furrow, shallow, wide, widening slightly abaxially. Large concave facets seen only in internal moulds. Prominent crescentic, strongly convex, long (sag.) articulating half-ring. Articulating furrow, wide, almost straight, shallow at centre, deeper at extremities. Axis outlined by moderately wide, deep furrows which shallow posteriorly; axis tapers evenly to rounded posterior and stands out well above pleural areas. Axis does not quite reach border furrow; it consists of five segments and a terminus. Eirst three segments quite convex; each bears a central median sized pustule flanked by two smaller ones. Transverse furrows separating these segments, deep laterally, shallow at centre. Fourth and fifth segments fused, bear a large spine base. In specimen UT 92003 lower part of spine preserved (PI. 44, fig. 10). Spine probably directed upwards and backwards. Terminus, short, with two small pustules. Pleural fields, highly pustulate; weak segmentation with about four discernible segments faintly delineated by small notches on abaxial margins of axial furrows. On pleural fields, first two pleural segments outlined by two rows (in each case) of pustules, orientated transverse to axis. These rows run outwards and backwards from axis. Less organization of smaller pustules towards pygidial posterior. Doublure not seen. Discussion. The large pustules over the surface of both the pygidium and the cephalon, as well as the presence of well developed schizochroal eyes and palpebral lobes, clearly 232 PALAEONTOLOGY, VOLUME 15 differentiate Opsidiscus argusi sp. nov. from other species of Opsidiscus. The cephalic pleural regions of O. argusi curve further around the front of the glabella than in O. bilobatiis, which gives the pre-glabellar depression of argusi more the look of a furrow than in bilobatus. Opsidiscus argusi has a much better developed transverse glabellar furrow than has O. depolitus. The occipital spine of O. altaicus is wider than that of O. argusi. The pygidial axis of O. argusi is narrower and more clearly segmented than that of O. altaicus. Order ptychopariida Swinnerton 1915 Suborder ptychopariina Richter 1933 Superfamily burlingiacea Walcott 1908 Family burlingiidae Walcott 1908 Genus schmalenseeia Moberg 1903 Schmalenseeia Moberg 1903, p. 93; Westergard 1922, p. 119; 1929, p. 8; 1948, p. 3; Hupe 1955, p. 198; Poulsen 1959, p. 293; Chernysheva 1960b, p. 130; Lazarenko 1960, p. 253. Type Species: Schmalenseeia amphiomira Moberg 1903, p. 93, pi. 4, figs. 1-4, 7-10. Discussion. Westergard (1948, p. 3) placed Schmalenseeia along with Burlingia in the family Burlingiidae Walcott, 1908. Hupe (1955) and Poulsen (1959) agreed with this grouping, but Chernysheva (1960b) also included Fissocephalus in the Burlingiidae. However, Fissocephalus belongs in the family Harpididae Whittington 1950 (Whitting- ton 1959, p. 418). Prior to this paper there were only three described species placed in Schmalenseeia. These were the type species S. amphiomira Moberg 1903 from Sweden (lowest part of the Agnostus pisiformis Zone), S. acutangula Westergard 1948 (Zones of Ptychagnostus atavus, Hypagnostus parvifrons and Ptychagnostus punctuosus of Sweden) and S. spinu- losa Lazarenko 1960 from the Agnostus pisiformis Zone of the North Siberian Platform. Schmalenseeia amphiomira Moberg, as illustrated in Chernysheva et al. (1960a, pi. 3, fig. 4) from eastern Siberia is different from S. amphiomira Moberg as illustrated by Westergard 1922 (pi. 1, fig. 19). The palpebral area of the form illustrated by Westergard is much narrower than that in the form illustrated by Chernysheva. Also the anterior thoracic segment in the Siberian form is curved markedly to the anterior, whereas in the Swedish form the anterior thoracic segment has a nearly straight anterior margin, and a posterior margin which is curved to the posterior. The anterior glabellar lobe is much larger in the Swedish form than in that illustrated by Chernysheva; the pre- glabellar ridge in the latter appears to be much more pronounced than in the former. Although the specimen of S. amphiomira illustrated by Westergard (1922, pi. 1, fig. 19) is a young individual (Westergard 1948, p. 4) the differences noted above seem much too pronounced to be accounted for by changes during growth. Thus the Siberian form is a different species from S. amphionura and is in need of revision. A rubber mould of the specimen of Schmalenseeia amphionura which was illustrated by Westergard (1922, pi. 1, fig. 19) reveals that in fact this figure has been printed reversed. Westergard’s figure shows the preglabellar ridge much more prominently than it appears in the specimen. However, an unfigured rubber mould of S. amphionura has a more prominent ridge than the figured specimen. Westergard’s figure also shows the posterior cranidial margin as straight, whereas in the available mould the postero- lateral corners are slightly, but distinctly, turned to the posterior. JAGO: TASMANIAN CAMBRIAN TRILOBITES 233 The cranidia of Schmaienseeia acutaiigula as illustrated by Westergard 1948 (pi. 1, figs. 2, 3, 5, 6) appear to include two separate forms; form (1), figures 2 and 3; and form (2), figures 5 and 6. In form (2) the free cheeks are bigger in proportion to the size of the cranidium than in form (1). The transverse glabellar furrows in form (1) extend from the lateral margins of the glabella towards the centre of the glabella, but in form (2) they appear more as shallow depressions and do not extend from the lateral margins but commence some distance inside them. A detailed comparison between forms (1) and (2) is difficult because of the poor reproductions of figures 2 and 3 and the lack of pygidia of form (2). The palpebral lobe in form (2) is much larger than in form (1), and it appears to be narrower in comparison with the glabellar width. Figures 5 and 6 have the appearance of internal moulds, but no mention is made of this in Westergard’s text. The cranidium of form (2) of acutangula is so markedly different from that of Schmaienseeia amphionura that it cannot be included in the same genus. The glabella of form (2) is much larger in relation to the cranidium than that of amphionura. The glabellar furrows of form (2) do not reach the lateral glabellar margins, whereas those of amphionura are deepest near the glabellar margins. Neither forms (1) or (2) of acutangula have the preglabellar longitudinal ridge of amphionura and other species of Schmaienseeia. It cannot be determined from Westergard’s figures whether in fact forms (1) and (2) of acutangula as discussed above belong in the same genus. If both forms (1) and (2) of acutangula are removed from Schmaienseeia, then this genus as far as is known is restricted to the lowest Upper Cambrian (Siberia and Sweden) and to the highest Middle Cambrian or Middle/Upper Cambrian transition beds (Tasmania). It is very small for a polymerid trilobite with the complete Schma- ienseeia spinulosa figured by Lazarenko 1960 (pi. 53, fig. 18) having a length of only 7-7 mm. The very small size of Schmaienseeia, its lack of convexity, and its widespread distribution probably indicate that it led a pelagic existence. Because of its size and lack of convexity, Schmaienseeia is difficult to see in the rock and it can be expected that further examples of this genus will be found in scattered locations around the world. The nomenclature of the facial suture given below is similar to that of Hupe (1953, text-fig. 37). Schmaienseeia gostinensis sp. nov. Plate 44, figs. 19-22 Holotype. UT 92012, incomplete cranidium. Material. Only two specimens are available, one of which is the holotype UT 92012, which is a moder- ately well preserved cranidium, about two-thirds of which is present. The complete cranidium would have a length of about 1-25 mm. and a width of about 2-3 mm. The other specimen, UT 92013, is one in which part of the thorax and all of the pygidium is known, although only part of the pygidium is preserved as the external mould. Associated with this partial thorax and pygidium is a partial cranidium which is preserved only in the internal mould (PI. 44, fig. 21 ). It is possible that this cranidium belongs with the associated thorax-pygidium. Internal and external moulds of both specimens are available. Diagnosis. Schmaienseeia with pronounced posterior marginal furrow on the fixed cheek, short genal spines, and dome-shaped anterior glabellar segment which bears a large node. From this node emerges a distinct ridge which extends to the centre of the anterior cranidial margin. Occipital ring with a well developed node or spine base. At least eighteen thoracic and pygidial segments. Pleurae flat, with a narrow ridge along 234 PALAEONTOLOGY, VOLUME 15 both anterior and posterior margins; short pleural spines. Pygidium has no distin- guishable border. Description. Complete cephalon would have semicircular outline and be almost twice as wide as is long. Cranidium, almost flat, except for elevated glabella and palpebral lobes. Librigenae unknown, probably flat. No frontal border. Posterior margin almost straight across base of occipital ring; adaxial parts of margin arched slightly to posterior; abaxial parts arched slightly to anterior, terminating in short genal spines. Posterior border furrow located a little distance anterior of posterior margin; it extends from near occipital furrow to close to tip of genal spine. Posterior border areas slightly raised above level of posterior areas of fixigenae. Facial sutures, proparian, burlingiiform. Posterior end of each facial suture cuts lateral cephalic margin about one-third of distance from genal spines to cranidial front. From this point (a>) the facial suture runs at about 90° to cephalic margin. ‘Posterior’ section of facial suture is straight except for the most adaxial part which curves around until the very end of it is directed inwards and forwards. At this point (e), facial suture is very close to glabella. From e, suture is curved gently forward and outward, up to a point about 0-4 of distance along the palpebral lobe, from where it curves gently inward and forward to y. y is close to the glabella and opposite the centre of anterior glabellar segment. From y to a, facial suture straight, meets cranidial margin at about 90°. Posterior areas of fixigenae, large, flat, narrow (exsag.) near glabella. Small, flat palpebral areas; prominent, long, narrow, steep palpebral lobes; moderately wide, shallow palpebral furrows. Small knob at anterior of each palpebral lobe; there may be a smaller knob at posterior, but this cannot be determined with certainty. Frontal area, large, flat, featureless except for a pronounced ridge which commences at centrally placed node on anterior glabellar segment and continues to midpoint of anterior cephalic margin. Ridge becomes narrower and lower toward cranidial front; at posterior it is bounded by faint furrows. Glabella stands well above fixigenae; it consists of four segments, plus occipital ring, which appears to be an integral part of the glabella and is described as such. Length and width of glabella respectively about two-thirds and one-third those of cranidium. From occipital ring, glabella tapers to third glabellar segment; second glabellar segment slightly wider than third segment. Glabellar front, subangular; glabellar furrows, deep. Frontal glabellar segment has length about one-third that of glabella. First pair of glabellar furrows commence very close to, and just to the posterior of the knobs at the anterior ends of the palpebral lobes. They are directed inwards and backwards quite markedly and are concave abaxially. In the centre of the subelliptical dome, which is the anterior glabellar segment, there is a large node, from which runs the ridge across the frontal area. Second glabellar segment may have a small central node, but further specimens will be required to confirm this point. Second pair of glabellar furrows curve gently inwards and backwards ; deepest adaxially with distinct pits near the abaxial extremities as is the case in other glabellar furrows and the occipital furrow. Pits probably represent muscle attachments. Posterior pair of glabellar furrows run almost straight across glabella and meet in the middle. Oceipital ring, narrow (sag.), well developed node or spine base on anterior part of central region. Occipital furrow, wide, deep, separated at centre by the node. JAGO; TASMANIAN CAMBRIAN TRILOBITES 235 Thorax of at least nine, and possible twelve or more segments. As noted above only one partial thorax is available. Axial region not present except for what are probably the last two or three segments. Narrow axis raised slightly above pleural areas. Along anterior margin of axis of each known thoracic segment is a low convex ridge, which is the axial half-ring. All known thoracic and pygidial segments are narrow (sag.). Immediately behind axial half-ring is a relatively wide furrow, which is of moderate depth abaxially; it shallows adaxially, where it is interrupted by a low hemispherical node. Low ridge along posterior margin of axis. Thoracic pleurae, basically flat ; low, narrow, convex ridges along anterior margins ; somewhat higher, narrow, convex ridges along posterior margins. Small transversely elongated depression antero-laterally placed on each pleura. From these depressions, poorly defined, shallow pleural furrows run outwards and backwards until they meet the posterior pleural ridges about one-third of the distance to segment margins. For the rest of its course each furrow runs just in from the posterior ridges. Pleural furrows, narrower and better defined abaxially. Pleural margins make an angle of about 120° with anterior border; they are straight and end in very short pleural spines. Pleurae widen slightly abaxially. On the most anterior pleural segment present on specimen UT 92013 the anterior margin is curved; its outline is concave to the anterior (PI. 44, figs. 21, 22). In the more posterior segments the margins gradually straighten until in the most posterior segment which can be definitely assigned to the thorax the curvature is slightly in the reverse sense. On the available specimen it is impossible to determine the junction between thorax and pygidium. Pygidial axial region is similar to that of thorax. Pointed pygidial axis terminates some distance in front of broadly rounded pygidial margin. No distinguish- able pygidial border. In posterior part of axis, the central axial nodes tend to merge to give the appearance of a ridge. Near the thoracic posterior there is a slight posterior geniculation where posterior axial ridges continue on to posterior pleural ridges. This feature becomes more pro- nounced to the posterior, until on the third last pygidial segment these ridges are aligned almost parallel to the axis. On the last two segments the pleural ridges are directed inwards and backwards. The available specimen has a total of at least eighteen thoracic and pygidial segments. Discussion. Schmalenseeia gostinensis sp. nov. differs from all other described and illus- trated forms of Schmalenseeia in that it has a pronounced posterior marginal furrow on the fixigenae. 5'. gostinensis is probably closest to 'S. amphionura" as illustrated by Chernysheva ( 1 960a, pi. 3, fig. 4), because the latter appears to have faint posterior marginal furrows on the fixigenae. However, S. gostinensis differs from this form in that the anterior glabellar lobe of gostinensis is much more pronounced, the posterolateral limbs of the fixigenae are much bigger and it has more thoracic and pygidial segments. Schmalenseeia gostinensis differs from S. amphionura as illustrated by Westergard (1922, pi. 1, fig. 19) in the much more pronounced preglabellar ridge that the former possesses. S. amphionura does not possess the well developed node on the most anterior glabellar segment as does S. gostinen- sis. A third difference is that the anterior thoracic segments in gostinensis are curved to the anterior, whereas those of amphionura are straight or curved to the posterior. C 8908 R 236 PALAEONTOLOGY, VOLUME 15 Schmalenseeia gostiuensis differs from S. sphmlosa Lazarenko in that the latter has pronounced axial spines or at least large nodes on each glabellar segment; the posterior cranidial margin of spinulosa is much more curved forward than in gostinensis; the glabella of spinulosa tapers more than that of gostinensis, and the most anterior glabellar lobe in the latter is slightly bigger than that of spinulosa. Although one and probably both forms of Schmalenseeia acutangula as described by Westergard (1948) do not belong in Schmalenseeia (see above) they are briefly compared with S. gostinensis for the sake of completeness. S. gostinensis differs from both forms of acutangula in that it has a distinct preglabellar median ridge and that its palpebral areas are comparatively much larger. The glabella of gostinensis does not extend as far forward as that of either form of acutangula. S. gostinensis also differs from form (1) of acutangula in that the anterior thoracic segments of the latter are curved to the posterior. REFERENCES BANKS, M. R. 1956. The Middle and Upper Cambrian Series (Dundas Group and its Correlates) in Tasmania. El Sistema Cambrico, Proc. 20th Int. geol. Coiigr. 2, 165-212. 1962. Cambrian System in The Geology of Tasmania. J. geol. Soc. Amt. 9, 127-145. BLissETT, A. H. 1962. Gcology of the Zeehan Sheet, 1-mile Geol. Map Series K 55-5-50. Explan. Rep. Geol. Surv. Tasin. BURNS, K. L. 1964. Geology of the Devonport Sheet, 1-mile Geol. Map Series K 55-6-29. Explan. Rep. Geol. Surv. Tasni. CHERNYSHEVA, N. E. (ed.), 1960a. [Arthropoda, Trilobitomorpha and Crustacea]. Osnovy Paleontologii. Moscow. Akad. Nauk SSSR, pi. 1-12. In Russian. 1960b. Burlingioidea, 130-131 in Chernysheva, N. E. 1960a. ELLiSTON, j. N. 1954. Gcology of the Dundas District, Tasmania. Pap. Proc. R. Soc. Tasm. 88, 161-183. GEE, c. E., JAGO, J. B., and QuiLTY, p. G. 1970. The age of the Mt. Read Volcanics in the Que River area. Western Tasmania. J. geol. Soc. Amt. 16, 761-763. HOWELL, B. F. 1959. Eodiscidae and Pagetiidae, in Moore, R. C. 1959, 187-190 (q.v.). HUPE, p. 1953. Classification des trilobites. Annls Paleont. 39, 61-168 (1-110). 1955. Classification des trilobites. Ibid. 41, 91-325 (111-345). JAGO, J. B., and BUCKLEY, J. H. 1 97 1 . An abrupt Upper Middle Cambrian faunal change, Christmas Hills, Tasmania, Australia. Pap. Proc. R. Soc. Tasm. 105, 83-85. JELL, p. A. 1970. Pagetia ocellata, a new Cambrian trilobite from northwestern Queensland. Mem. Qd Mas. 15, 303-313, pi. 23-24. KOBAYASHi, T. 1962. The Cambro-Ordovician Formations and faunas of South Korea, Part IX. Palaeontology VIII. J. Fac. Sci. Tokyo Univ. Sec. 2, 14, 1-152, pi. 1-12. LAZARENKO, N. p. 1960. In Kryskov, L. N., Lazarenko, N. P., Ogienko, L. V., and Chernysheva, N. E. New early Palaeozoic trilobites of Eastern Siberia and Kazakhstan in Markovsy, B. P. (ed.) [New species of prehistoric plants and invertebrates of the U.S.S.R., part 2.] VSEGEI, Moscow, 211-255, pi. 50-53. In Russian. MOBERG, J. 1903. Schmalenseeia amphioniira, en ny trilobit-typ. Geol. For. Stockh. Fork. 25, 93. MOORE, R. c. (ed.) 1959. Treatise on Invertebrate Palaeontology, Part O, Arthropoda I. Univ. Kansas Press and Geol. Soc. Am. OPiK, A. A. 1961. Cambrian geology and palaeontology of the headwaters of the Burke River, Queens- land. Bull. Miner. Resour. Surv. Aust. 53, pi. 1-24. 1967. The Mindyallan Fauna of North-Western Queensland. Ibid. 74, pi. 1-67. 1970. Nepeid trilobites of the Middle Cambrian of northern Australia. Ibid. 113, pi. 1-17. PALMER, A. R. 1968. Cambrian trilobites of East-Central Alaska. Prof. Pap. U.S. geol. Surv. 559-B, pi. 1-15. PIKE, G. 1964. Geology of the region around St. Valentine's Peak, Tasmania. Unpubl. Thesis, Univ. Tasm. JAGO: TASMANIAN CAMBRIAN TRILOBITES 237 POKROVSKAYA, N. V. 1959. [Trilobite fauna and stratigraphy of the Cambrian deposits of Tuva.] Trudy geo!. Inst., Akad. Naiik SSSR. 27, 1-200, pi. 1-11. In Russian. 1960. Eodiscoidea, in Chernysheva, N. E. 1960a, 54-56 (q.v.). POLETAEVA, o. K., and ROMANENKO, YE. V. 1970. [Middle and Late Cambrian trilobites of the Altay.] Paleont. Z!t. [for 1970] 2, 72-83, pi. 10-11. In Russian. POULSEN, c. 1959. Burlingiacea, in Moore, R. C., 1959, 293-294 (q.v.). RASETTi, F. 1952. Revision of the North American trilobites of the family Eodiscidae. J. Paleont. 26, 434-451, pi. 51-54. 1966a. Revision of the North American species of the Cambrian trilobite genus Paget ia. Ibid. 40, 502-511, pi. 59-60. 1966b. New Lower Cambrian trilobite faunule from the Laconic Sequence of New York. Smithson, misc. Coll. 148, (9), pi. 1-12. 1967. Lower and Middle Cambrian Trilobite fauna from the Laconic Sequence of New York. Ibid. 152, (4), pi. 1-13. REPINA, L. N. 1964. [Palaeontological Atlas, 2, Trilobites], in Repina, L. N., Khomentovsky, V. V., Zhuravleva, I. T., and Rozanov, A. Yu. [Biostratigraphy of the Lower Cambrian of the Sayan-Altai folded region.} Akad. Nauk SSSR Sibirskoe Otdelenie Institut Geologii i Geofyziki. Moscow. 252- 364, pi. 1-48. In Russian. RUSHTON, A. w. A. 1966. The Cambrian trilobites from the Purley Shales of Warwickshire. Palaeontogr. Soc. {Monogr.), 120, 1-55, pi. 1-6. SHAW, A. B. 1950. A revision of several Early Cambrian trilobites from eastern Massachusetts. J. Paleont. 24, 577-590, pi. 79. WESTERGARD, A. H. 1922. Svcriges Olenidskiffer. Sver. geol. Unders. Avh., ser. Ca, 18, pi. 1-16. 1929. A deep boring through Middle and Lower Cambrian strata at Bornholm, Isle of Oland. Ibid, ser. C, 355. 1946. Agnostidea of the Middle Cambrian of Sweden. Ibid. 477, pi. 1-16. 1948. Non-Agnostidean trilobites of the Middle Cambrian of Sweden. I. Ibid. 498, pi. 1-4. 1949. Opsidisciis, new name replacing Aulacodiscus Westergard 1946. Geol. For. Stockh. Forh. 71, 606. WHITTINGTON, H. w. 1959. Harpididac, in Moore, R. C., 1959, 418-19 (q.v.). J. B. JAGO Dept. Applied Geology South Australian Institute of Technology Adelaide S. Australia Revised manuscript received 7 October 1971 REVIEW OF FOSSIL RODENTS FROM THE NEOGENE SIWALIK BEDS OF INDIA AND PAKISTAN by CRAIG C. BLACK Abstract. Sixteen species of rodents belonging to nine genera and five families are now known from the Neogene Siwalik Series of India and Pakistan. Detailed descriptions, illustrations and discussion are given for all species of rhizomyids, ctenodactylids and thryonomyids; brief mention is made of the hystricids and murids. The most abundant material is that of rhizomyids for which two distinct lineages are recognized: Rhizomyoides to Rhizomys and Kanisamys-Protachyoryctes to Tachyoryctes. The Asian and African rhizomyids and cteno- dactylids are compared, and Paraulacodus incidiis is recognized as the only thryonomyid known outside Africa. Fossil vertebrates from the ‘Siwalik Hills’ and the Salt Range of India and Pakistan have been known for more than a 150 years. The first serious student of vertebrate fossils found in the middle and later Tertiary sediments along the southern edge of the Himalaya Mountains was Dr. Hugh Faukner who, together with Lt. P. T. Cautley, began publishing on Indian fossil vertebrates in the 1830s. Their series entitled Fauna Antiqiia Sivaleusis was the first monographic treatment of this material. Their studies were added to and expanded upon by Richard Lydekker in the latter part of the 19th century. Since Lydekker’s time, many students have published on Siwalik fossil verte- brates. Notable among these later students are Drs. Guy E. Pilgram, W. D. Matthew, and E. H. Colbert. More recently there has been renewed interest in the collection and study of vertebrate fossils from this area as is evidenced by the work of K. N. Prasad of the Indian Geological Survey and the recent expeditions to northern India of the Peabody Museum of Yale University under the direction of E. L. Simons. Throughout the history of the study of vertebrates from the Siwalik Hills, there has been a noticeable absence of papers dealing with the smaller vertebrates, lizards, snakes, birds, insectivores, and rodents. In most collections from the Siwaliks, small vertebrate specimens are extremely rare. In 1933, Colbert was able to record only ten specimens of fossil rodents as having been recovered from all of the Siwalik beds. There were other specimens of fossil rodents present at that time in the collections of both the Indian Geological Survey and the British Museum of Natural History but these were unknown to Colbert. The presence of such additional materal was indicated by Hinton’s (1933) short note in the Annals and Magazine of Natural Ffistory in which he very briefly diagnosed several new species of fossil rodents. In 1937, A. E. Wood pub- lished a description of additional fossil rodent material collected by the Yale University Expedition in Northern India in 1932. In recent years a great deal of new material of small vertebrates has been added to the fauna of the Siwalik series by both Prasad and Simons (personal communication). These collections include a number of rodents and primates which are as yet undescribed. The purpose of the present paper is two-fold. Of greatest importance, perhaps, is the description and presentation of figures of the material upon which Hinton (1933) based his brief diagnosis of new genera and species of Indian Tertiary rodents. Some [Palaeontology, Vol. 15, Part 2, 1972, pp. 238-266.] BLACK: SIWALIK RODENTS 239 confusion has resulted in the subsequent literature on Asian fossil rodent material due to the brevity of Hinton’s original descriptions and the absence of ilustrations of type specimens in that note. These various areas of confusion are discussed and clarified below. The second function of this report is to form a basis on which the description of the new collections can be built. The newer materials have been collected with a much better understanding of the need for exact stratigraphic information accompany- ing each individual specimen. Unfortunately, this is not true of the older materials and exact locality and stratigraphic position are in many cases either poorly or totally unknown. All fossil rodents described from the Siwalik series are at least briefly con- sidered here; however, the later Pleistocene occurrences of rodents in Asia are not dealt with. The fossil murids and hystricids of the Siwaliks have not been examined personally by me. Therefore, only brief citations are given for specimens belonging to these two families of rodents. For many years the whereabouts of the collection which formed the basis for Hinton’s (1933) brief note was unknown. After Dr. Hinton’s death, much of the material upon which he had been working was sent to the British Museum of Natural History. A search of these collections by the author in 1964 and again in 1965, failed to disclose the Siwalik rodent specimens. However, in 1965 through the kindness of Professor R. J. G. Savage at the University of Bristol, I learned that this portion of the Hinton collection was in his care in the Geology Department at the University of Bristol. While in India in 1964, and before the whereabouts of the India Geological Survey collection of rodents from the Siwaliks was known, I was very kindly given permission to study this material if it could be found. In this regard I want to thank, particularly, the Director of the Geological Survey of India, Dr. R. C. Roy, the Chief Palaeontologist, Mr. M. B. A. Sastry, and Mr. K. N. Prasad, vertebrate palaeontologist with the Indian Geological Survey, for allowing me to complete Hinton’s preliminary work. In 1968, I was able to visit R. J. G. Savage at Bristol and at that time he very kindly turned over to me all of the Indian Geological Survey specimens mentioned in Hinton’s original paper. Dr. Savage also put at my disposal all of Dr. Hinton’s original notes on this collection, together with a series of illustrations prepared by Mr. Terzi for the mono- graph which Hinton had envisaged on the Indian Siwalik rodents. The illustrations in this paper are Mr. Terzi’s. I offer my sincerest thanks to the members of the Indian Geological Survey mentioned above and to Dr. R. J. G. Savage for making this paper a possibility. Abbreviations used: A.M.N.H. — American Museum of Natural History G.S.I. — Geological Survey of India Y.P.M. — Yale Peabody Museum a-p — antero-posterior mm — millimetres tr — transverse Suborder sciuromorpha Brandt 1855 Family ctenodactylidae Zittel 1893 Schaub (1958, p. 780) was the first to separate the Tataromyidae as a family of rodents distinct from the living ctenodactylids. In so doing, he recognized Bohlin (1946) as the 240 PALAEONTOLOGY, VOLUME 15 original describer of the family. Lavocat (1961, p. 52) also used the family Tataro- myidae, attributing first usage to Bohlin (1946). He included within this family the genera Tatarornys, Karakoromys, Africanomnys, Sayimys, and Metasayimys. The Tataromyidae together with the Family Ctenodactylidae he grouped together in the Superfamily Ctenodactyloidae. Bohlin (1946), however, never used the name Tata- romyidae as a formal, familial designation. He (1946, p. 75) placed the genus Tatarornys in the family Ctenodactylidae and later (p. 132) he said, Tn conclusion, I may say that I can see no serious objection to the hypothesis that Tatarornys and Sayimys are closely related forms.’ Later (p. 133) Bohlin says, ‘The similarity between Sayimys and Cteno- dactylus is so great that it seems superfluous to separate the fossils from the living Ctenodactylidae, which may be survivors of the Sayimys line.’ Unfortunately, Bohlin then went on (1946, p. 133-134) and used the term ‘Tataromyidae’ (his quotation marks) when talking about a subfamilial grouping of ctenodactylids. However, nowhere in his 1946 work did Bohlin use the term Tataromyidae as a family unit — distinct from the living ctenodactylids. Wood (1955, 1965) has recognized the Family Ctenodactylidae as including both the living genera and those extinct forms placed by Schaub and Lavocat in the ‘Tataromyi- dae.’ This procedure is followed here. Genus sayimys Wood 1937 Type species. Sayimys perplexiis Wood, 1937, p. 73. Diagnosis. ‘Jaw shallow with very heavy masseteric crests and gently sloping coronoid; angle not continuous with lower end of masseteric fossa, but begins to diverge from corpus beneath Mg; P4 quadrate with V-shaped loph and postero-external cingulum; molars with anterior V-shaped crests and posterior crest connected to middle of posterior arm.’ (Wood 1937, p. 73.) Included species. S. per plexus, S. sivalensis, and S. obliquidens. Range. Chinji and Nagri Zones of the Siwalik Series, and Miocene (Taben-buluk) of China. Does not include Sayimys and Metasayimys of Lavocat ( 1 96 1 ) for which see below. Sayimys perplexus Wood 1937 Sayimys perplexus Wood, p. 73 Holotype Y.P.M. 13800, partial left mandible with P4-M3. Horizon and locality. ‘Nagry Zone, Survey of India Map no. 53NE/4, B-6, East of Hari Talyangar’ (Wood, op. cit.). Diagnosis. Larger than Sayimys sivalensis; anterior loph on Mi and Mg bent at mid- point rather than running straight across tooth; metaconid and entoconid more widely separated on Mg-Mg than in S. sivalensis. Description. A thorough description has been given by Wood (1937). The relationships of the two Siwalik species of Sayimys are discussed below under S. sivalensis. BLACK: SIWALIK RODENTS 241 Sayimys sivalensis (Hinton) Text-fig. 1 1933 Pectinator sivalensis Hinton, p. 622. Holotype. G.S.I. D284 (register number K16/326), left mandibular fragment with M2-M3. Horizon and locality. Lower Siwaliks, Chinji Zone, Late Miocene; Chinji Beds, near Chinji, Attock District, Salt Range, Pakistan. TEXT-FIG. 1. Sayimys sivalensis, G.S.I. D284, Holotype. a. Internal view of mandible, X 8. b. External view of mandible reconstructed, X 3. c. External view of mandible, x 8. d. Internal view of mandible reconstructed, X 3. e. Occlusal view M2-M3 (P4-M1 hypothetical), x 8. Diagnosis. Smaller than Sayimys perplexus; anterior loph straight, perpendicular to axis of tooth row; hypolophids shorter transversely than in S. perplexus or S. obli- quidens; valley between metaconids and entoconids shallow; only faint posterior shelf, or cingulum, on M2, absent on M3. Description. There is only a small portion of the mandible preserved with the dia- stema, alveolus for P4 and the ascending ramus missing. The mandible under Mg and M3 is quite shallow. Internally, there is a deep groove under M3 which extends below the posterior root of M2; here it merges into the internal face of the mandible. The 242 PALAEONTOLOGY, VOLUME 15 masseteric crest is very prominent and forms a heavy ihelf under and the anterior half of Mg. The incisor ends below Mg at the point where the internal mandibular furrow ends. Judging from the roots, is smaller than Mg and M3. Mg is evidently the largest tooth in the series as it is slightly larger than M3. Both Mg and M3 are moderately worn. The anterior borders of both teeth are straight, lacking the central projection seen on the anterior faces of M1-M3 in Sayimys perplexus and S. obliquidens. The entoconid is set close to the metaconid with a rather narrow valley separating these cusps. This results in a more nearly transverse direction for the crest connecting entoconid and protoconid. The valley between the entoconid and hypoconulid passes further into the interior of the tooth than does the metaconid-entoconid valley. On the postero-buccal slope of the hypoconid there is a slightly swollen ridge representing the posterior cingu- lum but there is no such structure on M3. The hypoconulid is large and the posterolophid broad on both teeth. The valley between entoconid and posterolophid is closed by a low connection from the posterolophid into the slope of the entoconid. Measurements in mm Mg a-p occlusal 2-25 maximum 2-60 M3 „ 1-95 „ 2-30 Mg transverse maximum 2-25 2-30 M3 „ „ 2-30 2-10 Discussion. This specimen was originally described as a new species of the ctenodactylid genus Pectinator (Hinton 1933, p. 622). As there were no illustrations accompanying this note. Wood (1937) was unable to compare his material with Hinton’s and described a new genus of rodent, Sayimys perplexus, based upon a jaw fragment with P4-M3. The specimen described by Wood was from the Nagri Zone of the Siwaliks. At the time of his work. Wood was not able to place Sayimys as to family or even suborder because of its peculiar morphology. Bohlin (1946), evidently without consulting Hinton’s paper, recognized that Sayimys was a ctenodactylid and made extensive comparisons between Sayimys and the Recent Ctenodactylus and Pectinator. Bohlin, of course, knew of Wood’s work but did not refer to Hinton’s brief diagnosis of Pectinator sivalensis. Sayimys sivalensis (Hinton) appears to be directly ancestral to S. perplexus Wood of the Nagri Zone. S. sivalensis is slightly more primitive than S. perplexus in that the masseteric crest does not extend forward under P4 but rather ends under Mi, nor does it form as wide a shelf as it does in S. perplexus. The molars of S. sivalensis are lower crowned, have straighter anterior margins, more transversely directed protoconid- entoconid connections, and shallower metaconid-entoconid valleys than do those of S. perplexus. In all of these characters, S. sivalensis is more primitive than S. perplexus but it is clearly ancestral to the later species. There is now general recognition of the ctenodactylid affinities of Sayimys. That the Siwalik material belongs in Wood’s genus rather than in the living African genus, Pectinator, also appears certain. Sayimys differs from the modern form in having larger and more complex P*^^ and in possessing molars which are lower crowned and which exhibit a more complex occlusal pattern. Sayimys lower molars are in turn less complex and higher crowned than those of the late Oligocene Karakoromys, Tatarornys, and Leptotatoromys. A fourth late Oligocene genus, Yindirtemys (Bohlin 1946), is known BLACK: SIWALIK RODENTS 243 from only a single tooth and cannot be adequately compared with other members of the family. Lavocat (1961) has described two genera of ctenodactylids, Africanomys and Metasayimys, as well as a new species of Sayimys, all from the late Miocene of Morocco. Africanomys is clearly distinct from the Asian ctenodactylids in the isolated condition of the metacone of the upper molars and the small trigonid basin of the lower molars. No isolated premolars are known for this genus. Africanomys and Sayimys evidently represent two independent lines of development from a Tataromys- like stock. Metasayimys and Sayimys jebeli (Lavocat 1961) are based upon a total of three isolated teeth and are insufficiently known to be compared with other cteno- dactylids. From Lavocat’s descriptions and illustrations, it appears possible that only a single genus of ctenodactylid is actually present in the Beni Mellal fauna and this is Africanomys. A third genus, Dubiomys, was described by Lavocat from the same fauna and is based upon two teeth. Lavocat (1961, p. 66-67) discussed the similarity of these two teeth to milk premolars of ctenodactylids (tataromyids in his sense) as figured by Bohlin (1946, fig. 19). However, Lavocat preferred to consider Dubiomys as Rodentia incertae sedis because of the distinct anterior tubercule on the occlusal surface. Bohlin (1946) has shown that this tubercule is extremely variable in the ctenodactylid Tataromys and it could easily have been so in the African ctenodactylids as well. I believe Dubiomys is probably based on nothing more than two deciduous lower premolars of Africanomys. Dawson (1964) has described an extremely interesting rodent from the late Eocene of Mongolia. She recognized two species, Adveninius burkei and Advenimus bohlini, and assigned three other jaws to Advenimus sp. Advenimus was placed with question in the family Sciuravidae while a number of similarities to ctenodactylids were pointed out. These include (1) reduced P4; (2) enlarged hypoconulid; (3) increase in size from P4 to M3; and (4) a shallow mandible. Advenimus appears to be close to the ancestry of the Ctenodactylidae if not actually in the direct line of descent. From an animal of this type the late Oligocene genera of ctenodactylids could have been easily derived. Ctenodactylids evidently arose and first radiated in Asia with the group persisting there until the Pliocene. Sometime during the Miocene a Tataromys-Wko. stock migrated into North Africa where it gave rise to Africanomys. From this base, the group radiated into the four genera of ctenodactylids which are now found living in North Africa. The Asiatic portion of the family evidently did not persist after the Pliocene with the termi- nal genus, Sayimys, playing no part in the ancestry of the African radiation. Suborder indet. Family thryonomyidae Pocock 1922 Genus paraulacodus Hinton Type species. Paraulacodus indiciis Hinton 1933, p. 621. Diagnosis. LJpper incisor with two grooves; cheek teeth increase in size from P^-M^; mure complete on P^-M^; metaloph not completely fused into posteroloph on M^; central valley wide on P'^-M^, open buccally; ectolophid complete on Mg; anteroconid on Mg. Included species. Type only. Range. ?Upper Chinji Zone, Siwalik Series, Pakistan. 244 PALAEONTOLOGY, VOLUME 15 Paraulacodus indicus Hinton Text-fig. 2 1933 Paraulacodus indicus Hinton, p. 621 Holotype. G.S.I. D283, partial right maxillary with Hypodigm. G.S.I. D281, left upper incisor, D282 fragment of right mandible with Ms and the type. TEXT-FIG. 2. Paraulacodus indicus, all approx, x 6. a. External view, P^-M\ G.S.I. D283, holotype. b. Internal view, same. c. Occlusal view, same. d. Posterior view, RMj, G.S.I. D282. e. Occlusal view, same, f, g, h. Lateral, medial, and anterior views of upper incisor, G.S.I. D281. Horizon and locality. The type D283 is listed on a sheet sent by the Indian Geological Survey to Dr. Hinton as being unregistered and locality unknown, horizon Upper Chinji ?. D282 is also unregistered but the locality is given as near Chinji, Salt Range and horizon as upper Chinji. The incisor, lamentably, is the only specimen catalogued with a register number [Rie/sosj locality is given as ‘below Kookar Dhok, Attock District, Salt Range area. Upper Chinji Zone’. There is no basis for assuming that these specimens were associated in any way when collected although they were all BLACK: SIWALIK RODENTS 245 in one vial when I received the collection. Likewise, there is no certainty that these specimens are contemporaneous or from the same approximate horizon. Diagnosis. Same as for genus. Description. The upper cheek teeth, P^-M^, are essentially identical in structure differing primarily in an increase in size from to M-. Also, on there is preserved a short remnant of the metaloph with a very shallow pit between it and the posteroloph. On P^ and the metaloph and posteroloph are completely fused. The teeth have three lophs with the anteroloph and protoloph separated by a narrow valley while the proto- loph and posteroloph are separated by a wide central valley which opens buccally. The mure is complete on P^-M^ with the narrow lingual valley curving anteriorly behind the protocone as it passes into the tooth. The lower molar also displays three lophs with the valleys separating the lophs of nearly equal size. The protolophid and hypolophid both run at right angles to the long axis of the tooth. The posterolophid curves from the hypoconid through a distinct hypoconulid around to the base of the entoconid. The posterolophid lies slightly below the level of the protolophid and hypolophid. There is a very faint line of separation between the hypoconid and buccal end of the hypolophid; nevertheless, the buccal valley is completely closed off from the posterior valley. The posterior arm of the proto- conid forms most of the ectolophid passing directly posteriorly to fuse with the buccal end of the hypolophid. The upper incisor displays two grooves which set off a wide median ridge on the anterior face of the tooth. These grooves are set in equally from the lateral and medial margins of the tooth. Enamel overlaps only slightly onto the side of the incisor. In cross section the tooth is narrowly triangular with the posterior border rounded. Measurements in mm a-p tr p 3-20 210 P' 2-55 2.95 Ml 2-55 3.45 2-95 4-00 Ma 3-60 3-50-3-20 Discussion. This is the first and only record of the Thryonomyidae, or cane rats, in Asia. The group today is restricted to Africa south of the Sahara and there is only a single living genus with six species. Walker (1964, p. 1069) gives a geologic range of Miocene to Recent in Africa and Pliocene of Europe and Asia for the Thryonomyidae but to my knowledge there is no African record earlier than the Pleistocene and there is no European record. Those genera listed in Simpson (1945) as ‘^Thryonomyidae incertae sedis are now considered to be members of the Eamily Rhizomyidae (Wood 1955, 1968). The identification of a thryonomyid in Asia on the basis of only a few teeth is of course open to question. However, many other Asian-African ties seen in the Siwalik fauna suggest that the presence of cane rats in Asia during the later Tertiary is certainly a possibility to be considered. These faunal similarities coupled with the rather remark- able morphological approach of Paraulacodiis to Thryonomys strongly suggest, to my 246 PALAEONTOLOGY, VOLUME 15 mind at least, that cane rats were part of the early Pliocene Asiatic fauna south of the Himalayas. Other than the details of morphological proximity (i.e. the grooved incisors, the three lophed upper and lower cheek teeth, the construction of the mure and ectolophid) little can be said about the relationship of Paraulacodus to Thryonomys. The Siwalik form is certainly much more generalized in structure with the wide posterior valley of the upper cheek teeth and the wide valleys of the lower molar than is the Recent genus. Nevertheless, there is great overall resemblance between the two genera and Hinton’s (1933) original description of this material as being related to the Recent Thryonomys seems probable. Lavocat (1961) and Wood (1968) would derive the Thryonomyidae from the African Phiomyidae. This certainly seems the most probable ancestry for the group on the basis of available evidence. There is nothing known in the Tertiary fauna of Europe or Asia which could serve as an ancestor for the Family. If one assumes an African origin for the Thryonomyidae from some mid-Tertiary phiomyid, then ParaJaiicodus probably moved from Africa to Asia at the time that ctenodactylids were moving in the other direction. Suborder hystricomorpha Brandt 1855 Family hystricidae Burnett 1830 Genus sivancanthion Colbert 1933 Type species. Sivancanthion cornplicatiis Colbert 1933, p. 3. Diagnosis. ‘An hystricomorph of medium size, considerably smaller than the modern species of Hystrix and Acanthion. Dental formula 1-0-1-3. Angle of mandibular ramus very strong, as in other Hystricidae. Hystricomorph pattern of the molar enamel complicated by secondary foldings.’ (Colbert, 1933). Sivancanthion complicatus Colbert 1933 Sivancanthion complicatus Colbert, p. 3. Holotvpe. A.M.N.H. 19626, a partial left mandible with P4-M2 and a partial right mandible with P4-M2. Horizon and locality. Chinji Zone, level of Chinji Rest House, 4 miles northeast of Chinji Rest House, Salt, Range northern Punjab. Diagnosis. As for genus. Description. This material has been adequately described by Colbert. Discussion. Colbert considered Sivancanthion complicatus to be a specialized offshoot from the main evolutionary sequence leading to Acanthion. Genus hystrix Linnaeus 1758 Hystrix sivalensis Lydekker 1878 Hystrix sivalensis Lydekker, p. 98 Holotype. G.S.I. D96, a partial right mandible P4 (incomplete) and Mj-Mj. BLACK; SIWALIK RODENTS 247 Horizon and locality. Siwaliks, Punjab. Lydekker (1884) could give no more precise data for the type specimen which was found by Mr. Theobald. Matthew (1929, p. 559) states that the type is from the Middle Siwaliks of Hasnot, Punjab. Diagnosis. P4 large; cheek teeth low crowned. Description. This specimen has been described by Lydekker (1884), Matthew (1929) and Colbert (1935). Hystrix cf. H. leucurus Text fig. 3 1884 Hystrix sivalensis Lydekker (in part), p. 110, fig. 5. 1929 Hystrix cf. leucurus Matthew, p. 559, fig. 55. 1935 Hystrix sivalensis Colbert, p. 72, fig. 32. Specimens: B.M. 15923, immature skull and jaws; A.M.N.H. 19909, LMi. Discussion. These specimens are from the Upper Siwaliks and have much higher crowned cheek teeth than those of H. sivalensis. Matthew ( 1 929) was evidently the first to recognize that this material was distinct from the earlier H. sivalensis. As Matthew states (1929, p. 560), this material may well belong to a distinct species ancestral to H. leucurus. Colbert assigned the AMNH lower molar to H. sivalensis but this tooth is much higher crowned than is M^ in H. sivalensis and compares favourably with the BM skull and jaws in this character. The illustration prepared by Mr. Terzi for Dr. Hinton of the British Museum skull and jaws is included here as an adequate illustration of this denti- tion has never been published. Suborder myomorpha Brandt 1855 Family rhizomyidae Miller and Gidley 1918 Specimens belonging to various members of this Family are by far the most common of Siwalik rodent fossils. While some genera, i.e. Kanisamys and Protachyorctes, are clearly distinct from the modern Rhizomys, Cannomys, and Tachyoryctes, a larger number of specimens are difficult to distinguish from Rhizomys. Several genera from the Chinese Tertiary and one from the Siwaliks have been described on the basis of sup- posed distinctions between the extinct populations and modern species of Rhizomys. These genera are : Pararhizomys Chardin and Young 1931, p. 11. Distinguished from Rhizomys by small size, simple molar pattern, and low crowned molars; Pontian of China. Tachyoryctoides Bohlin 1937, p. 43. Distinguished from other rhizomyids by anterior cingulum which is free at its lingual and buccal ends, there being short valleys be- tween the anterior cingulum and metaconid and protoconid. M^-Mg have a square occlusal outline and the occlusal pattern of M^ is quite different from that of the other genera; late Oligocene of China. Brachyrhizomys Chardin 1942 (original reference not seen). Distinguished from other rhizomyids by brachyodont cheek teeth (Schaub 1958, p. 718), otherwise with pattern as in modern Rhizomys (Bohlin 1946, p. 68). Rhizomyoides Bohlin 1946, p. 68. Distinguished from Rhizomys by the presence of three main lingual re-entrants in all lower molars; Miocene-early Pleistocene of India and Pakistan. 248 PALAEONTOLOGY, VOLUME 15 TEXT-FIG. 3. Hystrix cf. H. leiicurus, B.M. 15923. a. Ventral and b, lateral views of skull, c. d, and e. Occlusal views LM®, RM^-M^ f. Lateral view LMi-Mj, occlusal view Mg. g. Occlusal view, Mg. I have not had an opportunity to see any of the material assigned to Tachyoryctoides, Pararhizomys or Brachyrhizomys. For this reason and as these genera are based on material from China which was evidently a distinct and separate faunal province from India, at least during the Pontian (Kurten 1952, p. 31), I have not considered the validity of these taxa in discussion of the various Siwalik rhizomyid species. The three modern rhizomyid genera inhabit Africa (Tachyoryctes) and southeastern Asia {Rhizomys and Cannomys). Cannomys is monotypic while three species of Rhizomys BLACK: SIWALIK RODENTS 249 (Walker 1964, p. 867) and fourteen (Allen 1939) or two (Bigalke 1968, p. 276) of Tacky oryctes are presently recognized. The cheek teeth of Tachyoryctes and Cannomys are higher crowned than are those of Rhizomys. The incisors are heavier in Rhizomys than in either Cannomys or Tachyoryctes and the upper incisors of Rhizomys are opistho- dont (project nearly vertically) while those of Cannomys and Tachyoryctes are proodont (project forward). In Rhizomys the proximal end of the massive upper incisor lies just above the divergent roots of Mj and has suppressed any development of a hypsodont first upper molar. Suppression of hypsodonty in an upper molar must of necessity be coupled with suppression of hypsodonty in the opposing lower. Consequently, in Rhizomys but not in Cannomys or Tachyoryctes, the first upper and lower cheek teeth are lower crowned than are the two behind. This character can be seen in many of the fossil specimens and has been quite useful in helping to determine relationships of the extinct forms. Finally there is a considerable difference in the shape of the lower incisor between the three living species of Rhizomys. The lower incisor is nearly equilaterally triangular in R. sinensis; it is greatly compressed transversely in R. priiinosus; and it is massive and nearly triangular in R. sumatrensis. This range of variation of incisor shape is also seen in the Siwalik species. Two distinct groups of rhizomyids can be recognized in the Siwalik material. One appears to be related to the Recent African Tachyoryctes while the other includes Rhizomyoides and Rhizomys. These two lines of rhizomyids can be recognized as distinct back into the Miocene, Chinji Zone, where Kanisamys indicus and Rhizomyoides pimjabiensis occur together. I have retained Bohlin’s genus Rhizomyoides for one group of the Siwalik rhizomyids. In order to do so, I have had to emend his diagnosis. There is only one feature which consistently distinguishes all fossil species from Rhizomys. This is the presence of three lingual re-entrants on Ma but not on all the lower molars as he thought. Rhizomyoides was undoubtedly ancestral to Rhizomys and possibly to Cannomys. Kanisamys stands in a similar position to the Recent Tachyoryctes through Protachy oryctes. Tachyoryc- toides, the oldest known rhizomyid may occupy an ancestral position for all later rhizo- myids but there is a considerable gap between Tachyoryctoides of the upper Oligocene and Rhizomyoides and Kanisamys of the upper Miocene. No new species of rhizomyids are added to those already described. However, the full description of the specimens available to Hinton does add significantly to our knowledge of the Siwalik rhizomyids. Genus rhizomyoides Bohlin 1946 Type species. Rhizomys sivalensis (Lydekker) 1884. Emended diagnosis. Three main lingual re-entrants in M2. Included species. Rhizomyoides sivalensis, R.punjabiensis,R.nagrii,R.pilgrimi,R.pinjoricus. Range. Chinji, Nagri and Pinjor Zones of the Siwalik series, Miocene to Pleistocene. Rhizomyoides sivalensis (Lydekker) Text-figs. 4-5 1884 Rhizomys sivalensis 'Lydekker, p. 106. 1933 Rhizomys lydekkeri Hinton, p. 621. 1946 Rhizomyoides sivalensis (Lydekker) Bohlin, p. 68. 250 PALAEONTOLOGY, VOLUME 15 TEXT-FIG. 4. Rhizomyoides sivalensis, G.S.I. D277. a. Lateral view of skull fragment, X 3. b and c. Lateral and occlusal views, LM^-M^, X 7. Holotype. G.S.I. D97, partial left mandible with M2-M3 (figured by Lydekker, 1884, fig. 1, p. 106). Referred specimens. G.S.I. D275 (formerly D97a) partial right mandible with M2-M3 and D276 (formerly D97b) partial right mandible with M1-M3, D277, partial skull and jaws with R and L M 1/1-M3/3, BM 15925, type of R. lydekkeri, partial right mandible with M1-M3, 15926 partial right mandible with M2, 15927, partial left mandible with M1-M2 and 15927a, two isolated molars. Horizon and locality. Probably Middle Siwaliks for the type. The G.S.I. registry number for the type and all other specimens except D277 is H.T. 17 with locality given as Haritalyangar, Simla Hills. D277 is listed as from Asnot, Punjab, Middle Siwaliks. The BM specimens are described (Lydekker 1885, p. 233-334) as being from the Pliocene BLACK: SIWALIK RODENTS 251 TEXT-FIG. 5. Rhizomyoides sivalensis, G.S.I. D277. a. Lateral view mandible, x 3. b and c. Medial and occlusal views Mj-Mg, X 7. of the Siwalik Hills. In sum all the specimens may be from the Nagri Zone, Middle Siwaliks. Emended diagnosis. Medium sized; mandible rather shallow and thin; incisors only slightly deeper than wide; molars hypsodont; anterior and central lingual re-entrants confluent internally on Mg only during early wear stages; anterior lingual re-entrant of Mg with anterior and posterior arms. Description. The mandible is rather shallow under Mj-Mg in D277 but is deeper in the in the specimens from Haritalyangar. The masseteric ridge is also more swollen on the mandibles from Haritalyangar than on those from Asnot. There are also slight dental differences between the specimens from the two localities. These include some- what larger overall size and greater reduction in the lingual re-entrants on M^-Mg in the Haritalyangar material. All of these characters suggest that the type and other C 8908 S 252 PALAEONTOLOGY, VOLUME 15 specimens from Haritalyangar, listed together under the G.S.I. registry number H.T. 17, are slightly younger than the associated partial skull and jaws from Asnot. Other than the slight size difference and reduction in the length of the lingual re- entrants, the molars of all specimens are quite similar. They are moderately hypsodont with Mg having three lingual re-entrants while Mi and Mg have two. The small anterior fossettid seen in Mi-Mg in text-fig. 5, has been isolated from the end of the anterior lingual re-entrant. At advanced wear stages there are three isolated internal fossettids on Mg but the anterior two of these are both derived from the anterior lingual re-entrant, not from two separate lingual re-entrants. The upper cheek teeth have their primary buccal fossettids, mirroring the condition seen in Mg-Mg. The crown height of the molars is shown in text-fig. 4. M^ is longer than either M^-M^ but is also lower crowned. The single lingual re-entrant of M’^-M^ is rather short. Upper and lower incisors are slightly deeper than wide and both have the anterior face of the teeth rounded. The enamel overlaps on to about one-fifth of the lateral and medial faces of both the upper and lower incisors. There is a distinct median ridge along the centre of the anterior face of the lower incisor. Discussion. As indicated in text-fig. \ \,Rhizomyoides sivalensis appears to be areasonable ancestor for Rhizomyoides pinjoricus and hence, ultimately, of Recent Rhizomys. Rhizomyoides pimjabiensis (Colbert) 1933 Rhizomys pimjabiensis Colbert, p. 1. Holotype. A.M.N.H. 19762, partial right mandible with Mj-Mg. Referred specimen. G.S.I. D287, a partial mandible with Mg-Mg and posterior bit of Mj. Horizon and locality. Type from the Lower Siwaliks, Chinji Zone, Miocene, near the base, 23 miles west and north of Bilaspun, Punjab. G.S.I. D287 from the Middle Siwaliks, Nagri Zone, 1^ miles west of Kaulial, Attock District, Punjab. Emended diagnosis. Smallest species of Rhizomyoides', mandible light; lower incisor nearly equilaterally triangular in cross section; cheek teeth brachyodont; three lingual re-entrants on Mg, two on Mg. Description. This is an extremely small species (Table 1) and is by far the most general- ized of Rhizomyoides species. The cheek teeth are low crowned and the mandible is slender and shallow. The incisor of Rhizomyoides punjabiensis is nearly equilaterally triangular in cross section. It shows a flattened medial face and slightly convex lateral one (Colbert 1933, p. 2). The occlusal surfaces of the cheek teeth are tilted so that the lateral margins of Mg-Mg are higher than the medial margins; they face inward and upward. This orientation of the lower cheek teeth is characteristic of all known species of rhizomyids, fossil and Recent. The lingual and buccal re-entrants of Mg-Mg are shallow and the anterior and middle lingual re-entrants of Mg tend to fuse with wear leaving two lingual re-entrants in Mg as there are in Mg. Discussion. Hinton (1933, p. 621) evidently did not recognize that D287 was a specimen of Colbert’s species, as he stated ‘This [R. punjabiensis] is a smaller species than any of TABLE 1. 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