cetitertaesets eescrermtststs seterestite Hi oy + = Ss 7 ra SS i 7 ‘ i=ag? gf po tt. “ cfs iT aa 2s en wi pees “ pik eine I eel aad 6 : ie Fa Ke © aa : Pe eo TR AE. ahs wiyt. ae An © rary ff a is f f ae a Lo BRITISH AVONIAN (CARBONIFEROUS) CONODONT FAUNAS, AND THEIR VALUE IN LOCAL AND INTERCONTINENTAL CORRELATION F. H. T. RHODES, R. L. AUSTIN, and E. C. DRUCE % ay BULLETIN OF _ THE BRITISH MUSEUM (NATURAL HISTORY) _ GEOLOGY SUPPLEMENT 5 ! LONDON : 1969 Freee tes aie ET aa tate Lik coe fei x ris BRITISH AVONIAN (CARBONIFEROUS) CONODONT, BAUNAS, AND. THEIR. VALUE IN LOCAL AND INTERCONTINENTAL CORRELATION BY FRANK HAROLD TREVOR RHODES, RONALD LEYSHON AUSTIN and EDRIC CHARLES DRUCE 31 Plates ; 92 Text-figures BUELETIN OF THE BRITISH MUSEUM (NATURAL HISTORY) GEOLOGY SUPPLEMENT 5 LONDON : 1969 THE BULLETIN OF THE BRITISH MUSEUM (NATURAL HISTORY), instituted in 1949, is issued in five series corresponding to the Departments of the Museum, and an Historical series. Paris will appear at irregular intervals as they become ready. Volumes will contain about three or four hundred pages, and will not necessarily be com- pleted within one calendar year. In 1965 a separate supplementary series of longer papers was instituted, numbered serially for each Department. This paper is Supplement No. 5 of the Geological (Palaeontological) series. The abbreviated titles of periodicals cited follow those of the World List of Scientific Periodicals. World List abbreviation : Bull. Br. Mus. nat. Hist. (Geol.) © Trustees of the British Museum (Natural History) 1969 TRUSTEES OF THE BRITISH MUSEUM (NATURAL HISTORY) Issued 21 February 1969 Price {1a BRITISH AVONIAN (CARBONIFEROUS) CONODONA..BPAUNAS, AND THEIR S-ALUE IN .LOCAL AND INTERCONTINENTAL CORRELATION by Pon: f. RHODES; RYE ZACS PIN SE. C. DRUCE CONTENTS I. PURPOSE AND SCOPE OF PRESENT STUDY II. HisToRY OF PREVIOUS RESEARCH (a) Conodont research in Britain . (b) Carboniferous conodont zonation and cee III. STRATIGRAPHY (a) Introduction to ne eee of the Carbonierons of Britain : : - - : : F : (b) The Avonian succession . : (c) Previous research on the Gomcleinen of fhe decteiient ie the Carboniferous of Europe (d) The stratigraphy of areas from whieh conodonts are described . (i) The Avon Gorge, ‘Basel (ii) South Wales (ii) Shropshire . (iv) Yorkshire (v) Scotland IV. MeEtTHODsS OF STUDY V. CONODONT FAUNAS (a) General Review (b) Stratigraphical distribution of conodént faanas: (c) Avonian conodont biostratigraphical zones (d) Intra-Avonian correlation in Britain (i) Avon Se Sage Be (ii) Farlow (iii) Yorkshire (iv) Scotland (e) Correlation of the veuied His Europe and North ‘measles VI. SYSTEMATIC PALAEONTOLOGY . VII. SUMMARY AND CONCLUSIONS VIII. ACKNOWLEDGMENTS IX. REFERENCES. X. APPENDIX (a) Sample Resister : (b) Register of Figured Specimens XI. INDEX. ; : : c 4 BRITISH AVONIAN CONODONT FAUNAS ABSTRACT THE conodont faunas of the Lower Carboniferous of the South West Province, the Yoredales and the Midland Valley of Scotland are described. A complete series of samples was collected from the Avon Gorge section, Bristol, and also from composite sections from the North Crop of the South Wales Coalfield, the Clee Hills, Wensley- dale, Dunbar, Fife, Roxburgh, Midlothian, Ayrshire and Argyll. A total of over 600 samples was collected at intervals ranging from ten feet (Avon Gorge) to six inches (Dunbar). The calcareous samples were dissolved in either 8° acetic acid or 15% formic acid, and the argillaceous samples subjected to 100 vol. hydrogen peroxide. Some 3 tons of rock was processed. All collected sections are illustrated and charts of the conodont abundance (number of specimens per kilog.) and weight of rock dissolved, together with sample numbers, are presented. In all, the samples yielded over 25,000 identifiable specimens, referable to 167 species, belonging to 29 genera, of which 2 named genera (Clydag- nathus and Patrognathus), 40 species and 13 subspecies are new. All species are described and illustrated, and range charts of their vertical distribution are pre- sented. The faunas are divided into a total of 14 conodont assemblage zones and correla- tions are made between standard sections in the various Carboniferous provinces of Great Britain. There is a strong general similarity between the succession of conodont faunas in North America, Germany and Britain, although there are also some striking local differences. These are analysed in the light of conodont phylo- geny, distribution, and of possible sedimentary breaks in various sections. Correla- tions are made with the standard goniatite sections of Germany and with the type sections of the Mississippi Valley. Within the South West Province the basal part of the K Zone is correlated with the Cu I goniatite zone and the upper part with Cu II « ; the uppermost K to the Upper Se Subzone is correlated with the Cu II Zone, and the Dj, Dg, and D3 Subzones with the Cu III goniatite zone. The upper part of the Calciferous Sandstone Measures of the Midland Valley of Scotland is of Cu III « age, the Lower Limestone Group is of Cu III @—y age, and the Upper Limestone Group is of E;—-E2 (Namurian) age. I. PURPOSE AND SCOPE OF PRESENT STUDY Conodonts were first described in 1856, and, although they were described in only a few papers in the subsequent seventy-five years, there is now a total of some 1,200 publications devoted to them. Doubt and controversy concerning their function and affinities remain greater now than a century ago. One recent author (Fahlbusch, 1964 ; see also Beckmann et al., 1965) has argued that they represent algae, and another that they were internal supports in some ciliated tentacle apparatus of an unknown filter-feeding organism (Lindstrém, 1964), while still another (Foss, 1960) has suggested that the similarity of their carbonate fluorapatite composition to that of scales of the Ordovician chordate Astraspis implies an affinity between the two. BRITISH AVONIAN CONODONT FAUNAS 5 Studies of amino acid content and of ultramicroscopic structure of conodonts at present in progress may provide important new information on their affinities (Schwab, 1966 ; Armstrong & Tarlo, 1966). In spite of the uncertainty concerning their nature and function, studies on cono- dont successions during the last decade have shown conodonts to be one of the most sensitive and useful fossil groups available for stratigraphic correlation. Recent work by German palaeontologists (see p. 8 for detailed references) on the conodont faunas of the type sections of the Upper Devonian and Lower Carboniferous has provided the means of making even more precise regional correlation than those recognized by goniatites upon which “ standard ”’ correlations have been established (see, for example, Ziegler 1962). Furthermore, a broadly similar zonal sequence of conodonts has been established in the Mississippi Valley. The purpose of the present paper is to describe conodont faunas from the “ Lower ”’ Carboniferous rocks of the type section in the Avon Gorge, Bristol, from various parts of South Wales, and from Shropshire, Yorkshire and Scotland. Over 600 samples from these areas have been processed, and have yielded over 25,000 identifiable specimens. The sequence of the conodont faunas at present described provides the basis for a conodont zonation, which not only assists intra- and inter- basinal correlation in Britain, but also allows the first precise correlation with North America and Continental Europe. iE HISTORY OF PREVIOUS RESEARCH (a) History of previous conodont research in Britain Conodonts were first described by Pander (1856) and, although they were reported shortly afterwards from several localities in Britain, comparatively little attention has been paid to them in this country. Walliser (1958) recorded the oldest known stratigraphic occurrence in Britain, when he discovered a “‘ paraconodont ”’ from the Upper Cambrian Comley Limestone of Shropshire. Ordovician conodont faunas from Britain have been described from the Arenigian of the Southern Uplands (Smith 1907 ; Lamont & Lindstrém 1957) ; the Llan- deilian Llandeilo Limestone of Carmarthenshire (Rhodes 1953), and Castell Lime- stone of Pembrokeshire (Bergstr6m 1964) ; the Upper Llandeilian and Lower Caradocian of the Southern Uplands ; the Caradocian wilsoni Shales of the Southern Uplands (Lindstrém 1957), Gelligrin, Pen-y-garnedd, Crig and Bryn Pig Limestones of Wales (Rhodes 1953: Lindstrém 1959: Bergstrém 1964) and the Ashgillian Keisley Limestone of Westmorland (Rhodes 1955) and Birdshill Limestone of Carmarthenshire (Bergstrém 1964). A number of early workers, including Harley (1861), Moore (1864), Young (1880A) and Smith & Jones (1881), recorded conodonts from Silurian rocks in Britain. A basal Llandovery fauna referable to the celloni Zone of Walliser (1964) from the Malverns was described by Brooks & Druce (1965). Llandoverian conodonts have also been noted by Whittard (1927) from the Pentamerus Beds of Shropshire and by Squirrell & Tucker (1960) from the Upper Llandoverian of the Woolhope Inlier. 6 BRITISH AVONIAN CONODONT FAUNAS Wenlockian conodonts have been collected from the Welsh Borderland by Hill (1936) and systematically described from Usk by Austin & Bassett (1967). Conodonts from the Woolhope, Wenlock, Aymestry and Whitcliffian Limestones of the Welsh Borderland were reported by Ireland (1958, 1962). Rhodes (1953) with Newall (1963) systematically described a fauna from the Aymestry Limestone of Shropshire and South Staffordshire. Squirrell & Tucker (1960) listed Upper Ludlovian cono- donts from the Woolhope Inlier and Collinson & Druce (1966) systematically described a fauna from the Whitcliffe Flags of Shropshire which was referable to the eosteinhornensis Zone of Walliser (1964). Dineley & Rhodes (1956) described Devonian conodonts from the Upper Givetian at Torquay, from the Lower Frasnian near Chudleigh, from the Lower Frasnian at East Ogwell and from the Lower Pilton Beds (Strunian) at Saunton, North Devon. They also described (1957) an Upper Devonian fauna from the limestones of the Bishopsteignton borehole. Matthews (1962) reported a late Eifelian fauna from a Middle Devonian limestone at Neal Point in the Tamar Valley. | House (1963, table 2) and House & Selwood (1964) have summarised known Devonian conodont occurrences in South West England. The only new conodont record noted by House & Selwood was an Upper Givetian conodont fauna from the Marble Cliff Beds, identified by Rhodes. Rhodes also identified Lower Givetian conodonts from the Middle Gramscatho Limestones for Hendriks (1966). Other limestones yielding Siegenian, Emsian and Middle Devonian conodonts are also mentioned. Ziegler (Hendriks 1966) has also extracted Frasnian conodonts from limestones interstitial with the Mullion Island pillow lavas. British Lower Carboniferous conodont studies have been few and brief. Moore (1863, 1870) listed conodonts from the Carboniferous Limestone of Yorkshire and Cumberland, Fowler (1955) mentioned conodonts obtained from a borehole in South- East County Tyrone, Eire, and Robbie (1955) reported conodonts from the Rossmore and Edenbrook beds of Lower Carboniferous age obtained from the subsurface at Edenork, County Tyrone, Ireland. Dineley & Rhodes (1956) studied eight samples from the Tournaisian of South West England. Small faunas from the Shirehampton Beds, the Lower Limestone Shale, the Black Rock Limestone, the Fish Bed and Horizon y, collected in the Avon Gorge, Bristol, were described, as also were faunas from the ? Black Rock Limestones of Windsor Hill, Somerset and Waterlip Quarry, Somerset. Matthews (1961, 1966) has identified anchoralis faunas collected at Viverdon Down near Callington, and from the St. Mellion area of South West England. Varker (1967) has described conodonts referable to the genus A patog- nathus from the Yoredales of Northern England. Young (1880, 1880A) mentioned the occurrence of Scottish Carboniferous Lime- stone conodonts, in addition to those of the Silurian and Devonian of England. Smith (1900) reported conodonts from the Carboniferous limestones of Western Scotland and figured those described by Hinde (1879, 1900). These were sub- sequently refigured and redescribed by Clarke (1960) who also described faunas from the Scottish Carboniferous Limestone Series. Craig (1952, 1954) reported conodonts from the Top Hosie Shale, of Lower Carboniferous age, near Kilsyth, Scotland. BRITISH AVONIAN CONODONT FAUNAS a Namurian conodonts were found in a borehole in a Yoredale type of deposit in the Cleveland Hills by Fowler (1944). Dunham & Stubblefield (1945) noted the occurrence of a platform conodont in the Colsterdale Marine Beds of the Millstone Grit of Yorkshire. Conodonts have also been noted in the Millstone Grit of the Midlands by Stevenson & Mitchell (1955). The only published systematic des- cription of British Namurian conodonts is that by Higgins (1961) who described a fauna from the Namurian of North Staffordshire. Collinson & Druce (in press) have described a conodont fauna from the lower boundary of the Namurian in County Clare, Eire. There have been no detailed systematic descriptions of British Pennsylvanian conodonts, but many workers have noted the presence of conodonts in the British Coal Measures. In Scotland, Currie, Duncan & Muir-Wood (1937) described conodonts from Skipsey’s Marine Band, and the Upper Coal Measures in Central and West Scotland. Manson (1957) listed conodonts from a marine band in the Anthra- conaia modiolaris Zone of Scotland. Smith (1907A) recorded conodonts from the Upper Coal Measures (above the Craigmore Ironstone). Stevenson & Mitchell (1955), Stubblefield & Calver (1955), Mitchell (1954) and Eden (1954) reported conodonts from the Midland Coalfields, as also have Mitchell & Stubblefield (1941) from the Leicestershire and South Derbyshire Coalfield, Mitchell, Stubblefield & Crookall (1942, 1945) from the Warwickshire and northern part of the South Staffordshire Coalfields, Edwards & Stubblefield (1948) from the Derbyshire and Nottinghamshire Coalfields, and Edwards (1954) from the Clown Marine Band in Derbyshire and Nottinghamshire. Earp & Magraw (1955) listed conodonts from the Tonge’s Marine Band in the Lower Coal Measures of Lancashire, and Magraw (1957) recorded conodonts from various marine bands in Lancashire, Derbyshire and Yorkshire. Ramsbottom (1952) and Woodland, Archer, Evans & Calver (1957) noted the presence of conodonts in the South Wales Coal Measures. There has been no reference to the occurrence of post-Pennsylvanian conodonts in the British Isles. (b) Carboniferous conodont zonation and correlation Although the Upper Devonian and Lower Carboniferous rocks of West Germany, the latter of which provide the standard for Carboniferous correlation, are tradi- tionally correlated on the basis of their cephalopod faunas, recent studies by German palaeontologists on the conodont faunas have shown that the latter offer a new degree of precision in problems of regional correlation. The most notable contribu- tions in this field are those of Bischoff (1955, 1956, 1957), Bischoff & Ziegler (1956, 1957), Bartenstein & Bischoff (1962), Boger (1962), Kronberg, Pilger, Scherp & Ziegler (1960), Meischner (1962), Sannemann (1955, 1955A), Voges (1959, 1960), Walliser (1958, 1960) and Ziegler (1958, 1959, 1962, 1962A, 1962B). These workers described conodonts, which were associated with the classic Devonian and Lower Carboniferous cephalopod zones in West Germany, and a detailed Devonian and Lower Carboniferous conodont faunal succession has thus been established. 8 BRITISH AVONIAN CONODONT FAUNAS This conodont succession has been applied to rocks of Upper Devonian and Carboniferous age in other parts of Western Europe, notably by Dvorak & Freyer (1961), Helms (1959, 1961), and Miiller (1959) in East Germany ; Flugel & Ziegler (1957) in Austria ; Lys & Serre (1958), Higgins (1962), Higgins, Wagner-Gentis & Wagner (1964) in Spain ; Lys & Serre (1957), Lys, Serre & Deroo (1957), Lys, Serre, Mauvier & Grekoff (1961) in France and the Sahara ; Boogaard (1963) in Portugal ; and by Serre & Lys (1960) and Conil, Lys & Mauvier (1964) in Belgium. Germany The zonation of the Lower Carboniferous in Germany is based chiefly on the work of Bischoff (1957) and Voges (1959). Bischoff (1957) studied the conodont faunas of the Wocklumeria, Gattendorfia, Pericyclus and Goniatites Stages of the Rhenoherzynicum. He subdivided the Pericyclus Stage into two conodont subzones—the Siphonodella Subzone (Cull «—8) and the anchoralis Subzone (Cull y). He also described the conodont faunas of the three goniatite zones of the Gonzatites Stage. Voges (1959) described conodonts from the Lower Carboniferous Gattendorfia and Pericyclus Stages. He recognized three zones within the Gattendorfia Stage: the Gnathodus kockeli—Pseudopolygnathus dentilineatus Zone ; the Siphonodella— Pseudopolygnathus triangulus inaequalis Zone and the Siphonodella—Pseudopoly- gnathus triangulus triangulus Zone. Three zones were recognized by Voges within the Pericyclus Stage ; the Siphonodella crenulata Zone (Cull «), which was sub- divided into a lower and an upper subzone, the Scaliognathus anchoralis Zone (Cu II By), and a Scaliognathus anchoralis—Gnathodus bilineatus “ interregnum” (Cu II 3). Voges thus gave a more detailed and refined zonation than Bischoff (1957) for the Gattendorfia and Pericyclus Stages, and also differed from Bischoff by extend- ing the Scaliognathus anchoralis Zone into Cu II £ (Bischoff confined the anchoralis Zone to Cu II y). The German workers were thus the first to attempt a conodont zonation of the Lower Carboniferous. Whilst not detracting in the least from the excellent work of Bischoff and of Voges it is true to say that there are a number of deficiencies and gaps in our knowledge of German conodont faunas. The reasons for these gapsare twofold. Firstly the nature of the outcrops is such that it is impossible to collect from con- tinuous exposures. The different samples collected by both Voges and Bischoff are from widely separated areas. Secondly, the sediments are such that in any one locality not all horizons yield conodonts (e.g. Hangenberg Schiefer, and the cherts immediately beneath the ‘“‘ Erdbach Kalk’’). There has also been a marked tendency for German conodont workers to give total stratigraphic ranges of species, rather than the exact distribution and abundance of individual species, although more recently, for example Kronberg, Pilger, Scherp & Ziegler (1960) and Ziegler (1963), these have been given. It is becoming increasingly apparent from conodont studies in other parts of the world that numbers of stratigraphic breaks exist in the German succession, even where these have not hitherto been suspected. BRITISH AVONIAN CONODONT FAUNAS 9 The Franco-Belgian Province Studies of the Franco-Belgian Lower Carboniferous conodont faunas are com- paratively recent. Serre & Lys (1960) described the distribution of Tournaisian and Viséan conodonts in the Avesnois, Boulonnais and Hainault regions of Northern France and Belgium, and Conil, Lys & Mauvier (1964) recorded the ranges of conodont species in the type formations of the Dinantian in the Franco-Belgian Province. More recently Bouckaert & Ziegler (1965) have published an account of the conodont faunas of the Famennian Stage in Belgium. Conodont studies in the Franco-Belgian Province are important because these sections have yielded the type specimens of many Lower Carboniferous cephalopods. Unfortunately, however, neither Serre & Lys nor Conil, Lys & Mauvier have system- atically described or illustrated their specimens, and they have given no exact distribution or abundance data for individual species. Thus the work at present is of limited value. Few correlations can be made, although one which can be made with a fair degree of certainty is based on the distribution of Scaliognathus anchoralis. This species is restricted to Tng, in the Franco-Belgian Province and to the Cu II 8 y horizon in Germany. This is important, because hitherto it has been con- sidered likely that the Tournaisian—Viséan boundary in Germany should be drawn at the base of Cu II 8 y, based on the distribution of Pericyclus princeps. This is the zonal fossil for Cu II « in Germany and was first found and described from the Tn 3c of Belgium. If the conodont correlations based on anchoralis are accepted, they are at variance with the “ well established ”’ goniatite evidence, although the literature does not contain a single reference to Pericyclus princeps having ever been found in Germany. It is therefore a very dubious “ zonal fossil ’’. The need for systematic descriptions and illustrations of the Franco-Belgian conodonts is thus urgent for it may provide the key for unravelling the German succession and for filling the gaps which are present in Germany. The United States Lower Carboniferous conodont research in North America began in the mid nineteen-thirties. Huddle (1934) described the conodont fauna of the New Albany Shale in Indiana and Branson & Mehl, working in Missouri, described the conodont faunas of the Bushberg Sandstone (1934A), of the ‘‘ Lower Mississippian Formations”’ (1938A), of the Caney Formation (1940) and of the Keokuk Formation in Iowa and Missouri (1941A). E.R. Branson (1934) also described conodonts from the Hannibal Formation in Missouri. Cooper (1939) described conodonts from the Bushberg Hannibal strata in Okla- homa and later, with Sloss (1943), described a fauna from a Lower Mississippian black shale in Montana and Alberta. Mehl & Thomas (1947) described the conodont fauna of the Fern Glen Formation in Missouri, and Thomas (1949) described the faunas of Lower Mississippian age from the English River and Prospect Hill Siltstones of South East Iowa. Hass described Lower Carboniferous conodonts from the Arkansas Novaculite of 10 BRITISH AVONIAN CONODONT FAUNAS Arkansas (1956A), the Maury Shale of Tennessee (1956), the Barnett Formation (1953) and the Chappel Limestone of Texas (1959). Scott & Collinson (1961) described a fauna from the Louisiana Limestone and from the McCraney Limestone. Youngquist & Patterson (1949) described conodonts from the Prospect Hill Sand- stone of lowa. The fauna of the Lower Mississippian Wassonville Dolomite of Iowa was described by Youngquist & Downs (1951). Youngquist, Miller & Downs (1950) described Burlington conodonts from Iowa. Rexroad (1957) described Chester conodonts from I[linois and later (1958) from the Glen Dean Formation. Rexroad & Clarke (1960) described Glen Dean conodonts from Kentucky, Virginia and West Virginia. Golconda Group conodonts were described by Rexroad & Jarrell (1961). Those of the Kinkaid Formation in Illinois were described by Rexroad & Burton (1961) and those of the Paoli and equivalent formations in Illinois by Rexroad & Liebe (1962). From the work of these and other workers, it became clear that conodonts were abundant in Mississippian rocks and were useful for correlation of strata. As a result, the Illinois State Geological Survey, in co-operation with the University of Texas, the State University of Iowa, Texas Technological College, the University of Houston, and the Indiana Geological Survey, conducted a programme of research in the Mississippi Valley. In 1962 Collinson, Scott & Rexroad published a paper in which they described 17 conodont biostratigraphic zones, which were present in the Mississippian rocks of the Mississippi Valley. The limits and characteristic species of each zone were described and they also attempted to correlate these zones with the conodont zones present in Germany. Subsequent workers have systematically described the faunas of the biostrati- graphic zones established in 1962. Thus Rexroad & Collinson (1963) not only described the conodonts of the St. Louis Formation, but also indicated, described and illustrated the species characteristic of the Taphrognathus varians—A patognathus Assemblage Zone and of the A patognathus ? geminus—Cavusgnathus Assemblage Zone. In the same way Rexroad & Scott (1964) when describing the conodont faunas of the Rockford Limestone and the lower part of the New Providence Shale of Indiana described and illustrated the conodont fauna characteristic of the Szphonodella tsosticha—S. coopert, Gnathodus seniglaber—Pseudopolygnathus multistriatus, Bactro- gnathus—Polygnathus communis and Bactrognathus—I aphrognathus Assemblage Zones. They also showed in tables the numerical distribution and stratigraphic ranges of specimens. Rexroad & Collinson (1965) provided the same data for the Taphrognathus varians— Apatognathus Assemblage Zone, when describing the conodonts of the Keokuk, Warsaw and Salem Formations of [linois. Rexroad & Furnish (1964) referred their fauna from the Pella Formation of South- Central Iowa to the Gnathodus bilineatus—Cavusgnathus charactus Assemblage Zone of the Mississippi Valley, and to the St. Genevieve Limestone in particular. Rexroad & Nicoll (1965) described the faunas of the Menard Formation, which they referred to the Kladognathus—Cavusgnathus naviculus Zone, drawing the lower BRITISH AVONIAN CONODONT FAUNAS II limit of that zone at the base of the Menard. Klapper (1966) described Upper Devonian and Lower Mississippian faunas from Montana, Wyoming and South Dakota, and identified the local equivalents of the German Cu I and Cu IT « faunas. These studies have provided a most useful basis for the correlation of our Avonian faunas with those of the Mississippi Valley. Australia Recent studies by Glenister & Crespin (1959), Glenister (1960), Jones & Druce (1966) and Glenister & Klapper (1966) have shown the similarity of European— North American Devonian and Lower Carboniferous conodont faunas to those of comparable age in Australia. Ill. STRATIGRAPHY (a) Introduction to the stratigraphy of the Carboniferous of Britain Rocks of Lower Carboniferous age form one of the most extensive outcrop belts in the geology of Britain but, in spite of their extensive outcrop, generally good expo- sure, and the wealth of study devoted to them, precise correlation is often difficult between basins, and sometimes also within them. The distribution and character of Lower Carboniferous rocks is so well known that it needs only the merest introduc- tion in a study such as this, as it has recently been reviewed by George (1958). Lower Carboniferous rocks were deposited on an archipelago-like basement (Fig. 1) dominated by a landmass to the north-west, by a caledonoid-trending massif which extended from north-eastern Ireland into the Southern Uplands, by a stable block in north-eastern England, and a great, east-west landmass, stretching from Leinster through Central Wales into the Midlands of England. To the south of this landmass, the south-western Province of the Carboniferous represented a basin of more or less continuous deposition, which extended westwards into Ireland and was bounded by a landmass in south-western Cornwall. It was marked by the deposi- tion of two distinctive facies groups. In the south, the Culm facies of Devon and Cornwall and southern Ireland included dark argillaceous and sometimes calcareous shales and mudstones, containing a few thin, impure, dark limestones and cherts, as well as subordinate sandstones and grits. To the north of this facies, in Somerset, Gloucestershire and South Wales, there was deposited the “‘ limestone facies,”’ consisting mainly of grey or light-blue bioclastic limestones, with subordinate dolomites, oolites and argillaceous limestones. These rocks contain a rich fauna of brachiopods and corals, as well as crinoids, ostracods, foraminifera and algae. In some parts of the section there is developed a “‘ lagoon’”’ facies, characterized by drab grey, calcite-mudstones, with subordinate calcareous shales and oolitic rocks. Calcareous algae, ostracods, gastropods and pelecypods are the main fossils of this group, which is present in the Modiola phase of south-western England. Both the Culm facies and the bioclastic limestone facies extend westwards into southern Ireland. Northern England was separated from Southern England for at least part of Carboniferous times, by the combined St. George’s Land—Midland Barrier. In the BRITISH AVONIAN CONODONT FAUNAS a JE ¢ ‘ALSTON =f —— aw y VASKRIGG ——==a aN t BLOCKS a = ose STAWES IC YORKSHIRE S— “YOREDALE Svaee CENTRAL PROVINCE = os — Ae Se = z ———= = ASKEATON S_=-_===_=. —— (= ST. GEORGE'S LAND +S FARLOW & ORETON — —— NORTH) CROP AVON GORGE ‘LIMESTONE FACIES * anicncl —— SOUTHWESTERN OVINCE ———————— ROX.=ROXBURGH MIO-LTHN =MIDLOTHIAN Fic. 1. Generalized palaeogeographic map of Britain during Early Carboniferous times, showing main depositional régimes,and localities described in the text. Based partly on George (1958) and Wills (1952). BRITISH AVONIAN CONODONT FAUNAS 13 Central Province, lying to the north of this barrier, rocks of Yoredale facies were deposited. These include cyclothemic limestones, non-marine sandstones, shale, and coal sequences, with a fauna of corals, brachiopods, bivalves, occasional goniatites and non-marine plants. Bioclastic limestones and spectacular reefs also developed in various places in this region, such as the reef knolls of Derbyshire and the Craven Lowlands, and the larger sheet-like apron reefs of Southern Ireland. In the Northumbrian trough, lying to the north of the Central Province, as well as in the trough of the Midland Valley of Scotland, which was separated from it, a distinctive facies of the Cementstone type was developed, consisting of alternating thin argillaceous limestones, sandstones and grey-black shales. Fossils are rare and include fish, ostracods, inarticulate brachiopods and spirorbid worms. These rocks are overlain by sandstones, coal-bearing strata and limestones, the total Northum- brian section including some 7,000 ft. of strata. In the Midland Valley of Scotland, a broadly similar variety of rock types is found, although there is no detailed equivalence in age ; clastic deposits predominate there, and include the Oil Shales and the Calciferous Sandstones. There are also thick lavas in places. In north-western Ireland great thicknesses of deltaic strata were deposited, which pass southwards into limestone-shale and bioclastic limestones (George 1955). Rocks of Lower Carboniferous age present formidable problems of correlation and these arise largely from the rapid and almost continuous lithological and faunal changes which they display. The general problems of correlation have been reviewed by Rayner (1953) and by George (1952 and 1958). The first successful attempt to provide a palaeontological subdivision of the rocks of the South-West Province was that of Vaughan (1905) who proposed the now widely-applied coral- brachiopod system for the limestones of south western England. This was based upon exhaustive and meticulous collecting of faunas, especially from the Avon Gorge. Vaughan established his zonal scheme on the first appearance of particular genera and species, although the zones as interpreted today are partly assemblage zones, based on the occurrence of a number of species. To a varying extent the demarca- tion of Vaughan’s zones was influenced by the marked lithological changes which occur in the Avonian strata of south-western England (see p. 17). It was early recognized that Vaughan’s zonal scheme was inapplicable to the different facies of northern England and in that area the work of Bisat (1924) on goniatites provided the basis for much of the present classification. Present views on the validity of these various zonal schemes are sharply divided. There is general agreement that, in the sense in which they were originally established by Vaughan, the coral-brachiopod zones can no longer be applied in detail, but some workers, especially Kellaway & Welch (1955), reject the whole zonal scheme which they represent. The detailed problems of correlation are discussed on p. 52. (b) The Avonian Succession The Avon Gorge, Bristol, has long been regarded as the type area for the British “ Lower ” Carboniferous. The base of the Lower Limestone Shale was selected by Buckland & Conybeare (1824) and by De la Beche (1846) as the base of the Lower CONODONT FAUNAS AVONIAN BRITISH ‘s]JUNWIOUYoI 19}e] pue UeYSsNeA JO UOT}eUOZ [LUTSTIO oY} SUIMOYS ‘ULIUOAY 9} JO UOISIAIpqns oy], AYVONNOS NVISIVNYNOL— NVASIA ——— —— N Vv . l N vVuwOdOlsl3a1o fo) q z z Zi Z z Z 3 ae A SILNSY¥YHdVvZ by S| SNOZ 7 VININVO 43MO1 2) tyes 7: eae 3NOZ VININVD ¥3ddn N Vv > 2 z z 2 | VIANIWAS Z S S S S S S 7 7 a L L L L L L fa] a G fa q a {e) I 7 3NOZ 2 WNITIAHDONNGIG z “q “q Anstruther Pittenween Glengarnock Dairy Machrihanish ROXBURGH 3 2 miles oHarden Burn | Fic. 9. Outline map of Southern Scotland, showing localities mentioned in the text. 30 BRITISH AVONIAN CONODONT FAUNAS limestones, including the Hosie Limestones, and inter-bedded shales, with sub- ordinate ironstone nodules and coals. Alternating sandstones, shales, fireclays, and workable coals and ironstones mark the Limestone Coal Group, while the Upper Limestone Group consists predominantly of sandstone, with subordinate shales, limestones and coals. I. Dunbar. Samples were collected from limestone bands within the Lower Limestone Group near Catcraig (NT 715772). The beds collected were the Long Craig Upper (NT 749752), Skateraw Lower (NT 748752), Skateraw Middle (NT 743754), Skateraw Upper (NT 738758), Chapel Point (NT 722774), Barness East (NT 724773) and the Dryburn Foot (NT 732763) Limestones. II. Midlothian. The Lower Limestone Group was collected from various points in the Midlothian Coalfield. The ‘‘ Gilmerton ’’ Limestone was collected 14 miles S.S.E. of Carlops (NT 172544) where it consists of grey crystalline limestone and shales, with a limestone breccia at the top. The North Greens Limestone was collected in Bilston Burn (NT 270649) and in the banks of the River North Esk, 250 yds. S.W. of Newhall House. It consists of about 35 ft. of impure, thinly- bedded, argillaceous limestone. The Vexhim Limestones were collected in Glencorse Burn, 350 yds. upstream from Milston Bridge (NT 250628). The overlying Bilston Burn Limestone was collected in Bilston Burn, where it consists of about 40 ft. of thinly-bedded limestone, with an overlying bed of cal- careous shale and a 5 ft. bed of dolomitic limestone. Ill. Fife. A thick succession of the Calciferous Sandstone Measures and the Lower Limestone Group is exposed (Figs 85, 86) near Pittenweem (NO 548027) on the shore of the Firth of Forth, between Anstruther and Coal Farm. Samples were collected from the limestone and shale beds, the limestones yielding abundant conodonts, whereas the Calciferous Sandstone Measures, apart from three beds (15, 43, 388), were barren. ; IV. Ayrshire. Sections through the Lower Limestone Group and the Upper Limestone Group were collected. The Broadstone Limestone was collected at Auchenmade (NS 342486) where it is overlain by the Dockra Limestone, which was also collected here. The Hosie Lime- stones were collected in a railway cutting at Glengarnock (NS 333525). In the Upper Limestone Group the Index Limestone was collected near Glonbeith Castle (NS 332458) and near Drumbuie House (NS 361506) where it was about six feet thick. The Lower and Upper Linn Limestones were collected at the Linn Spout near Dalry (NS 287487, NS 284485). V. Roxburghshire. The Main Algal ‘ Series ’ of Garwood (1931) was collected in Harden Burn (NY 517907) and the limestone bands, apart from the algal bed, yielded abundant conodonts. VI. Argyll. The Carboniferous Limestone ‘Series’ at Machrihanish (McCallien 1928 ; McCallien & Anderson 1930) was examined and the limestones were collected where they were exposed on the beach (NR 632208). ae 85 Lect BRITISH AVONIAN CONODONT FAUNAS 31 The general geology of the Scottish collecting areas is described in the following publications : Carruthers et al. (1927), Clough et al. (1925), Craig (1965), Currie (1954), Dinham & Holdane (1932), Goodlet (1957), George (1958), Mitchell & Mykura (1962), Richey e¢ al. (1930), Robertson et al. (1949) and Tulloch & Walton (1958). IV. METHODS OF STUDY Samples were collected from the successions at intervals of 10 ft. and in many parts of the sections these were supplemented by collections made at 5 ft. or 2 ft. intervals. Most of the original samples from the reconnaissance survey weighed about 25 lbs. but the samples from the smaller intervals weighed only 2—4 lbs. These samples were weighed and then digested in 8% commercial acetic acid, contained in plastic buckets. Shales were disintegrated with concentrated hydro- gen peroxide, and formic acid was used for some of the limestones. After the rock had dissolved, the sludge was sieved under water on 25, 50, 100 and 200 mesh screens, the fractions being dried and then separated in bromoform. The heavy residues were searched with a binocular microscope and the conodonts picked and mounted (see Collinson 1963 for further details). Photography was carried out by Mr. S. Osborn, using a Leitz Aristophot apparatus and Adox KB 14 film, developed in Acutol or I.D. 48 developer. The specimens were coated with ammonium chloride. Prints were cut out and mounted but no retouching was undertaken. V. CONODONT FAUNAS (a) General Review The present study is based upon 600 rock samples, and has involved the solution of some 3 tons of rock, which yielded over 25,000 identifiable conodonts. We regard this total collection as satisfactory, although the average abundance of conodonts per kilogram of rock is considerably lower than the yields from some other areas. The distribution of conodonts within the various sections studied was far from uniform, and abundance ratios for each sample are included with each of the litho- logical sections (Figs 59-92). The succession in the Avon Gorge illustrates the problems involved in the less fossiliferous parts of the section. The average number of conodonts per kilogram was 8 for the K Zone, with a range from o—47 per kilogram. In general the shales provided poor yields or were barren, while intervening lime- stones were relatively fossiliferous. Shale samples 7 and 8, for example, were barren, but they are separated by two thin limestones, yielding 20 and 16 conodonts per kilogram. The Z Zone consists predominantly of massive, blue-grey calcarenite, and has an average yield of 19 conodonts per kilogram. There is again a fair range of variation _ (0-66 per kg.), the lowest yields being in limestones with a high haematite content. The upper beds of the Zone had high yields (45-66 per kg.). In contrast, the Lower C,, the Laminosa Dolomite, yielded an average of only 3 conodonts per kilogram, probably reflecting either the destructive results of second- 32 BRITISH AVONIAN CONODONT FAUNAS ary dolomitisation, or possibly an unfavourable depositional environment, while the upper C; Caninia Oolite had an average yield of only 1 conodont per kilogram (range o-3 per kg.). Other conodont students have commonly found lithologically similar oolites to have low yields, and this may be the result of relatively rapid deposition. Of the 23 samples of the Caninia Dolomite which were processed, only one, a shelly calcarenite, yielded conodonts. S Zone samples had a yield of less than 1 per kilogram, and almost three quarters of the 72 samples processed were barren. Only 5 samples yielded an average of more than one conodont per kilogram. The Zone is marked by relatively little change in the conodont faunas, and, like the low yielding (1 per kg.) D Zone beds, probably represents rapidly deposited sediments. Broadly comparable variations in abundance are seen in strata of similar litho- logies from other sections. In the D Zone of South Wales, for example, the mean yield was 29 conodonts per kilogram of limestone dissolved, with a range from 0-198. In the Z Zone of the North Crop, the mean yield was g conodonts per kilogram, with a range from o-60. In general the lowest yields were those of the saccharoidal dolomites, and the highest were those of the basal beds of oolites. (b) Stratigraphical distribution of conodont faunas The precise ranges of all conodont species recovered for each of the various areas are shown on Figs. 49-58. The present section provides only a general view of the distribution of some of the more useful genera and species. Patrognathus gen. nov. is restricted to the K Zone. The genus Clydagnathus gen. nov. is found in the K Zone and in the lower part of the Z Zone of the North Crop and in Shropshire. It is rare in large faunas of the same age from the Avon Gorge, although it occurs abundantly in some other countries, e.g. Australia. The lowest occurrence of the genus is represented by the species C. gilwernensis gen. et sp. nov. and C. cavusformis gen. et sp. nov., which are rapidly replaced by Clydagnathus sp. A gen. et sp. nov. The Lower Z Zone species are C. unicornis gen. et sp. nov. and C. darensis gen. et sp. nov. The genus Siphonodella, which has proved to be abundant and of great stratigraphical value in other areas, is rare in the Avonian. It is con- fined to the upper part of the K Zone in both the Avon Gorge and the North Crop. The limited stratigraphic range of the genus in the Avonian is also reflected in an absence of the sequence of species, which has been described from the Mississippi Valley. The genus Pseudopolygnathus is one of the most distinctive components of the faunas of the K and Z Zones, extending from the base of the K Zone into the C Laminosa Dolomite. It is represented by a considerable number of species, most of which have restricted stratigraphical ranges. Pseudopolygnathus vogesi sp. nov. and Pseudopolygnathus expansus sp. nov. are confined to the lowest part of the K Zone, where they are distinctive species. The Z Zone is characterized by the incoming of abundant pseudopolygnathids, referable to the species P. primus Branson & Mehl and P. cf. dentilineatus E. R. Branson. These are replaced vertically by P. postino- dosus sp. nov. and P. nodomarginatus E. R. Branson. In contrast to the abundance BRITISH AVONIAN CONODONT FAUNAS Distribution and relative abundance of species of Spathognathodus and related genera. Pseudopolygnathus sp. S.tridentatus Scrassidentatus tatu eat ee S.costatus ss. S.elongatus S.anteposicorni Sure susie S.cyrius Percentage of total conodont S.plumulus ss. Clydagnathus cavusensis fauna S.plumulus 01%. nodosus Pseudopolygnathus 4-5°%o vogesi B16 oe = lo 2044S plumul ig nae shirleyae Fic. 10. Distribution and relative abundance of species of Spathognathodus and related genera in the Z and K Zones of the Avonian of the North Crop. 33 34 BRITISH AVONIAN CONODONT FAUNAS of Pseudopolygnathus in the Lower Z Zone of the Avon Gorge, the genus is absent in strata of similar age from the North Crop. In these latter faunas it is presumably represented by functional homoeomorphs in the natural conodont assemblages. These could well be spathognathodids, from which Pseudopolygnathus seems to have arisen. The Lower Z Zone assemblage is replaced by abundant P. multistriatus Mehl & Thomas near the base of the Zz Subzone, which is in turn replaced by abundant P. longiposticus (Branson & Mehl) towards the top of the Zz Subzone. The genus is rare in the Lower C; Subzone. The genus Gnathodus is one of the longest ranging in the Avonian, but its restricted and distinctive species have been particularly useful in some of our correlations. Its oldest occurrence is near the base of the Zz Subzone, where G. delicatus Branson & Mehl is found. On the North Crop, G. sitmplicatus sp. nov. also occurs in Lower Z Zone faunas. G. delicatus is associated near the top of the Zz Subzone with G. semi- glaber (Bischoff), a distinctive Upper Z Zone species, which is in turn replaced by G. antetexanus Rexroad & Scott at the top of the Z Zone. G. punctatus (Cooper), G. avonensis sp. nov. and G. simplicatus sp. nov. also occur in the Upper Z Zone. A single specimen of G. cuneiformis Mehl & Thomas was collected in the middle of the S; Subzone. Gnathodus is rare or absent in the higher C and S faunas, but is represented by several distinctive species in the D Zone. G. bilineatus (Roundy) appears at the base of the Dg Subzone, together with G. girtyi girtyi Hass. In the highest part of the Dz Subzone G. girtyi simplex Dunn, G. commutatus (Branson & Mehl), G. mononodosus sp. nov. and G. homopunctatus Ziegler appear. G. girtyi collinsoni sub. sp. nov. appears in the middle of the Dg Subzone, and G. girtyi turritus Collinson & Druce near the top (Fig. 11). The genus Spathognathodus has an extended range, being present throughout the Avonian. The dominant species of the Lower K Zone is S. plumulus sp. nov., which is represented by several subspecies. The Upper K Zone is marked by a variety of spathognathodids, including S. elongatus (Branson & Mehl), Spathognathodus cf. vobustus (Branson & Mehl), S. anteposicornis Scott, and S. tridentatus (E. R. Branson). The three former species, though never abundant, extend into the Lower Z Zone, while the latter, together with S. cvassidentatus, which first appears in the basal K Zone, is abundant in the Lower and Middle Z Zone. S. costatus costatus (E. R. Branson) and S. costatus sulciferus (Branson & Mehl) appear in the Lower Z Zone in the North Crop and are abundant in the middle part of the Zone. S.cyrius (Cooper), a rare species throughout the K and Lower Z Zones, overlaps the lower occurrence of these species, and S. cf. cristulus Youngquist & Miller is also present, extending upwards into the C Zone. S. pulcher Branson & Mehl occurs high in the Z Zone and S. coronus sp. nov. in the C Zone. S. scitulus (Hinde) is present in the Canima Oolite and extends into the D Zone. S. cristulus Youngquist & Miller is character- istic of the Dz Subzone and S. campbelli Rexroad of the Ds. Polygnathus first appears near the base of the K Zone and extends to the top of C). Polygnathus communis Branson & Mehl extends from near the base of the K Zone to the middle of the Laminosa Dolomite. Polygnathus inornatus inornatus Branson & Mehl, P. lobatus lobatus Branson & Mehl, P. inornatus rostratus subsp. nov., P. al i =r || juosul||o> lmeaniioomiasarb = | snsopou« >) S Tsnsopououow’ To) e ED 5n3D}2undowoy'S [__ snyoynwwos'9 xajduiis 1Ay415'9 ~~ 1Ay416 1Kya15'9 of 7) snypaulliq’S eo ae) S1W4oj}!aun> “9 — oom? fo) 2 co 3 2 | i Ew SORA 6) ——$—__—. coc g : a) S ; tia : tS O snupxajaju0 9 BS : One ‘ fe x sisusuon0 O|— eG (eo) 2 Bz z |: 2 & O LL snyorijdwis 9 | — => (e) ft te SnyD}2und ‘5 }— age TS) Z o daqpjBiwas ‘9 — ame aw SHADENOD ~ (——$_—_—$—_—__—— S 2 Ci Z K — SANOZ GOdOIHDVYE-1VYOD NVINOAV BRITISH AVONIAN CONODONT FAUNAS 35 inornatus vexatus subsp. nov. and P. lobatus inflexus subsp. nov. appear in the Middle K Zone. The P. inornatus group becomes extinct in the upper part of the K Zone. The P. lacinatus Huddle group appears in the uppermost Z Zone, together with P. lacinatus asymmetricus subsp. nov. The C Zone is characterized by P. lacinatus s.s. and P. bischoffi sp. nov. The genus Mestognathus first appears in the upper part of the Cy Subzone, where it is represented by M. beckmanni Bischoff, which extends into the D Zone. M. bipluti Higgins first appears in the D; Subzone and extends into the higher part of Dz, where M. neddensis sp. nov. is also present. Neither extends into the Dg Subzone. Cavusgnathus is most characteristic of the Cz, S and D Zones. C. unicornis Youngquist & Miller is present in the Cz Caninia Dolomite and extends into the D Zone. C. charactus Rexroad first occurs in the C2S; Zone, and C. convexus Rexroad is characteristic of the Middle S Zone. The genus Taphrognathus is restricted to the Upper Sz Subzone, where it is represented by a single species, T. vartans Branson & Mehl. The striking genera Bactrognathus, Doliognathus, Scaliognathus and Staurognathus, which are distinctive components of faunas of comparable age in other areas, are unrepresented in our Avonian faunas, in which the genus Elictognathus is represented by only a single fractured specimen. It seems probable that these genera were geographically or ecologically restricted. Most of the genera of “‘ bars and blades” have a long stratigraphic distribution, but a number of species have proved valuable in local correlation. Ligonodina beata nom. nov., Hindeodella corpulenta Branson & Mehl, and H. subtilis Ulrich & Bassler are common Upper K and Z Zone forms. Apatognathus makes its first appearance in the Zz Subzone. A. geminus (Hinde) is present in the C; Subzone and extends into the D Zone. A. scalenus Varker appears in the Upper C; Subzone. A. bladus sp. nov. is confined to the Dz Subzone. Prioniodina laevipostica (Rexroad & Collinson) is limited to the Upper Dz Subzone. Neoprioniodus scitulus (Branson & Mehl), N. peracutus (Hinde), Hindeodella undata Branson & Mehl, and H. antecomplex Collinson & Druce first appear in the Lower Dg Subzone. Magnilaterella clarkei sp. nov. is confined to the D Zone, as is Kladognathus. The precise ranges of these and other species are given on Figs. 49-58. The low yield of conodonts from many samples makes reliance upon any single “‘ index fossil ”’ an unreliable method of correlation, but the general characteristics of the individual conodont assemblages are distinctive for each of our main stratigraphic divisions, and these provide the basis of a relatively precise scheme of correlation. (c) Avonian Conodont Biostratigraphical Zones A series of 14 conodont assemblage zones has been established. We have used the Avon Gorge and the North Crop successions as our type sections, using the latter to provide the three highest Avonian Zones, which are largely represented by non- _ carbonate sediments in the Avon Gorge area. We have therefore included in this section a detailed discussion of the correlation between these two areas, in order to provide a basis for the zonal scheme, which we have used (p. 46) to establish correla- 36 BRITISH AVONIAN CONODONT FAUNAS tions between these type sections and Avonian sequences in Central England and Scotland. We believe that these conodont zones provide a useful method of correlation throughout the British Avonian, and that they offer a considerably higher degree of precision than existing coral-brachiopod zones. They show no detailed correspondence to the conodont zones established in either the Mississippi Valley or in West Germany, although the general faunal sequence in the three areas has enough broad resemblances to allow us to correlate between them with some confidence. The sequence and relationship of the 14 zones are shown in Fig. 12. They are defined and described below, and the detailed correlation between the Avon Gorge and the North Crop is discussed. The intercontinental correlations given for each zone below are generalized and approximate. There is a full discussion of correlation on p. 52. Patrognathus variabilis—Spathognathodus plumulus Assemblage Zone CHARACTERISTIC SPECIES: Patrognathus variabilis gen. et sp. nov., Spatho- gnathodus plumulus plumulus sp. nov., Pseudopolygnathus vogest sp. nov., Spatho- gnathodus plumulus shirleyae sp. et subsp. nov. and, in North Crop, Clydagnathus gilwernensis gen. et sp. nov. Limits :_ The base of the assemblage zone is not identified, but probably corres- ponds to the first appearance of P. variabilis gen. et sp. nov. The upper limit coincides with the oldest stratigraphic occurrence of Polygnathus inornatus inornatus Branson & Mehl, Polygnathus lobatus lobatus Branson & Mehl, and also of the genus Siphonodella. REMARKS : This zone occupies the lower and middle of the K Zone (Samples K 1— K ir in the Avon Gorge and Samples KL 1-KL 13 on the North Crop). It is correlated with part of the Cu I of West Germany, the lower and middle parts of the Hannibal Formation of North America and with the Tng, and Lower Tne, of Belgium. The lowest Lower Limestone Shale, which immediately overlies the Old Red Sandstone in the Avon Gorge, does not contain conodonts. The basal limestone stratum (Sample K 3) is characterized by the presence of S. plumulus plumulus subsp. nov. and P. variabilis gen. et sp. nov. Sample K 4 is the oldest from the Avon Gorge to contain pseudopolygnathids, whereas these pseudopolygnathids occur in the North Crop in the basal beds of the Lower Limestone Shale which directly overlies the Old Red Sandstone. Fic. 13. Chart to show the characteristic species of the conodont zones proposed in the present paper. Where a species is shown breaking the boundary between two successive zones, it is present in both. Patrognathus variabilis—Spathognathodus plumulus Assemblage Zone. 1a. Patrognathus variabilis gen. et sp. nov.—oral view. 1b. Patrognathus variabilis gen. et sp. nov.— lateral view. 2a. Spathognathodus plumulus plumulus sp. nov.—lateral view. 2b. Spathognathodus plumulus plumulus sp. nov.—oral view. 3a. Pseudopolygnathus vogest sp. noy.—oral view. 3b. Pseudopolygnathus vogest sp. nov.—aboral view. 4a. Spathognathodus plumulus shirleyae subsp. noy.—lateral view. 4b. Spathognathodus == + north | mississippi vatuer Mississipp! VALLEY EUROPEAN AVONIAN CoNoDONT zoKES sampte | CORAL AMERICAN FORMATIONS. CONODONT ZONES. ZONES NUMBERS AC HIDEO) Senies = Yo GLEN DEAN Jineatus-Klagognathodus meni = 2 = | manoivapunc Gnathedus bilineatus-Cavuygnathus cristalua pan climes 7 GOLCONDA 91 Gnathodus girtyi collins ee bce 5 CYPRESS cullY 0 | mloennawen = é aoorva9 Goathedus bilineetus-Cavusgrathus cheractus — Gnethodvs mononodosus culls cro7 st. GENEVIEVE Gres Mestogneihus| beckmenni-anethedus bilinectus 22 = crot culi« D9 o Apstognetnus geminn- Cavusgnothus Apstognathus gemins-Covusgnathus on [b2a2=3 sr Louis arr Tepnregnetnus| varians- Cavusgnatnus- Apetognetnus Bn s45 2 [ener reorERrONp wares NEALE aaa g Covusgnotnus unicornis - Apetognatnus WAReAW = 29 iu cul Pa cis ia <5, | neon Icnethedial texernteeeTepnresnethts Ne Conodonts 3) 26 < c2s5 BS Hestegnainosilbeckmenni=lFalvancinvs)ielsehott UrreR BURLINGTON Bactrognathus - Taphrognathus eat c cia Gretheeus/entetexenus)- Pelvenstnus ltecinates IDOLE ase LOWER 1 Bactrognathus - Polygnathus communis A A ere oe FERN GLEN z Pueudopolygnsinus |e -r-longiposticus 233 732 “seoauia Groteean Inet A Polyaneihis tecinatus 2. Pseudopolygnathus multistriatus DCONFORMITY ase UPPER CHOUTEAU Siphonodelia isosticha-5 cooper q FB || Seethognatnodus costotus costatus- Gnethesus delicatus LOWER. CHOUTEAU. \ A 9 3 cat ) K19 z 2 S 1 Kies rs Spatnognothodus cf 5S robustus- S$ trigentatus ee eee Sipnenedelia. quadruplicata - $.crenuteta L-pruc 2 rer} Fa a Siphonedella- Polygnatnus inernetus a 2 v2 K = MIDDLE HANNIBAL Siphonodelia duplicata mu Patrognainus veriobilis - Spethognathogus plumulin Cowen HaNNieAl Sipnonodelle suicate Fs divi Zonation of the Avonian on the basis of conodonts, showing the relations ions of the Avon Gorge, and the North Crop, and also the relationship of the Yoredale strata in the upper part of the succession. A comparison is made with the conodont zones established in the Mississippi V ley and with the goniatite zones of Europe ip of the zones proposed in this paper to the coral/brachiopod gui -pjlapouoydis s = anyengos's 2 snpoyyouBoyjods = 22s Se ae smyeojiap snpoy ous ao Tas = = €> S&S gmpulao) snyjoubfjog =smouise) |nyyouSKiog RE eS SP a ae Sy Ga = ${uso3}un snyjeubenno> =sup|40n anyyoubosydo) snuiwa6 cenyyoubojody id am ‘ is Py ie = = an], PEE yee ESS Pi (es =| sanoz S3NO0Z LNOGONOD | qodoovua Woo. BRITISH AVONIAN CONODONT FAUNAS 37 plumulus shirleyae subsp. nov.—oral view. 5a. Clydagnathus gilwernensis gen. et sp. nov.—oral view. 5b. Clydagnathus gilwernensis gen. et sp. nov.—lateral view. Siphonodella—Polygnathus imornatus Assemblage Zone. 6a. Polygnathus inornatus imornatus—lateral view. 6b. Polygnathus inornatus imornatus—oral view. 7a. Poly- gnathus lobatus lobatus—oral view. 8. Polygnathus lobatus inflexus—oral view. 9a. Poly- gnathus inornatus vostvatus—oral view. 9b. Polygnathus inornatus rostvatus—aboral view. toa. Siphonodella isosticha—aboral view. to0b. Siphonodella isosticha—oral view. Spathognathodus cf. robustus—S. tridentatus Assemblage Zone. 11. Spathognathodus cf. vobustus—lateral view. 12. Spathognathodus elongatus—lateral view. 13a. Spatho- gnathodus tridentatus—lateral view. 13b. Spathognathodus tridentatus—oral view. 13c. Spathognathodus tridentatus—aboral view. 14. Spathognathodus crassidentatus— lateral view. 15. Spathognathodus anteposicornis—iateral view. Spathognathodus costatus costatus—Gnathodus delicatus Assemblage Zone. 16a. Spatho- gnathodus costatus costatus—lateral view. 16b. Spathognathodus costatus costatus—aboral view. 17a. Spathognathodus costatus sulciferus—lateral view. 17b. Spathognathodus costatus sulciferus—oral, view. 18a. Spathognathodus cf. cristulus—lateral view. 18b. Spathognathodus cf. cristulus—oral view. 19. Spathognathodus cf. cyvius—lateral view. 20a. Gnathodus delicatus—lateral view. 20b. Gnathodus delicatus—oral view. 21. Ligonodina beata nom. nov.—inner lateral view. 22. Hindeodella corpulenta—lateral view. 23. Hindeodella subtilis—-lateral view. 24a. Pseudopolygnathus primus—oral view. 24b. Pseudopolygnathus primus—aboral view. 25. Pseudopolygnathus cf. dentilineatus—oral view. 26a. Pseudopolygnathus multistvriatus—aboral view. 26b. Pseudopolygnathus multistvriatus—oral view. 27. Gnathodus simplicatus sp. nov.—oral view. 28a. Clydagnathus unicornis gen. et sp. nov.—oral view. 28b. Clydagnathus unicornis gen. et sp. nov.—lateral view. 29a. Pseudopolygnathus postinodosus sp. nov.— oral view. 29b. Pseudopolygnathus postinodosus sp. nov.—lateral view. Polygnathus lacinatus Assemblage Zone. 30. Polygnathus lacinatus lacinatus—oral view. 31a. Polygnathus lacinatus asymmetricus subsp. nov.—lateral view. 31b. Poly- gnathus lacinatus asymmetricus subsp. nov.—oral view. 32. Polygnathus nodomarginatus— oral view. 33a. Cavusgnathus sp. nov. A.—oral view. 33b. Cavusgnathus sp. nov. A.—lateral view. 34. Pseudopolygnathus multistriatus—oral view. Polygnathus lacinatus—Pseudopolygnathus cf. P. longiposticus Assemblage Zone. 35. Gnathodus semiglabey—oral view. 36a. Gnathodus delicatus—lateral view. 36b. Gnathodus delicatus—oral view. 37. P. cf. longiposticus—lateral view. 38. Polygnathus lacinatus lacinatus—oral view. 39a. Spathognathodus pulcher—oral view. 39b. Spatho- gnathodus pulcher—lateral view. 40. Gnathodus simplicatus sp. nov.—oral view. 4Ia. Gnathodus avonensis sp. nov.—oral view. 41b. Gnathodus avonensis sp. nov.—lateral view. Gnathodus antetexanus—Polygnathus lacinatus Assemblage Zone. 42. Apatognathus geminus—inner lateral view. 43. Apatognathus scalenus—inner lateral view. 44. Apatognathus petilus—outer lateral view. 45a. Spathognathodus cf. cristulus—lateral view. 45b. Spathognathodus cf. cristulus—oral view. 46. Gnathodus antetexanus—oral view. Mestognathus beckmanni—Polygnathus bischoffi Assemblage Zone. 47a. Mestognathus beckmanni—iateral view. 47b. Mestognathus beckmanni—oral view. 48a. Polygnathus bischoffi sp. nov.—oral view. 48b. Polygnathus bischoffi sp. nov.—aboral view. Cavusgnathus unicornis—A patognathus Assemblage Zone. 49. Cavusgnathus unicornis —inner lateral view. 50a. Spathognathodus cristulus—iateral view. 5o0b. Spathognatho- dus cyristulus—oral view. 51a. Mestognathus beckmanni—inner lateral view. 51b. Mestognathus beckmanni—oral view. 52a. Gnathodus cuneiformis—oral view. 52b. Gnathodus cuneiformis—lateral view. 53a. Cavusgnathus chavactus—oral view. 53b. [Caption to Fig. 13 continued on p. 38 38 BRITISH AVONIAN CONODONT FAUNAS In addition, on the North Crop two subzones can be delineated, the lower being characterized by the presence of Spathognathodus plumulus nodosus sp. et subsp. nov., Clydagnathus gilwernensis gen. et sp. nov. and Pseudopolygnathus vogesi sp. nov. The upper is recognized by the absence of the above-mentioned species and by the presence of Clydagnathus sp. nov. A. Siphonodella—Polygnathus inornatus Assemblage Zone CHARACTERISTIC SPECIES : Polygnathus inornatus inornatus Branson & Mehl, Polygnathus lobatus lobatus Branson & Mehl, Polygnathus lobatus inflexus subsp. nov., Polygnathus inornatus rostratus subsp. nov. and Siphonodella isosticha (Cooper). Limits: The base of this zone is marked by the first occurrence of Siphonodella tsosticha (Cooper), P. inornatus inornatus Branson & Mehl, P. lobatus lobatus Branson & Mehl, and P. inornatus rostratus subsp. nov. The top of the zone is marked by the Continuation of Fig. 13 caption] Cavusgnathus chavactus—inner lateral view. 54a. Cavusgnathus cristatus—inner lateral view. 54b. Cavusgnathus cristatus—oral view. Taphrognathus varians—Cavusgnathus—A patognathus Assemblage Zone. 55a. Taphrognathus varians—oral view. 55b. Taphrognathus varians—lateral view. 56a. Spathognathodus cristulus—oral view. 56b. Spathognathodus cristulus—lateral view. Apatognathus ? geminus—Cavusgnathus Assemblage Zone. 572. Cavusgnathus cristatus—inner lateral view. 57b. Cavusgnathus cristatus—oral view. 58. Apato- gnathus ? geminus—inner lateral view. Mestognathus beckmanni—Gnathodus bilineatus Assemblage Zone. 59a. Mestognathus beckmanni—inner lateral view. 59b. Mestognathus beckmanni—oral view. 60. Cavus- gnathus unicornis—inner lateral view. 61. Spathognathus scitulus—lateral view. 62a. Apatognathus bladus sp. nov.—inner lateral view. 62b. Apatognathus bladus sp. nov.—outer lateral view. 63. Hibbardella abnoymis—inner lateral view. 64. Neo- prioniodus singulavis—lateral view. 65a. Gnathodus girtyi givtyi—oral view. 65b. Gnathodus girtyi givtyi—lateral view. 66a. Gnathodus bilineatus—oral view. 66b. Gnathodus bilineatus—lateral view. Gnathodus mononodosus Assemblage Zone. 67a. Gnathodus girtyi simplex—tiateral view. 67b. Gnathodus girtyt simplex—oral view. 68a. Gnathodus mononodosus sp. nov.—lateral view. 68b. Gnathodus mononodosus sp. nov.—oral view. 68c. Gnathodus mononodosus sp. nov.—aboral view. 69a. Gnathodus commutatus—lateral view. 69b. Gnathodus commutatus—oral view. 70a. Gnathodus homopunctatus—lateral view. ob. Gnathodus homopunctatus—oral view. 71a. Spathognathodus cf. cristulus—lateral view. 71b. Spathognathodus cf. cristulus—oral view. Gnathodus girtyi collinsoni Assemblage Zone. 72a. Gnathodus girtyi collinsoni subsp. nov.—oral view. 72b. Gnathodus girtyi collinsoni subsp. nov.—lateral view. 73a. Gnathodus girtyt simplex—oral view. 73b. Gnathodus girtyi simplex—iateral view. 74a. Gnathodus girtyi givtyi—oral view. 74b. Gnathodus girtyi girvtyi—lateral view. 75a. Gnathodus nodosus—lateral view. 75b. Gnathodus nodosus—lateral view. 75c. Gnathodus nodosus—aboral view. 76a. Gnathodus mononodosus sp. nov.—lateral view. 76b. Gnathodus mononodosus sp. nov.—oral view. 76c. Gnathodus mononodosus sp. nov.— aboral view. 77a. Gnathodus bilineatus—oral view. 77b. Gnathodus bilineatus—iateral view. 78. Prioniodina stipans—iateralview. 79. Prioniodina subaequalis—iateral view. 80. Neoprioniodus scitulus—lateral view. 81. Neoprioniodus tulensis—lateral view. 82. Ligonodina levis—inner lateral view. BRITISH AVONIAN CONODONT FAUNAS 39 first appearance of Spathognathodus cf. robustus (Branson & Mehl), S. tvidentatus (E. R. Branson) and S. anteposicornis Scott. REMARKS : This zone occupies nearly all the Upper K Zone in the North Crop and the lower part of the Upper K Zone in the Avon Gorge (Samples K 12—KgI in the Avon Gorge and Samples KL 16-KL 18 on the North Crop). It is correlated with the Upper Cu I and basal Cu II « of West Germany, the lower part of the Upper Hannibal Formation of North America and with part of the Tne, of Belgium. On the North Crop a covered shale interval is present between Samples KL 13 and KL 16. Inthe Avon Gorge Samples K 12-K 17 contain P. variabilis gen. et sp. nov. and S. plumulus s.s. sp. nov., associated with the P. inornatus group. On the North Crop (Samples KL 16-KL 18) P. variabilis gen. et sp. nov. and S. plumulus s.s. sp. nov. are absent from the zone. __S. tsosticha (Cooper) has not been found in the Avon Gorge, but there is a concealed interval above K 17 and below Kg1. There are thus two subzones within this assemblage zone. The lower corresponds to Samples K 12-K 17 in the Avon Gorge and occupies the covered interval between KL 13 and KL 16 on the North Crop ; the upper subzone (KL 16-KL 18 of the North Crop) occupies the concealed interval above K 17 and below Kel in the Avon Gorge. Spathognathodus cf. robustus—Spathognathodus tridentatus Assemblage Zone CHARACTERISTIC SPECIES :_ S.cf. vobustus (Branson & Mehl), S. elongatus (Branson & Mehl), S. tvidentatus (E. R. Branson), S. crassidentatus (Branson & Mehl) and S. anteposicornis Scott. Limits : The base of this zone is marked by the first occurrence of Spathognathodus cf. vobustus (Branson & Mehl), S. tvidentatus (E. R. Branson) and S. anteposicornis Scott. The top of the zone is marked by the first occurrence of Spathognathodus costatus costatus (E. R. Branson). The final appearance of the Polygnathus inornatus group is within the lower part of the zone. REMARKS : This zone occupies the upper part of the Upper K Zone in the Avon Gorge (Sample Ker) and the uppermost K and basal Z Zone on the North Crop (Samples KL 19-ZLA 1). It is correlated with the upper part of the Hannibal Formation of North America, with the Lower Cu II « of Germany and with the Upper Tng, of Belgium (see also p. 56). The lower part of this zone (with the P. inornatus group) probably occurs in the concealed interval beneath Sample Ket in the Avon Gorge. Spathognathodus costatus costatus—Gnathodus delicatus Assemblage Zone CHARACTERISTIC SPECIES: In both the Avon Gorge and the North Crop: S. costatus costatus (E. R. Branson), S. costatus sulciferus (Branson & Mehl), S. cf. cristulus Youngquist & Miller, S. cyrius (Cooper), S. crassidentatus (Branson & Mehl), G. delicatus Branson & Mehl, Ligonodina beata nom. nov., Hindeodella corpulenta 40 BRITISH AVONIAN CONODONT FAUNAS Branson & Mehl, Hindeodella subtilis Ulrich & Bassler. In the Avon Gorge : Pseudopolygnathus primus Branson & Mehl, Pseudopolygnathus cf. dentilineatus E. R. Branson, Pseudopolygnathus postinodosus sp. nov. On the North Crop: Clyda- gnathus unicornis gen. et sp. nov., and Gnathodus simplicatus sp. nov. Limits: The base of this assemblage zone is marked by the first occurrence of S. costatus costatus (E. R. Branson) and S. cf. cristulus Youngquist & Miller. The top of the assemblage zone is recognized by the incoming of abundant Pseudopolygnathus multistriatus Mehl & Thomas and by the replacement of G. delicatus Branson & Mehl by G. semiglaber (Bischoff) and G. antetexanus Rexroad & Scott. REMARKS : This zone occupies the uppermost K, the Z; and the lower part of the Zz Subzones in the Avon Gorge and most of the Z Zone on the North Crop. (Avon Gorge Samples K 18-Z 25 : North Crop Samples ZLA 2-ZLA 28). It is correlated with the uppermost Hannibal, the Lower and Upper Chouteau Formation of North America, with the Middle and Upper Cu II « of Germany, and with the uppermost Tng, and the Tng, of Belgium. This assemblage zone shows some geographical differences. Spathognathodus costatus costatus (E. R. Branson) first appears in the North Crop at the base of Sample ZLA 2, some distance within the Z Zone, and is quickly followed by S. costatus sulciferus (Branson & Mehl). In the Avon Gorge, on the other hand, these two species are present in the uppermost beds of the K Zone. It is believed that Pseudo- polygnathus primus Branson & Mehl evolved from S. costatus sulciferus Branson & Mehl. In the Avon Gorge at the base of the Z Zone there is a burst of pseudopoly- gnathids and the genus Pseudopolygnathus dominates the early Z Zone fauna. The genus Pseudopolygnathus is not present in the Lower Z Zone in the North Crop, its position in the natural conodont assemblages of the Z Zone on the North Crop being represented by other form genera. As a result, the following three subzones are recognized on the North Crop : C. Clydagnathus unicornis (Samples ZL 11-ZLA 28). B. Gnathodus simplicatus (Samples ZLA 15-ZL Io). A. Spathognathodus costatus costatus-Spathognathodus costatus sulciferus (Samples ZLA 2-ZLA 14). The base of the Spathognathodus costatus costatus-Spathognathodus costatus sulciferus Assemblage Subzone is marked by the first occurrence of S. costatus costatus (E. R. Branson) and S. cf. cristulus Youngquist & Miller. The subzone is recognized by the presence of the above, together with S. costatus sulciferus (Branson & Mehl), Gnathodus delicatus Branson & Mehl, and Apatognathus varians Branson & Mehl. The Guathodus simplicatus sp. nov. Assemblage Subzone is recognized by the first occurrence of Gnathodus simplicatus sp. nov. and the presence of Gnathodus sp. B. The top of this assemblage subzone is marked by the final occurrence of P. communis Branson & Mehl, N. barbatus (Branson & Mehl), S. costatus sulciferus (Branson & Mehl) and A. varians (Branson & Mehl). The C. unicorns gen. et sp. nov. Assemblage Subzone is marked by the paucity of the conodont fauna. What fauna there is, is dominated by the presence of C. unicornis gen. et sp. nov., which up to this point has been extremely rare. The top of this subzone is marked by the BRITISH AVONIAN CONODONT FAUNAS 41 disappearance of S. tvidentatus (E. R. Branson), Clydagnathus darensis gen. et sp. nov., C. unicornis gen. et sp. nov. and S. crassidentatus (Branson & Mehl). In the Avon Gorge there are two subzones : a lower subzone characterized by the presence of S. costatus costatus (E. R. Branson), S. costatus sulciferus (Branson & Mehl) and S. cf. cvistulus Youngquist & Miller, with very few pseudopolygnathids present, (Samples K 18-Z g) and an upper zone of pseudopolygnathids (Samples Z 10-Z 25). In the subzone of abundant pseudopolygnathids, Pseudopolygnathus primus (Branson & Mehl) and Pseudopolygnathus cf. dentilineatus are abundant. Pseudopolygnathus multistriatus Mehl & Thomas has its lowest stratigraphic occur- rence in Sample Z 23. Polygnathus lacinatus Assemblage Zone CHARACTERISTIC SPECIES : Polygnathus lacinatus s. s. Huddle, Polygnathus lacinatus asymmetricus subsp. nov., Pseudopolygnathus nodomarginatus (E. R. Branson), Spathognathodus pulcher Branson & Mehl and Pseudopolygnathus multi- striatus Mehl & Thomas. Gunathodus antetexanus Rexroad & Scott, is present near the base of the zone in the North Crop and at Farlow. Limits: The lower limit is marked by the incoming of the P. Jacinatus group and of Gnathodus semiglaber (Bischoff). It is also a zone of abundant Pseudopolygnathus multistriatus Mehl & Thomas. The upper limit is marked by the incoming of Pseudopolygnathus cf. longiposticus (Branson & Mehl). REMARKS: This zone occupies the uppermost part of the Z sequence in the North Crop and occurs near, but not at the top of, the Z Zone in the Avon Gorge, (North Crop Samples ZLA 29-ZL 19 : Avon Gorge Samples Z 26-Z 32). It is correlated with the unconformity at the base of the Sedalia Formation of North America, with the lowest Cu II @-y of Germany and with the base of Tng, of Belgium. The presence of G. semiglaber and P. multistriatus in this zone indicates its broad equiv- alence to the Sedalia Formation, but the fact that it also contains abundant G. delicatus also implies a similarity to the underlying Upper Chouteau Formation. These two formations are separated by an unconformity in the Mississippi Valley, below which abundant G. delicatus occur, but above which this species is absent. It seems probable that beds Z 26-28, in which the two groups of species overlap, are broadly equivalent to the Chouteau—Sedalia unconformity time interval of the Mississippi Valley (see also p. 59). Polygnathus lacinatus—Pseudopolygnathus cf. longiposticus Assemblage Zone CHARACTERISTIC SPECIES : G. semiglaber (Bischoff), G. delicatus Branson & Mehl, P. cf. longiposticus (Branson & Mehl), Polygnathus lacinatus s.s. Huddle, Spatho- gnathodus pulcher Branson & Mehl, Guathodus simplicatus sp. nov. and Gnathodus avonensis Sp. Nov. Limits: The lower limit is marked by the lower limit of abundant P. cf. longi- posticus (Branson & Mehl). It is also a zone of abundant Guathodus. The upper 42 BRITISH AVONIAN CONODONT FAUNAS limit is marked by the disappearance of P. cf. longiposticus (Branson & Mehl) and by the replacement of G. semiglaber (Bischoff) by G. antetexanus Rexroad & Scott in the Avon Gorge. REMARKS: This assemblage zone occupies the uppermost part of the Z Zone in the Avon Gorge (samples Z 33-Z 38). It is absent, owing to an unconformity, in the North Crop. It is correlated with the Fern Glen Formation of North America, the Middle Cu II 8-y of Germany, and the Tnz, in Belgium. Gnathodus antetexanus—Polygnathus lacinatus Assemblage Zone CHARACTERISTIC SPECIES: Polygnathus lacinatus s.s. Huddle, Apatognathus geminus (Hinde), Apatognathus scalenus (Varker), Apatognathus petilus Varker, S. cf. cristulus Youngquist & Miller and G. antetexanus Rexroad and Scott. Limits : The lower limit of the zone is marked by the youngest occurrence of P. cf. longiposticus (Branson & Mehl). The lower limit of the genus A patognathus in the Avon Gorge is near the lower limit of the zone. The upper limit of the zone is marked by the oldest stratigraphic occurrence of Mestognathus beckmannt Bischoff. REMARKS : This zone occupies the lower part of the C; Subzone in the Avon Gorge (Samples C 1-C 14). It is not present on the North Crop. It is correlated with the lower, middle and lower upper parts of the Burlington Formation of North America, with the upper part of Tng, and possibly the lowest Tn, of Belgium and with the Upper Cu II B-y of Germany. In this assemblage zone conodonts are sparse. The genus Pseudopolygnathus is represented by a considerably smaller number of specimens than in the underlying zone. Specimens of the P. lacinatus group, S. cf. cristulus Youngquist & Miller and A. scalenus (Varker) dominate the fauna. The youngest stratigraphic occurrence of P. communis communis Branson & Mehl in the Avon Gorge is within this zone. Mestognathus beckmanni—Polygnathus bischoffi Assemblage Zone CHARACTERISTIC SPECIES: Mestognathus beckmanni Bischoff, S. cf. cristulus Youngquist & Miller, Polygnathus bischoffi sp. nov., A. scalenus Varker, A. petilus Varker, and A. geminus (Hinde). Limits: The lower limit of the zone is defined by the oldest stratigraphic occurrence of Mestognathus beckmannmi. The upper limit probably coincides with the zone of maximum abundance of G. texanus (Roundy). REMARKS :_ This assemblage zone occupies the upper part of the Cy Subzone in the Avon Gorge (Samples C 15-C 25). It is correlated with part of the Upper Burlington Formation of North America, with the lowest Cu II 5 of Germany and with part of the Tn3. of Belgium. The upper limit of this assemblage zone cannot be defined in the Avon Gorge, because the lower beds of the Caninia Dolomite do not contain conodonts. The conodont fauna obtained from the Upper Avonian Cz, S;, Sz, and D Zones of the Avon Gorge is sparse in comparison with that obtained from the Lower Avonian. BRITISH AVONIAN CONODONT FAUNAS 43 A gap is present in the conodont record of the lower part of the Caninia Dolomites (Samples C 26-C 28). Dr. S. C. Matthews (personal communication) has a small fauna of anchoralis—bilineatus interval aspect from an oolitic facies in the Mendips, which represents the lateral equivalent of the Caninmia Dolomite. This fauna correlates with part of the Cu II 6 of Western Europe and with the Keokuk Formation of North America. Cavusgnathus unicornis—Apatognathus libratus Assemblage Zone CHARACTERISTIC SPECIES : Apatognathus libratus Varker, Cavusgnathus unicornis Youngquist & Miller, S. cristulus Youngquist & Miller, M. beckmanni Bischoff, Gnathodus cuneiformis Mehl & Thomas, Cavusgnathus charactus Rexroad, and Cavusgnathus cristatus Branson & Mehl. Limits: The lowest occurrence of the zone in the Avon Gorge coincides with the oldest stratigraphic occurrence of Cavusgnathus unicornis Youngquist & Miller, although the true base of the assemblage zone cannot be accurately defined because of the absence of conodont faunas in the Caninia Dolomite. One sample (C 39) of the Canina Dolomite has yielded a fauna containing C. umicornis Youngquist & Miller and M. beckmanmi Bischoff. This indicates that at least the upper part of the Canima Dolomite is within this assemblage zone. The upper limit of the assemblage zone coincides with the oldest stratigraphic occurrence of Taphrognathus varians Branson & Mehl, which is found in the Upper Sz Subzone. REMARKS: This assemblage zone occupies the CzS; Zone and the lower and middle of the Sg Subzone (Samples C 39-S 44). Together with the overlying Taphrognathus varians—Cavusgnathus—A patognathus Assemblage Zone, it is equiva- lent to the middle and upper part of Cu II 8 in Europe and to the Warsaw, Salem, and lower part of the St. Louis Formation of North America. The very small number of conodonts present in this stratigraphic interval precludes a more detailed division, although the presence of G. cuneiformis Branson & Mehl at the base of the assemblage zone may provide the basis for future correlation. The overall aspect of the conodont faunas from this and the overlying conodont assembl- age zone of the Avonian are similar to those described by Rexroad & Collinson (1963 and 1965) (see p. 61 for detailed discussion). Taphrognathus varians—Cavusgnathus—Apatognathus Assemblage Zone CHARACTERISTIC SPECIES: TJ. varians Branson & Mehl, C. unicornis Youngquist & Miller, and S. cristulus Youngquist & Miller. Limits : The limits of this assemblage zone coincide with the stratigraphic range of T. varians Branson & Mehl as at present known in the Avonian. REMARKS : This assemblage zone is present in the upper part of the Sz Subzone of the Avonian (Samples S 45-S 58). It is tentatively correlated with the lower part of the St. Louis Formation of North America. It is equivalent to the uppermost Cu II § in Germany. Specimens transitional between Cavusgnathus and Taphrognathus, which are 44 BRITISH AVONIAN CONODONT FAUNAS identical to those from the St. Louis illustrated by Rexroad & Collinson (1963), have been found in this assemblage zone. Apatognathus geminus—Cavusgnathus Assemblage Zone CHARACTERISTIC SPECIES : Cavusgnathus spp. and A patognathus geminus (Hinde). Limits : The lower limit is marked by the last appearance of Taphrognathus varians Branson & Mehl. The upper limit of the zone is marked by the first appear- ance of Gnathodus bilineatus (Roundy). REMARKS: This assemblage zone occupies the Upper Seg and the D; Subzones (Samples S 59-D 9). No D; Subzone conodonts were recovered from the North Crop. The assemblage zone is one of few conodonts, but is characterized by the presence of the genera A patognathus Branson & Mehl and Cavusgnathus Harris & Hollingsworth. It is tentatively correlated with the A patognathus geminus—Cavusgnathus Assemblage Zone of North America, which is found in the upper part of the St. Louis Formation. This is equivalent to the lowest part of Cu III « in Germany. Sample D 10 which marks the first appearance of G. bilineatus (Roundy) is tenta- tively taken as the basal sample of Dz although the D;—D2 boundary in the type section is difficult to determine. One anomalous feature of this zone is the occurrence of a fauna from the North of England associated with Bollandoceras hodderense (Bj). This would generally be correlated with Sg of the Avonian (e.g. Thomas & Prentice 1965 : 43). This fauna includes M. bipluti Higgins with G. symmutatus sp. nov., G. girtyt simplex Dunn, G. commutatus Branson & Mehl), G. bilineatus (Roundy) and G. homopunctatus Ziegler. The subsequent assemblage zones were established from the Dz and Dg successions on the North Crop. The few scattered conodonts of this age that were recovered from the Avon Gorge show a general similarity to the North Crop faunas. Mestognathus beckmanni—Gnathodus bilineatus Assemblage Zone CHARACTERISTIC SPECIES: Mestognathus beckmanni Bischoff, Cavusgnathus unicorms Youngquist & Miller, Spathognathodus scitulus (Hinde), Apatognathus bladus sp. nov., Hibbardella abnormis Branson & Mehl, Neoprioniodus montanaensis (Scott), Gnathodus girtyi girtyt Hass, G. bilineatus (Roundy), and indeterminate magnilaterellids. Limits : The lower limit of the zone is tentatively taken as the first appearance of G. bilineatus (Roundy), but the absence of conodonts in samples of D; North Crop strata makes this position provisional. Further collecting will probably reveal an earlier occurrence of this species, which is present in Cu III « of Germany. The top of the zone is marked by the incoming of G. mononodosus sp. nov. REMARKS : This assemblage zone is represented by the lowest 60 ft. of the De Subzone of the North Crop (Samples CYD 1-CYD 6). It is equivalent to part of the Cu III « in Germany, and broadly equivalent to the St. Genevieve Formation of the Mississippi Valley. The zone is no younger than the Pj, Subzone of Northern England. BRITISH AVONIAN CONODONT FAUNAS 45 Gnathodus mononodosus Assemblage Zone CHARACTERISTIC SPECIES : Gunathodus girtyi simplex Dunn, G. girtyi givtyi Hass, G. mononodosus sp. nov., G. bilineatus (Roundy), G. commutatus (Branson & Mehl), G. homopunctatus Ziegler, and Spathognathodus cristulus Youngquist. Mestognathus neddensis sp. nov. and M. bipluti Higgins are characteristic of this zone in the North Crop. Limits :_ The lower limit is marked by the first appearance of G. mononodosus sp. nov. The upper limit is marked by the first appearance of Gnathodus girtyi collinson subsp. nov. The latter subspecies has not yet been recorded from the Midlothian section, however. REMARKS : This zone is represented by the highest ro ft. of the Dg Subzone and by the lowest 6 ft. of the Dg Subzone (Samples CYD 7—3D 7) in the North Crop. Our Yoredale samples have yielded no mestognathids. No mestognathids are present in the Fife faunas and Collinson & Druce (in press) failed to recover them from their Irish Viséan fauna. We agree with their suggestion that the genus has an irregular geographic distribution. It is not present in the prolific Upper Mississippi Valley faunas of this age. The top of this zone in the Yoredales is the top of the Simonstone Limestone (Pq). It is equivalent to the Cu III @ of Germany and to the late Valmeyran of the Upper Mississippi Valley. Gnathodus girtyi collinsoni Assemblage Zone CHARACTERISTIC SPECIES: Gnathodus girtyi collinsoni subsp. nov., G. girtyt simplex Dunn, G. girtyi girtyi Hass, G. nodosus Bischoff, G. mononodosus sp. nov., G. bilineatus (Roundy). Prioniodina stipans (Rexroad) and P. subaequalis (Higgins) are characteristic of the lower part of this zone in the North Crop and in Dunbar. Neopriomodus scitulus (Branson & Mehl), N. tulensis (Pander) and Ligonodina levis (Branson & Mehl) are characteristic of the higher part in Scotland. Limits: The lower limit is marked by the first appearance of G. girtyi collinsont subsp. nov. The upper limit is not defined in the present study. REMARKS: This zone is represented by the uppermost 18 ft. of the D3 Subzone of the North Crop (Samples 3D 8-3D 23). In the Yoredale section it is represented by samples Y 29-Y 10 comprising the Middle Pq, the Five Yard, the Three Yard and the Underset Limestone (P2:—P2.). | The zone is equivalent to the Cu III y of Germany and broadly equivalent to the Lower Chesterian of the Mississippi Valley. It may be partly equivalent to the Lower Namurian, depending on where the upper boundary is ultimately defined. G. givtyi turritus Collinson & Druce is known to extend into the Namurian in Eire (Collinson & Druce in press). It is broadly equivalent to the pre-Middle Glen Dean Chesterian faunas of North America. The establishment of zonal limits in the upper part of the D succession was difficult. The last appearance of Mestognathus beckmanni, Mestognathus bipluti, Gnathodus homopunctatus, and the first appearance of Cavusgnathus naviculus, Gnathodus nodosus and Gnathodus girtyi turritus were each in turn considered as 40 BRITISH AVONIAN CONODONT FAUNAS possible markers for zonal limits, but the first appearance of Gnathodus girtyi collinsont subsp. nov. was the one in our opinion with the most widespread and meaningful application. Within a broad depositional basin there is a general similarity between the species of “ bar and blade ”’ conodonts in each of the upper zones, but these similarities do not extend to more distant areas, and we have therefore not listed them as character- istic of the zones as a whole. (d) Intra-Avonian correlation in Britain (i) Avon Gorge—North Crop (Figs. 49-52). There is a close overall similarity between the Lower K conodont faunas of boththe Avon Gorge and the North Crop (Fig. 14). The lowest beds of both are characterized by the presence of Spathognathodus plumulus plumulus sp. et subsp. nov. and Patro- gnathus variabilis gen. et sp.nov. The absence in the lowest beds of the North Crop of Pseudopolygnathus vogest sp. nov. which is present in the basal beds of the Avon Gorge, probably implies a slightly older age for the North Crop strata. Siphonodella, a most important diagnostic genus for the Carboniferous, and the Polygnathus inornatus group first appear at comparable horizons in the North Crop and the Avon Gorge. The last appearance of Siphonodella in both sections coincides with the first appearance of Spathognathodus robustus, a species whose first appearance overlaps the last appearance of the Polygnathus inornatus group. In the Avon Gorge, Spathognathodus costatus costatus first appears just below the traditionally accepted K—Z Zone boundary, whereas in the North Crop, it occurs just above it. The general ranges of all these species are so similar in the two areas, that correlation is relatively straightforward. Details are given on p. 36 in the zonal discussion and in Fig. 14. In spite of the overall lithological similarity between the Lower Z Zone strata in both areas, there is a lack of any detailed resemblance in their platform conodont faunas. We tentatively interpret this as the result of geographical isolation of certain conodontifers (see p. 36). | This probably reflects the influence of palaeo- geographical factors, in spite of the fact that other studies have suggested a relatively uniform depositional basin in this area during early Z times. The incoming of Polygnathus lacinatus and of characteristic Pseudopolygnathus multistriatus in the higher part of the Z Zone of both areas provides a firm basis for correlation. The absence of Pseudopolygnathus cf. longiposticus in the North Crop suggests that the higher part of the Z Zone is unrepresented there. Se and C2S; rocks from the North Crop have yielded no conodonts, and Avon Gorge faunas of this general age and also of the D; Subzone are also sparse. The presence of Gnathodus bilineatus near the base of Dg in both areas re-establishes the correlation in the higher part of the Avonian. Above this level, conodonts are so rare in the Avon Gorge that no useful comparison can be made with the abundant faunas of the North Crop. 47 BRITISH AVONIAN CONODONT FAUNAS NORTH ‘QUOZ SN4vIYap *“)—sSNJHISOI ‘S ayy JO ed IaMOo[=eh ‘QUOT SNvIUapI4y “S—sNASNGOA “JO "S=€ (AjeAtyoedsar sauozqng seddq pue s3MOT =4 % &) ‘oUuO0Z snywusour “q—wvjjapoucygrg=z ‘auoz snjnunjd "S—syiqniswa *q=1 “SP9IV OM} OY} UI Sotdads Jo sosueI oY} UseM40q drysuorzejer ay} Surmoys ‘[oystig ‘93105 uoAy oy} pue PIeyleoD seyeA\ YINOS ay} jo doi) YON ey} UO UoOTssa00ns ULTUOAY oY} Jo zxed JaMoOT 24} JO UOl}e[aII09 oY, “FI “DIA CROP AVON GORGE / es ge Ee ert omna roar nee ier aa ay & io} se} vt bp nN ¥ TIlmOITN Se |e eed el een le NS ROHS Veale lee reac ao |e as eee eel eed Lae tf RCE DjjapouUOYdiS | [OGIUUDH sippIA e6u0y yung 1}2QiuuUDH seddn nda}NOUD 4aMo07 SnyOUJOU| snyyoUuBAlog D}aIOSQo DjjapOUOK\dIS ByYrIZSOS! DJjapOUdKYdIS noaynoud seddn snisnqos snpoyjouBboujods 2u0yspuos ebug $N30}S02 snpoyyoubouods ISN.49j12/NS $NJOSOD SNPOYOUBOYOdS suojsewiy snwijdeas ONOpas ual) uses uoybuijung snjou1Bsowopou snyuyOuBs\jodopnasg ISMOIySIINW snyyDUBA|odopnasg snujouBA\og- snyj}0ub0s390g 2U0Z 0yOjnuas> Djjapouoydis = D}021|dnNuponb ojjapououdis @Uu0Z 14ad005 DijapouoKydiS — DYDdI}SOS! DjjapouoKdiS eu0Zz - 49qo)Biwas snpoyyou9 9uoZ siuNnWWOD ouIeos cub: ‘snusngos ANDQUIO! siaPououdis eerie 1 DisiosaG Cj spOUOUTIS PlisDouoUgIS, B1O3INS BIlapOUoUTIS Diojnuss> oi|spOUBUaIS Te wivusou smuroub Arg JL euo7Z sninwnid sninwinid snpoyyoubouyods =SI|QDISOA SnyyOUBOUj0g 2Uu0Z D.DUJOU snuj0uBAjod- DjjapouoKudisS 2u0z $N{O,UePI4y S - SNySNqou'’sS “42 snpoyyoubouyods 2U0Z Sn4D>1\ap SnMpouyoOUd - snjz0js0> $nj0}s0> snpoyzouBouyods au07z $M} ouUID0} snyyoUBA\og 2uU07 Snd1;sodiBu0j; g 32 snyyouBbAjodopnasg =SN}DUIDD) SnyyOUBAjOdg “‘pyjapouoyq1s jo so1oeds eqoibiwes snpoulouS suroubowa 01910800 CI@POUOUTIS Ae st te NOISS399NS vinvausny ‘91ND 3iuvdvNOS 8 ABTIWA 18 ["nyo1so> snpowisuBouIodS BW3HOS IddISSISSIW sebuoy qyuopouoD Cosme 26109 uoAW dOYD HLYON 39x09 NOAV O3S11V83N39 9U0Z DYOIjNS DjjapouoYydiS 2U0Z D}DD1|dNp DjjapouoYdiS 2u0Z DyO|NUas> ODjjapOUoKUdIS 0y031|dnsponb ojjapououdis "2u0z 142000) Djjapououdis - DYDIISOS! DiJapouUOoKdIS ISnyOI4ysiyinW SsnuyOUBAjodopnesg — saqojGiwes snpouyouD 2u0Z siunwWwod sny DUBAjog- snyjyoubos20g sa6uoy yuopouod Vv 3SW3HOS AZTIVA Idd ISSISSIW BRITISH AVONIAN CONODONT FAUNAS 59 Australia one of us (in Jones & Druce 1966) has recently discovered a series of abundant conodont faunas extending through some 3,000 ft. of Lower Carboniferous strata. There is a striking resemblance between the Australian and the Avonian conodont successions, and although Siphonodella is abundant in the Australian faunas, it does not extend up as high as the Spathognathodus costatus group (Fig. 16). This could mean that all the Siphonodella zones of the Mississippi Valley lie below the first occurrence of S. costatus in the Avonian, and would therefore be of K age. The other implication of such a correlation would be that the North American and the German successions are more incomplete than has formerly been supposed, for it would be difficult to find any North American equivalent of the two overlying Avonian assemblage zones, if the correlation of the Avonian Polygnathus lacinatus Zone and the Mississippian Gnathodus semiglaber—Pseudopolygnathus multistriatus Zone (which seems to us to be very well established, p. 57) is accepted. This would suggest that the unconformity known to exist beneath the Sedalia Formation of the Mississippi Valley, is of greater magnitude than is generally assumed. There may not be such a break in the Oklahoma or parts of the Missouri successions (Cooper 1939 ; Branson & Mehl 1934A : 265). The Rockford Limestone fauna (Rexroad & Scott 1964) reveals an apparent transition in northern Indiana from the Siphonodella isosticha—S. cooperi Zone into the Gnathodus semiglaber—Pseudopoly- gnathus multistriatus Zone, however, and represents an anomaly if the present correlation is accepted, although most of the sections come from cores. There is, however, an unconformity in southern Indiana between the Rockford and the over- lying New Providence Shale. Even in areas of apparent transition of the two assemblage zones within the Rockford Limestone, the faunal transition is abrupt (Rexroad & Scott 1964, Table 1). Rexroad & Scott (1964 : 16-17) have written “ Although a number of species are common . . . this break between the Kinderhook and Osage Series is unusually well marked. The faunal break is sharp, but a number of species confined to the lower zone gradually decrease in number upward. Thus an unconformity within the Rockford at the Kinderhook—Osage boundary is not necessarily indicated. At the type section near Rockford (locality 10) the formation is exposed only in the bed of the East Fork of White River, and even at low water the evidence relating to a possible unconformity cannot be interpreted.” It may also be that the overlap of the Siphonodella and anchoralis faunas in Germany implies a stratigraphic break between them, in which case part of the Upper Cu IT « and Lower Cu II 8 could be unrepresented. One of the major problems concerning the anchoralis fauna is its patchy geographic distribution (p. 65). It is possible that its limited distribution in North America (it is recorded from the Pierson Formation of Missouri and the “ Sedalia’”’ of Illinois, above the uncon- formity) may mean that in places it is represented by the unconformity which we have postulated. This alternative correlation has stressed the inadequate numbers of siphonodellids in British Lower Carboniferous faunas, and its weakest point is the lack of a more detailed series of species of this genus in the Avonian. The first provisional correla- 60 BRITISH AVONIAN CONODONT FAUNAS lation, in which the ranges of gnathodid species were compared, is also limited by a comparable, tantalizing “zone of few gnathodids”’ in the Middle and Upper Hannibal of North America, and if, as we believe, both correlations are equally reasonable, they are also equally vulnerable, because of a comparable lack of detailed phylogenetic development in Britain and the United States. The present available data are insufficient to allow us to make a final choice between the two alternative correlations ; although we have shown the second on our main correlation table (Fig. 12), we have summarized the evidence for both on Fig. 16). The total stratigraphic differences involved between them are not great, and it is perhaps a paradoxically satisfying aspect of the precision which we believe conodonts offer, that we should be dissatisfied with an uncertainty of some 80 ft. in such a transatlantic correlation. A new conodont fauna associated with the goniatites Protocamites and Muen- steroceras from the Berwick Formation of Australia (Dr H. T. B. Jenkins, personal communication) contains a fauna which is similar to the Z Zone fauna of the Avonian in many respects. The pseudopolygnathids are identical to Z; and Lower Zz speci- mens. Associated with the pseudopolygnathids are many gnathodids, most of which are new species, although a few are similar to G. punctatus, a species characteristic of the upper part of Zz. Two specimens of Bactrognathus also occur in the Australian fauna, suggesting that Bactrognathus is older than has hitherto been thought likely. The fauna of Samples Z 31 to Z 38 with Gnathodus semiglaber and Pseudopoly- gnathus multistriatus is similar to that of the Gnathodus semiglaber—Pseudopoly- gnathus multistriatus Assemblage Zone of the Mississippi Valley. This Assemblage Zone coincides with the “ Sedalia ’’ Formation of the Mississippi Valley and has been correlated with the lowermost part of the Cu II 8 Zone of Western Europe. Dr W. Ziegler (personal communication) believes that the gnathodid fauna of Samples Z 34-Z 38 is identical to that found in Western Europe in beds equivalent to the Siphonodella crenulata Zone (Voges 1959) and thus of Cu II « age. C Zone. In the upper part of the Z Zone and in the lower part of the Laminosa Dolomite, Gnathodus antetexanus has been found, associated with Pseudopolygnathus cf. triangulus triangulus, Polygnathus communis and Polygnathus lacinatus. The lower limit of the Bactrognathus—Polygnathus communis Assemblage Zone in the Mississippi Valley coincides with the earliest abundance of Guathodus antetexanus, and the upper with the youngest stratigraphical occurrence of Polygnathus communis. In the Avonian of the Avon Gorge, the youngest stratigraphical occurrence of Polygnathus communis is in the middle of the Laminosa Dolomite (the base of Sample C Io). The Bactrognathus—Polygnathus communis Assemblage Zone is characterized by the presence of Polygnathus communis, Pseudopolygnathus multistriatus, Pseudopoly- gnathus triangulus pinnatus and by being the zone of abundant Gnathodus ante- texanus. Samples Z 38-C g are correlated with this Assemblage Zone. In North America, the zone extends from the base of the Fern Glen Formation to the top of BRITISH AVONIAN CONODONT FAUNAS 61 the Middle Burlington Formation. In Western Europe it ranges from upper Cu II B into lower Cu II y. In West Germany Bischoff (1957) recorded the first appearance of Mestognathus beckmanni at the base of Cu III «, but Voges (1959) found a single specimen near the base of Cu II 6/y. Kronberg, Pilger, Scherp and Ziegler (1960) also found Mesto- gnathus beckmanmi in beds of Cu II 8/y age. Meischner (1962) in his chart of strati- graphic ranges (p. 31, fig. 10) showed the stratigraphic range of Mestognathus beckmanmi as commencing at the base of Cu II 8/7. The lowest occurrence of M. beckmanmi in the Avonian is in the upper part of the Laminosa Dolomite (the base of Sample C 15). Thus the upper part of the Laminosa Dolomite appears to be of Cu II 6/y age. In North America the base of the Bactrognathus-Taphrognathus Assemblage Zone is marked by the highest occurrence of Polygnathus communis, and the top by the lowest abundant occurrence of Gnathodus texanus, which makes its first appearance near the top of the zone. The youngest stratigraphic occurrence of Polygnathus communis in the Avonian is in the middle of the Laminosa Dolomite. It is con- sidered that the middle of the Laminosa Dolomite, above the youngest occurrence of Polygnathus communis (base Sample C 10), corresponds to the base of the Bactro- gnathus—T aphrognathus Assemblage Zone of North America. In North America this zone is confined to the upper part of the Burlington Formation and is correlated by Collinson, Scott & Rexroad (1962) with the upper part of the European Cu II 8/y Zone. Since Mestognathus has not been recorded from North America, our inter- mediate faunas provide important confirmation of this correlation. The Caninia Oolite in the Avon Gorge is characterized by the presence of two species, Polygnathus bischoffi sp. nov. and Mestognathus beckmanni. In Western Europe the youngest stratigraphic occurrence of Polygnathus bischoffi sp. nov. is at the top of Cull B/y. Gnathodus texanus s.s. occurs with Mestognathus beckmanni and Polygnathus bischoffi sp. nov. in the Caninia Oolite of Fall Bay, Gower. Since the youngest occurrence of Gnathodus texanus s.s. in North America is near the top of the Bactrognathus-T aphrognathus Assemblage Zone, the upper part of the Laminosa Dolomite and the Canimia Oolite are correlated with the Taphrognathus—Bactro- gnathus Assemblage Zone and with the upper part of the European Cu II 8/y Zones. A conodont fauna from Askeaton, Eire, contains specimens of G. texanus, P. triangulus pinnatus and G. girtyi. The specimens of G. girtyi are identical to those illustrated by Hass (1953) and clearly have developed from G. texanus. The Askeaton fauna is therefore younger than the Caninia Oolite fauna and is best correlated with the Caninia Dolomite. S and D Zones. The Cavusgnathus unicornis—A patognathus libratus and the Taphrognathus varians— Cavusgnathus—A patognathus Zones of the Avonian cannot be precisely correlated with the American assemblage zones. Although they have elements in common with both the Taphrognathus varians—A patognathus and the A patognathus? geminus— Cavusgnathus Assemblage Zones of the Mississippi Valley, there are also important 62 BRITISH AVONIAN CONODONT FAUNAS differences between the two faunal successions. The Taphrognathus varians— A patognathus Assemblage Zone includes the Warsaw, Salem and the lower part of the St. Louis Formations, and it is probably equivalent to the upper part of the Cu II 8 Zone of Western Europe. The limits of this assemblage zone were defined by Collinson, Scott & Rexroad (1962) as follows : “‘ The lower limit is marked by the lowermost occurrence of Apatognathus? in the Valmeyeran Series plus the highest occurrence of common Taphrognathus varians. The upper limit is distinguished by the lowermost occurrence of Cavusgnathus and the youngest occurrence of Taphro- gnathus as well as by the lower limit of the upper zone of abundant Apatognathus”’. The lowest stratigraphic occurrence in the Avonian of specimens identical to the apatognathids illustrated by Rexroad & Collinson (1963) is near the base of Cj. Taphrognathus does not appear in the Avonian until the upper part of the S Zone, well above the first appearance of Cavusgnathus. Specimens transitional between Cavusgnathus and Taphrognathus, identical to those illustrated by Rexroad and Collinson from the boundary between the lower and upper St. Louis Formation, are found in Samples S 49 to S 58 of the Avonian. Cavusgnathus first appears in the Avonian in the middle of the Caninia Dolomite, well above the first appearance of Apatognathus, and well below the first appearance of Taphrognathus. In North America, however, the first appearance of Cavusgnathus is above the first appearance of Taphrognathus and A patognathus. In the Scottish conodont faunas, Taphrognathus varians occurs with Polygnathus lacinatus, a species which in the Avonian is common in the upper part of Zz and in the C Zone. Thus it would appear that the lowest occurrence of Taphrognathus in Britain may be considerably lower than that noted from the Avonian of the South West Province and it would then correspond more closely with the North American occurrence. The Apatognathus geminus—Cavusgnathus Assemblage Zone (Upper Se—D, of the Avon Gorge) is equivalent to the upper part of the St. Louis Formation of the Mississippi Valley and to the basal Cu III « of Germany. In Germany, Mestognathus beckmanni ranges from the base of Cu II @/y (and may extend into Cu II «) to the middle of Cu III y (Bischoff 1957) although Meischner (1962) gives the upper limit as Middle Cu III 8. Gnathodus bilineatus is present in the Cu III and E Zones of Germany and Britain (Collinson & Druce im press : Higgins 1961), and G. girtyi girtyi ranges from Cu II y into the Namurian (Bischoff 1957), although Meischner (G. givtyi Form A = G. girtyi girtyt) restricts it to the Cu III « Zone, with the possibilities of homeomorphic development throughout Cu III. In view of Bouckaert & Higgins’ (1963) record of the species from the Eg, of the Belgian Dinant Basin and its presence in P; and Pg of the Yoredale succession, the German ranges cannot be used as the basis of correlation. The absence of the gnathodids, G. semiglaber and G. texanus, as well as species of the genus Polygnathus, from this Lower Dg Subzone indicates that it is younger than Cu II y. Meischner (1962 : 31) has shown that G. girtyi simplex (G. girtys Form B of Meischner) first occurs very near the base of Cu III 8, while G. homopunctatus occurs just below the base of Cu III 8. Thus the upper boundary of the Mestog- BRITISH AVONIAN CONODONT FAUNAS 63 nathus beckmanm—Gnathodus bilineatus Zone appears to be at the base of the Cu III 8 Zone, the zone being confined to Cu III «. The fauna resembles that of the St. Louis Limestone, and has a very close similarity to that of the overlying St. Genevieve Formation. The base of Dg in the Avonian is within the Gnathodus bilineatus—Cavusgnathus charactus Assemblage Zone of North America. G. bilineatus first appears in the base of this zone in the Mississippi Valley, but the details of this North American zone are not yet fully studied (Collinson, Scott & Rexroad 1962 : 25). The species first appears in the higher part (Unit C) of the Pella Formation of Iowa (Rexroad & Furnish 1964). One anomalous aspect of this correlation is the reported first appearance of the Gnathodus girtyt group at the top of this zone in the Mississippi Valley (Collinson, Scott & Rexroad 1962 : 25). The Gnathodus mononodosus Zone includes the last appearance of M. beckmannz, which is last found in the Middle Cu III 8 of Germany (Meischner 1962). The fact that our zone is established on the basis of a new species makes more precise correla- tion difficult. G. nodosus, which first appears at the base of this zone in the North Crop, first appears in the Middle Cu III 8 zone of Germany (Meischner 1962). The overlying Gnathodus girtyi collinsoni Zone represents the first appearance of G. girtyi collinsom (= G. girtyi Form C of Meischner 1962), which first appears at the base of Cu III y, in the Middle Rhenaer Kalk of Germany. The last appearance of G. _ homopunctatus on the North Crop falls within this zone, and this is closely similar to its last appearance in Germany (Meischner 1962 : 31, Chart 10). The overall aspect of this Avonian Zone is similar to that of the pre-Middle Glen Dean Chesterian Formations of the Mississippi Valley. (i) France and Belgium There are no adequately illustrated accounts of the Lower Carboniferous faunas of France or Belgium, and our comparisons are made on the basis of published faunal lists. We have not been able to study the original specimens, and our correlations are, therefore, tentative and provisional. : Conil, Lys & Mauvier (1964) have studied the conodont faunas of the Tournaisian : and Viséan in Belgium and France. They showed that Taphrognathus (synonymous with Patrognathus gen. nov. or Clydagnathus gen. nov.) occurs in beds that are of | Tnj,-Ing, age. Associated with Taphrognathus in Tnyp are Polygnathus inor- natus, Pseudopolygnathus dentilineatus, Elictognathus costatus and Siphonodella _obsoleta, a fauna which is closely similar to that of the Upper K Zone. In Tngp Siphonodella duplicata, Siphonodella lobata and Siphonodella quadruplicata appear, whilst in Tn. Siphonodella sexplicata makes its first appearance. Tn. is characterized by the presence of the genera Pseudopolygnathus, Siphono- della and Elictognathus. The base of Tng, would appear to correlate with the upper part of the Middle Hannibal Formation of North America, based on the first occur- rence of the species Siphonodella cooper and Siphonodella sexplicata. At the base of Tn3, in Belgium and France, the following species have their first 64 BRITISH AVONIAN CONODONT FAUNAS occurrence : Gnathodus commutatus, Gnathodus delicatus, Gnathodus semiglaber and Polygnathus communis. Stphonodella obsoleta and Siphonodella duplicata are also present. In the Avonian Gnathodus delicatus first appears in Z;. It is followed in the Lower Zz Subzone by Gnathodus simplicatus and in the upper part of Zz by Gnathodus semi- glaber. Thus the upper part of Z; and the Zz Subzone would appear to be broadly equivalent in age to Tng,. There are, however, two peculiarities in the Franco- Belgian Tng, conodont fauna: firstly, the late first occurrence of Polygnathus communis, and secondly, the occurrence of Pseudopolygnathus triangulus inaequalis. Tng» is characterized in the Franco-Belgian Province by the presence of Gnathodus delicatus, Polygnathus communis, Doliognathus excavatus, Scaliognathus anchoralis, Hindeodella segaformis, Gnathodus bilineatus, Gnathodus homopunctatus and Gnathodus girtyt. In Germany two of these species, Scaliognathus anchoralis and Hindeodella sega- formis, and also one of the genera, Doliognathus, are confined to the Scaliognathus anchoralis Zone (Cu II 8/y). Gnathodus delicatus first appears at the base of the anchoralis Zone. The youngest occurrence of Polygnathus communis is within the anchoralis Zone. Gnathodus homopunctatus is present at the top of the zone, as too is Gnathodus girtyt. Gnathodus bilineatus in Germany does not appear until after the youngest strati- graphic occurrence of Scaliognathus anchoralis (the anchoralis—bilineatus interval). In the Franco-Belgian Province, on the other hand, the first appearance of the two species is contemporaneous. In the Franco-Belgian Province the youngest stratigraphic occurrence of the genus Siphonodella coincides with the oldest stratigraphic occurrence of the genus Scalio- gnathus at the base of Tng,. In Germany Siphonodella extends into Cu III « in the Hartz Mountains of the Sauerland (Voges 1959). It extends into the same zone in Spain (Dr W. Ziegler, personal communication), but in North Africa (Dr G. Bischoff, personal communication) it is limited to Cu Il. The Genus Elictognathus became extinct a short distance beneath the anchoralis Zone, at the base of the upper Siphonodella crenulata Zone (Middle Cu II «), whereas, in the Franco-Belgian Province, the latter genus became extinct at the base of Tng,. Dr S.C. Matthews is at present investigating the distribution of the anchoralis Zone fauna in Europe. In North America the base of the Sedalia Formation is an unconformity and the genera Elictognathus and Siphonodella have their youngest stratigraphic occurrence at the top of the Upper Chouteau Formation. Scaliognathus anchoralis first appears at the base of the Sedalia Formation. At the base of the Fern Glen Formation the genera Doliognathus, Staurognathus and Bactorgnathus first appear. Gnathodus delicatus, Gnathodus cf. girtyit, Gnathodus semiglaber, Gnathodus cuneiformis and Gnathodus antetexanus also are present above the base of the Sedalia Formation. In Germany there is a gap in the known conodont sequence beneath the anchoralis Zone. It appears likely, however, that Tng, of the Franco-Belgian succession is equivalent in age to the German Cu II 8/y anchoralis Zone and the Cu II 8 anchoralis— bilineatus interval combined. It also correlates with the Fern Glen and Burlington BRITISH AVONIAN CONODONT FAUNAS 65 Formations of North America. Pseudopolygnathus dentilineatus of Conil e¢ al. in Tngp is synonymous with Pseudopolygnathus multistriatus of Mehl & Thomas in the U_S-A. This would also suggest that the Tournaisian—Viséan boundary in the cephalopod facies of Germany should not be drawn as at present at the top of Cu II «, but higher in the succession at the top of Cu II. There are, however, two complications. Firstly, the type fossil of the Cu II « horizon, Pericyclus princeps, although never recorded from Germany, is recorded from the Ing, horizon of Belgium. Secondly, Pseudopolygnathus triangulus inaequalis is confined to Tng, in the Franco-Belgian Province and to the middle of the Cu I in Germany. This might imply that the German Upper Cu I and Cu II « horizons are equivalent in terms of the Franco-Belgian Tournaisian to the bedding plane boundary of Tn3.-Tngp,, but we have some reservations about the general applicability of the subspecies of Ps. tviangulus established by Voges. In Britain none of the genera Scaliognathus, Staurognathus, Doliognathus, or Bactrognathus have been found in the Avonian, although Matthews (1961) did record Scaliognathus anchoralis, Hindeodella segaformis and Doliognathus latus from the Lower Carboniferous in East Cornwall. Thus these fossils, characteristic of the anchoralis Zone in Germany were present in the British Lower Carboniferous seas. One possible explanation of their non-appearance in the Avonian is that the anchoralis Zone of Germany is represented in the Avonian by the Zz Fish Bed, which would thus represent a considerable non-sequence. Alternatively Scaliognathus anchoralis and its typical zonal associates may be limited in their distribution, either by facies or geography. This is supported by the fact that in North America, from which it was first described, S. anchoralis is known only from Branson & Mehl’s type specimen, and further intensive sampling of the type locality by Dr. C. W. Collinson has failed to produce even one additional specimen (personal communication). It does not seem to be present in Australia, although it is abundant in Germany, France, Belgium, Spain and North Africa. Some of the typical associated genera display similar anomalies in distribution. Doliognathus is abundant in some sections in Germany, but absent in others, even though its zonal associates are present in both. It may be that this group of rather bizarre genera are components of one or more natural conodont assemblages of limited tolerance. If this alternative explanation is correct, the anchoralis Zone of Germany may be represented not by a hiatus but by a succession with a different fauna in the Avonian. The exact limits of correlation are difficult to determine, but would lie within the Upper Z to Lower C Zones. It seems possible, however, that the anchoralis horizon is equivalent to the lower part of the Canimia Dolomite of the Avon Gorge, which has yielded no conodont faunas. VI. SYSTEMATIC PALAEONTOLOGY The following section contains descriptions of the species recorded in the present study. The ranges recorded in the descriptions refer to sample numbers that are listed on p. 292. 66 BRITISH AVONIAN CONODONT FAUNAS The following prefixes are used to describe the various collecting areas : Avon Gorge :_ the section at the Avon Gorge, Bristol, and immediately adjacent areas (see p. 18 and Figs. 59-69). North Crop: the northern limb of the synclinal structure of the South Wales Coalfield in Brecknockshire and Monmouthshire (see p. 22 and Figs. 7, 70-73). Scotland :_ the various sections from the Midland Valley of Scotland (see p. 29 and Figs. 79-91). Farlow: the Avonian section at Farlow, Shropshire (see p. 25 and Figs. 74-75). In numbers of cases we have made use of open nomenclature in our specific and generic assignments. We have followed this method where either the preservation or numbers (or both) of specimens were so poor that we felt it unjustifiable to use a formal name, even though we have sometimes recognized particular forms as representing new species, and, in two cases, new genera. Ranges for species are given only for the Avon Gorge and North Crop, except where species are not present in these areas. Ranges for other areas are shown on the appropriate range charts. In all cases, the ranges represent the maximum distribution of the species, which may not always be present in every sample residue between its first and last appearance. In most such cases, its absence is attributable to particular samples proving barren or producing very low yields. Catalogue numbers refer to specimens deposited in the British Museum (Natural History). Genus ANGULODUS Huddle 1934 1934 Angulodus Huddle : 76. Type sPEcIES. AHindeodella walrathi Hibbard 1927. Angulodus walrathi (Hibbard) Plate 209, fig. 8 1927 Hindeodella walvathi Hibbard : 205, text fig. 4a, b. 1934 Angulodus walvathi (Hibbard) Huddle: 77, Pl. 4, fig. 15 ; Pl. ro, fig. 5. 1934 Angulodus demissus Huddle: 77, Pl. ro, fig. 15. 1940 Angulodus elongatus Stauffer (partim) : 419, Pl. 58, figs. 1, 2 only. non 1957 Angulodus walvathi (Hibbard) Bischoff : 17, Pl. 5, figs. 44, 45. non 1961 Angulodus walvathi (Hibbard) Higgins : tro, fig. 16. MATERIAL. 21 specimens : figured, X 36. RANGE. North Crop KL 3-ZLA 6, Avon Gorge Z 4-Z 37. DescripTion. An arched elongated unit, with a straight anterior bar which is laterally compressed and deflected through 45° in a vertical plane. The anterior bar bears a series of at least 6 fine, laterally compressed, confluent, posteriorly inclined denticles, their apices being discrete. The apical denticle is about twice as high and three times as wide as the other denticles, and is of the same general form. The BRITISH AVONIAN CONODONT FAUNAS 67 posterior bar is about three times longer than the anterior bar and up to twice as deep. The denticles are fine, laterally compressed, needle-like, fused for about half their length, and posteriorly inclined at about 60° to the horizontal in the anterior third. In the posterior portion, the inclination tends to increase, so that in the recurved posterior terminus of the bar, the denticles lie parallel to the main posterior bar. The denticles of the posterior bar tend to have a hindeodellid arrangement. The posterior bar bears up to 23 denticles, about 18 of which lie anterior to the recurved posterior terminus. It has a straight aboral edge in the posterior two- thirds. The basal cavity is small and confined to the area immediately anterior to the apical denticle. Posterior bar Apical denticle N q nN hs ae > ee mae ss “sr. c 7 See ie 2 war Bas Posterior part of posterior bar : Anterior bar Anterior part of posterior bar Point of depression Fic. 17. Angulodus sp. showing morphological terms used in the text. Angulodus sp. nov. B Plate 29, figs. 5a, b MATERIAL. 8 specimens : figured, X 37. LOCALITY AND HORIZON. North Crop, River Clydach, Nr. Gilwern, upper part of Lower Z Zone. Sample ZLA 14. Rance. North Crop ZLA 8-ZLA 14, Avon Gorge Z 34-C 7. DeEscripTion. An Angulodus with robust bar, the short anterior portion being depressed and deflected. Posterior bar up to five times as long as anterior, with go° posterior depression. Stout discrete denticles. The whole unit is robust. The bar bears rather rounded lateral faces, and lacks any conspicuous lateral compression. The unit is depressed downward at both the 68 BRITISH AVONIAN CONODONT FAUNAS posterior and the anterior extremities. The apical denticle is of the same size as the denticles of the anterior bar. The anterior bar is short, depressed downward through 70° and deflected inward up to go°. It bears isolated sub-circular denticles, which tend to increase in size anteriorly. The posterior bar is about four to five times as long as the anterior bar. It is deflected through about go° at its posterior termina- tion, and bears irregular, isolated, sub-circular denticles, which increase in size posteriorly to the point of depression, when they decrease in size towards the posterior end. Those in the anterior portion of the posterior bar bear smaller denticles (about one third the width of the larger ones) between them. In aboral view the unit is excavated beneath the apical denticle and possesses an inverted basal cavity over its whole length. Here and elsewhere “‘ inverted ”’ is used to describe a basal cavity with wide flaring opening and more or less restricted internal form (see Lindstrém 1964). This is visible as a basal flange in lateral view. Angulodus sp. nov. C Plate 29, figs. 3a—4c MATERIAL. 18 specimens : figured, X 38, X 39. LOCALITY AND HORIZON. North Crop, River Clydach, Nr. Gilwern, K and Lower Z Zones. Sample ZLA Io. RANGE. North Crop KL 1-ZLA 14, Avon Gorge Z 34-Z 38. DeEscrRIPTION. A simple, stout, short unit, with a few stout, isolated denticles ; bars are deflected and depressed in at least two directions on the inner side. The apical denticle is relatively small, sub-circular in cross-section, posteriorly inclined and continuously curved at various angles towards the inner side. The short, stout anterior bar is deflected through 90° and then depressed downward through go°. It bears 3 to 4 massive, discrete, sub-circular denticles, which tend to decrease in size distally. The posterior bar is massive and very short, the anterior portion being about equal in length to the anterior bar and only slightly longer than the posterior portion. It is stout, with broadly convex lateral faces, and is slightly twisted. The posterior depression may be strong or gentle, but the distal end is depressed through about go° in both cases. It bears only 3 to 5 stout, sub-circular, posteriorly inclined, isolated denticles, the largest being at the point of depression. In aboral view the unit is expanded, the cavity being large and extremely shallow, in some cases approaching an inverted basal cavity ; it is largely confined to the anterior portion of the posterior bar (PI. 29, fig. 3c). REMARKS. This is a very unusual form, the only comparable species being Centrognathodus spurius Branson & Mehl (1934 : 198). The present specimens differ from this in the relative position of the basal cavity and the lack of an “‘ outer spur ”’. A form described as Angulodus demissus Huddle by Bischoff & Ziegler (1957 : 43) is also similar. This latter form, which is not Angulodus demissus Huddle, could be the same as our specimens. Angulodus sp. C differs from Angulodus sp. D in the nature of the posterior termination. BRITISH AVONIAN CONODONT FAUNAS 69 Angulodus sp. nov. D Plate 29, figs. Ia—2c MATERIAL. 10 specimens : figured, X 40, X 41. LOCALITY AND HORIZON. North Crop, River Clydach, Nr. Gilwern, upper part of Lower Z Zone. Sample ZLA II. Rance. North Crop ZLA 8-ZLA 14, Avon Gorge Z 34-Z 38. DescripTIon. A simple bar unit similar to Angulodus sp. C but with a longer anterior portion of the posterior bar and a less marked and distinctly denticulated depression of the posterior termination. The apical denticle is fairly small, sub-circular in cross-section, inclined posteriorly and towards the inner side, so that it does not lie in the same plane as the other denticles or the rest of the unit. The anterior bar is short, massive, deflected through go° ; horizontal or feebly arched upward and then depressed through 90°. It commonly bears 4 to 5 stout, irregular, isolated, sub-circular denticles, which tend to be tallest in the anterior part. The anterior part of the posterior bar is one and a half to twice as long as the anterior bar. The oral surface bears 3 to 4 discrete pointed denticles, their diameter being about two thirds that of the apical denticle, and their cross-sections sub-circular to biconvex. They are inclined at about 45° to the posterior bar, and are separated by irregular smaller ‘‘ hindeodellid ”’ denticles. They tend to decrease in size posteriorly towards the point of depression. The posterior part of the posterior bar is depressed at an angle of 90°. It is very short, and its oral surface is limited to a single, large, fang-like denticle. This is strongly laterally compressed, with flat to gently convex lateral faces, and anterior and posterior edges. It lies almost parallel to the anterior part of the posterior bar. The posterior termination of the unit is pointed to sharply spatulate. A minute secondary denticle may be developed on the posterior edge of the most posterior denticle. The basal cavity is confined to the area below the apical denticle. The posterior bar commonly has a very fine aboral keel along its whole length. In aboral view the sub-apical pit is large and extremely shallow, approaching the form of an inverted basal cavity. Remarks. A form similar to this species is described by Bischoff & Ziegler (1957 : 43, Pl. 20, figs. 3, 6) as Angulodus gravis Huddle. The holotype of A. gravis differs greatly from the specimens figured by Bischoff & Ziegler, but there is a marked similarity between their forms and the present specimens. Genus APATOGNATHUS Branson & Mehl 1934 1934 Apatognathus Branson & Mehl: 201. TYPE SPECIES. Apatognathus varians Branson & Mehl 1934 Apatognathus bladus sp. nov. Plate 20, figs. 15a-16b DERIVATION OF NAME. From Latin blade. 70 BRITISH AVONIAN CONODONT FAUNAS Diacnosis. Apatognathus in which denticles on anterior bar and apical denticle have very conspicuous anterior and posterior keels developed on edges. They are unusually wide and blade-like. Two largest denticles of anterior bar separated by single denticle from apical denticle. Denticles of posterior bar adjacent to apical denticle are minute. Whole unit sharply depressed at apex and strongly inwardly twisted. Inner lateral faces of both bars bear conspicuous ridges near point of contact with denticles and are flat to concave below these ridges. MATERIAL. 8 specimens : Holotype X 45, Paratype X 46 (both figured). TYPE LOCALITY AND HORIZON. North Crop, Craig-y-dinas, Breconshire. Sample CYD 7. RANGE. North Crop CYD 7. DEscrIPTION. Anterior bar of unknown length ; it is deep and thin, bearing more than 4 strong, greatly laterally compressed denticles on its oral surface, the largest two being separated from the apical denticle by a single small denticle. The denticles of the anterior bar, as well as the apical denticle, are so strongly lat- erally compressed that they have strong lateral keels developed on their anterior and posterior edges. The combined width of these keels equals or exceeds the width of the ‘‘core’’ of the denticles. The denticles are basally confluent but are discrete for most of their lengths. They are inclined slightly posteriorly. Below the base of these denticles the apical bar bears a conspicuous longitudinal ledge which is rounded and parallels the oral surface of the bar. Below this ledge the aboral surface is relatively wide and there is a slight ledge developed on its inner lateral face. It is not conspicuously excavated. The apical denticle is strongly biconvex in cross-section but the anterior and posterior edges are conspicuous features on both margins. It is elongated, but is not conspicuously greater in width than the largest denticle on the anterior bar. It is straight and tapers gradually. The posterior bar is only about one-third the depth of the anterior, but it is thicker than it is deep. Its oral surface bears a series of crowded, minute and more or less sharply pointed denticles. In cross-section the posterior bar is more or less quadrate with a sharp longitudinal ridge developed on the upper inner lateral face and a more or less smooth to flat outer lateral face. Its basal surface is the widest part of the bar and is flat. In outer aie Apical denticle __— Outer face -~ Twisted distal ly — ~~ Anterior bar Inner face Fic. 18. Apatognathus sp. showing morphological terms used in the text. Posterior bar BRITISH AVONIAN CONODONT FAUNAS 71 lateral view the lateral walls of the bar and the denticle faces are flat, and the whole unit is continuously recurved so that all denticles point inward. The slight lateral flange on the outer aboral lateral face of the anterior bar and the wide posterior aboral surface are conspicuous features. Remarks. Although our specimens are fragmentary the distinctive size and character of the denticles, as well as the form of the base, appear to set this species apart from all those previously described. Apatognathus chauliodus Varker Plate 20, figs. 1a, b, ; 2a, b 1967 Apatognathus ? chaulioda Varker : 129, 131, Pl. 17, figs. 1-3, 5. MATERIAL. 2 Specimens: figured, X 44, X 550. RANGE. Avon Gorge D 7. DescrirTion. The bars diverge at an angle of 25°-35° and in inner lateral view are inclined inwards to slightly face one another. The apical denticle is as wide as the prominent bar cusps, widest at its base and sharply pointed. It is slightly curved and inclined to the posterior. A prominent denticle is present on each of the lateral bars. These bar cusps are equal in size to the apical denticle, but are separated from it by up to 5, but commonly 2 or 3, small compressed denticles, which are shorter in length than the depth of the bar and are fused with one another. The denticles of the bar adapical to the bar cusp may be longer than the height of the bar, and are discrete. The aboral edge of the bar is straight, but the bar itself increases in depth towards the apex from its shortest depth at the adapical extremity. The bar denticles are slightly inclined inwards. The aboral edge of the bars is sharp, an aboral groove is present and the basal cavity beneath the apical denticle is circular. Apatognathus geminus (Hinde) Plate 20, figs. 3a—4b, 6a—7b 1900 Prioniodus geminus Hinde: 344, Pl. 10, fig. 25. 1928 Prioniodina ? gemina (Hinde) Holmes: 1g, Pl. 5, fig. ro. 1960 Apatognathus geminus (Hinde) Clarke : 4, Pl. 1, figs. 1, 2. 1963 non Apatognathus ? gemina (Hinde) Rexroad & Collinson: 7, Pl. 1, figs. 12-17. (=A patognathus scalena Varker). MATERIAL. 4 specimens : figured, X 54, X 55, X 56, X 57. Rance. North Crop CYD 6-3D 14/15, Avon Gorge C 16. DEscRIPTION. The most distinctive features of this species are the prominent apical denticle and the large size of two denticles on the anterior bar adjacent to that denticle. The whole unit is strongly recurved and strongly laterally flexed, so that in outer lateral view the aboral surface is visible along almost the whole length of the unit. Both bars are strongly flexed inwards so that the denticles appear to radiate 72 BRITISH AVONIAN CONODONT FAUNAS away from the apical junction. The anterior bar is relatively short and straight with a flat outer lateral face. It bears up to 7 denticles, not including the apical denticle, and these are basally confluent but apically discrete. Their outer lateral faces are strongly convex and they have sharp anterior and posterior edges and they decrease in size towards the anterior tip. The apical denticle is about twice as long as the largest of the denticles of the anterior bar. It is inclined posteriorly and is paralleled by the denticles of the anterior bar ; it is straight with a very strongly convex outer lateral face and sharp anterior and posterior edges ; it is not expanded on the outer aboral margin. The posterior bar is very slightly shorter than the anterior, and its denticles are conspicuously smaller ; they are of more or less subequal height and they are about 7 in number. They are basally confluent but apically discrete with sharp anterior and posterior edges and feebly to gently convex outer lateral faces ; these are less conspicuously convex than the faces of the anterior denticles ; on the outer lateral aboral margin of the posterior bar there is a more or less con- spicuous longitudinal ridge developed parallel to the base. We take this to be the “laterally tumid ”’ character referred to by Clarke (1960). The angle of divergence of the two bars when viewed from the outer lateral side is about 30°-40° ; they are also strongly flexed inwardly and join each other at an angle of about 40° in the inner lateral view, in such a way that the denticles of the posterior bar are erect and those of the anterior bar point outwards towards the observer. The bars are strongly flexed inward and the denticles curve inward, as well as posteriorly ; the denticles of the posterior bar are inclined anteriorly and tend to parallel the main denticle. The inner lateral faces of both the anterior and posterior bars are flat and a rather bevelled aboral edge is developed from them, excavated throughout its length by a narrow, slit-like cavity, which does not increase markedly in size below the apical denticle. Remarks. Clarke’s illustration of Hinde’s specimens makes it clear that the characteristics of the species are the relatively larger size of the denticles adjacent to the apical denticle, and the almost platform-like lateral edges developed on the posterior bar. Apatognathus petilus Varker Plate 20, figs. 12a-14b; 17a, b 1967 Apatognathus petila Varker : 135, 136, Pl. 17, fig. 11, Pl. 18, figs. 7, Io, If. MATERIAL. 23 specimens : figured, X 50, X 51, X 52, X 53. Rance. North Crop CYD 7-3D 14/15, Avon Gorge C 7-C 16, D 7. DEscRIPTION. The orientation of these units is arbitrarily defined by regarding the longer bar as posterior, although the inclination of the apical denticles does not always justify this. Apatognathus with slender elongated lateral bars continuously and strongly recurved and flexed ; apex of arch formed by them marked by develop- ment of 5 large denticles, of which three medial are largest but no single apical denticle is conspicuously larger than rest. BRITISH AVONIAN CONODONT FAUNAS 73 The dental units are slender with a straight, elongated, posterior bar. The posterior bar is about one third longer than the anterior, and has 17-24 crowded denticles, their apices being sharply to bluntly pointed but discrete ; they tend to be more or less uniform in size, though those near the distal end of the bar are slightly smaller than the rest of the series. The inner lateral face of the bar is flat and the base of the aboral edge of the bar when seen in lateral view is straight or very feebly convex. The posterior bar makes an angle of about 45° with the anterior when seen in lateral view : the posterior bar itself is slightly flexed inwards, although both the distal and proximal thirds are more or less straight. The anterior bar is shorter than the posterior, and its aboral edge is conspicuously straight. In lateral view it bears a series of crowded denticles which are confluent at their bases but apically discrete, and which have bluntly pointed free tips ; they number up to twelve and increase more or less steadily in size towards the apex. The apex is rounded on the aboral margin and is marked by the development of five rather large and conspicuous denticles, of which the three medial ones are the largest. They are curved inward and sometimes slightly posteriorly, but in most specimens they are more or less erect. They are basally confluent but apically discrete and are biconvex in cross-section, with sharp anterior and posterior edges, and gently convex lateral faces. The largest denticles tend to be large and conspicuous and, when viewed laterally, they tend to radiate from the apex of the arch. There is a slight tendency for the denticles of the posterior bar to increase in size apically. The whole inner lateral face of the unit is continuously recurved, although at any one point on the face the denticles tend to have a flat to only feebly concave surface. In outer lateral view the surface is feebly convex to flat and the aboral margin is marked by a more or less conspicuous ridge, developed on the outer lateral face. The whole aboral cavity is excavated below the apex. Remarks. The distinctive features of this species are the general form and curvature of the anterior and posterior bars and the development of the apical denticulation, in which a series of denticles, rather than any individual denticle, are of major size. Apatognathus porcatus (Hinde) Plate 31, fig. 27 1900 Prioniodus porcatus Hinde : 344, Pl. ro, fig. 26. 1928 Prioniodus porcatus Hinde ; Holmes: 22, Pl. 3, fig. 26. 1960 Apatognathus porcata (Hinde) Clarke: 5, Pl. 1, figs. 3, 4. 1963 non Apatognathus ? porcata (Hinde) Rexroad & Collinson : 8, Pl. 1, figs. 7-11. MATERIAL. 10 Specimens : figured, X 220. Rance. North Crop CYD 6-7, Avon Gorge C g-C 16. DESCRIPTION. Clarke’s diagnosis of this species, as well as his illustration of Hinde’s holotype, make it clear that its distinctive features are the relatively uniform size of the denticles, and the very strong bilateral extension of the oral surface of the 74 BRITISH AVONIAN CONODONT FAUNAS anterior bar. This is well shown by the view of the specimen illustrated on PI. 1, fig. 4 of Clarke. It seems, therefore, that the specimens described by Rexroad and Collinson must be excluded from the species, for in them the anterior bar does not appear strongly laterally expanded. Material from both Scotland and the North Crop representing this species is fragmentary but the anterior bar shows the charac- teristic very strong lateral expansion. Apatognathus scalenus Varker Plate 20, figs. ga—11b 1963 Apatognathus ? gemina (Hinde) Rexroad & Collinson : 8-9, Pl. 1, figs. 12-17. 1967 Apatognathus ? scalena Varker : 136, 137, Pl. 18, figs. 1, 2, 4, 5. MATERIAL. 10 specimens : figured, X 47, X 48, X 49. RANGE. North Crop CYD 6-3D 14/15. DeEscRIPTION. The characteristic features of this species are the strong lateral flexing of the anterior bar, the general form of the unit, the development of a strong, elongate, laterally compressed denticle at the apex, an apical angle of about 30° in lateral view, and the development of at least one strong denticle in the medial portion of the posterior bar. Varker has given a detailed description of this species. The anterior bar is about equal in length to or slightly longer than the posterior. It bears 10-14 laterally compressed, pointed, sharp edged, basally confluent, inwardly curving denticles, which increase in size proximally. The apical denticle is at least two to three times as long as the largest of the remaining denticles ; it has sharp anterior and posterior margins and a convex inner lateral face, the convexity decreasing distally. The posterior bar develops about 10 denticles, of which the one in the medial position is twice as large as its neighbours and slightly larger than that adjacent to the apical denticle. These denticles are rather less closely spaced than those of the anterior bar, and in some of them even the basal surfaces are discrete ; they are sharply pointed and stand more or less erect to the bar, but those nearest the apical denticle are recurved so that they lie more or less parallel to it. The lateral faces of both bars are marked on the inner side by a more or less conspicuous shoulder below the origin of the denticles. Both bars are twisted laterally and they diverge when viewed orally at an angle of about 30°, as well as being twisted in a horizontal plane, so that in oral view all the denticles radiate away from the apical area. In outer lateral view a conspicuous longitudinal ridge is developed at about mid- height. In both bars the aboral surface is excavated by a narrow slit-like groove, which is only slightly expanded below the apical denticle. REMARKS. In some specimens the posterior bar is marked by the development of two conspicuously large denticles, although one of these is always larger than the other. BRITISH AVONIAN CONODONT FAUNAS 75 Apatognathus varians Branson & Mehl Plate 20, figs. 5a, b 1934 Carina Medial trough Basal cavity Oral view Aboral view Fic. 20. Clydagnathus sp. showing morphological terms used in the text. 86 BRITISH AVONIAN CONODONT FAUNAS MATERIAL. 20 specimens: Holotype X 75, Paratypes X 71, x 72, X 73, X 74 (all figured). TYPE LOCALITY AND HORIZON. R. Clydach, Nr. Gilwern, K Zone. North Crop. Sample KL 5. RANGE. North Crop KL 1-KL 12, Avon Gorge K 12-K 17. DESCRIPTION. The blade is short, being only a quarter to a fifth the length of the platform. It is lateral in position, sub-triangular in profile and bears 4 to g fused, erect denticles with distinct apices. The largest denticle of the anterior blade is near the posterior end. The anterior aboral tip is bluntly spatulate. The platform is long and rather pointed, bearing lateral nodes separated by a medial trough, which usually deepens anteriorly (e.g. Pl. 1, fig. 11). In adult specimens the lateral ridges may coalesce medially, to form a sharply sinuous longitudinal ridge in the posterior portion, the medial trough then being confined to the anteriormost portion of the platform (e.g. X 72, Pl. 1, fig. 9). In other specimens the lateral ridges may be con- tinuous across the platform dividing it into a series of isolated laterally elongated troughs (e.g. X 73, Pl. 1, fig. 10), with a more or less prominent longitudinal marginal ridge on one side. The platform may be very slender, elongate and sinuous (e.g. X 74, X 75, Pl. i, figs. 13, 11). The posterior part may bear a short restricted carina of rounded, isolated nodes (e.g. X 75, Pl. 1, fig. 11) which can be produced as a short posterior blade. The inner oral rim of the platform is deflected through 80°, at the anterior end, so preventing the trough from opening anteriorly. The cavity is large, asymmetrical with thickened lips and is conspicuously laterally expanded. Remarks. This species is closely related to C. gilwernensis, from which it differs by having a lateral blade rather than a medial one. It can be distinguished from the genus Cavusgnathus by the closed medial trough and the ee gee gr type of asymmetrical sub-circular basal cavity. Clydagnathus darensis sp. nov. Plate 2, fig. 6a—7d DERIVATION OF NAME. From the type locality at Daren Ddu. DiaGnosis. Clydagnathid with relatively low, short anterior blade, consisting of 4 or 5 more or less erect denticles, those at the anterior end being only slightly smaller than those at the posterior. MATERIAL. 23 specimens : Holotype X 77, Paratype X 76 (both figured). TYPE LOCALITY AND HORIZON. R. Clydach, Nr. Gilwern, Lower Z Zone. Sample ZLA. 27. RANGE. North Crop ZL 3-ZLA 27, Avon Gorge K 17. DESCRIPTION. The unit is asymmetrical, the blade always being on the right when viewed from the posterior. The blade is low, consisting of 4 or 5 denticles all of approximately equal height, the tallest denticle being either the posterior or the BRITISH AVONIAN CONODONT FAUNAS 87 penultimate posterior. The platform is ornamented by two rows of irregular nodes. The margins are separated by a shallow trough, which generally tends to close towards the anterior, and occasionally possess a short carina at the posterior extremity. The lateral denticles on the blade side of the platform tend to be rather larger than those on the other side. In smaller specimens, the basally confluent platform denticles have sharply pointed, discrete apices in lateral view, but they become more blunt in larger specimens. The platform walls are deep, and the aboral outline is straight over the anterior two-thirds, but the posterior one-third can be deflected downwards, especially in smaller specimens. In aboral view, the unit is excavated, the cavity being large, flaring and asym- metrical, extending from nearly the posterior extremity of the platform to its junction with the anterior blade. REMARKS. This species can be distinguished from all other clydagnathids by the character of the blade. Clydagnathus gilwernensis sp. nov. Plate 2, fig. ra—d DERIVATION OF NAME. From the locality at Gilwern. Dracnosis. Clydagnathid with short, high, medial, anterior blade, and short posterior carina occasionally developed into a short posterior blade. MATERIAL. 7 specimens : Holotype X 78 (figured). TYPE LOCALITY AND HORIZON. R. Clydach, Nr. Gilwern, K Zone. North Crop. Sample KL 1. Rance. North Crop KL 1-KL 6, Avon Gorge K 6. DEsScRIPTION. The anterior blade is short and situated medially. It commonly bears three denticles, the posteriormost being the tallest and most massive. The blade denticles, which have blunt or chevron tips, are laterally compressed, and are fused at their bases. They decrease rapidly in size anteriorly. The anterio-aboral portion of the blade is strongly protruding and bluntly spatulate in profile. The platform is long, slender and posteriorly sharply pointed ; it has two lateral rows of blunt, triangular lateral nodes, with a shallow medial trough which is filled at the posteriormost extremity by a short carina of 2 to 4 nodes, which may extend beyond the platform to give a short posterior blade. On some specimens the carina may be absent. In lateral view the posterior platform of young forms is “‘ upstepped ”’ relative to the blade, but in mature specimens the unit is arched about the cavity. In aboral view there is an asymmetrical medial cavity situated in the anterior third of the platform. It has longitudinally thickened lips ; a faint groove some- times runs a short distance either side of the cavity. REMARKS. In gross morphological terms C. gilwernensis is similar to Patrognathus variabilis but the vastly different cavity, the distinctive blade and excavated medial trough serve to distinguish it. It would appear that the two forms were the result 88 BRITISH AVONIAN CONODONT FAUNAS of convergent evolution, since the ancestors of C. gilwernensis were of spathogna- thodid stock. They may have been functionally similar. Clydagnathus unicornis sp. nov. Plate 2, figs. 2a—3d, 5a, b DERIVATION OF NAME. From the single large denticle on the blade. DiaGnosis. Clydagnathid with restricted anterior lateral blade, consisting essentially of one large denticle ; median trough opens anteriorly ; basal cavity elongated and symmetrical. MATERIAL. 25 specimens : Holotype X 79, Paratypes X 80, X 81 (all figured). TYPE LOCALITY AND HORIZON. R. Clydach, Nr. Gilwern, Lower Z Zone. North Crop. Sample Z 2A. RANGE. North Crop ZL 4-ZLA 27, Avon Gorge Z I. DEscRIPTION. The unit is asymmetrical, the blade always occurring on the right side viewed from the posterior, and consisting essentially of one large denticle, sub- triangular in shape and posteriorly inclined. The tip of the denticle is sharply pointed and the anterior edge convex, forming a continuous curve with the spatulate antero-aboral margin of the blade. The anterior face of this denticle occasionally bears 2 or 3 small denticles which are fused with it, so that only thin blunt apices are visible. The platform is uneven, consisting of two rows of low irregular marginal nodes, separated by a very shallow, but rather wide, medial trough. A short carina may sometimes be present in the posterior extremity. The platform walls are deep, and on the basal faces are disrupted by the flaring of the lips of the basal cavity. In lateral view, the marginal nodes are sharply pointed in smaller specimens, but blunt or flat in larger specimens. In aboral view the unit is excavated, the cavity being asymmetrical, expanded more on the inner side than the outer. The cavity runs posteriorly, becoming narrower and shallower towards the posterior termination. It is grooved along its whole length. REMARKS. This species probably arose from Clydagnathus cavusformis by fusion of the anteriormost blade denticles to give an essentially unidenticulate blade, and by the elongation of the cavity, rather than the laterally expanded cavity of C. cavusforms. Clydagnathus sp. nov. A Plate 2, figs. 4a—d MATERIAL. 2 Specimens : figured, X 82. RANGE. North Crop KL 7-KL 13. BRITISH AVONIAN CONODONT FAUNAS 89. DEscrIPTION. A clydagnathid with a high, equally tridenticulate anterior blade, a short posterior blade, and a heavy asymmetrical basal cavity. The unit is arched and triangular in cross-section. The blade is short and high, consisting of three equal denticles fused into a blade but with free tips which are slightly divergent. The platform is lanceolate, nearly four times as long as wide, and is ornamented with two rows of denticles along the platform margins, separated by a straight, shallow, smooth trough. The denticles tend to be transversely elongate. The posterior part of the platform possesses a short carina, of about three nodes, which is produced posteriorly to give a short posterior blade. In lateral view the platform posterior to the basal cavity is deflected continuously downwards through 30°, and its depth decreases markedly towards the posterior. The basal cavity is large, ovate, nearly symmetrical and is confined to the anterior part of the platform ; it flares slightly in lateral view. Remarks. This clydagnathid is similar to C. davensis, but the blade is much higher, has fewer denticles and the deflected posterior platform is unique. The cavity is also different in that all other clydagnathids have an obviously asymmetrical cavity, whereas this form possesses a nearly symmetrical cavity. Genus EUPRIONIODINA Ulrich & Bassler 1926 1925 Euprvioniodina Bassler: 219. (nom. nud.) 1925 Synpyviontodina Bassler: 219. (nom. nud.) 1926 Euprioz:: :2 Ulrich & Bassler: 29. 1926 Synprioniodina Ulrich & Bassler: 42. TYPE SPECIES. Evuprioniodina deflecta Ulrich and Bassler 1926. DEscrRIPTION. This genus is characterized by its general pick-shape, with a short, denticulated, highly compressed anticusp. The posterior limb is long and bears numerous erect denticles. Apical denticle Anterior bar Bee, Posterior bar Outer lateral face Aboral margin Fic. 21. Euprioniodina sp. showing morphological terms used in the text. go BRITISH AVONIAN CONODONT FAUNAS REMARKS. The genera Synprioniodina, Euprioniodina and Neoprioniodus have essentially the same outline and differ in the presence, or absence, of denticles on the anticusp. The genera Synprioniodina and Euprioniodina are here considered synonyms and are characterized by a denticulated anticusp. Neoprioniodus is a similar pick-shaped form to Euprioniodina, but has no denticulated anticusp. As Scott and Collinson (1961) pointed out, there appears to be a number of forms intermediate between Euprioniodina and Neoprioniodus. Sannemann (1955), Bischoff (1956) and Helms (1959) have assigned all such specimens to the genus Prioniodina. However, the specimens they refer to Prioniodina do not closely resemble the type species of Prioniodina, Prioniodina subcurvata. A detailed revision of the pick-shaped forms is necessary, but as few specimens referable to the genus Ewprioniodina have been found in the present faunas, it is impossible to under- take this study. It is difficult to distinguish Euprioniodina from some species of Apatognathus. We have divided the two genera by assigning to A patognathus those species in which there is conspicuous lateral flexing of one or both bars. Euprioniodina caverna (Collinson & Druce) Plate 22, figs. 11a, b Synprioniodina caverna Collinson & Druce in press. MATERIAL. 14 specimens : figured, X 83. Rance. North Crop 3D 14/15. DESCRIPTION. The present specimens have a greatly elongated anterior bar, which is more or less straight, and which bears a series of at least twelve laterally compressed, confluent denticles on its anterior edge. These are small and of uniform size, being considerably smaller than any of those on the posterior bar. The apical denticle, which is aligned with the main line of the anterior bar, is relatively short ; it is sharply pointed, with sharp anterior edges and a gently convex outer lateral face. The junction of the anterior and posterior bars is marked by the development of an apical lamella, which is depressed and has a flat surface in outer lateral view. The posterior bar is straight to feebly convex in outer lateral view and is also flexed inwardly. It bears a series of about 14 denticles on its oral edge, which show a broad tendency to increase in size posteriorly, though this is not a regular feature. They are basally confluent but apically discrete and are elongated and pointed, being at least two to three times as long as those of the anterior bar. They are directed forward parallel to the apicle denticle and are also curved gently inward. In inner lateral view the surface of the posterior bar is gently convex, and that of the anterior bar more or less flat. The denticles are distinctly curved inward and there is a very sharp aboral flexure below the apical denticle with an angular to strongly convex apical lamella. The aboral surface is excavated by a narrow groove along the whole of its length, this being a continuation of the wide flaring cavity below the apical lamella. BRITISH AVONIAN CONODONT FAUNAS 91 Euprioniodina microdenta (Ellison) Plate 22, figs. 16a, b 1933 Synprioniodina sp. Gunnell : 260, Pl. 31, fig. 6. 1941 Synprioniodina microdenta Ellison : 108-111, 119, Pl. 20, figs. 43-46. 1941 Synprioniodina microdenta Ellison ; Ellison & Graves : 3-4, Pl. 1, fig. Io. 1944 Synprioniodina microdenta Ellison ; Branson : 327. 1952 Synprioniodina microdenta Ellison ; Rhodes : 893, Pl. 126, fig. 4. MATERIAL. 2 Specimens : figured, X 84. RANGE. North Crop 3D 4-3D 14/15. DESCRIPTION. The present specimens are characterized by a very short anterior bar and a greatly elongated posterior bar. In outer lateral view the posterior bar is greatly elongated, tending to increase in depth posteriorly. Its outer lateral face is flat to gently convex, and it is about equal in depth to the length of the free denticles. Its oral surface bears about 14 long, slender denticles, more or less subcircular in cross-section, though showing a slight tendency to lateral flattening. They are discrete for most of their length and are sharply pointed. They are separated by very much finer needle-like denticles, which are only a quarter to a third the width of those of the major series. All denticles slope anteriorly, and are also more or less curved inwards. They tend to increase in size towards the posterior third of the bar. The outer lateral face of the main cusp is gently convex and it has conspicuously sharp anterior and posterior edges. The anterior bar is very short, being only about one-sixth the length of the posterior ; it tapers rapidly towards its distal end. It bears 3 or 4 minute denticles, which lie parallel to the main cusp. In inner view the whole unit is gently flexed, so that the inner lateral faces are very feebly concave. The aboral margin of the posterior bar is more or less straight in lateral view, apart from its rapid curvature below the apical denticle. The two bars diverge at an angle of about 60°. The apical denticle is about three times the width of the largest denticles of the posterior bar. Euprioniodina sp. nov. A Plate 22, figs. 13a, b MATERIAL. I specimen: Holotype X 86 (figured). LOCALITY AND HORIZON. Hosie Limestone, Fife Coalfield. Sample HOSIE 2B. RANGE. Scotland HOSIE 2B. DeEscripTIon. A Euprioniodina with a massive, laterally compressed, incurved and recurved apical denticle. The anterior bar is short and pointed with up to three confluent denticles. The posterior bar is short with three minute denticles developed on the posterior edge of the apical denticle. The present specimen is very fragmentary, but it shows a massive apical denticle which is laterally compressed with sharp anterior edges and gently convex lateral faces. It is recurved sharply posteriorly in its lower portion. The short anterior bar is pointed and bears a series of two or three confluent denticles on its oral edge 92 BRITISH AVONIAN CONODONT FAUNAS which tend to decrease in size anteriorly. Three very small, confluent, laterally compressed denticles are developed on the posterior edge of the apical denticle. These are of minute size. The anterior aboral lateral face of the apical denticle is very strongly expanded laterally. whereas that of the outer lateral face is flat to feebly convex. The posterior bar is shallow and strongly laterally compressed, its outer lateral face being flat and its inner very feebly convex. The apical denticle is incurved as well as recurved. Euprioniodina sp. Plate 22, figs. 15a, b MATERIAL. 16 specimens : figured, X 85. RANGE. Avon Gorge K 4-Ke I. DEscRIPTION. The apical denticle is relatively short and compressed, with a denticulate anticusp equal in length to the apical denticle. The apical denticle is strongly compressed laterally, with sharp anterior and posterior edges. The anticusp is a continuation of the main denticle and both are slightly concave inward. The anticusp bears up to 5 laterally compressed denticles, the anterior margins of which are subparallel to the apical denticle. The posterior limb is long and thin, and is sharply bowed immediately posterior to the apical denticle, with little additional bowing behind this. The entire unit is sharply arched. The posterior limb is straight and bears at least 14 confluent, sub-equal, sub-rounded to laterally com- pressed denticles. The minute pit is located at the base of the cusp and has slightly flared lateral lips. The pit is deep, with a sharp point extending into the base of the apical denticle. Genus GENICULATUS Hass 1953 1953 Geniculatus Hass : 77. TYPE SPECIES. Polygnathus ? claviger Roundy 1926. Geniculatus sp. Plate 31, fig. 24 MATERIAL. 2 Specimens : figured X 327. RANGE. Scotland DUN 59. DESCRIPTION. Two broken specimens are present in one sample from Dunbar. Both specimens are anterior bars which are greatly inflated and bear a series of laterally compressed fused denticles with free chevron tips. In aboral view the bar is broad and has a fine median groove. RemMARKsS. The inflated bar enables the present specimens, although broken, to be referred to Geniculatus. BRITISH AVONIAN CONODONT FAUNAS 93 Genus GNATHODUS Pander 1856 1856 Gnathodus Pander : 33. TYPE SPECIES. Gnathodus mosquensis Pander 1856. Gnathodus antetexanus Rexroad & Scott Plate 18, figs. 6a—c, 8a, b, 13a-d 1947 Gnathodus texanus Roundy ; Mehl & Thomas: to, PI. 1, fig. 3. 1957 Gnathodus texanus Roundy ; Bischoff (partim) : 25, Pl. 3, fig. 22 only. 1959 Gnathodus texanus Roundy ; Voges (partim) : 284, Pl. 33, figs. 40, 42 only. 1962 Gnathodus n. sp. aff. Gnathodus texanus Roundy; Collinson, Scott & Rexroad : chart 3. 1964 Gnathodus antetexanus Rexroad & Scott : 28, Pl. 2, figs. 7-10. MATERIAL. I0 specimens : figured, X 412, X 413, X 414. Rance. North Crop ZLA 32-ZLA 33, Avon Gorge Z 33-C 9. Description. Most of our specimens are broken, but the platforms are preserved. They show the typical narrow outer platform, with a sparse covering of nodes, and the broader inner platform with the large upstanding node, which are characteristic Posterior Posterior Inner side of ) Se platform Outer side of —_ platform Node eae ——_-—— Basal cavity —— Keel Anterior Anterior A. Oral view B. Aboral view Denticles of blade Nodes of platform ————. Platform C. Lateral! view Fic. 22. Gnathodus sp. showing morphological terms used in the text. 04 BRITISH AVONIAN CONODONT FAUNAS features of the species. They are very similar to the specimens illustrated by Rexroad and Scott. Gnathodus avonensis sp. nov. Plate 18, figs. ga—d DERIVATION OF NAME. After the type section in the Avon Gorge. DiaGnosis. Gnathodus avonensis sp. nov. is closely similar to Gnathodus simplicatus sp. nov. but bears a node on one side of upper surface of platform. MATERIAL. 2 Specimens : Holotype X 411 (figured). TYPE LOCALITY AND HORIZON. Avon Gorge Zz Limestone. Sample Z 38. RANGE. Avon Gorge Z 38. Description. The platform is confined to the posterior third of the unit and is unornamented except for the presence of a single node on one side of the platform. It is biconvex in outline and narrow. In lateral view the blade is rather rectangular in outline, the 10 or more denticles being of uniform size. The anterior edge is straight, and forms a right angle with the aboral edge of the blade, which may be slightly curved. The oral edge is straight in the anterior half of the unit and slightly arched in the posterior half of the unit. The platform has a concave aboral margin in lateral view, and is less deep than the blade. There is a flaring and elongate basal cavity below the platform. REMARKS. Gnathodus avonensis sp. nov. developed from G. simplicatus sp. nov. by the formation of a single node on the side of the platform. G. avonensis sp. nov. is a homoeomorph of G. nodosus Bischoff. Gnathodus bilineatus (Roundy) Plate 18, figs. 14a-17d 1900 Polygnathus (Gnathodus) Mosquensis Pander (sic) Hinde : 342, Pl. 9, figs. 2-4. 1926 Polygnathus bilineatus Roundy : 13, Pl. 3, figs. toa—c. 1926 Polygnathus texanus Roundy : 14, Pl. 3, figs. 13a, b. 1928 Gnathodus mosquensis (Pander) Holmes : 6, fig. 31. 1939 non Gnathodus bilineatus Cooper : 388, Pl. 42, figs. 59-60. 1941 Gnathodus pustulosus Branson & Mehl: 172, Pl. 5, figs. 32-39. 1953 Gnathodus bilineatus (Roundy) Hass: 78, Pl. 14, figs. 25-29. 1956 Gnathodus bilineatus (Roundy) Elias: 118, Pl. 3, figs. 23-29. 1956 Gnathodus pustulosus (Branson & Mehl) Elias: 115, Pl. 3, figs. 1-8. 1957 Gnathodus bilineatus bilineatus (Roundy) Bischoff: 21, Pl. 3, figs. 11, 15-20 ; Pl. 4, fig. 1. 1957 Gnathodus bilineatus bilineatus (Roundy) Ziegler im Fliigel & Ziegler : 38, Pl. 3, figs. I, 2 only. 1957 Gnathodus modocensis Rexroad : 30, 31, Pl. 1, figs. 15-17. 1958 Gnathodus modocensis Rexroad ; Rexroad: 17, 18, Pl. 1, figs. 1, 2. 1959 Gnathodus bilineatus (Roundy) Voges: 282, Pl. 33, figs. 28-30. 1959 Gnathodus (Harltonodus) bilineatus (Roundy) Elias : 145, Pl. 1, figs. 3-12. 1959 Gnathodus (Harltonodus) bransom Elias : 147, Pl. 1, figs. 13-18. 1959 Gnathodus (Harltonodus) minutus Elias : 148, Pl. 1, figs. 22-25. 1959 Gnathodus (Harltonodus) multilineatus Elias : 149, Pl. 1, figs. 26-28. BRITISH AVONIAN CONODONT FAUNAS 95 1960 Gnathodus smithi Clarke : 26, Pl. 4, figs. 13-14 ; Pl. 5, figs. 9 & Io. 1961 Gnathodus bilineatus (Roundy) Higgins: PI. to, fig. 5. 1962 Gnathodus bilineatus (Roundy) Higgins : (partim), Pl. 2, fig. 25 only. 1962 Gnathodus bilineatus bilineatus (Roundy) Meischner : 31, fig. ro. 1965 Gnathodus bilineatus (Roundy) Dunn: 1148, Pl. 140, figs. 7-9. Gnathodus bilineatus (Roundy) Collinson & Druce in press. MATERIAL. 765 specimens, North Crop : figured X 416, X 417, X 93, X 94. Rance. North Crop 3D 10-3D 23. DEscRIPTION. This is one of the most abundant species in the higher parts of the section of the North Crop and, although it displays considerable variation, its main features agree closely with those described by earlier authors, especially Hass (1953) and Bischoff (1957). There is considerable variation in the ontogeny of this species. The main variation concerns the increase in the relative size and angularity of outline of the outer lateral platform, and its increasingly strongly developed ornamentation. In young forms this tends to be inconspicuously nodose and rather irregular, but in older forms it becomes either longitudinally linear or broadly concentric in disposition, and the nodes become stronger, tending to form elongate ridges. There is also considerable variation in the strength of the inner lateral platform and of the transverse denticles developed upon it. In numbers of specimens it is pinched inwards in the anterior half when seen in oral view. There is also appreciable variation in the depth and relative width of the sulcus that separates these denticles from the carina. In spite of its extent, the variation appears to be continuous, and there is no obvious difference between specimens collected from different parts of the range of the species. Gnathodus commutatus (Branson & Mehl) Plate 19, figs. ga—-12d 1941 Spathognathodus commutatus Branson & Mehl : 98, Pl. 19, figs. 1-4. 1941 Spathognathodus commutatus Branson & Mehl; Ellison & Graves: 3, 4. Pl. 2, fig. 6, (non Pl. 2, fig. 4=Gnathodus symmutatus?). 1953 Gnathodus inornatus Hass : 8o, Pl. 14, figs. 9-11. 1956 Spathognathodus commutatus Branson & Mehl; Elias: 1109, Pl. 3, figs. 19-22. 1956 Spathognathodus inornatus Hass ; Elias: 1109, Pl. 3, figs. 37-39. 1956 Spathognathodus cf. inornatus Elias : 1109, Pl. 3, figs. 41, 42, (non Pl. 3, figs. 62, 63=G. symmutatus?). 1957 Gnathodus commutatus commutatus (Branson & Mehl) Bischoff : 22, Pl. 4, figs. 2-6, 15. 1957 Spathognathodus cf. S. commutatus Branson & Mehl ; Rexroad : 38, Pl. 3, figs. 23, 24. 1957 Gnathodus commutatus commutatus (Branson & Mehl) Ziegler in Flugel & Ziegler 39, Pil 3; fig. 21. 1958 Gnathodus inornatus Hass ; Stanley : 465, Pl. 68, figs. 5, 6. 1958 Spathognathodus cf. S. commutatus Branson & Mehl ; Rexroad : 26, Pl. 6, fig. 8. ~w 96 BRITISH AVONIAN CONODONT FAUNAS non 1958 Gnathodus commutatus commutatus (Branson & Mehl) Lys & Serre: 8o1, Pl. 9, figs. 2a, b (=G. symmutatus). 1959 Gnathodus commutatus commutatus (Branson & Mehl) Voges: 281. 1960 Spathognathodus commutatus Branson & Mehl ; Clarke : 109, Pl. 3, figs. 4, 5. 1960 Gnathodus commutatus commutatus (Branson & Mehl) Serre & Lys : 39, fig. 3. 1961 Gnathodus commutatus (Branson & Mehl) Rexroad & Burton : 1153, Pl. 1309, figs. I-3. 1961 Gnathodus commutatus var. commutatus (Branson & Mehl) Higgins: 212, Pl. 10, figs. 6, text-fig. 1a, (left figure only). 1962 Gnathodus commutatus commutatus (Branson & Mehl) Higgins: PI. 2, fig. 22. 1962 Gnathodus commutatus commutatus (Branson & Mehl) Meischner : 31, text-fig. ro. 1963 Gnathodus commutatus commutatus (Branson & Mehl) Bouckaert & Higgins: 17, fig. 3. 1964 Gnathodus commutatus pellaensis Rexroad & Furnish : 671, Pl. 111, fig. 3. Gnathodus commutatus (Branson & Mehl) Collinson & Druce in press. MATERIAL. 425 specimens : figured, X 418, X 95, X 96, X 97. RANGE. North Crop CYD 7-3D 22, Avon Gorge S 53. DESCRIPTION. This species has recently been redefined by Collinson & Druce (in press) and it is their revised description which is accepted here. Although the species, which is represented by many specimens in the present collections, shows appreciable variation, the distinctive characteristics are the regular sub-rectangular outline of the blade when seen in lateral view, the regular height and thickness of the confluent denticles which make up the blade, the rather square anterior profile of the blade, and the small posteriorly restricted sub-oval to sub-circular unornamented platform. This platform is always asymmetrical in detail, and shows considerable variation in its basal outline and in the degree of flexure of its basal margin. This variation is so obviously transitional, however, that it seems impossible to dis- tinguish any discrete categories on the basis of it. The chief variation is in the general form of the posterior platform, which varies from slenderly sub-elliptical to sub-circular, in the degree of symmetry of the posterior platform, which is generally marked by the inner margin being wider anteriorly than it is posteriorly, and in the relation of the carina to the posterior margin of the platform. In some cases the posterior margin of the platform tends to be relatively elongated, while in others it tends to be bluntly rounded. The carina may, in some specimens, extend slightly beyond the posterior margin when seen in oral view (PI. 19, fig. 9d) but in others it terminates anteriorly to the margin. In a few cases the posterior portion of the carina is strongly deflected laterally. In most individuals the central blade tends to become thicker posteriorly, where it forms the carina of the posterior platform (e.g. Pl. 19, fig. rod). The surface of the posterior platform is smooth and the platform itself occupies only the posterior quarter or third of the total length of the unit. The broad variation within this species noted by Collinson and Druce is also shown by the present specimens. REMARKS. In many specimens the blade is straight, but in others it is gently curved in a horizontal plane ; in these cases the wider of the two platforms in the anterior position is always that on the concave side of the blade. BRITISH AVONIAN CONODONT FAUNAS 97 Gnathodus cuneiformis Mehl & Thomas Plate 8, figs. 6a—c 1939 Gnathodus mosquensis Pander ; Cooper (partim) : 388, Pl. 41, figs. 23-25 only ; Pl. 42, figs. 75, 76. 1939 Gnathodus stinus Cooper : 388, Pl. 14, figs. 40, 41. 1947 Gnathodus cuneiformis Mehl & Thomas : 1o, Pl. 1, fig. 2. 1962 Gnathodus cunetformis Mehl & Thomas ; Collinson Scott & Rexroad : Chart 3, p. Io, 2223 MATERIAL. I specimen : figured, X 98. RANGE. Avon Gorge S II. DEscRIPTION. This species is characterized by a high, slightly asymmetrical, arrow-shaped platform, bearing a single row of nodes on either side of the carina. The flanks of the platform are smooth and steep. ReMARKS. The shape of the platform and the single row of nodes on either side of the carina distinguish this species from other gnathodids. In North America this species is characteristic of the Sedalia, Fern Glen and Burlington Formations. Gnathodus delicatus Branson & Mehl 1938 Plate 18, figs. 12a-d. Plate 30, figs. 6a-c 1938 Gnathodus delicatus Branson & Mehl: 145, Pl. 34, figs. 25-27. 1938 Gnathodus perplexus Branson & Mehl: 145, Pl. 45, fig. 24. 1939 Gnathodus texanus (Roundy) Cooper: 388, Pl. 41, figs. 26, 27. 1951 Gnathodus delicatus Branson & Mehl ; Hass : 394, Pl. 46, figs. 3-7. 1957 Gnathodus commutatus punctatus Bischoff ; Fliigel & Ziegler : Pl. 111, figs. 16, 17, 24. 1959 Gnathodus delicatus Branson & Mehl ; Voges: 283, Pl. 33, figs. 31-33. 1960 Gnathodus delicatus Branson & Mehl; Kronberg, Pilger, Scherp & Ziegler: PI. 4, figs. 7-12. 1962 Gnathodus delicatus Branson & Mehl ; Collinson, Scott & Rexroad : 10, Chart 3, 21, 22. 1962 Gnathodus delicatus Branson & Mehl ; Higgins : 13, Pl. 3, fig. 33 ; Pl. 2, figs. 23, 24. 1962 Gnathodus delicatus Branson & Mehl‘ Zeigler: Pl. 4, fig. 4. 1963 Gnathodus delicatus Branson & Mehl ; Ziegler : 327, Pl. 2, figs. 5, 7, 8, 9, 13, 14. 1963 Gnathodus delicatus cuneiformis Ziegler : Pl. 2, fig. 12. 1964 Gnathodus delicatus Branson & Mehl ; Rexroad & Scott : 29-30, Pl. 2, figs. 4-6. 1964 Gnathodus delicatus Branson & Mehl ; Higgins, Wagner-Gentis & Wagner : 226, Pl. V, fig. 24. 1964 Gnathodus cf. delicatus Branson & Mehl ; Higgins, Wagner-Gentis & Wagner: 226, Pl. V, fig. 23. MATERIAL. II specimens : figured, X 87, X 426. RANGE. North Crop ZLA 5—-ZLA 6, Avon Gorge Z 28-Z 37. DESCRIPTION. The asymmetrical platform of this species is ornamented by two rows of nodes, one on the narrower inner side, and one on the wider outer side, both running parallel to the carina. The inner platform bears a row of up to g denticles parallel to the carina, and slopes steeply at its margin. The outer platform bears a row of 5 denticles, parallel to the carina, on its inner side, and may also show traces of 98 BRITISH AVONIAN CONODONT FAUNAS the development of a second row. There is a uniform sharp slope towards the margin. The platform is arrow-shaped, being widest at the anterior. It becomes pointed towards the posterior. The inner platform extends further anteriorly than does the outer. The denticulate blade is equal in length to the platform. In lateral view, the oral and aboral edges of the blade are straight ; the oral and aboral edges of the platform are slightly curved. The anterior and posterior edges are straight. REMARKS. Specimens from the Zg beds of the Avon Gorge have a row of nodes on either side of the carina. In some examples, the anterior nodes of the inner side of the platform are fused to form a parapet. These forms are considered to be transi- tional with Gnathodus sennglaber, or possibly with Gnathodus antetexanus. This species is common in conodont faunas of late Kinderhookian and early Valmeyerian age in North America. Rexroad & Scott (1964) after studying hundreds of specimens, came to the conclusion that the low, broad, asymmetrical outline of the platform, and the linear arrangement of nodes seem to be consistent characters, and similar specimens obtained in the present study have, therefore, been placed in this species. Gnathodus girtyi girtyi Hass Plate 17, figs. ga—-12d 1953 Gnathodus girtyi Hass : 80, Pl. 14, figs. 22-24. 1956 Gnathodus girtyi Hass ; Elias : 118, Pl. 3, figs. 30, 31. 1957 Gnathodus girtyi Hass ; Bischoff (partim) : 24-25, Pl. 4, figs. 16-17, 22-23 (non Pl. 4, fig. 21=Gnathodus girtyi simplex Dunn). 1957 Gnathodus girtyi Hass: Lys & Serre : 1043, Pl. 2, figs. 7a—c. 1958 Gnathodus ? sp. Rexroad : 18, Pl. 1, figs. 3-5. 1960 Gnathodus clavatus Clarke : 28, Pl. 4, figs. 4-6 (non Pl. 4, figs. 7-9=G. girtyi simplex Dunn). 1961 Gnathodus givtyi Hass ; Higgins : 220, Pl. fo, fig. 4. 1961 Gnathodus n. sp. Rexroad & Collinson : PI. 1. 1961 Gnathodus givtyi Hass ; Rexroad & Jarrell : 2015. 1962 Gnathodus girtyi Hass ; Collinson, Scott & Rexroad : Chart 4. 1962 Gnathodus givtyi Hass Form A Meischner : 31, text-fig. Io. 1963 Gnathodus girvtyi Hass Form C Bouckaert & Higgins : 17, text-fig. 3. Gnathodus girtyi givtyi Hass ; Collinson & Druce in press. MATERIAL. 780 specimens : figured, X 103, X 104, X 105, X 106. RANGE. North Crop CYD 5-3D 23, Avon Gorge D 26. DESCRIPTION. The main features of this subspecies have been described in detail by Collinson & Druce (in press) and the present specimens, although showing some variation, agree in all major respects with their description. The most distinctive features are the long slender form of the unit, with the anterior blade commonly being strongly laterally compressed and relatively high in relation to its length ; it occupies at least half the total length of the unit. It is straight to curved in oral view. The unit as a whole is straight or curved in a horizontal plane, and the curvature is chiefly concentrated in the posterior portion of the carina (e.g. Pl. 17, BRITISH AVONIAN CONODONT FAUNAS 99 . figs. 11, 12). The blade is generally highest at its anterior end, although the two most anterior denticles may be relatively small ; the posterior end of the unit tends to be lower. The blade has a bluntly spatulate to rectangular anterior end and a more or less straight or very feebly convex aboral edge. The denticles are fused to about mid-height but their apices are discrete. The carina consists of low, fused denticles, of about equal height to those at the posterior portion of the anterior blade. The carina is depressed in the posterior half of the platform, and the level of the denticles tends to be relatively higher than those of the lateral ornament, which reaches about two thirds of the total depth of the posterior platform from the top of the carina. The posterior platform itself is characterized by a variably asymmetrical basal outline. In some specimens the basal outline is almost biconvex, but in most the outer aboral margin is more con- spicuously flared than the inner ; in a few individuals it is so strongly flared that it gives to the basal outline a form reminiscent of such species as G. bilineatus or G. semiglaber (e.g. Pl. 17, fig. 12a). In spite of this, the platform ornament remains distinctive ; the ornament on the inner lateral surface of the platform extends further forward than that on the outer, and consists of a low series of fused nodes, running sub-parallel to the carina but converging with it in the posterior platform, and looping round the posterior end of the carina to give a bluntly rounded, pointed outline (e.g. cf. Pl. 17, figs. 11b, 12b). The outer platform ornament tends to be less conspicuous than that of the inner; the lateral ridges, which characterize the denticles of the inner platform, are absent from the outer platform. The basal cavity is flaring and asymmetrical, being deepest in the anterior third of the platform and continuing for a variable distance below the posterior portion of the anterior blade. REMARKS. In some individuals (e.g. Pl 17, fig. rob) the posterior carina tends to continue somewhat beyond the level of the lateral denticles, which then tend to merge with it anterior to the termination of the platform. In this they approach other subspecies of the genus but are otherwise distinguishable from them. Gnathodus girtyi collinsoni subsp. nov. Plate 16, figs. 5a—-8d 1962 Gnathodus givtyi Form C Meischner : 31, fig. Io. 1963 Gnathodus girtyi B Hass ; Bouckaert & Higgins: 17. 1965 Gnathodus roundyi Gunnell ; Murray & Chronic (partim) : 598, Pl. 71, figs. 5, 6 only. DERIVATION OF NAME. After Dr. Charles W. Collinson. Dracnosis. Subspecies of Gnathodus girtyi in which lateral denticulation of platform is confined to inner lateral side. Very feeble nodes may sometimes be developed on outer lateral platform. MATERIAL. 13 specimens : Holotype X 99, Paratypes X 100, X ror, X 102 (all figured). TYPE LOCALITY AND HORIZON. North Crop. Sample 3D 14/15. 100 BRITISH AVONIAN CONODONT FAUNAS RANGE. North Crop 3D 8-3D 14/15. DescripTION. In broad morphology this subspecies resembles Gnathodus girtyi girtyi. The form of the anterior blade, and its general denticulation, the general outline and the size and depth of the posterior platform are generally similar. The number of denticles in the main blade (including the carina) ranges from 21 to 25. The distinctive feature of this subspecies is the denticulation of the posterior platform. The inner-lateral oral surface of the platform has a conspicuously developed, parapet-like series of denticles, those at the anterior end being higher than those at the posterior. These denticles are individually rather small and incon- spicuous, but the ridge which they form is itself made conspicuous by the general height and thickness of the base. They number about g, and are small rounded discrete node-like structures. Those at the anterior end of the series are separated from the carina by a shallow longitudinal groove. Towards the posterior end of the series the denticles converge with the main carina, which they meet near the anterior end of the fourth denticle from the posterior terminus of the unit. In lateral view these denticles form a conspicuous shoulder-like feature of the platform. The sloping anterior aboral margin terminates near the anterior end of the basal cavity. On the outer lateral platform, very indistinct node-like denticles may sometimes be developed but they are always a relatively inconspicuous feature, though in a very few specimens they are barely discernible in both lateral and oral view (e.g. Pl. 16, figs. 7a—-d). Gnathodus girtyi simplex Dunn Plate 16, figs. 1a—4d 1957 Gnathodus girtyi Hass ; Bischoff : 24, 25, Pl. 4, fig. 21 (non Pl. 4, figs. 16, 17, 22, 23=G. girtyi givtyt Hass ; non Pl. 4, figs. 18-20=G. girtyi turritus Collinson & Druce. 1957 Gnathodus girtyi Hass ; Ziegler in Fliigel & Ziegler: 40-41, Pl. 3, figs. 6, 9-13, 20., 1957 Gnathodus bilineatus semiglabey Bischoff ; Ziegler 7m Fligel & Ziegler: Pl. 3, fig. 22 (non Pl. 3, figs. 5, 8, 14, 23 =Gnathodus semiglaber). 1959 Gnathodus texanus Roundy ; Voges: 284-285, Pl. 33, figs. 40-43. 1960 Gnathodus clavatus Clarke (partim) : Pl. 4, figs. 7-9 (non pl. 4, figs. 4-6=Gnathodus givtyt givtyi Hass). 1962 Gnathodus texanus Roundy ; Higgins : Pl. 3, fig. 28. 1962 Gnathodus girtyi Form B Meischner : 31, text-fig. Io. 1963 Gnathodus girtyi Form A Hass ; Bouckaert & Higgins : 17, text-fig. 3. 1965 Gnathodus girtyi simplex Dunn: 1148, Pl. 140, figs. 2, 3, 12. Gnathodus girvtyi simplex Dunn ; Collinson & Druce in press. Di1aGnosis. Subspecies of G. givtyi in which lateral denticles on both inner and outer lateral margins of platform are more feebly developed than in G. girtyi girtyi and are also restricted to anterior and medial parts of platform. MATERIAL. 260 specimens : figured, X 107, X 108, IIO, III. Rance. North Crop CYD 7A-3D 23, Avon Gorge D 26. Description. In lateral and aboral views the main features of this subspecies are closely similar to those of G. girtyi girtyi especially in the form of the anterior blade BRITISH AVONIAN CONODONT FAUNAS 101 and of the basal cavity. The most conspicuous difference is in the character of the accessory lateral denticles on the posterior platform. The denticles on the inner lateral platform are relatively more strongly developed than those on the outer. They consist of up to 9 denticles, the highest and most massive being at the anterior end, and are separated by a trough from the main median carina. Those towards the posterior end of the series tend to be smaller and also to be developed nearer to the carina. The denticles of the outer lateral platform are smaller and fewer in number and extend further posteriorly than those on the inner lateral platform. In oral view both series of lateral nodes converge posteriorly and fuse with the median carina, the carina extending further posteriorly than either series of lateral denticles. In lateral view the denticles of the inner series approach the height of those on the median carina, but are still fractionally shorter. In outer lateral view the denticles at the posterior end of the outer lateral series tend to be slightly larger and more con- spicuous than those at the anterior end. The apron on the outer lateral platform, when seen in oral view, is relatively much more laterally expanded than that of the inner lateral platform. The denticles on the inner lateral platform tend to be developed in a semi-transverse form, their outer edges being higher than their inner. They show semi-radiate development around the central point of the inner lateral platform, but this is not strongly marked in all individuals. RemARKS. This subspecies was recognized as a distinct group by Meischner (1962) and Bouckaert & Higgins (1963). Gnathodus girtyi soniae subsp. nov. Plate 17, figs. 5a—8d DERIVATION OF NAME. After Miss Sonia J. Kostromin. DraGnosis. Subspecies of Gnathodus girtyi resembling G. girty: girtyi in having ornamentation developed continuously around posterior platform and encircling posterior termination of carina, but differing in development of 1 or 2 low rounded inconspicuous nodes on outer-anterior-lateral surface of platform. MATERIAL. 18 specimens: Holotype X 113, Paratypes X 115, X 112, X 114 (all figured). TYPE LOCALITY AND HORIZON. North Crop. Sample 3D 12. RANGE. North Crop 3D 2-3D 14/15. DeEscriPTION. A subspecies of Gnathodus girtyi with greatly expanded apron-like posterior platform, the sides sloping sharply down. The median carina is strongly developed and its posterior end is completely encircled by the lateral denticles of the platform. The inner-lateral parapet is the highest single feature of the platform ornament. It begins at a point anterior to the origin of the ornament, on the outer lateral side, and has 3 or 4 massive laterally elongate denticles, the highest of which tend to be those at the posterior end ; they are separated from the carina by a narrow sulcus, which opens anteriorly into a siphonodellid-like spout. The denticles decrease posteriorly in size, and are arranged as a linear series of low node-like forms. 102 BRITISH AVONIAN CONODONT FAUNAS On the outer-lateral margin of the platform one or two low rounded denticles are developed. These tend to be developed about midway along the length of the platform, and are visible but not conspicuous in lateral view. The aboral cavity is large and flared, and the quadrate outline of the outer lateral margin of some specimens is strongly reminiscent of G. bilineatus. Gnathodus girtyi turritus Collinson & Druce Plate 31, fig. 23 1957 Gnathodus girtyi Hass ; Bischoff: 24, 25, Pl. 4, figs. 18-20 (non figs. 16, 17, 22, 23= Gnathodus girtyi givtyi Hass ; non pl. 4, fig. 21=G. girtyi simplex Dunn). Gnathodus girtyi turritus Collinson & Druce in press. MATERIAL. 5 specimens : figured, X 116. RANGE. North Crop 3D 19-3D 23. DEscRIPTION A subspecies of G. girtyi with a low posteriorly reduced carina. The lateral denticle ridges are generally continuous around the posterior edge of the platform. The sides of the posterior platform are nearly vertical. REMARKS. The subspecies is extremely rare in our collections. Transitional specimens of G. girtyi girtyi are present in faunas from Yorkshire and the North Crop. It is difficult to refer these transitional specimens to one or other subspecies with any certainty. Gnathodus girtyi subsp. nov. A Plate 17, figs. 1a—3d MATERIAL. 3 specimens : figured, X 117, X 118, X 119. Rance. North Crop CYD 7. DEscRIPTION. A subspecies of G. girtyi characterized by the development of 1 or 2 vertical lateral pillars near the anterior inner end of the platform. The pillars extend from the oral surface almost to the aboral margin. The three specimens upon which this new subspecies is based show the general features which are characteristic of G. girtyi girtyi. They differ from that subspecies, however, in being left forms in which the longer inner lateral denticulated margin of the platform is produced downwards by an unornamented, vertical column. In one specimen (PI. 17, figs. 3a—d) this column reaches the aboral margin which is deflected by it. In this particular specimen the vertical pillar occurs about one quarter of the platform length behind the anterior end of the inner lateral denticle ridge. In the specimen illustrated in Pl. 17, fig. 1, the vertical pillar occupies the same relative position but is much less conspicuous, and the lateral margin only is conspicuously offset by it. In this specimen the oral margin of the denticulation is not disturbed in any way by a development of the lateral pillar. In the specimen shown in PI. 17, fig. 2, two sharply angular vertical ridges are developed in the same relative position, but neither of these extends into the aboral margin ; between them there is a BRITISH AVONIAN CONODONT FAUNAS 103 regularly ‘‘ U”’ shaped concave depression in the lateral face ; their upper termina- tions are bluntly pointed, and in this case they are joined to the main ridge of plat- form denticles by inconspicuous lateral ridges, although the denticle line is not broken by them. The ridge is not denticulated or ornamented in any obvious way in any of the three specimens. REMARKS. It is possible that these three forms are pathological variants of G. girtyi girtyi but their restriction to a single sample and the fact that all three are left lateral forms makes this seem unlikely. Gnathodus homopunctatus Ziegler Plate 19, figs. 5a—8d 1957 Gnathodus commutatus punctatus Bischoff : 24, Pl. 4, figs. 7-11, 14. non 1957 Gnathodus commutatus punctatus Bischoff ; Ziegler in Fliigel & Ziegler : 40 (Pl. 3, fig. 16 = juvenile of Gnathodus bilineatus punctatus (Cooper) 1939 ; PI. 3, figs. 17, 24=Gnathodus sp.). 1959 Gnathodus commutatus homopunctatus [Ziegler] Voges : 281. 1960 Gnathodus commutatus homopunctatus Ziegler : 39, 5, Pl. 4, fig. 3 (nom. nov. for Gnathodus commutatus punctatus Bischoff 1957 non Cooper 1939). 1961 Gnathodus commutatus homopunctatus Ziegler ; Higgins: Pl. ro, fig. 9, text-fig. Ic. 1962 Gnathodus commutatus homopunctatus Ziegler ; Higgins: Pl. 2, fig. 21. Gnathodus homopunctatus Ziegler ; Collinson & Druce in press. MATERIAL. 146 specimens : figured, X 120—-X 123. Rance. North Crop CYD 7-3D 14/15. DEscRIPTION. There is some similarity and degree of transition between this species and G. symmutatus, but the present species differs in having a relatively shorter and more symmetrical posterior platform, with the development of more conspicuous denticulation. There is some variation in this denticulation ; in immature specimens (e.g. Pl. 19, fig. 5c) it is barely developed, and is present only as rather dark, slightly elevated lateral ridges. In other specimens it tends to be arranged at an acute angle to the anterior part of the blade, and consists only of short barb-like lines of denticles. In most specimens, however, it forms more or less symmetrical lines of low blunt denticles, developed parallel to the outer margin of the platform, about midway between its lateral margin and the position of the carina. In most individuals the development on the two sides of the carina is equal, but in others it is asymmetrical. Gnathodus mononodosus sp. nov. Plate 19, figs. 13a-15d 1961 Gnathodus commutatus var. nodosus Bischoff ; Higgins : PI. ro, fig. 7 only, text-fig. rb. DERIVATION OF NAME. From single node on the inner side of cup. Diacnosis. Straight to slightly curved blade with subcircular to sub-quad- rangular cup, bearing strong, generally elongate node on inner side. 104 BRITISH AVONIAN CONODONT FAUNAS MATERIAL. 230 specimens : Holotype X 124, Paratypes X 125, X 126 (all figured). TYPE LOCALITY AND HORIZON. North Crop. Sample 3D 14/15. RANGE. North Crop CYD 7-3D 19. DescripTION. The blade is generally slightly curved. In lateral view both the oral and aboral outlines are nearly straight, although the anterior is slightly higher in some specimens. The denticles tend to be larger and more distinct at the anterior end and become increasingly small and fused toward the posterior. Most are fused to their tips. Both ends of the blade are nearly vertical in most specimens. The posterior end of the cup may project beyond the blade. In oral view the cup is characteristically sub-quadrangular and slightly asym- metrical. The inner half bears a single node which is characteristically large and elongate but in some specimens round. The blade is typically more than twice the length of the cup. REMARKS. This species is very close to G. nodosus. That it is not merely a random variant of nodosus, in which one or the other node is undeveloped, is shown by the fact that the single node occurs only on the inner side of the cup. The present specimens tend to show all the main forms of variation exhibited in the platform by G. commutatus. They also show the rectangular profile of the blade of that species when seen in lateral view, and also the relative variation in the curvature and termination of the carina on the posterior end of the platform. In a very few specimens the outline of the platform is more reminiscent of G. symmutatus, but it differs from that species in having the square lateral profile of the blade, the oral surface being of more or less uniform height, and not showing the pronounced decrease in size of the posterior denticles over most of the length of the platform (see p. 108). In a few specimens the inner platform is more elongate than in typical members of the species, the anterior margin being elongated at right angles to the line of the blade. These individuals are further distinguished by the presence of two denticles on the inner platform developed in a line lying at about 45° to the blade and pointing anteriorly, and both being rather laterally compressed and basally confluent but with more or less distinct apical tips. These specimens are so close in every other respect to those with a single denticle, that there seems no good reason for separating them. In some specimens the denticle is not fully developed, but is represented by a slight swelling occupying the same relative positions on the inner lateral platform, and directed at about 45° to the anterior portion of the blade. There are transitions between this partial development of the denticle and full development of the denticle itself. Gnathodus nodosus Bischoff Plate 19, figs. 16a—20c 1957 Gathodus commutatus nodosus Bischoff (partim) : 23-24, Pl. 4, figs. 12, 13. 1957 Gnathodus commutatus nodosus Bischoff ; Ziegler in Fliigel & Ziegler : 40, Pl. 111, fig. 4. BRITISH AVONIAN CONODONT FAUNAS 105 1958 Gnathodus commutatus nodosus Bischoff ; Lys & Serre : 891, Pl. 9, figs. 3a, b, 4a, b. 1961 Gnathodus commutatus var. nodosus Bischoff ; Higgins (partim) : 213, Pl. to, figs. 8 (non fig. 7) ; text-fig. 1b (non figs. in lower left or in uppermost left). 1962 Gnathodus nodosus Bischoff ; Higgins: Pl. 2, fig. ro. 1962 Gnathodus comm. nodosus Bischoff ; Meischner : 31, text-fig. 10. 1963 Gnathodus commutatus nodosus Bischoff ; Bouckaert & Higgins : 17, fig. 3. Gnathodus nodosus Bischoff ; Collinson & Druce in press. MATERIAL. 220 specimens: figured, X 509, X 510, X 127, X 128, X 129. RANGE. North Crop 3D 10-3D 22. DESCRIPTION. This species shows some characteristics with both G. mononodosus and G. commutatus. These include the posteriorly restricted laterally expanded sub-circular to asymmetrical platform, and the rectangular lateral profile of the uniform blade. The distinctive feature of the present species is the development of denticles on both sides of the posterior platform. These are generally unevenly developed, the one on the inner lateral side (represented by the concave lateral flexure of the blade) generally being the more strongly developed of the two. Where the denticles are more strongly developed, they tend to make angles of 45° with the anterior part of the blade and to be laterally elongate. In some specimens the outer lateral denticle is very feebly developed in comparison with the inner, but wherever there is a suggestion of such bilateral denticle development, specimens are included in the present species. Like the other species referred to above, this species shows considerable but continuous variation in the symmetry and degree of lateral expan- sion of the posterior platform, the form of the denticles, and the relationship of the posterior portion of the carina to the posterior end of the platform ; there is also variation in the degree of lateral deflection of the blade, and the outer lateral denticle may also be developed posterior to the position of the inner lateral denticle. The blade is similar in general form to that of G. commutatus and G. mononodosus, having about 15 to 20 regular denticles, fused almost to their tips, and developing straight oral and aboral margins. There is a tendency in some specimens for the two anterior denticles to be relatively larger than the rest (e.g. Pl. 19, fig. 18a). The basal cavity is wide and flaring. Gnathodus punctatus (Cooper) Plate 18, figs. ra—c, Ioa—11d 1939 Dyryphenotus punctatus Cooper : 386, Pl. 41, figs. 42, 43, Pl. 42, figs. 10, 11. 1939 Dryphenotus litus Cooper : 386, Pl. 42, figs. 34, 35. 1939 Dryphenotus macrolobus Cooper : 386, Pl. 41, figs. 48, 49; Pl. 42, figs. 45, 46. 1939 Dryphenotus oxys Cooper : 386, Pl. 42, figs. 12, 13. 1944 Gnathodus (Dryphenotus) macrolobus Cooper; Branson & Mehl: 245, Pl. 94, fig. 69. 1951 Gnathodus punctatus (Cooper) Hass : 2539, Pl. 1, fig. 2. non 1957 Gnathodus commutatus punctatus Bischoff ; 24, Pl. 4, figs. 7-11, 14. 1957 Gnathodus bilineatus semiglaber Ziegler in Fliigel & Ziegler : Pl. 111, fig. 23 only. non 1957 Gnathodus commutatus punctatus Bischoff ; Ziegler im Fliigel & Ziegler : 40, Pl. 111, figs. 16, 17, 24. 1959 Gnathodus punctatus (Cooper) Hass : 395, Pl. 47, figs. 11-18. 106 BRITISH AVONIAN CONODONT FAUNAS 1959 Gnathodus punctatus (Cooper) Voges : 283-284, Pl. 33, figs. 34-37. 1960 Gnathodus punctatus (Cooper) Kronberg, Pilger, Scherp & Ziegler : Pl. 4, figs. 15-18. 1963 Gnathodus punctatus (Cooper) Ziegler : Pl. 2, fig. 4. MATERIAL. 13 specimens : figured, X 131, X132, X 133. RANGE. Avon Gorge Samples Z 33-38. DESCRIPTION. This species is characterized by the adult specimens having the nodes of the inner and outer sides of the platform fused with those of the carina in the posterior two thirds of the platform. The pattern of nodes on the platform is also characteristic, there being four rows, radiating from the junction of the platform and blade. The platform is asymmetrical, being widest at the anterior end and pointed at the posterior ; the outer side is wider than the inner. In juvenile examples the carina is high, but in adult specimens the carina is fused with a row of nodes on the inner and outer sides of the platform. A double row of nodes is present on the outer side in fairly juvenile examples, but frequently there is only one row of nodes developed on the inner side in juveniles. The blade is slightly longer than the platform. REMARKS. Hass (1959) has illustrated growth stages of this species. The specimens obtained in the present study most closely resemble those figured by Hass in Pl. 47, figs. 12, 13. Typically, the smaller inner side of the platform bears one node, whereas the wider outer side of the platform has a few scattered nodes. The outer side of the platform extends to the posterior tip of the unit. The inner side of the platform does not extend to the posterior tip of the unit, but extends further to the anterior than does the outer side of the platform. In North America Gnathodus punctatus is abundant in the middle faunal zone of the Chappel Limestone, and also occurs in the Siphonodella cooperi and Bactro- gnathus communis zone. In the Avon Gorge it is characteristic of the Zz beds. Gnathodus semiglaber Bischoff Plate 30, fig. 1 1947 Gnathodus perplexus (Branson & Mehl) Mehl & Thomas: to, PI. 1, fig. 4. 1957 Gnathodus bilineatus semiglaber Bischoff : 22, Pl. 3, figs. 1a, b, 2-10, 12-14. 1957 Gnathodus bilineatus semiglaber Bischoff ; Ziegler in Fliigel & Zeigler: p. 38, l. p11, figs. 5, 8, 14, 19 only (non pl. 111, fig. 23 =Gnathodus punctatus, Pl. IV, fig. 11, non PI. 3, fig. 22=Gnathodus girtyi simplex Dunn). 1959 Gnathodus semiglabey Bischoff ; Voges: 285, Pl. 33, figs. 38, 39. 1960 Gnathodus semiglaber (Bischoff) Ziegler in Kronberg, Pilger, Scherp & Ziegler: PI. 4, figs. 3-6. 1962 Gnathodus semiglabey (Bischoff) Collinson, Rexroad & Scott : 10, 22, Chart 3. 1962 Gnathodus semiglaber (Bischoff) Higgins: 13, Pl. 3, fig. 26. 1962 Gnathodus semiglaber (Bischoff) Miller : 1388, fig. 1. 1962 Gnathodus semiglaber (Bischoff) Meischner : 31, text-fig. 1o. 1964 Gnathodus semiglaber (Bischoff) Rexroad & Scott: 30, Pl. 2, figs. 1, 2. MATERIAL. 3 Specimens : figured, X 421. RANGE. Avon Gorge Z 28-Z 30. BRITISH AVONIAN CONODONT FAUNAS 107 DEscRIPTION. This species, which is well known and widely distributed in both Europe and North America, is characterized by a low, small parapet on the inner side of the platform, and a few scattered nodes developed on the middle part of the low outer side of the platform. The carina tends to be laterally expanded in the posterior part of the platform. Our specimens of this species agree closely with those described by other authors. Gnathodus simplicatus sp. nov. Plate 8, figs. 5a-c. Plate 18, figs. 2a—5b 1957 Spathognathodus subrvectus Holmes ; Fliigel & Ziegler : 53, Pl. 11, fig. 12. 1960 Spathognathodus strigosus Branson & Mehl ; Dvorak & Freyer : PI. 1, fig. 17. DERIVATION OF NAME. From the simple form. Diacnosis. A species showing Spfathognathodus—Gnathodus transition, with characteristic anterior blade, its highest point being at or near the anterior end, and with oral surface sloping regularly towards the posterior end of unit. Platform very feebly developed. MATERIAL. 105 specimens: Holotype X 89, Paratypes X 88, go, 91, 415 (all figured). TYPE LOCALITY AND HORIZON. North Crop. Sample ZLA 33. RANGE. North Crop ZLA 15-ZLA 33, Avon Gorge Z 33-Z 38. DEscrRIPTION. The unit is slightly bowed and slightly arched, highest in the anterior quarter, and sloping posteriorly. The anteriormost one to three denticles may be slightly shorter than the penultimate denticles, but otherwise the oral outline is straight to slightly convex. The denticles, which number 13 to 15, are small and laterally compressed with free chevron tips. The basal cavity is situated in the posterior half and runs to the posterior termination ; the lips flare over the whole length and the cavity widens to the mid-point where it becomes constricted and then runs as a narrowing groove towards the anterior. The basal margin is lipped and slightly stepped in lateral view. RemMARKS. Middle and Upper Devonian forms similar to those described above have been named as Spathognathodus bidentatus by Bischoff and Ziegler (1957) and Freyer (1961). Bischoff and Ziegler’s specimens have a greater number of denticles (about 17 total) than ours, and the cavity is different, not quite reaching the posterior end, and being greatly flared anteriorly. Freyer’s specimens have only about Io denticles and are much lower towards the posterior. The present species is transitional between Spathognathodus and Gnathodus, but is included in Guathodus because the basal cavity is developed posteriorly, is longi- tudinally extended, and the lips show a tendency to lateral flare. There is some similarity between the forms described here and S. cristulus, which is considered by American workers to be the basic stock for all spathognathodid lineages. It is possible that the two species are the root stocks for successive gnathodid developments, the genus Gnathodus being polyphyletic. 108 BRITISH AVONIAN CONODONT FAUNAS In a few specimens the highest denticles are developed above the anterior end of the basal cavity (e.g. Pl. 18, fig. 2c ; X 89). In all other respects, however, these specimens resemble the holotype. Gnathodus symmutatus sp. nov. Plate 19, figs. Ia—4c ? 1941 Spathognathodus commutatus Branson & Mehl; Ellison & Graves: PI. 2, fig. 4 (non Pl. 2, fig. 6). ? 1956 Spathognathodus cf. inornatus Hass ; Elias: Pl. 3, figs. 62, 65 (non PI. 3, figs. 41, 42). 1958 Gnathodus commutatus commutatus Branson & Mehl; Lys & Serre: 8g1, Pl. 9, figs. 2a, b. MATERIAL. 42 specimens : Holotype X 134, Paratypes X 135-7. TYPE LOCALITY AND HORIZON. North Crop Sample 3D 14/15. RANGE. North Crop CYD 7-3D 22. Di1aGnosis. Small gnathodids with elongate blades, and relatively little expanded posterior platforms, convex in outline, tapering at both ends, and unornamented. DescriPTIon. The blade is more or less regular in height or has a gently convex oral profile in the anterior portion, but for most of the length of the platform the denticle height decreases uniformly towards the posterior end of the unit. In mature specimens the anterior blade occupies about half of the total length of the unit ; it is often deepest at its posterior end, and the oral surface bears about g or 10 denticles anterior to its junction with the posterior platform. These denticles tend to be more or less erect, discrete from about their mid points upwards, and sharply pointed ; they are strongly laterally compressed and are of sub-equal size, the largest tending to occur in the posterior portion of the anterior blade. The lateral faces of the bar are gently convex and the anterior aboral margin is rounded to bluntly angular ; the anterior edge is straight, and the bar is straight or gently deflected in a horizontal plane. The blade is continued posteriorly as a central carina on the platform, the denticles being short, and partly fused ; the total number of denticles in the blade and the carina is about 22. The posterior platform occupies the posterior half to two-thirds of the unit ; it is relatively unexpanded laterally and tapers uniformly at its anterior and posterior ends. It tends to be steep sided, the lateral faces forming an acute angle below the carina ; one face is often more strongly laterally expanded than the other. The surface is smooth and no ornamen- tation is developed, although in some specimens there is a tendency for the appear- ance of incipient marginal denticulation, similar to that in G. homopunctatus. The basal cavity is wide and flaring, and is continued anteriorly as a narrow groove on the base of the anterior blade. The growth of the posterior platform in mature specimens tends to reduce the angle which its lateral faces form at their junction. In most specimens its depth is about equal to the height of the carina on its surface. BRITISH AVONIAN CONODONT FAUNAS 109 Gnathodus ? sp. nov. Plate 18, figs. 7a—c MATERIAL. I specimen : figured, X 92. LocaLiTy AND HORIZON. North Crop. Sample ZL 8. Rance. North Crop ZL 8. Description. A gnathodid ? with transversely ridged posterior half of platform ; anterior part of platform unornamented except for marginal nodes. Base deeply excavated. Anterior bar unknown. The anterior blade is broken but the platform is preserved. The carina consists of a row of low nodes ; in the posterior half of the platform, a row of smaller nodes runs either side of the carina, with which they fuse to give a series of trinodate transverse ridges. The inner platform is expanded slightly more than the outer, and both are unornamented, except for a short marginal row of fused nodes occurring in the anterior half and diverging posteriorly. In aboral view the cavity occupies the whole area of the platform and is grooved along its mid-length. REMARKS. This species is unlike any described gnathodid and does not bear any obvious phylogenetic relationship to other species. Gnathodus sp. Plate 17, figs. 4a—d MATERIAL. I specimen : figured, X 138. RanGe. Scotland HOSIE 2A. DeEscripTIon. A single specimen of Guathodus appears to be close to G. girtyi, but differs from it in the character of the lateral denticles of the posterior platform. In the present specimen the development on the two lateral areas of the platform is highly asymmetrical, and the platform of the inner-lateral margin, which begins anterior to the point of origin of that on the outer-lateral margin, is short, and consists of only three or four fused blunted denticles. Just anterior to its fusion with the carina, a less conspicuous fused, inner series of lateral denticles is developed on the outer-lateral platform. These become confluent with the carina just in front of its posterior termination, but do not reach the posterior end of the carina. The apron is wide and flaring, and is asymmetrical in both oral and aboral views. In lateral view the denticles of the anterior blade are sharp and erect, and those of the carina are also sharply tipped and distinct, standing higher than the lateral denticles on either side of the platform. The denticles of the inner lateral process form blunted parapet-like nodes in lateral view. The denticles of the carina decrease rapidly in size towards the posterior in the posterior half of the platform. 110 BRITISH AVONIAN CONODONT FAUNAS Genus HIBBARDELLA Ulrich & Bassler 1926 1925 Hibbardella Bassler ; 219 (nom. nud.). 1926 Hibbardella Ulrich & Bassler : 37. TYPE SPECIES. Prioniodus angulatus Hinde 1879. Description. Ulrich & Bassler established the genus Hzbbardella with the type species Hibbardella (Prioniodus) angulata Hinde for a group of arched blade-like conodonts in which a striking apical denticle was developed. The whole structure was bilaterally symmetrical and the apical denticle sharp-edged, erect and greatly elongated. The denticles of the anterior bar were relatively few in number, widely spaced and turned slightly inward. Ulrich & Bassler did not mention the character of the basal cavity, nor the possibility of the development of a denticulated posterior bar. Topotype material studied by Dr. J. W. Huddle, of which he has kindly provided us with photographs, shows that both these features are well preserved. A more or less short stout denticulated posterior bar is developed, and there is a thin groove-like basal cavity which extends along both the anterior bars and the posterior bar. Subsequent authors have erected several genera of essentially similar general form which have been distinguished on minor morphological differences. These include Roundya Hass (1953) Ellisonia Miller (1956) and possibly also Diplododella Bassler (1925). There has been some discussion as to the validity of these and other genera, especially the genus Tvichonodella. The most satisfactory solution to the present situation seems to be to subdivide the genus Hzbbardella into three subgenera, based on the following characteristics : 1. HIBBARDELLA< s.s. arched denticulated conodonts, with a bilaterally symmetrical anterior bar and a strongly developed apical denticle. The apical denticle is strongly compressed antero-posteriorly and has sharp \ - Main cusp a \ \ 4 A. VI j Lateral bar WW ; Af \Z Posterior bar Denticles jen Lotenol ibair \ Position of basal cavity Anterior view Fic. 23. Huibbardella sp. showing morphological terms used in the text. BRITISH AVONIAN CONODONT FAUNAS TRE lateral edges. The basal cavity is small and restricted to the aboral surface of the apical denticle, but aboral grooves are developed on both the anterior and the posterior bars. There is a short stout denticulated posterior bar, which bears a series of discrete denticles. TYPE SPECIES. Prioniodus angulatus Hinde 1879. 2. ROUNDYA conodonts of similar overall form to Hibbardella s.s. but charac- terized by distinctive basal cavities and by the form of the apical denticle. The basal cavity is relatively much larger than that of Hibbardella, although it is still confined to the lower surface of the apical denticle. The whole aboral surface of that denticle is hollowed out, but the cavity does not flare beyond its basal area. The denticle itself is characterized by its distinctive cross-section. In its lower half it is broadly sub-circular and robust in form, the posterior surface having a longitudinal broad concave cavity which is deepest at the proximal end, and decreases in depth towards the mid-length of the denticle. The lateral faces of the apical denticle are smooth and strongly convex, but in their medial areas a conspicuous groove is developed longitudinally in the lower part. From this a strong lateral costa develops on each lateral face. In the distal half of the apical denticle it becomes strongly anterio-posteriorly compressed, but the lateral edges remain sharp, and the anterior and posterior faces broadly convex. TyPE SPECIES. Roundya barnettana Hass 1953. 3. HASSOGNATHUS subgen. nov. conodonts whose general form is similar to Hibbardella, but which are characterized by the fact that the anterior bars are essentially unexcavated, their aboral surfaces being shallow, concave, depressions. The basal cavity is conspicuous, but is largely developed below the posterior bar, although it extends and is continuous with one below the apical denticle. The apical denticle is usually sub-circular in cross-section and unornamented. The whole appearance of members of this subgenus is of a Ligonodina which has developed an additional lateral bar. TYPE SPECIES. Tvichognathus separata Branson & Mehl 1934. Subgenus HIBBARDELLA (HIBBARDELLA) Ulrich & Bassler 1926 Hibbardella (Hibbardella) abnormis Branson & Mehl Plates3rjai¢. 6 1940 Hubbardella abnormis Branson & Mehl: 184, Pl. 6, fig. 14. 1963 Hibbardella abnormis Branson & Mehl ; Rexroad & Collinson 10, Pl. 2, figs. 15, 18, 20, 21. 1965 Hibbardella abnormis Branson & Mehl ; Rexroad & Collinson : 9, Pl. 1, figs. 8, 9. 112 BRITISH AVONIAN CONODONT FAUNAS MATERIAL. 3 specimens : figured, X 508. RANGE. North Crop CYD 7-3D 8. DeEscrRIPTION. Rexroad & Collinson (1963) have shown that the holotype of this species is broken and that the limbs are longer than the original description suggests. The present specimens are fragmentary, but they show the specific characteristics. The posterior bar tends to be rather strongly developed, and the lateral bars are sharply flexed posteriorly. Hibbardella (Hibbardella) acuta Murray & Chronic Plate 25, figs. Iga—20 1961 Hibbardella fragilis Higgins : 213, Pl. 12, fig. 4, text-fig. 2. 1963 Hibbardella fragilis Higgins ; Bouckaert & Higgins : 17, fig. 3. 1965 Hibbardella acuta Murray & Chronic : 598, Pl. 73, figs. 3-5. Hibbardella higginsi Collinson & Druce in press. MATERIAL. Ig specimens : figured, X 139, X 422. RANGE. North Crop 3D 4-3D 17. DescriPTION. The most distinctive features of this species are the greatly elongated anterior and posterior bars, the relatively slender denticulation and the lateral twisting of the anterior bars. The apical denticle, although relatively long, is only about half the length of the anterior bars ; it is slender, with a feebly convex to flat anterior face and sharp lateral edges ; the posterior part of the face of the apical denticle is developed into a posterior knife edge, the posterior lateral faces tending to be rather flat. The anterior bars are long and are longitudinally twisted so that the denticles tend to originate from the anterior surface. The bars bear up to Io lateral denticles which are basally confluent but apically distinct and are more or less com- pressed anterior-posteriorly. In addition to their longitudinal flexure, the bars are recurved posteriorly, so that their anterior faces are gently convex. They diverge from each other at an angle of about 30°. The posterior bar is elongated and decreases in depth posteriorly. Its aboral margin is gently concave, most of the curvature being concentrated near the mid- point of the unit. Its oral surface bears a series of confluent, but apically distinct, hindeodellid-type denticles. The larger members of the series tend to increase in size toward the mid-point of the bar, and then to decrease toward the posterior end. There are about 8 or g main denticles, each separated by two or three smaller denticles. The denticles are more or less laterally compressed, but tend to have rather strong convex lateral faces. The lateral faces of the posterior bar are gently convex. The whole appearance of the posterior bar is strikingly deep and elongated. Shallow longitudinal slit-like grooves extend along the anterior and posterior bars, and there is a very small pit below the apical denticle. BRITISH AVONIAN CONODONT FAUNAS o 113 Hibbardella (Hibbardella) milleri Rexroad Plate 25, figs. 23a-25b 1957 Hibbardella n. sp ? Rexroad : 31, Pl. 1, fig. 19. 1958 Hibbardella milleri Rexroad : 18, Pl. 2, figs. 13-16. 1960 Hibbardella milleri Rexroad ; Clarke: 6, Pl. 1, fig. 6. 1961 MHibbardella milleri Rexroad ; Higgins: Pl. 12, fig. 7. 1961 AHibbardella milleri Rexroad ; Rexroad & Burton: 1153, Pl. 140, figs. 3, 4. 1964 Hibbardella millevi Rexroad ; Rexroad & Furnish : 671, Pl. 111, fig. 17. 1965 Hibbardella millevri Rexroad ; Rexroad & Nicoll: 19, Pl. 1, fig. 13. MATERIAL. 3 Specimens: figured, X 140, X 141, X 142. RANGE. North Crop 3D 14/15. DEscRIPTION. Individual specimens of this species bear a strong resemblance to those described by Rexroad, but differ from his description in having no denticle developed anterior to the apical denticle. The most characteristic features of individuals are the short, deep and obtusely divergent anterior bars, the distal ends of which are spatulate to sharply pointed. The denticles of the anterior bars are massive, increasing in size distally and numbering 3 or 4. They are more or less anteriorly compressed and sharp edged. The apical denticle is massive, elongate, sub-circular to oval in cross-section ; in some specimens it is very elongate (e.g. Pl. 25, fig. 24). In well preserved specimens the apical denticle is sharply pointed at its distal end, and is sub-circular in cross-section. In the proximal third its posterior surface is marked by either a very faint groove or a very faint depression. The posterior bar is short, narrow and deep, with two or three small, isolated denticles on its oral surface. The basal cavity is developed as shallow grooves which run along the posterior and the anterior bars, and the base of the apical denticle is slightly excavated. The aboral groove does not extend the whole length of the anterior bars, and the posterior groove decreases in width and depth posteriorly. Hibbardella (Hibbardella) ortha Rexroad Plate 25, figs. 22a, b 1900 Prioniodus angulatus Hinde (partim) : 343, Pl. ro, fig. 18 (non fig. 19). non 1926 Hibbardella angulata (Hinde) Ulrich & Bassler : 37, Pl. 3, figs. 1-4. 1928 Hubbardella angulata (Hinde) ; Holmes: 11, Pl. 4, fig. 32. 1958 Hibbardella ortha Rexroad : 18, Pl. 2, figs. 9-12. 1960 HAibbardella ovtha Rexroad ; Clarke: 6, Pl. 1, fig. 7. 1961 Hubbardella ortha Rexroad ; Rexroad & Burton : 1153, Pl. 140, figs. 5, 6. 1964 Hibbardella ovtha Rexroad ; Rexroad & Furnish : 671, Pl. 111, fig. 16. 1965 Hibbardella ortha Rexroad ; Rexroad & Nicoll: 19, Pl. I, fig. 12. Hibbardella orvtha Rexroad ; Collinson & Druce in press. MATERIAL. 780 specimens : figured, X 143. RANGE. North Crop 3D 10-3D 22. DESCRIPTION. The present specimens are more complete than those described by 114 BRITISH AVONIAN CONODONT FAUNAS Rexroad, but they agree in all the essential details with his description. Their most striking features are the deep and strongly antero-posteriorly compressed anterior bars, which diverge from each other at an angle of about 130°. They are relatively short, and bear on their oral surfaces up to 6 discrete and sharply pointed denticles. The two nearest the apical denticle and the distal denticle on each bar are small, but the three intervening denticles are larger and tend to increase in size distally. The ends of the anterior bar are bluntly spatulate, and the aboral margin is straight to feebly convex. The anterior face of the apical denticle is convex, the apical denticle itself being about twice the length of the largest denticle of the anterior bar, slender and pointed ; it tends to have rather feeble anterior lateral edges in its lower portion, but becomes sub-oval in cross-section towards its distal end. Both it and the denticles of the anterior bar tend to stand rather erect to the bar itself and are not obviously posteriorly recurved, although the denticles of the lateral bar tend to be inwardly curved towards the apical denticle. The posterior bar is long, slender, strongly laterally compressed and relatively deep. It has feebly convex lateral faces, and bears a series of up to 6 crowded, but apically discrete, laterally compressed, short denticles on its oral surface. A small pit below the apical denticle extends posteriorly as a faint groove along the posterior bar, and also along the proximal portions of the anterior bars. The posterior margin of the apical denticle is sharp-edged. Beneath the apical denticle the posterior-aboral margin of the anterior bar is excavated by an indented depression to join the basal margin of the posterior bar. Hibbardella (Hibbardella) parva sp. nov. Plate 25, figs. 21a, b Diacnosis. Hibbardellid with very small, delicate structure ; anterior bars flexed forwards diverging in vertical plane at a very obtuse angle. At their junction deeply indented aborally on anterior margin. Posterior bar strong ; apical denticle elongate, strongly laterally compressed. Basal cavity minute or non-existent. MATERIAL. 5 specimens : Holotype X 144 (figured). TYPE LOCALITY AND HORIZON. North Crop. Sample 3D 14/15. Rance. North Crop 3D 14/15. DESCRIPTION. The anterior bars are relatively deep, short and laterally com- pressed, and each bears about 5 oral denticles. They diverge anteriorly in a horizontal plane, so that the angle between them in a horizontal plane is about go°. They are little flexed in a vertical plane, and the angle between them is very obtuse. The aboral surface has a concave general appearance. This anterior curvature is most obvious in aboral view. It is relatively inconspicuous in oral view, where it is obscured by the development of the apical denticle, nor is it continued along the medial and distal parts of the bars which tend to straighten out and lie in a single plane relative to one another. Remarks. This species is closest to H. (H.) ortha Rexroad 1958, but it differs in BRITISH AVONIAN CONODONT FAUNAS 115 the distinctive form of the apical denticle, and in the characteristic angle of the anterior bars as seen in the vertical plane. In H. (H.) ortha this angle approaches go° but it is nearer 180° in H. (H.) parva. H. (H.) ortha also lacks the strong posterior recurvature of the apical denticle and the denticles of the anterior bar. Hibbardella (Hibbardella) cf. macrodentata Thomas Plate 25, figs. 16a-18c 1949 Hibbardella macrodentata Thomas : 422, Pl. 4, fig. 25. MATERIAL. 75 specimens : figured, X 147, X 148, X 146. RANGE. North Crop KL 2-ZLA 33, Avon Gorge K3-Z 38. DESCRIPTION. The apical denticle is tall, laterally compressed and inclined posteriorly. The anterior arch is deep with each limb curved posteriorly. The anterior bars diverge at an angle of approximately go°, and the aboral edge of the anterior bars is lower than that of the posterior bar. The denticles of the arch are isolated, sub-circular and of unequal height. The posterior bar is narrow, long (though broken in the majority of our specimens) and finely denticulate. All the denticles are sub-circular and posteriorly inclined. The cavity is minute and situated beneath the apical denticle. REMARKS. The holotype is broken, but, from Thomas’s illustration and description it would appear that our specimens are very close to H. macrodentata. Although Thomas describes the posterior bar as blunt and non denticulate, the holotype (shown in PI. 4, fig. 25) is clearly broken. Hibbardella (Hibbardella) sp. Plate 25, figs. 15a, b MATERIAL. I specimen: figured, X 441. Rance. North Crop KL 16. DESCRIPTION. This specimen is characterized by the massive form of its anterior bars. The anterior bars are short, deep and strongly downcurved, their oral and aboral margins being strongly convex in anterior view, although there is a conspic- uous indentation in the aboral profile below the apical denticle. The strongest downflexing is in the distal thirds of the bars. The lateral faces of the anterior bars are convex, and both are characterized by prominent longitudinal ridges developed just below mid-height, and extending along the length of the bars. The oral surfaces of the anterior bars bear up to six discrete and rather stout denticles, the largest being in the medial portions of the bars. They are discrete, more or less rounded in cross- section, and the larger ones are slightly inflexed towards the apical denticle. Their length is unknown, but the largest is longer than the depth of the basal bars. The ends of the bar are spatulate. The apical denticle is relatively slender, being only slightly greater in width than the largest of the denticles of the anterior bars. The anterior face is rounded, but 116 BRITISH AVONIAN CONODONT FAUNAS the posterior face is blunt and has a median groove. The apical denticle in posterior view is widest at the oral edge of the bar and tapers uniformly to the tip. The aboral surface is sharp, being broken only by a small triangular shaped pit directly beneath the apical denticle. Subgenus HIBBARDELLA (ROUND YA) Hass 1953 TYPE SPECIES. Roundya barnettana Hass 1953. Hibbardella (Roundya) barnettana Hass Plate 25, figs. 2a—5b 1953 Roundya barnettana Hass : 89, Pl. 16, figs. 8, 9. 1957 Roundya barnettana Hass ; Bischoff: 52, Pl. 5, figs. 19, 20. 1958 Roundya costata Rexroad : 26, Pl. 2, figs. 5-8. 1961 Roundya subacoda (Gunnell) Higgins : 220, Pl. 11, fig. 13. 1961 Roundya costata Rexroad ; Rexroad & Collinson, PI. 1. 1962 Roundya subacoda (Gunnell) Higgins : 11, Pl. 1, fig. 1. 1962 Roundya barnettana Hass ; Collinson, Scott & Rexroad : 12. MATERIAL. 14 specimens: figured, X 151, X 152, X 153, X 154. Rance. North Crop 3D 14/15, Avon Gorge Z 38-C 15. DEscRIPTION. Individuals of the present species agree closely with the very detailed description given by Hass (1953 : 89). They are characterized particularly by the massive apical denticle, with longitudinal grooves and lateral keels which are very prominent in the proximal portion, and sharp lateral edges which are prominent in the distal half. There is a conspicuous posterior concave longitudinal depression in the proximal quarter of the apical denticle, which becomes obsolescent towards the mid-point. The denticle is strongly recurved in its lower portion, but its distal portion is straight. The anterior bars are broken in the present specimens, but appear massive and bear more than two isolated denticles, which are sub-circular in cross-section, and curve upwards to parallel the apical denticle. The anterior bars diverge at an angle of about 70°—80° in the vertical plane, and the junction between them is rounded in anterior view. They shallow distally. The posterior bar is broken in the present specimens, but is clearly massive with flat to gently convex lateral faces, and has a convex upper surface which bears more than one erect, massive, sub-circular denticle. The aboral surface of the apical denticle is deeply excavated and the excavation continues along the anterior end of the posterior bars. Hibbardella (Roundya) sp. Plate 25, fig. 1 MATERIAL. 2 Specimens: figured, X 423. Rance. North Crop ZLA 32. BRITISH AVONIAN CONODONT FAUNAS 117 DESCRIPTION. The anterior arch is broken but appears to be formed by aboro- lateral extensions of the basal cavity. The apical denticle is recurved posteriorly ; it has a convex anterior margin, lateral keels, and a concave posterior depression, becoming obsolescent toward the anterior arch. The posterior bar is formed by an extension of the posterior lip of the basal cavity and bears at least one inclined denticle. The basal cavity is large, the aboral region of the apical denticle being completely excavated. Subgenus HIBBARDELLA (HASSOGNATHUS) nov. TyPE SPECIES. Tvrichognathus separata Branson & Mehl 1934. Hibbardella (Hassognathus) separata (Branson & Mehl) Plate 25, figs. 13a-14 1934 Tvichognathus sepavata Branson & Mehl : 290, Pl. 23, fig. 30. 1934 Tvichognathus breviolata ? Branson & Mehl: 291, Pl. 23, fig. 29. 1938 Tvichognathus sepavata Branson & Mehl ; Branson & Mehl: PI. 33, fig. 42. 1939 Tvichognathus sepavata ? Branson & Mehl ; Cooper: 421, Pl. 46, figs. 45, 49. 1944 Trichognathus sepavata Branson & Mehl; Branson & Mehl, im Shimer & Shrock: 243, Pl. 93, fig. 72. 1944 Tvrichognathus sepavata Branson & Mehl; E. B. Branson: Pl. 32, fig. 42. 1959 Roundya sp. B Hass: 385, Pl. 46, fig. 11. MATERIAL. 58 specimens : figured, X 150, X 149. RANGE. North Crop KL 19-ZLA 27, Avon Gorge K 21-C 17. DescripTion. The posteriorly recurved apical denticle is tall and ovate in cross- section, being thickest at the anterior. The anterior arch is short with the anterior bars diverging at about 120°. The bars are narrow, each bearing 3 to 4 short, sub- circular posteriorly inclined denticles. The posterior bar is relatively long, being thick at the anterior end, and becoming much thinner over the posterior half, where it bears a few fine posteriorly inclined denticles. In aboral view the unit is excavated, with a large cavity occurring beneath the apical denticle and extending along the posterior bar, but becoming gradually narrower and ending abruptly. A faint groove runs for a short distance from the cavity along either limb of the anterior arch. RemMARKS. The large basal cavity distinguishes this species from H. macro- dentata. Hibbardella (Hassognathus) ? sp. Plate 31, fig. 3 MATERIAL. I specimen : figured, X 319. RANGE. Scotland DUN 77. 118 BRITISH AVONIAN CONODONT FAUNAS DeEscRIPTION. The present specimen is fragmentary but has a very distinctive appearance. The posterior bar is elongated and tapers towards the posterior end. The main cusp is strongly recurved and strongly laterally compressed in its distal half, the proximal half tending to be more rounded. Posterior to it there is a denticle adding about a third of the total length of the main cusp, and the denticles posterior to this decrease in size posteriorly. They are short, bluntly pointed and discrete. The aboral surface of the posterior bar is straight, and the oral surface curves down to meet it. The two lateral bars are developed well in front to the line of the main cusp, so that the general appearance of the unit in lateral view resembles that of a Ligonodina. They are not down-flexed and their aboral margin is in line with that of the posterior bar. They make an angle of about 90° with the posterior bar in a horizontal plane. They share a single short, but stout, recurved denticle, which lies directly anteriorly to the main cusp. The aboral surface of the posterior bar is excavated by a wide elongate depression. The whole margin tapers towards the posterior end. There is no conspicuous cavity below the main cusp. REMARKS. One distinctive feature of this specimen is the presence of the denticle anterior to the main cusp. This might ultimately justify the recognition of speci- mens of this kind as a new genus, but our present material is inadequate to provide a full description. Other fragmentary, but different, hassognathids have a much greater stratigraphic range. Genus HINDEODELLA Ulrich & Bassler 1926 1925 Hindeodella Bassler : 219 (nom. nud.). 1926 Hindeodella Ulrich & Bassler : 38-41. Type sPEcIES. Hindeodella subtilis Ulrich & Bassler 1926. Hindeodella antecomplex Collinson & Druce Plate 28, figs. 25, 28 Hindeodella antecomplex Collinson & Druce in press. MATERIAL. 7 specimens : figured, X 157, X 156. RANGE. North Crop 3D 4-3D 17. DEscRIPTION. The present specimens agree closely with the description given by Collinson & Druce. The most striking features of the specimens are their small size, the general form of the main denticle, which is relatively massive in relation to the general size of the unit, being curved posteriorly and inwardly with a very convex interior antero-lateral face. The denticles of the posterior bar range up to about Io in number, and the two massive posterior denticles are very prominent in lateral view. The denticles show a general increase in size posteriorly, as does the depth of the posterior bar. The aboral margin of the posterior bar is straight, and each of its aboral lateral surfaces is marked by a flange-like structure. The anterior lateral BRITISH AVONIAN CONODONT FAUNAS 119 process is short, and bears two oral denticles. It is strongly depressed vertically and strongly inflexed, forming a right angle in its lateral curvature with the posterior bar when viewed from above. The aboral surface of the unit is excavated by a narrow, shallow, groove. Hindeodella brevis Branson & Mehl Plate 31, fig. 17 1934 Hindeodella brevis Branson & Mehl : 195, Pl. 14, figs. 6, 7. 1934 Htndeodella cf. byevis Branson & Mehl: PI. 14, fig. 12. 1956 Hindeodella brevis Branson & Mehl ; Bischoff & Ziegler : 147, Pl. 14, figs. 10, 11. 1957 Hindeodella brevis Branson & Mehl ; Bischoff: 26, 27, Pl. 6, fig. 24. MATERIAL. 17 specimens : figured, X 514. Rance. Avon Gorge K 2-Z 38, North Crop 3D 14/15-3D 22. DeEscriPTIon. The posterior bar is short, deep, straight and relatively thick at its oral edge. It bears on its oral surface four or five major denticles, which increase in size posteriorly. They tend to be straight, strongly biconvex in cross-section, and only slightly inclined posteriorly. Each is separated by up to 3 smaller denticles, which are crowded but discrete. The anterior bar is relatively long, and is bent almost at right angles to the posterior bar. Its oral surface bears up to 7 short denticles, which decrease in size posteriorly. Each of these major denticles of the anterior process tends to be separated by a single smaller denticle. The posterior bar is excavated by a shallow groove in its anterior portion, and this flares somewhat below the main denticle. { Apical denticle Denticles of posterior bar Anterior bar bine tht Anterior Posterior Posterior bar Position of basal cavity Aboral edge Fic. 24. Huindeodella sp. showing morphological terms used in the text. 120 BRITISH AVONIAN CONODONT FAUNAS Hindeodella cooperi (Elias) Plate 31, figs. 18, 19 1956 Hamulosodina cooperi Elias : 109, Pl. 1, figs. 28, 29. Hindeodella cooperi (Elias) ; Collinson & Druce in press. MATERIAL. 2 specimens : figured, X 159, X 158. Rance. North Crop 3D 14/15. DeEscriPTION. The original description of this species is scarcely adequate to differentiate it from several others of the genus Hindeodella. The most distinctive features of the present specimens, and also of the specimens shown in Elias’ illustra- tions, are the greatly elongated posterior bar, the more or less subequal character of the denticulation, and the character of the antero-lateral process. The height of the denticle is consistent although major denticles can be identified in some parts of the bar. The anterior-lateral process is short, vertically depressed, slightly laterally deflected, and bears 1 to 4 denticles anterior to the main denticle, with the whole of the antero-lateral face undenticulated, and a more or less sharp convex edge. In lateral view the aboral surface of the unit is straight to gently concave. Its outer face is flat to steeply convex in the anterior part, but becomes more strongly convex in the medial and posterior part. The main denticle is not conspicuously larger than those which lie behind it. The denticles of the main part of the posterior bar are crowded and fused for most of their length, being slightly inclined posteriorly and tending to increase slightly in size towards the mid-point of the unit in some specimens. In other specimens the main denticle is up to twice as large as the main denticles of the posterior series, and in the latter, the hindeodellid character is more or less conspicuously developed. The inner lateral face of the unit is flat to gently convex. The antero-lateral process makes an angle of about 90° with the posterior bar. Its postero-aboral edge is straight and points vertically, and makes an antero-aboral angle at the anterior edge of about 45°. The denticles anterior to the main denticle tend to be about equal in height to those of the major denticles of the posterior bar, and curve upwards to lie more or less parallel to the main denticle. The lowermost anterior edge of the antero-lateral process is undenticulate. The posterior bar is strongly laterally compressed. Beneath the main denticle there is a cavity which flares slightly at the edges, and this is extended posteriorly, and to a less extent, anteriorly as a narrowing groove. Hindeodella corpulenta Branson & Mehl Plate 29, figs. 16a-17¢ 1934 Hindeodella sp. Branson & Mehl: PI. 14, fig. 15. 1934 Hindeodella corpulenta Branson & Mehl: 281, Pl. 22, figs. 32, 33. 1934 Metaprioniodus fractus Huddle : 58, Pl. 11, figs. 14, 15. 1934 Ligonodina conidens Huddle : 63, Pl. 12, figs. 18, 19. 1938 Ligonodina angulata Branson & Mehl: 142, Pl. 34, fig. 43. 1939 Ligonodina conidens Huddle ; Cooper : 390, Pl. 45, fig. 45. BRITISH AVONIAN CONODONT FAUNAS 121 1944 Ligonodina angulata Branson & Mehl; E. B. Branson: PI. 39, fig. 43. 1947 Hindeodella millerella ? Youngquist & Peterson : 245, Pl. 38, figs. 1-5. 1949 Hindeodella cf. Hindeodella corpulenta Branson & Mehl ; Thomas: 408, Pl. 1, fig. 4. 1957 Hindeodella ? sp. Lys, Serre & Deroo : 800, Pl. 9, fig. 1. MATERIAL. 168 specimens : figured, X 160, X 161. Rance. North Crop KL 1-ZLA 33, Avon Gorge K 2-Z 37. DeEscriPpTIon. The main denticle is massive with a sub-circular cross-section at the oral extremity. It is ovate at its base, feebly recurved and posteriorly inclined. It is about one and a half times as wide as the next largest denticle. The anterior lateral process is deflected laterally through 90°, and depressed downward through go°. It commonly bears 6 isolated, sub-circular denticles, which increase in size in the mid part. The posterior bar is massive, laterally compressed and bears about 5 massive, discrete, feebly laterally compressed, posteriorly inclined denticles, the largest being in the posterior third. No smaller “ hindeodellid’”’ denticles are present. The posterior bar is deflected downward slightly towards the posterior end. In aboral view the large cavity is situated just anterior to the main denticle, and extends beneath the anterior lateral process. It is grooved along its mid-length. The inner lateral face may bear a feeble longitudinal ridge. REMARKS. Most specimens of this species have the posterior bar broken, but the distinctive anterior lateral process and the basal cavity serve to identify it. Hindeodella croka Collinson & Druce Plate 28, figs. 15-17 1957 Hindeodella brevis Branson & Mehl ; Bischoff: 26, Pl. 6, fig. 24. 1961 Hindeodella brevis Branson & Mehl ; Higgins: Pl. ro, fig. 14. Hindeodella croka Collinson & Druce in press. MATERIAL. 7 specimens : figured, X 164, X 162, X 163. Rance. North Crop 3D 9-3D 14/15. DeEscripTIon. The distinctive elongate form and enormously flexed anterior lateral process of the species are very distinctive features, and agree in all respects with the description of Collinson & Druce. There is a tendency in some specimens for the posterior bar to develop broadly hindeodellid denticulation, but this is not very clearly defined. In some specimens the anterior lateral process bears up to 8 denticles. Remarks. A single specimen (Pl. 28, fig. 29) is compared with this species, differing from it in the very strong lateral extension of the inner lateral face of the unit. It is extended laterally along the whole length of the unit posterior to the origin of the anterior lateral process, forming a platform-type flange, with a rather flat, oral surface and a convex to vertical outer lateral face. The relatively incon- spicuous main denticle is strongly inflexed, downflexed and less strongly recurved. 122 BRITISH AVONIAN CONODONT FAUNAS Hindeodella hibbardi Collinson & Druce Plate 28, figs. 18-20 1957 Angulodus walvathi (Hibbard) Bischoff : 17, Pl. 5, figs. 44, 45. 1961 Angulodus walrathi (Hibbard) Higgins Pl. ro, fig. 16. Hindeodella hibbardi Collinson & Druce in press. MATERIAL. 22 specimens : figured, X 167, X 168, X 169. RANGE. North Crop 3D 11-3D 14/15. DESCRIPTION. This species of Hindeodella is characterized by a relatively long anterior lateral process, which is one third to one quarter the length of the posterior bar, and which is depressed and deflected at the bottom. Immediately anterior to the main denticle the anterior lateral process is depressed at an angle of about 110° to the posterior bar. Then, at a distance of about one quarter of its total length from the main denticle, it is inflexed by lateral twisting, so that the denticles anterior to this point of inflection point both inwards and also are curved upwards. Ata further point about two-thirds of its length from the main denticle, it is again depressed in a vertical plane, and the remaining 3 distal denticles of the anterior lateral process are larger and more strongly recurved than those behind them. The oral surface of the anterior lateral process bears up to Io stout denticles, more or less sub-circular in cross-section, discrete, tending to increase in size distally from the main denticle, although the most anterior is smaller than those immediately behind it. The process becomes thinner towards the anterior end, the antero-aboral extremity being bluntly rounded or plough-like in general form. The proximal end of the anterior lateral process and virtually the whole length of the posterior bar have conspicuously and strongly convex lateral faces. The denticles of the posterior bar are strongly developed, and curve inward, being inclined posteriorly at an angle of about 45°. The denticles of the main series are each separated by up to 4 smaller, fused, crowded denticles, which are less than half the length and diameter of those of the larger series. The posterior third of the unit is slightly depressed vertically and is deflected laterally. A very conspicuous aboral groove runs the whole length of the unit, being wide but rather shallow, and having conspicuous lateral lips. It is reduced in width towards the anterior and posterior end, and is widest below the main denticle where it is marked by a more or less conspicuous biconvex pit, both ends of which are relatively pinched in relation to the rest of the cavity. The outer lateral face is rather less convex than the inner. The main denticle is relatively small and inconspicuous in comparison with other denticles of the series. The whole unit is elongate, but in some specimens the lateral faces tend to be less convex than others, giving the whole unit a more slender appearance. In complete specimens the aboral cavity is seen to extend only for about half the length of the posterior bar. BRITISH AVONIAN CONODONT FAUNAS 123 Hindeodella ibergensis Bischoff Plate 28, figs. 22-24, 30, 31 1957 Hindeodella ibergensis Bischoff : 28, Pl. 8, figs. 33, 37, 39. 1957 Hindeodella ibergensis Bischoff ; Ziegler in Fliigel & Ziegler : 42, Pl. 5, figs. 14, 21. 1957 Hindeodella germana Holmes ; Ziegler in Fliigel & Ziegler : 41, Pl. 5, fig. 16. 1958 Hindeodella vedunca Stanley : 466, Pl. 63, figs. 1-4. 1961 Hindeodella ibergensis Bischoff ; Higgins: Pl. 10, fig. 15. 1962 Hindeodella ibergensis Bischoff ; Higgins: Pl. 1, fig. 11. 1963 Hindeodella ibergensis Bischoff ; Bouckaert & Higgins: 17, fig. 3. Hindeodella ibergensis Bischoff ; Collinson & Druce in press. MATERIAL. 37 specimens : figured, X 170, X 171, X 172, X 173, X 174. RanGeE. North Crop 3D 10-3D Ig. DESCRIPTION. This species includes greatly elongate hindeodellids, with the oral edge crowded with a series of alternating denticles. The aboral edge is straight to sinuous. In complete specimens the posterior bar decreases in width progressively towards the more or less pointed posterior tip. The main denticle is distinct, incurved and posteriorly deflected through 45°, being about twice the diameter of the largest denticles of the main posterior series. The antero-lateral process is short, its total length being only about one eighth to one tenth that of the posterior bar. Its postero-aboral edge makes an angle of approximately go° with that of the posterior bar immediately adjacent toit. Its anterior inner edge is flexed slightly inwards and there is a series of 3 or 4 recurved, inwardly inclined denticles, which are more or less discrete pointed, and decrease in size towards the distal end, which is sharply pointed. Both the degree of “‘ hindeodellid ’’ alternation of the denticles of the posterior bar and the posterior inclination of the denticles show considerable variation, as also does the degree of convexity of the lateral faces of the posterior bar, which tends to increase posteriorly. All denticles of the posterior bar are either very closely spaced or fused for most of their length, the 3 or 4 which form the posterior end lying almost horizontally. RemARKS. The only substantial difference between this species and H. cooperi is the distinctive denticulation of the anterior lateral process, which in the present species extends as far as the aboral tip of the bar, in contrast to H. cooperi where it is restricted to the proximal part. Hindeodella montanaensis (Scott) Plate 28, figs. 21, 26 1942 Lochreia montanaensis Scott (partim) : Pl. 39, fig. 7, Pl. 40, fig. 18 (non pl. 39, figs. 1 4,9; Pl. 40, figs. 2, 9, Io, 12, 13, 15, 19). 1956 Hindeodella bigeniculata Elias (partim) : 106, Pl. 1, figs. 20, 21 (non PI. 1, fig. 16). 1956 Hindeodella mehli Elias : 108, Pl. 1, figs. 22-24. 1957 Hindeodella germana Holmes ; Bischoff (partim) : 27, Pl. 6, fig. 32, (non Pl. 6, fig. 34= H. secavata Collinson & Druce). 1958 Hindeodella montanaensis (Scott) Stanley (partim) : 465, Pl. 64, figs. 1-5. , 124 BRITISH AVONIAN CONODONT FAUNAS 1961 Hindeodella germana Holmes ; Higgins (partim) : Pl. 1o, fig. 12, (non Pl. 10, fig. 13=H. secavata Collinson & Druce). Hindeodella montanaensis (Scott) ; Collinson & Druce in press. MATERIAL. 80 specimens: figured, X 175, X 176. RANGE, North Crop 3D 10-3D Io. DeEscRIPTION. Members of this species are slightly constructed hindeodellids, having a massive main denticle with a very wide base, strongly convex lateral faces, and being inclined posteriorly at an angle of about 45°. The denticles on the posterior bar are minute in comparison with this denticle. They are crowded and laterally compressed, with sharp anterior and posterior edges, having a hindeodellid pattern with 2 or 3 smaller denticles between the larger ones. The lateral faces of the posterior bar are gently to strongly convex. The anterior lateral process is deep with three confluent denticles near its proximal end, but the distal end, which points strongly upward and inward, consists of a single fang-like denticle, about half the width of the main denticle. The basal anterior and posterior edges of the main denticle are also minutely denticulate. The outer lateral surface of the main denticle is flat. The aboral surface of the whole unit is excavated by a shallow groove which flares below the main denticle. The posterior bar is straight and about 5 to 6 times the length of the anterior bar in the present specimens, but these are broken. One specimen, which is also broken, shows a tendency for the denticles near the posterior end of the bar to be relatively larger, about twice as large as most of the denticles of the posterior bar, although the aboral cavity is little expanded below the main denticle. Hindeodella secarata Collinson & Druce Plate 29, figs. II, 13-15 1957 Hindeodella germana Holmes ; Bischoff (partim) : 27, Pl. 6, fig. 34 (non PI. 6, fig. 32=H. montanaensts). 1961 Hindeodella geymana Holmes ; Higgins (partim) : Pl. ro, fig. 13 (non Pl. to, fig. 12=H. montanaensis). 1963 Hindeodella germana Bischoff ; Bouckaert & Higgins ; 17, fig. 3. Hindeodella secavata Collinson & Druce in press. MATERIAL. 46 specimens : figured, X 184, X 181, X 182, X 183. RANGE. North Crop 3D 8-3D 1g. DESCRIPTION. The present specimens agree closely with the description given by Collinson and Druce. The posterior bar is greatly elongated and tends to taper towards the posterior end. It is straight to arched, with fine acicular denticles, and it lacks a well-developed anterior fang. The anterior process is very small, and is relatively feebly inflexed. The basal groove is conspicuous, but there is no obvious basal cavity at the anterior end. ww sad) PD: ~w sa) a). ~ 1926 1927 1928 1928 1931 1931 1931 1932 1934 1934 1934 1934 1934 1934 1935 1935 1935 1935 1938 1939 1939 1939 1940 1943 1943 1943 1943 1943 1943 1943 1945 1945 1945 1945 1945 1945 1947 1947 1947 1947 1947 1947 1947 1947 1955 1955 1957 1957 BRITISH AVONIAN CONODONT FAUNAS 125 Hindeodella subtilis Ulrich & Bassler Plate 29, figs. 6a—-7b, g—10b Hindeodella subtilis Ulrich & Bassler : 39, Pl. 8, figs. 17-19. Hindeodella deflecta Hibbard : 207, fig. 40. Hindeodella germana Holmes : 25, Pl. 9, fig. 9. Hindeodella subtilis Ulrich & Bassler ; Pl. 9, figs. ro, 11. Hindeodella subtilis Ulrich & Bassler ; Cooper : 147, Pl. 20, fig. 9. Hindeodella pumilla Cooper : 236, Pl. 28, fig. 18. Hindeodella subtilita Cooper : 236, Pl. 28, fig. 17. Hindeodella subtilis Ulrich & Bassler ; Bassler: Pl. 26, fig. 21. Hindeodella delicatula Branson & Mehl: 280, Pl. 22, fig. 30. Hindeodella alternidens Huddle: 44, Pl. 5, fig. 13 (non Pl. 5, fig. 12=Hindeodella sp.). Hindeodella angulus Huddle: 44, Pl. 5, fig. 15. Hindeodella aculeata Huddle : 40, Pl. 4, fig. 19 (non Pl. 4, figs. 20, 21 =Hindeodella sp. cf. H. similis Ulrich & Bassler), Pl. 5, figs. 2, 3. Hindeodella grandis Huddle : 41, Pl. 4, fig. 22. Hindeodella laticlavis Huddle: 43, Pl. 5, figs. 9, Io. Hindeodella subtilis Ulrich & Bassler ; Cooper : 309, 310, Pl. 27, fig. 27. Hindeodella germana Holmes ; Cooper : 310, Pl. 27, fig. 25. Hindeodella pumilla Cooper ; Cooper : 310, Pl. 27, fig. 26. Hindeodella subtilita Cooper ; Cooper : 310, Pl. 27, fig. 28. Hindeodella delicatula Branson & Mehl ; Branson & Mehl, Pl. 33, fig. 34. Hindeodella lineata (Pander) Cooper : 389, Pl. 46, figs. 28, 31. Hindeodella delicatula ? Branson & Mehl ; Cooper : 389, Pl. 46, fig. 33. Hindeodella acuta Branson & Mehl ; Cooper : 389, Pl. 46, figs. 15, 23, 29. Hindeodella moweri Stauffer : 424, Pl. 58, figs. 2, 10, 11. Hindeodella subtilis Ulrich & Bassler ; Cooper & Sloss : 170, Pl. 28, figs. 22, 32, 33. Hindeodella atteridens Huddle ; Cooper & Sloss: 170, Pl. 28, fig. 23. Hindeodella petila Cooper ; Cooper & Sloss : 170, Pl. 28, figs. 26, 35. Hindeodella deflecta Hibbard ; Cooper & Sloss : 170, Pl. 28, figs. 27, 34. Hindeodella germana Holmes ; Cooper & Sloss: 170, Pl. 28, fig. 28. Hindeodella grandis Huddle ; Cooper & Sloss : 170, Pl. 28, figs. 31, 37, 39. Hindeodella laticlavis Huddle ; Cooper & Sloss: 170, Pl. 28, fig. 38. Hindeodella aculeata Huddle ; Cooper: 613, Pl. 84, figs. 7, 9. Hindeodella votunda Hibbard ; Cooper: 614, Pl. 84, fig. 8. Hindeodella grandis Huddle ; Cooper: 614, Pl. 84, fig. ro. Hindeodella gracilis Huddle ; Cooper: 614, Pl. 84, fig. 11. Hindeodella prioniodon Huddle ; Cooper: 614, Pl. 84, fig. 12. Metaprioniodus biangulatus Huddle ; Cooper: 614, Pl. 84, figs. 13, 14. Hindeodella aculeata ? Huddle ; Youngquist & Petersen : 244, Pl. 38, fig. 9. Hindeodella aculeata Huddle ; Bond : 28, Pl. 1, figs. 19, 21. Hindeodella alternata Ulrich & Bassler ; Bond : 29, Pl. 1, fig. 23. Hindeodella germana Holmes ; Bond: 29, Pl. 1, fig. 22. Hindeodella germana Holmes ; Bond : 29, Pl. 1, fig. 22. Hindeodella subtilis Ulrich & Bassler ; Bond: 29, Pl. 1, fig. 25. Hindeodella sp. 1 Bond : 29, Pl. 1, fig. 24. Hindeodella sp. 2 Bond : 29, Pl. 1, fig. 20. Hindeodella germana Holmes ; Sannemann : 130, Pl. 2, fig. 45. Hindeodella deflecta Hibbard ; Sannemann : 129, Pl.s, fig. 6, Pl. 5, fig. 8. Hindeodella germana Holmes ; Lys, Serre & Deroo : 800, PI. 8, fig. 7. Hindeodella deflecta Hibbard ; Lys, Serre & Deroo : 800, PI. 8, fig. 6. 126 BRITISH AVONIAN CONODONT FAUNAS 1959 Hindeodella deflecta Hibbard ; Helms: PI. 4, fig. 32, Pl. 1, fig. 17. 1960 Hindeodella germana Holmes ; Zimmermann : PI. 1, fig. 16. 1960 Hindeodella germana Holmes ; Dvorak & Freyer: PI. 1, fig. 1. 1961 Hindeodella germana Holmes ; Biidurov : 262, Pl. 3, fig. rr. 1962 Hindeodella germana Holmes ; Spasov & Stevanovic : 58, Pl. 1, fig. 12. 1962 Hindeodella sp. Winder : 91, fig. 1, 6. 1965 Hindeodella germana Holmes ; Spasov : 86, 87, Pl. 1, fig. 10. 1965 Hindeodella similis Ulrich & Bassler ; Spasov : 87, Pl. 1, fig. 11. MATERIAL. 200 specimens : figured, X 180, X 177, X 178, X 179. RANGE. North Crop KL 1-ZL 19, Avon Gorge K 3-Z 38. DESCRIPTION. The main denticle is fairly massive, laterally compressed, biconvex in cross-section, recurved and posteriorly inclined. The anterior lateral process is curved inwards at an angle ranging from just a few degrees to nearly go°. The considerably laterally compressed anterior lateral process is finely denticulate, often with the largest denticles at the anterior. The posterior bar is very thin, compara- tively deep, and somewhat arched in some specimens, bearing fine, discrete, pointed denticles. The dentition tends to be cyclic, two major denticles being separated by three to four minute denticles, all more or less posteriorly inclined. There are up to 14 major denticles on the posterior bar. The posterior termination is composed of flat lying denticles, inclined at a low angle to the horizontal. It may be aborally convex (“ upswept ’’) in young forms. The basal cavity is small, fairly deep, and situated at the anterior end of the apical denticle. REMARKS. Throughout the Middle and Upper Devonian, and the Tournaisian and Viséan, there occurs a simple hindeodellid with a curved anterior lateral process. Many different authors have assigned different names to these hindeodellids, depend- ing on minor variations in such features as the amount of deflection. Within our collections all types of deflection and various types of dentition can be-seen to inter- grade, and it is probable that all these forms belong to the same variable species. Further work may show that some of these characteristics may be of specific import- ance, but at the present time none can be separated. Hindeodella tenuis Clarke Plate 28, fig. 27 1900 Ctenognathus obliquus Hinde (partim) : 344, Pl. ro, fig. 38. 1928 Hindeodella obliqua Holmes (partim) : 12, Pl. 5, fig. 5. 1960 Hindeodella tenuis Clarke : 8, 9, Pl. I, figs. ro, 11. MATERIAL. 4 Specimens : figured, X 187. RANGE. North Crop 3D 12-14/15. DESCRIPTION. The present specimens are similar to those described by Clarke. The posterior bar is elongated, deep, and decreases relatively little in depth towards its posterior end. The anterior two-thirds is straight and the posterior third gently down-flexed. The denticles tend to increase in size posteriorly, the most posterior BRITISH AVONIAN CONODONT FAUNAS 127 being both the largest and the most steeply inclined. The anterior fang is two to three times the basal width of the largest of the posterior denticles, and is slightly recurved. The anterior bar is relatively short and the denticles stand erect. The larger denticles of the posterior bar are separated by only 1 or 2 smaller denticles. The anterior lateral process is not strongly inflexed. Hindeodella undata Branson & Mehl Plate’ sx, fig: § 1941 Hindeodella undata Branson & Mehl: 169, PI. 5, fig. 3. 1941 Hindeodella sp. Branson & Mehl: 170, PI. 5, fig. 9. 1953 Hindeodella undata Branson & Mehl; Hass: 82, Pl. 16, figs. 5-7. 1956 MHindeodella undata Branson & Mehl; Elias: 108, Pl. 1, figs. 2, ro. 1956 Hamulosodina bransoni Elias : 108, Pl. 1, fig. 4. 1956 Hamulosodina hassi Elias : 108, Pl. 1, figs. 11, 12. 1961 Hindeodella undata Branson & Mehl ; Higgins: Pl. 12, figs. 10, 12. 1963 Hindeodella undata Branson & Mehl ; Bouckaert & Higgins: 17, text-fig. 3. Hindeodella undata Branson & Mehl ; Collinson & Druce in press, text-fig. Io. MATERIAL. 35 specimens : figured, X 185. RANGE. North Crop 3D 4-3D 22. DESCRIPTION. Specimens of this species are characterized by a relatively long, deep and straight posterior bar, the aboral margin of which is straight and sharp, and the sides relatively flat. The oral surface bears a series of alternating denticles which are acicular in general form, and discrete for the whole of their length. They taper sharply toa point. Larger denticles tend to be separated by groups of 2 or 3 smaller ones, which may be laterally offset from the denticles of the main series. The anterior fang is not greatly larger than the largest of the denticles of the posterior bar. It makes almost a right angle with the line of the posterior bar and is straight for the greater part of its length. The anterior inner lateral process is short and continuously inflexed. It bears one or more needle-like denticles on its oral edge. Hindeodella sp. Plate 29, figs. Iza, c MATERIAL. I specimen : figured, X 445. RANGE. North Crop ZLA 33. DEscRIPTION. A single specimen of a small distinctive hindeodellid is illustrated. The posterior bar is short and relatively deep and bears a series of 5 denticles which increase in size posteriorly. The inclination of the 4 most posterior is about 45° to the line of the posterior bar, but the most posterior denticle is more strongly inclined. The apical denticle is rounded in cross-section and the lower part is more or less erect. The anterior process is sharply down-flexed and continuously inflexed, so that its distal end makes an angle of about 45° with the posterior bar. There is a well- developed, elongated basal cavity below the fang and the proximal part of the anterior aboral process. 128 BRITISH AVONIAN CONODONT FAUNAS Hindeodella sp. nov. Plate 28, figs. 14a, b MATERIAL. I specimen: X 186 (figured). TYPE LOCALITY AND HORIZON. North Crop. Sample 3D 14/15. DescrIPTION. A single specimen is tentatively regarded as a new species of Hindeodella, although it may be a pathologic form. It is characterized by a con- tinuously recurved, hooked anterior lateral process and a very sinuous posterior bar. The general appearance of the unit is of a question mark, with the posterior end forming the base of the question mark. The posterior bar is shallow, being about equal in depth to the smaller series of denticles developed on its oral surface. Its aboral edge is strongly convex in its anterior half and concave in its posterior half, so that the whole effect is of a sinuous development. Its outer lateral face is strongly convex in the anterior half, and flat to gently convex in the posterior part. The oral surface of the posterior bar bears a series of about 18 denticles of variable size, which show no regular alternation. They are basally confluent but apically distinct, and are sharply pointed, with sharp anterior and posterior edges. Those near the posterior end tend to be more strongly inclined posteriorly than those in the anterior part, which are only gently inclined posteriorly. Although these denticles show no regular alternating arrangement, some of them are conspicuously larger than others and these are developed at variable intervals. The largest of them are about twice the length of the smallest, and they show a broad tendency to increase in size posteriorly. Their total number is probably greater than 18 as the present specimen is broken. The main denticle is about equal in size to the largest denticles of the posterior bar, being sharply recurved and incurved. Immediately posterior to it the aboral surface of the posterior bar is flat, although its general structure is still broadly convex. The antero-lateral process consists of two more or less distinct parts. There is a sharply up-flexed part, in which the aboral edge of the process makes an angle of about 70° with the aboral edge of the posterior bar immediately posterior to the main denticle. It is not greatly flexed to the natural plane, however. On the anterior end of this are two conspicuous denticles, which are incurved, as well as recurved, so that their ‘‘ anterior and posterior ”’ edges are in fact lateral in position. They are greater in size than the main denticle and exceed the size of the largest denticles of the posterior bar by about a half. The aboral surface of the unit is excavated by a very thin groove. Genus HINDEODUS Rexroad & Furnish 1964 1964 Hindeodus Rexroad & Furnish : 671 Type spEcIES. Tvichonodella imperfecta Rexroad. BRITISH AVONIAN CONODONT FAUNAS 129 Hindeodus alatoides (Rexroad & Burton) Plate 31, figs. 7, 10. 1961 Falcodus ? alatoides Rexroad & Burton : 1152, Pl. 140, fig. 8. 1964 Hindeodus alatoides (Rexroad & Burton) Rexroad & Furnish : 67, Pl. 111, figs. 18, 19. 1961 Falcodus (?) n. sp. Rexroad & Collinson : Pl. 1. 1965 Hindeodus alatoides (Rexroad & Burton) Rexroad & Nicoll: 20, Pl. 2, fig. ro. MATERIAL. 3 Specimens: figured, X 193, X 192. RANGE. Scotland HOSIE 2B-2C. DESCRIPTION. The present specimens are distinguished by the short laterally flexed anterior limb, which is deepest and bears the largest denticles distally. The apical denticle is only slightly inclined posteriorly and its distal portion is straight. It is little compressed laterally. The posterior bar is straight and elongated, its length being about three times that of the anterior bar. The denticles are short, discrete and bluntly pointed, tending to alternate in size and standing more or less erect to the posterior bar in some specimens, but being slightly inclined in others. The apical denticle is conspicuously elongated, and has a basal width of up to three times that of the adjacent denticles. The denticles of the posterior bar tend to increase in size posteriorly. The aboral cavity is relatively small. Hindeodus imperfectus (Rexroad) Plate 31, fig. 8 1957 Tvichonodella imperfecta Rexroad : 41, Pl. 4, figs. 4, 5. 1958 Tvichonodella imperfecta Rexroad ; Rexroad : 26, Pl. 4, fig. 6. 1961 LElsonella ? imperfecta (Rexroad) Rexroad & Collinson : 6. 1961 Elsonella ? imperfecta (Rexroad) Rexroad & Burton : 1152, Pl. 141, fig. 1. 1964 Hindeodus imperfectus (Rexroad) Rexroad & Furnish : 672, Pl. 111, figs. 13, 14. 1965 Hindeodus imperfectus (Rexroad) Rexroad & Nicoll : 20, Pl. 2, fig. 11. MATERIAL. I specimen : figured, X 194. RANGE. Scotland HOSIE 2B. DeEscrIpTIon. The present specimens are generally fragmentary, but they show =, Apical denticle Anterior Posterior Anterior bar aboral Outer lateral face margin Posterior bar Lateral view Fic. 25. Hindeodus sp. showing morphological terms used in the text. 130 BRITISH AVONIAN CONODONT FAUNAS the general symmetry of this species, a feature that is so striking that it led Rexroad in his initialdescription to assign it to the genus Tvichonodella. The denticles tend to increase in size towards the distal third of the bars, and the apical denticle tends to stand erect between the converging denticles of the anterior and posterior bars. There is a feeble basal flange below the apical denticle. Hindeodus sp. Plate 22, figs. 17a-20b 1964 Hindeodus sp. Rexroad & Furnish : 672, Pl. 111, fig. 11. MATERIAL. I0 specimens : figured, X 189, X 191, X 188, X Igo. RANGE. Scotland HOSIE 2A~-2B. DESCRIPTION. Certain of the present specimens, although showing minor varia- tions in form, are obviously closely related to one another. These specimens possess a short, deep, posterior bar which has a straight aboral margin in lateral view. The bar is slightly flexed inwards longitudinally and its oral surface bears at least ro confluent denticles, only their apices being discrete and bluntly pointed. They are inclined gently posteriorly and are more or less of uniform size. The apical denticle is about twice as long as the largest denticles of the rest of the bar. It is basally confluent to those on either side of it and has sharp anterior and posterior edges and a strongly biconvex cross-section. The anterior bar is shorter than the posterior, and is gently concave basally in lateral view. Its oral surface bears a series of about 5 denticles, similar in form to those of the posterior bar, which tend to decrease in size anteriorly and which are recurved so that they lie sub-parallel to the apical denticle. It makes an angle of about 90°-110° with the posterior bar. The denticles of the anterior bar tend on the whole to be rather broader than those of the posterior. The inner lateral face of the anterior bar is gently concave. In outer lateral view the whole unit is seen to be gently arched inwardly and its outer lateral face is flat to gently convex. There is a slightly expanded cavity below the apical denticle and very fine longitudinal grooves extend along the lengths of the two bars. Genus KLADOGNATAHUS Rexroad 1958 1958 Kladognathus Rexroad : 19 (pro Cladognathus Rexroad 1957, 28 non Burmeister 1847). 1961 Cladognathodus Rexroad & Collinson : 6 (abs. syn.). TYPE SPECIES. Cladognathus prima Rexroad. This genus was first described by Rexroad in 1957 under the name Cladognathus, a name later found to be a homonym of one used by Burmeister in 1847. The name Kladognathus was proposed by Rexroad 1958, as a substitute. Rexroad & Collinson (1961 : 6), however, changed this to Cladognathodus because they suggested that the replacement of a letter “‘ C”’ by a letter “ K ” did not represent a valid name change under the rules of nomenclature. Article 56A of the International Code makes it clear, however, that a difference of even one letter in the spelling of generic names represents a valid distinction between them. The name Kladognathus Rexroad 1958 BRITISH AVONIAN CONODONT FAUNAS 131 is thus the senior and correct name for the genus, and Cladognathodus Rexroad & Collinson 1961 is a junior synonym. We are grateful to Dr. Curt Teichert for pointing this out to us (see also Mound 1965). Kladognathus clarensis Collinson & Druce Plate 23, figs. Ia—2b Kladognathus clarensis Collinson & Druce (in press). MATERIAL. 3 specimens: figured, X 195, X 196. Rance. North Crop 3D 10-3D 23. DescriPTIon. In lateral view this species resembles the genus Metalonchodina. Its most striking feature is the greatly enlarged, laterally compressed denticle which comprises most of the posterior bar. This is inclined posteriorly but the curvature may be more or less continuous, or it may be chiefly confined to the base, with the upper part of the denticle having straight anterior and posterior edges. The inner lateral face tends to be rather more convex than the outer. The posterior aboral termination is more or less sharply pointed. The fang is relatively small in comparison with the posterior denticle. It is slender, posteriorly continuously recurved, and has sharp anterior and posterior edges. The anterior bar consists of 1 to 3 denticles and the anterior aboral margin is spatulate in form with the anterior aboral angle being rounded. In multidenticulate anterior bars the most anterior denticles tend to be more or less erect, but the more posterior ones tend to be recurved. The lateral process is short and bears at least one oral denticle. The whole unit tends to be laterally deflected, the outer lateral face tending to be concave. The aboral surface below the main denticle on the posterior bar is broad, and has a conspicuous flattened basal surface. It consists essentially of an inverted basal cavity, with a median groove which is continued along the anterior bar. All of the three present specimens have a short, laterally compressed, inconspicuous denticle lying between the fang and the main denticle of the posterior bar. Posterior Fang ae Anterior bor Posterior denticle she Inner lateral process Posterior bor Aboral margin Fic. 26. Kladognathus sp. showing morphological terms used in the text. 132 BRITISH AVONIAN CONODONT FAUNAS REMARKS. The present specimens show strong resemblances to those described by Clarke (1960) as Ligonodina complectens. Rexroad & Collinson (1963 : 13) transferred Clarke’s specimens to the genus Magnilaterella. The present specimens differ from those of Clarke chiefly in the presence of an anterior bar, and it is this distinctive feature which justifies their inclusion in the genus Kladognathus. Kladognathus macrodentatus (Higgins) Plate 23, figs. 3-6 1961 Lambdagnathus macrodentata Higgins : 214, Pl. 12, figs. 1-3, text-fig. 3. 1963 Lambdagnathus macrodentata Higgins ; Bouckaert & Higgins : 17, fig. 3. Kladognathus macrodentata (Higgins) Collinson & Druce (in press). MATERIAL. I5 specimens : figured, X 197, X 198, X 199, X 200. RANGE. North Crop 3D 10-3D 22. DESCRIPTION. This species is characterized by a long arched posterior bar which bears characteristically hindeodellid denticulation on its oral surface. The larger denticles are separated by 1 or 2 smaller denticles, which are basally confluent but apically discrete. In well preserved specimens the major denticles of the series are very long, the largest, in the middle of the posterior blade, commonly being about three times the depth of the posterior bar. The short laterally compressed anterior bar is downflexed, but lies in the same plane as the posterior bar. Its anterior aboral margin is bluntly spatulate. There tend to be 2 or 3 small denticles in front of the apical denticle. The lateral bar is short, deeply arched, laterally compressed, and strongly deflected posteriorly, making an angle of 25°-45° with the arcuate posterior bar when seen in oral view. The lateral bar carries I or 2 stout, discrete denticles on its oral surface. The aboral margin of the entire unit is excavated by a shallow groove. | Kladognathus mehli (Rexroad) Plate 31, fig. 15 1957 Cladognathus mehli Rexroad : 29, Pl. 1, figs. 11, 12. 1958 Kladognathus mehli (Rexroad) Rexroad : 19, Pl. 3, fig. 5. 1965 Kladognathus mehli (Rexroad) Rexroad & Nicoll : 20, 21, Pl. 1, fig. 7. MATERIAL. 3 specimens : figured, X524. Rance. North Crop 3D 14/15. DEscrRIPTION. This species is characterized by a very large, laterally compressed recurved fang, strong discrete denticles on the anterior and posterior bars, relatively strong curvature on the anterior and posterior bars, and a conspicuous attachment scar on the inner lateral face at the anterior end of the posterior bars. Our specimens agree closely with those illustrated by Rexroad. BRITISH AVONIAN CONODONT FAUNAS 133 Genus LIGONODINA Ulrich & Bassler 1926 1925 Ligonodina Bassler : 218 (nom. nud.). 1926 Ligonodina Ulrich & Bassler: 12, 13. Type spEcIES. Ligonodina pectinata Ulrich & Bassler 1926. Ligonodina beata nom. nov. Plate 26, figs. 4-6b 1934 Ligenodina delicata Branson & Mehl: 199, Pl. 14, figs. 22, 23. 1934 Ligonodina delicata Branson & Mehl; E. R. Branson : 328, Pl. 27, fig. 3. 1934 Ligonodina sp. Huddle: 62, Pl. 12, fig. 8. 1939 Ligonodina delicatula Cooper : 390, Pl. 45, figs. 50, 60, 61. 1943 Ligonodina tenerva Cooper & Sloss : 174, Pl. 29, fig. 34. 1944 Ligonodina delicata Branson & Mehl; Branson & Mehl im Shimer & Shrock: 241, Pl. 93, fig. 74. non 1944 Ligonodina delicata Branson & Mehl ; E. B. Branson : Pl. 26, fig. 23, (=Palmatolepis Sp). 1947 Ligonodina delicata Branson & Mehl ; Miller & Youngquist : 509, 510, Pl. 73, fig. 12. 1949 Ligonodina delicata Branson & Mehl ; Thomas: 408, 411, Pl. 4, fig. 22. non 1949 Ligonodina delicata ? Branson & Mehl ; Thomas: PI. 3, fig. 41, (=Ligonodina sp.). non 1964 Ligonodina delicata Branson & Mehl; Bergstr6m: 28, text-fig. 12. Bergstrém (1964, 28) has demonstrated that Phvagmodus delicatus Branson & Mehl, 1933, 123, Pl. 10, fig. 22) should be regarded as a species of Ligonodina. The name for this species, therefore, has precedence over that of Ligonodina delicata Branson & Mehl (1934, 199) and the latter species becomes a junior homonym of the former. In this case, it is necessary to select a new name, and we have selected the name Ligonodina beata. The holotype is University of Missouri Catalogue No. C. 243-4 (Branson & Mehl 1934 : 199). non 1964 Ligonodina delicata Branson & Mehl ; Budurov & Tschurner: PI. V, figs. 23a, b. MATERIAL. 361 specimens : figured, X 202, X 203, X 2oI. Rance. North Crop KL 19-ZLA 21, Avon Gorge K 3-C 25. Description. A fragile unit with a slender main denticle which has a sub-circular cross-section. The main denticle is recurved posteriorly at 45°. The anterior- aboral process originates immediately anterior to the main denticle, and commonly bears 3 or 4 isolated, discrete, sub-circular denticles, which are posteriorly inclined. The posterior bar is fairly long and rarely preserved. It bears up to 6 isolated laterally compressed denticles, which are posteriorly inclined, and tend to increase in size posteriorly. In aboral view, the anterior portion of the posterior bar is excavated, the deepest excavation being beneath the main denticle ; the cavity extends inverted beneath the anterior aboral process. The cavity is grooved, the groove running some way along the posterior bar and the complete length of the anterior aboral process. REMARKS. Our specimens agree very closely to the holotype described by Branson & Mehl. 134 BRITISH AVONIAN CONODONT FAUNAS Ligonodina levis Branson & Mehl Plate 26, figs. 15a, b, 17a-19b 1941 Ligonodina levis Branson & Mehl: 185, Pl. 6, fig. 10. 1949 Ligonodina sp. Youngquist & Miller (partim) : 620, Pl. ror, figs. 12 & 13 only. 1957 Ligonodina levis Branson & Mehl ; Bischoff: 30, Pl. 5, figs. 8, 9, Pl. 6, fig. 25. 1957 Ligonodina obunca Rexroad : 32, Pl. 1, figs. 22, 23. 1958 Ligonodina obunca Rexroad ; Rexroad : 21, Pl. 3, figs. 7, 8. 1961 Ligonodina levis Branson & Mehl ; Rexroad & Burton: 1154, Pl. 141, figs. 7, 8. 1963 Ligonodina levis Branson & Mehl ; Thompson & Goebel : 11, fig. 3. 1963 Ligonodina levis Branson & Mehl ; Rexroad & Collinson : 11, Pl. 2, figs. 24, 25. 1964 Ligonodina levis Branson & Mehl; Rexroad & Furnish : 672, Pl. 111, fig. 381. 1965 Ligonodina levis Branson & Mehl; Rexroad & Nicoll: 21, Pl. 2, fig. 24. MATERIAL. 25 specimens : figured, X 204, X 205, X 206, X 207. RANGE. North Crop CYD 6-3D 14/15, Avon Gorge Z 38-D 26. DESCRIPTION. Rexroad’s original description of this particular species was rather generalized, but the distinctive features seem to be the massive and rather rounded main denticle, which is continuously recurved, especially in its lower part, so that its distal portion makes an angle of about 45° with the posterior bar. The distal portion is not greatly laterally compressed, although it has sharp anterior and posterior edges ; the lateral faces are themselves strongly convex. The posterior edges become obsolescent towards the proximal end. The outer lateral aboral surface is expanded slightly laterally, but has a conspicuous flange-like structure developed along it, which slopes towards the aboral cavity. The proximal inner portion of the main denticle is very strongly convex. The posterior bar is of unknown length but is more or less quadrate in cross-section, with a broad aboral edge. It bears at least one, stump-like denticle, which is well separated from the base of the main denticle. The antero-aboral surface of the main denticle tends to be rather rounded, and in oral-outer lateral view extends below the main level of the denticle in a rather bluntly pointed termination. The main denticle extends in a continuous curve downward to form the inner anterior aboral process. The aboral surface of this process lies at an acute angle, often as small as 45°, to the posterior bar. Its oral surface bears up to 5 large denticles, of which those at the anterior end tend to be very large. They are straight to slightly curved Main denticle Bees Inner-lateral lamina if ff E (i 4 Posterior denticles Posterior bor Anterior aboral process Fic. 27. Ligonodina sp. showing morphological terms used in the text. BRITISH AVONIAN CONODONT FAUNAS 135 and are directed inwards and upwards. The denticles are discrete and more or less sub-circular in cross-section. The antero-aboral process decreases in thickness towards the distal end. The aboral surface is characterized by thick, aborally directed, lip-like, flange structures along the lateral edges of both the posterior bar and the antero-aboral process. There is a pit-like cavity below the main denticle and there are longitudinal grooves along the aboral surface of the posterior bar and the antero-aboral process. These decrease in width towards the distal end of the process. Ligonodina magnilaterina sp. nov. Plate 26, figs. 8a—11b DERIVATION OF NAME. From the resemblance of the species to the genus Mag- nilaterella. Diaecnosis. Ligonodinid with a denticle situated anterior to main denticle, forming continuation of denticle series of posterior bar. Anterior denticle only slightly smaller in size than main denticle, though tending to be rather more slender in general form ; lying at junction of antero-aboral process and posterior bar. MATERIAL. 6specimens : Holotype X 211, Paratypes (all figured) X 208, X 209, 270. TYPE LOCALITY AND HORIZON. Scotland Sample HOSIE 2C. RANGE. Scotland HOSIE 2C. DESCRIPTION. The main denticle is strong, the base being strongly developed anteriorly and posteriorly. It is of unknown length, sub-circular in cross-section in the lower part. The main denticle is recurved in its lower part, the inner and outer lateral faces being strongly convex. The posterior margin of the main denticle is extended to form the oral surface of the posterior bar. This bar is of unknown length, but is deep in its anterior part and bears at least 4 discrete denticles, which are only slightly laterally compressed and of variable size. It is possible that they may be arranged in a cyclic pattern. On the anterior face of the main denticle a thickened denticle is developed at the junction of the anterior denticle and the antero-aboral process. This denticle is distinct from those of the antero-aboral process and in inner lateral view it seems to represent a continuation of the posterior bar. In outer lateral view it may be seen to be recurved inwardly at its base ; its anterior face is strongly convex with sharp lateral edges. It is recurved slightly posteriorly to lie sub-parallel to the main denticle, and also slightly inwardly. It is fused at the base to the main denticle and arises from it at a strongly convex junction. It is long and slender, being sharply pointed at its distal end and is about half the diameter of the main denticle. The other denticles of the anterior aboral process, which number at least three, are discrete, sub-circular in cross-section with poorly defined, but rather sharp, lateral edges. They tend to decrease in size distally. The anterior aboral process appears to be relatively short, although none of the present specimens is complete. It is 136 BRITISH AVONIAN CONODONT FAUNAS strongly recurved in a vertical plane and its proximal aboral surface makes almost a right angle with the posterior bar. It is also strongly recurved with respect to the aboral surface of the posterior bar. The curvature of the anterior edge of the process is in line with the anterior denticle and not with that of the main denticle. It makes an angle of about 45° with the posterior bar in a horizontal plane. The aboral surface is excavated by a very shallow and rather inconspicuous groove, which runs along at least the anterior part of the posterior bar and is con- tinuous with a similar cavity below the anterior aboral process. The cavity below the main denticle is very narrow and not over-deep. REMARKS. This species is distinguished from all other ligonodinids by the form and the position of the denticle anterior to the main denticle. In this feature it approaches, but does not reach, the typical forms of the genus Magnilaterella Rexroad and it is also reminiscent to some extent of some Ordovician species of the genus Phragmodus. Ligonodina osborni sp. nov. Plate 26, figs. Ia—2c DERIVATION OF NAME. This species is named in honour of Mr. S. Osborn of the Geology Department, University College of Swansea. Diacnosis. Ligonodinid with a conspicuous continuously recurved main denticle, strongly biconvex in cross-section, with feeble anterior and posterior edges, distal portion not preserved in present specimens. Posterior bar of unknown length, strongly depressed in vertical plane, bearing on oral surface series of isolated, posteriorly inclined denticles, appearing to increase in size posteriorly ; separated by distance about equal to their basal width. A short, sinuous, sharply flexed, pointed anterior aboral process, bearing 2 isolated denticles ; proximal larger than distal. MATERIAL. 6 specimens : Holotype X 212, Paratype X 213 (both figured). TYPE LOCALITY AND HORIZON. North Crop. Sample 3D 14/15. Rance. North Crop 3D 8-3D 14/15. DEscRIPTION. The main denticle is large and strongly recurved, its whole anterior edge being strongly convex, and its posterior strongly concave. The distal portion is of unknown form but the basal part is biconvex in outline, with only inconspicuously developed anterior and posterior edges. It is extended posteriorly into a strongly arched posterior bar, the aboral edge of which is concave. Its lateral faces are flat or only very feebly convex, and there is a sharp basal ledge developed along its preserved length. Its oral surface bears at least 3 isolated, posteriorly inclined, denticles, which are biconvex in cross-section, and the third of which is larger than the first or second. These are inclined at an angle of about 45° to the posterior bar, and are separated by a distance about equal to their basal width. The antero-aboral process makes an angle in a vertical plane of about go0° with the line of the posterior denticle, so that its denticles point directly inwards and also a little posteriorly, because of their recurvature. It bears at least 2 isolated denticles, BRITISH AVONIAN CONODONT FAUNAS 137 which are biconvex in cross-section and have inconspicuous lateral edges. They are separated by a great distance and the distal is the smaller of the two. The whole anterior aboral surface tapers rapidly towards its distal tip ; although its depth remains constant, its width decreases conspicuously. Its distal tip is also flexed gently forward. In lateral view the most striking feature of the anterior aboral process is that it is so recurved posteriorly that it has an angular protruding junction with the base of the main denticle. It is then flexed forwards so that the whole appearance of the combined aboral process and anterior denticle is of a feebly sinuous line. In outer lateral view the flexure and decrease in width of the anterior aboral process are conspicuous features. The lip below the main denticie is also strikingly developed in lateral view, the whole inner lateral face of the unit being very feebly convex. In aboral view the unit is greatly expanded below the main denticle and there is a conspicuously flattened, but sloping, surface which is deeper on the outer lateral side. It narrows rapidly towards the posterior bar, which is excavated by a relatively deep, rounded groove. The main basal cavity is restricted to the median part below the main denticle. The anterior aboral process also has a very wide aboral surface, which is only partly excavated, but it narrows rapidly towards a pointed distal end and is somewhat twisted in aboral view. It is deflected to make an angle of go° in a vertical plane with the main denticle. Ligonodina roundyi Hass Plate 26, figs. 13a-14b, 16a—c 1926 Prioniodus sp. A. Roundy : 11, Pl. 4, fig. 9. 1926 Prioniodus sp. C. Roundy : 11, Pl. 4, fig. 11. 1953 Ligonodina roundyi Hass : 82-83, Pl. 15, figs. 5-9. 1956 Ligonodina roundyi Hass: Elias: 126, Pl. V, figs. 10-14. 1958 Ligonodina voundyi Hass ; Rexroad : 21, Pl. 3, figs. 1-4. 1961 ?Ligonodina typa (Gunnell) Higgins : 220, Pl. 11, fig. 6. Ligonodina voundyi Hass ; Collinson & Druce (in press). MATERIAL. 24 Specimens: figured, X 214, X 215, X 216. Rance. North Crop 3D 14/15. DeEscriPTION. This species of Ligonodina is characterized by a massive and elongate main denticle and a strongly developed antero-aboral process. The posterior bar is relatively slender in comparison with the proportions of the two latter elements. The main denticle is greatly elongated, and more or less strongly expanded anteriorly and posteriorly at its base. It is sharply pointed and in its distal half it is very strongly laterally compressed, the anterior and posterior edges being sharp and the lateral faces feebly convex. The curvature of the main denticle is concentrated in the proximal third, the remainder being straight. It is also twisted in the vertical plane, so that the anterior edge points inwardly ; in its outer aboral portion the main denticle is strongly rounded, but the corresponding inner lateral face is flat to feebly concave. Along the inner anterior margin a relatively strong and sharp keel is 138 BRITISH AVONIAN CONODONT FAUNAS developed, which is the main anterior edge of the denticle ; it extends aborally as a sharp ridge, which forms the edges of the denticles of the anterior aboral process. The posterior face of the main denticle tends to become rather depressed and may develop a low concave depression. The antero-aboral process points vertically downwards, making an angle of 80°—r100° with the posterior bar. It is not deflected out of line with the main denticle to any great extent. The oral surface of the anterior aboral process bears up to 6 denticles, the largest of which occurs in the medial portion ; the denticles are strongly compressed anteriorly and posteriorly in their distal portions. Though their bases are sub-circular in outline, they have strong lateral edges and are recurved inward and upward ; they are discrete but relatively closely spaced. The posterior bar is relatively slender and bears at least 2 (the present specimens are all broken) discrete, sub-circular, widely spaced, feebly posteriorly inclined, bluntly pointed, peg-like denticles. The outer lateral face of the main denticle is strongly flared and the edges of the cavity are thick ; there is a deep, but limited lip below the main denticle which is extended along the aboral anterior process as a conspicuous longitudinal groove on the aboral surface ; it is also extended for at least some distance along the posterior bar. The width and depth on the antero-aboral process decrease towards the distal extremity, which is bluntly rounded. The posterior bar is more or less quadrate in cross-section. Ligonodina tenuis Branson & Mehl Plate 31, figs. 4, 16 1941 Ligonodina tenuis Branson & Mehl: 170, Pl. 5, figs. 13, 14. 1949 Ligonodina sp. Youngquist & Miller (partim) : 620, Pl. ror, fig. 11 only. 1956 Ligonodina tenuis Branson & Mehl; Elias: 126, Pl. 5, figs. 4, 5. ‘ 1957 Ligonodina sp. Rexroad : 33, Pl. 1, figs. 20, 21. 1957 Ligonodina hamata Rexroad : 32, Pl. 1, figs. 24, 25. 1958 Ligonodina hamata Rexroad ; Rexroad : 21, Pl. 3, figs. 9-14. 1960 Ligonodina tulensis (Pander) Clarke 11, Pl. 2, fig. 4. 1961 Ligonodina obunca Rexroad ; Higgins: Pl. 11, fig. 9. 1961 Ligonodina hamata Rexroad ; Rexroad & Burton: 1154, Pl. 141, figs. 5, 6. 1964 Ligonodina tenuis Branson & Mehl ; Rexroad & Furnish : 672, Pl. 111, fig. 4o. 1965 Ligonodina tenuis Branson & Mehl; Rexroad & Nicoll: 22, Pl. 2, figs. 12-15. MATERIAL. 15 specimens : figured, X 320, X 321. RANGE. North Crop 3D 8-3D 22. DESCRIPTION. Specimens of the species, though generally fragmentary, display the distinctive features of the holotype. They have a characteristically strongly developed long, slender main denticle, which is continuously recurved, although the distal portion tends to be rather straight : the lateral faces are convex to flat, and the aboral margin tends to bear a more or less conspicuous ledge. The denticles of the posterior bar are relatively small in comparison with the size of the unit. BRITISH AVONIAN CONODONT FAUNAS 139 Ligonodina tulensis (Pander) Plate 31, fig. 9 1856 Prioniodus tulensis Pander (partim) : 30, tab. 2a, fig. 19 only. 1900 Prioniodus tulensis Pander ; Hinde (partim) : 343, Pl. 9, fig. 15 only. 1928 Prioniodus tulensis Pander ; Holmes (partim) : 22, Pl. 3, fig. 22 only. MATERIAL. 6 specimens : figured X 328. RANGE. North Crop CYD 6-CYD 7. DeEscriPTion. The present specimens are fragmentary but they display most of the features described by Clarke. The main denticle tends to be rather large in comparison with the size of the posterior bar ; its lateral faces are flat to gently convex, and in its lower portion the anterior and posterior edges tend to be blunted. The denticles of the posterior bar are relatively small, and are discrete. The anterior aboral process is strongly recurved laterally, and is also twisted, so that the denticles are directed anteriorly. Its distal end makes a right angle in a horizontal plane with the posterior bar. The denticles of the process tend to be rather larger than those of the posterior bar. Ligonodina sp. A Plate 26, figs. 3a—c MATERIAL. I0 specimens : figured, X 217. RANGE. North Crop ZLA 32-ZLA 33. Description. All the present specimens are broken, but the species appears to be a ligonodinid with a greatly excavated main denticle. The main denticle itself is massive, sub-circular in cross-section, with a sharp lateral costa developed in line with the anterior aboral process. The antero-aboral process is broken, but the posterior bar can be seen to be short, bearing three tall isolated denticles, and having its aboral side grooved. REMARKS. The overall appearance of this species is of a Rowndya with only one limb of the anterior arch developed. Youngquist, Miller & Downs (1950 : 527) illustrate and describe similar forms as Ligonodina? sp. Our material is too frag- mentary for a specific designation but it would appear that the two forms may be conspecific. Ligonodina ? sp. Plate 26, fig. 7 MATERIAL. I specimen : figured, X 218. RANGE. North Crop ZLA 11. DEscripTION. This appears to be a pathological form of L. beata. There is a secondary lateral process developed on the inner side of the posterior bar and it bears one low node. The angle of the process, and its inclination toward the posterior, are parallel to that of the antero-aboral process. The basal cavity is extended along it on the aboral side. 140 BRITISH AVONIAN CONODONT FAUNAS Ligonodina ? sp. Plate 26, figs. 12a—b MATERIAL. I specimen : figured, X 219. RANGE. North Crop 3D to. DeEscripTION. This single specimen is presumably a pathological form of the genus Ligonodina. It is characterized by the presence of the antero-aboral process and by the fact that the main denticle can just be discerned when the lighting is favourable. On the posterior edge of this denticle, however, and continuous with it, there is a sheet-like development of conodont material which extends in the same plane as the posterior bar. Only the anterior denticle is visible within this by reflected light. The denticles of the antero-aboral process are sub-circular in form, 3 in number, and discrete, the middle one of the three being the largest. The form of the outer lateral face of the extension of the anterior denticle suggests that the conodont was attached by this surface ; this then became an aboral surface although in “‘ normal” specimens it would have represented an upper lateral surface. Genus LONCHODINA Ulrich & Bassler 1926 1925 Lonchodina Bassler : 219 (nom. nud.). 1926 Lonchodina Ulrich & Bassler : TYPE SPECIES. Lonchodina typicalis Ulrich & Bassler 1926. Lonchodina bolbosa Collinson & Druce Plate 24, figs. 12a-14b 1957 Lonchodina nitela Huddle ; Ziegler in Fliigel & Ziegler : 44, Pl. 4, fig. ro. 1961 Lonchodina cf. projecta (Ulrich & Bassler) Higgins ; 220, Pl. XI, fig. ro. Lonchodina bolbosa Collinson & Druce (in press). MATERIAL. 12 Specimens : figured, X 223, X 222, X 224. RanGE. North Crop 3D 8-3D 14/15. DESCRIPTION. The distinctive features of this species are the relatively sub-equal short and rather slender bars, the conspicuous basal flaring below the apical denticle on the outer lateral face and the divergence of the two bars below the denticle at an angle of more than go° ; in some specimens the angle approaches a right angle, but in others, the angle may be as high as 110°. The present specimens are very fragmentary but they show the long recurved, laterally compressed apical denticle, the distinctive flaring cavity, and the straight and relatively short anterior aboral process described by Collinson & Druce. The basal excavation below the main denticle is large but shallow, and is extended as a very narrow groove along the anterior aboral process. BRITISH AVONIAN CONODONT FAUNAS 141 Lonchodina furnishi Rexroad Plate 24, figs. 20a—23c 1957 ?Lonchodina subsymmetrica Ulrich & Bassler ; Bischoff: Pl. 1, figs. 19, 21, 22. 1958 Lonchodina furnish Rexroad : 22, Pl. 4, figs. 11-13. 1961 Lonchodina furnish Rexroad ; Higgins: PI. 11, fig. 3. non 1962 Lonchodina furnish ? Rexroad ; Higgins: Pl. 1, fig. 4. 1963 Lonchodina furnisht Rexroad ; Bouckaert & Higgins : 17, fig. 3. Lonchodina furnishi Rexroad ; Collinson & Druce (in press). MATERIAL. 5 Specimens : figured, X 225, X 226, X 228, X 227. Rance. North Crop 3D 8-3D 19. DESCRIPTION. The distinctive feature of this species is the more or less sym- metrical development of the cavity below the apical denticle on both sides of the bar, rather than being restricted to only one side of it. The anterior bar is stout and deep increasing slightly in depth towards the anterior end. It bears about 5 stout denticles which are basally confluent but discrete for two thirds of their length. They tend to be sub-triangular in profile and to be sharply pointed, with sharp anterior and posterior edges and gently to strongly convex lateral faces. The curvature on the outer faces tends to be stronger than that on the inner, the denticles on the median third of the bar tending to be the largest. The anterior denticle is small and relatively inconspicuous. The apical denticle is about twice the length of the largest denticle of the anterior bar ; it is strongly posteriorly inclined rather than recurved, its edges being straight. It lies in approximately the same horizontal plane as the distal end of the anterior bar. Its inner lateral face is strongly convex at the base, becoming feebly convex in its upper surface ; its outer lateral face is rather more strongly convex. Throughout its length it is sharply pointed and is also directed inwardly as well as posteriorly. The outer lateral face of the anterior bar is feebly ridged longitudinally along its upper surface, about one third of its depth below the junction with the oral denticles ; below this point it slopes gently inwards and has a flat feebly concave surface. The bar itself is curved in a vertical plane and is also slightly deflected inwardly. Bar Apical denticle denticles ee, Posterior Anteclor Posterior Anterior bar bar Aboral margin Inner lateral face Flared basal cavity Fig. 28. Lonchodina sp. showing morphological terms used in the text. 142 BRITISH AVONIAN CONODONT FAUNAS The posterior bar is depressed, but is more or less straight ; it bears about 4 denticles which are discrete, sub-triangular in profile and sharply pointed, their bases being confluent ; they have sharp posterior and anterior edges, feebly convex lateral faces, and are inclined parallel to the apical denticle, though they are not recurved inwardly to the same extent. The posterior bar is more shallow and slender than any part of the anterior bar and is only about one third to a half the length of the latter. Both bars are excavated by fine longitudinal grooves and there is a conspicuous flaring cavity below the apical denticle on both the inner and outer lateral faces of the unit, about which it is sub-symmetrical, though not symmetrical in detail, the inner lateral flaring occurring rather posterior to the outer lateral flaring. ReMmArRKs. The denticles on the anterior bar may number up to 8 in some specimens. The species shows some variation in the degree of lateral deflection of the bars in a horizontal plane. Some specimens (e.g. Pl. 24, fig. 23b) show the posterior bar considerably flexed outward as well as vertically. Lonchodina obtunda Collinson & Druce Plate 24, figs. 7a-c 1957 Lonchodina projecta (Ulrich & Bassler) Ziegler in Fligel & Ziegler: 44, Pl. 4, fig. 14 (non Pl. 5, fig. 12). 1962 ?Lonchodina cf. projecta (Ulrich & Bassler) Higgins : Pl. 1, fig. 5. Lonchodina obtunda Collinson & Druce (in press). MATERIAL. 5 Specimens : figured, X 229. RANGE. North Crop 3D 8-3D 17. DescriPTION. The distinctive features of the species are the relatively delicate construction of the whole unit, the large sub-apical cavity which is developed on the inner lateral surface, and the very wide angle of divergence of the anterior and posterior bars, which in Collinson & Druce’s type specimens is I10°-135°. The present specimens are incomplete but they show a relatively slender anterior bar, with about 5 widely spaced though virtually basally confluent, denticles ; they are curved upward and inward and have biconvex lateral faces, the inner being the stronger, and relatively sharp edges. The denticles of the anterior bar range up to at least 5 in number. The apical denticle is strong and more or less sub-circular in cross-section, though it has prominent anterior and posterior edges in its proximal portions ; it is curved inwards and backwards, and its inner lateral face is very strongly expanded to give a wide flaring basal cavity which extends as a groove along the bars. The posterior bar is broken in the present specimens but it makes an angle of considerably more than go° with the anterior bar. REMARKS. Collinson & Druce (in press) have discussed the relationships of this species with other lonchodinids. BRITISH AVONIAN CONODONT FAUNAS 143 Lonchodina paraclarki Hass Plate 24, figs. 16a, b 1953 Lonchodina paraclarki Hass : 83, Pl. 16, figs. 15, 16. non 1958 Lonchodina paraclarki Hass ; Stanley : 468, Pl. 67, fig. 1. non 1958 Lonchodina cf. pavaclarki Hass ; Rexroad : 22, Pl. 4, figs. 4, 5. Lonchodina paraclarki Hass ; Collinson & Druce (in press). MATERIAL. 3 specimens: figured, X 231. RANGE. North Crop 3D 10-3D 14/15. DESCRIPTION. The most distinctive features are the very short posterior bar tending to develop only 2 denticles, the massive incurved and recurved apical denticle, and the very strong inner-lateral deflection of its aboral margin, giving a sub-triangular basal cavity that extends along most of the aboral surface of the unit. Hass has discussed the relationship of the species to Ligonodina clarki (1953 : 83) and Collinson & Druce have discussed the differences between Lonchodina paraclarki in the original sense of Hass and specimens referred to that species by Stanley & Rexroad. Lonchodina paraclaviger Rexroad Plate 24, figs. 15a, b, 18a, b 1958 Lonchodina paraclaviger Rexroad : 22, Pl. 4, figs. 7-10. Lonchodina paraclavigey Rexroad ; Collinson & Druce (in press). MATERIAL. 780 specimens : figured X 232, X 233. RANGE. North Crop 3D 13-3D 14/15. DEScRIPTION. This species is characterized by its stout general construction. The posterior bar is about half the length of the anterior bar. The stout, basally confluent, elongated, pointed denticles, number eight on the anterior bar, and four on the posterior. Both bars are straight except for slight curvature in the anterior, where they make an angle of about g0°-100° with each other. The lateral deflection of the posterior bar is about 45° out of the vertical plane of the anterior bar, and a large flaring asymmetrical cavity is strongly developed on the inner side, as a sub- triangular, to rounded expansion, that is flat on the outer lateral face and is extended along both bars as a deep groove. Both bars are relatively deep, with convex lateral faces. The denticles of the anterior bar, although basally confluent, are discrete for most of their length, and approach the apical denticle in size ; they may be of uniform size or they may increase in size towards the anterior end of the unit ; they are slightly recurved posteriorly and also inwardly, and lie more or less parallel to the apical denticle, which is sometimes only slightly larger than those of the anterior bar. The apical denticle is very strongly convex on its inner lateral face, with sharp anterior and posterior edges, and rather less strongly convex on its outer lateral face ; it is more or less straight in lateral view but is inclined posteriorly at about 60° to the anterior bar and is also recurved inwardly. The denticles of the posterior bar tend 144 BRITISH AVONIAN CONODONT FAUNAS to be rather straight, but are discrete, sharply pointed, and tend to be directed inwardly, being either erect to the posterior bar or in a few cases sloping slightly forward ; in most specimens, however, they are either erect or posteriorly inclined. The posterior denticles tend to decrease in size posteriorly. The basal cavity is strongly developed on the inner side of the unit, but it is wide, rather than deep ; it extends as a very narrow groove along the bars. Lonchodina transitans Collinson & Druce Plate 31, fig. 14 Lonchodina transitans Collinson & Druce (in press). MATERIAL. 3 specimens : figured, X 234. RANGE. North Crop 3D 4-3D 14/15. DEscRIPTION. The present specimens are incomplete but they show the essential features of the species, including the angle of divergence of the anterior and posterior bars of about 130° and the more or less bilaterally asymmetrical open “ ligonodina ”’ type cavity which is developed below the apical denticle. The apical denticle is recurved and relatively slender. The posterior bar is broken in the present speci- mens but bears at least 2 discrete, sharply pointed, posteriorly inclined denticles. The anterior bar is straight, and is slightly inflexed, as well as being depressed ; it bears at least 3 laterally compressed, recurved, slightly incurved denticles. Both bars are excavated by aboral grooves which extend into the shallow and rather flared cavity below the basal surface of the apical denticle. The apical denticle is biconvex in cross-section in its proximal part, and its strong lateral expansion on the outer face develops a suggestion of a median ridge on the lower part of that surface. RemaARKs. Collinson & Druce have pointed out that this species represents a transitional form between the genera Ligonodina and Lonchodina. Lonchodina sp. A Plate 24, figs. 17a, b MATERIAL. 6 specimens : figured, X 424. RANGE. North Crop ZLA 32-ZLA 33. DeEscRIPTION. All the present specimens are broken, but they appear to represent a short unit, the bars being restricted. The apical denticle is large, laterally com- pressed and inclined toward the inner side. The bars appear to be curved on the outer side. The basal cavity is large and occurs beneath the apical denticle. Genus MAGNILATERELLA Rexroad & Collinson 1963 1963 Magnilaterella Rexroad & Collinson : It. Type SPECIES. Magnilaterella robusta Rexroad & Collinson 1963. BRITISH AVONIAN CONODONT FAUNAS 145 Magnilaterella complectens (Clarke) Plate 23, figs. 14a-17c 1900 Prioniodus tulensis Hinde (partim) : 343, Pl. 9, fig. 16. 1928 Prioniodus tulensis Hinde ; Holmes (partim) : 22, Pl. 3, fig. 20. 1960 Ligonodina complectens Clarke : 9, Pl. 1, figs. 14, 15. MATERIAL. 14 specimens : figured, X 240, X 237, X 238, X 239. RANGE. Scotland HOSIE 2A—-HOSIE 2B. DESCRIPTION. This species is clearly a member of the genus Magnilaterella Rexroad & Collinson, but is not typical of that genus. The generic features are seen in the present specimens in the short form, strong inner lateral callus and basal groove of the lateral bar, and the deflected and upflexed general form of the posterior bar, the largest denticles of which are situated at the proximal end and which are strongly developed and strongly recurved and incurved. In contrast to other described forms of the genus Magnilaterella, however, the largest denticles of the lateral bar are situated at the anterior, and not at the posterior end. This form, therefore, seems to approach Ligonodina, to which Magnilaterella is closely related. Rexroad & Collinson (1963 : 13) have discussed the relationships between the two genera, but the character of the present specimen alters the view of the distinctive nature of the denticulation of the posterior bar. The lateral bar is short and in inner view is deep ; the most anterior denticle is enormously developed and strongly recurved in its lower portion, its distal half being more or less straight, although the distal posterior edge is so sharply pointed that it gives it almost a sigmoidal appearance. The two remaining denticles of the posterior bar are inconspicuous by comparison with the major denticle ; they are isolated, small, sub-circular, and more or less sharply pointed. The posterior bar is curved sharply backward and upward and the proximal denticle is very strongly developed. It approaches, but does not quite equal, the major denticle in size ; it is biconvex in cross-section, with bluntly developed anterior and posterior ridges in its upper half, but in the proximal half it is convex on the anterior face and has a concave posterior depression on its posterior edge. The inner lateral face is strongly convex and it bears at least one small isolated sub-circular denticle. The largest denticle of the posterior bar is recurved and deflected parallel to the major denticle. The aboral surface of the unit is conspicuously grooved; the outer aboral surface tends to be flat and rather extended below the major denticle, but the inner aboral surface is strongly developed as a callus, which runs up the inner face of the lateral bar. This slopes down to give a relatively narrow, horizontal, aboral surface, parallel to the base of the groove. In more complete specimens the lateral bar is seen to taper to a point at its distal end ; it may bear only 2 denticles including the most anterior denticle. In more complete specimens the posterior bar may bear up to 6 denticles in specimens which tend to decrease distally in size ; when viewed orally it makes an angle of about 30° with the lateral bar. In the specimen shown in Pl. 23, fig. 14 a small and relatively inconspicuous denticle is developed in front of the largest 146 BRITISH AVONIAN CONODONT FAUNAS denticle of the lateral bar, being about equal in height to the larger denticles of the posterior bar. When viewed aborally the most striking feature of this species is the broad extension of the aboral surface, represented by the flange, and the restriction of the warped and flexed sinuous cavity to the outer lateral margin of the scar, which the flange forms. Magnilaterella clarkei sp. nov. Plate 23, figs. 11-13b 1900 Polygnathus convexus Hinde (partim) : 342, Pl. 9, fig. 7. 1928 Lonchodus convexus (Hinde) Holmes (partim) : 14, Pl. 6, fig. 14. 1960 “Gen. et sp. nov?’”’ Clarke : 16, Pl. 11, figs. 10, 12, 13. DERIVATION OF NAME. After Dr. W. J. Clarke. Diacnosis. Magnilaterella characterized by massive development of strongly depressed, continuously curved posterior bar, gently flexed inward in its median part, its denticles tending to be largest in its mid-third. Denticles of lateral bar large, sub-triangular, separated by smaller single denticles. Posterior bar of insignificant size in comparison with lateral bar, but strongly inflexed. MATERIAL. 23 specimens: Holotype X 431, Paratypes X 241, X 432 (all figured). RANGE. Scotland DUN 52-80, GILM 3-BIL 1ro2. DeEscrIPTION. This is a rather typical species of the genus Magnilaterella, with a very elongated and very deep posterior bar, which becomes deeper in its posterior part. It has a very feebly convex inner-lateral face and is bowed slightly out- wards along itslength. It is continually recurved with a conspicuous concave aboral surface. The oral surface bears up to 4 main denticles, which tend to be largest in the median third and decrease in size in both directions. They are conspicuously triangular in lateral view and are sharply pointed. The denticles have very sharp Inner lateral face LS) “ye Lateral bar Posterior bar Basal groove Fic. 29. Magnilaterella sp. showing morphological terms used in the text. BRITISH AVONIAN CONODONT FAUNAS 147 anterior and posterior edges and feebly convex to flat lateral faces. They are separated by a single similar denticle, widely spaced between them but only about one fifth to one sixth of the length of the larger denticles they separate. The posterior end of the lateral bar is marked by one such denticle which extends downwards to form the bluntly triangular distal end of the bar. At the anterior end of the lateral bar there are 2 to 3 smaller denticles of this general kind. The inner aboral surface of the posterior bar is marked by a variably developed flange, which although laterally persistent is irregular in the extent to which it invades the lateral face of the unit. It tends to do this to a rather small degree and its greatest aboral extension is under the posterior third of the bar. The posterior bar is very small in comparison with the lateral bar and is strongly recurved, so that in oral view it makes an angle of about 30° with the lateral bar. It is also sharply convex and seems to bear rather small denticles although in the present specimens it is broken. The largest of these small denticles, occurs at its junction with the lateral bar. It tends to decrease in depth distally at its junction with the lateral bar, just anterior to the bluntly spatulate termination of the latter. In outer lateral view the outer lateral bar is flat and the outer lateral surface of the denticles are also markedly flat ; only a few of them show any degree of convexity. There is no sign in outer lateral view of the scar-like presence of the inner callus. In aboral view a thin slit occurs along the length of the lateral blade and is also developed, though in much reduced width, below the posterior bar. REMARKS. The specimens referred to this species show some variation in the development of the callus on the inner lateral face and also in the depth of the lateral bar, which tends in some specimens to be deeper in its medial third than its distal third. Magnilaterella contraria sp. nov. Plate 23, figs. 8a—c, 18a—c 1941 Ligonodina ? sp. Branson & Mehl: 171, Pl. 5, fig. 11. 1963 New Gen. et sp. Rexroad & Collinson : 21, Pl. 3, fig. 2. DERIVATION OF NAME. With reference to the morphology. DiaGnosis. Magnilaterella characterized by very delicate and slender construc- tion. Short lateral bar bearing three isolated and recurved denticles, the largest being the middle : bar very shallow decreasing in height posteriorly, and making an obtuse angle with posterior bar. MATERIAL. 3 specimens : Holotype X 553, Paratype X 517 (both figured). TYPE LOCALITY AND HORIZON. North Crop. Sample 3D 23. Rance. North Crop 3D 23. DEscRIPTION. The lateral bar is short and more or less straight in a vertical plane but is strongly recurved, so that its basal surface is continuously concave in lateral view. It is of very slender construction and bears only 3 or 4 denticles, the two in the medial part being much larger than those at either end. The denticles are 148 BRITISH AVONIAN CONODONT FAUNAS recurved, but their axes are straight and sharply pointed ; they have sharp anterior and posterior edges and strongly convex lateral faces, their proximal portions tending to become flatter towards their apices ; they are about four to five times as long as the other denticles on the unit. The inner lateral face of the lateral bar is marked by a callus, which is not conspicuous and does not extend far up the lateral face : the bar decreases in width posteriorly and its posterior end is marked by a very small denticle, the posterior aboral margin being bluntly rounded ; the bar may be very slightly flexed outward in a vertical plane, but it is essentially straight. The posterior bar is of unknown length; it bears at least one small denticle near its junction with the lateral bar. It is excavated by a narrow groove which extends continuously below the lateral bar. REMARKS. Rexroad & Collinson (1963 : 21), described forms closely similar to this species, but did not include them in the genus Magnilaterella. They did not state the reasons for this exclusion, but these presumably involve the relatively slight difference in the form of the basal cavity, which in the present specimens tends to be medial rather than lateral on the two bars, the restricted nature of the callus, and the fact that the posterior denticle of the lateral bar is not the largest of those developed. Other specimens described above in the present paper show that none of these characteristics is wholly distinctive of the genus Magnilaterella. Some species which are, on all other morphological criteria, “‘ good ’’ species of the genus, do not have the posterior denticle more strongly developed than the rest of the series, and the form of the callus is a highly variable feature ; it, therefore, seems to us that there is no good reason for excluding this species from the genus. Magnilaterella robusta Rexroad & Collinson Plate 31, figs. 25, 26, 27 1941 Lonchodina sp. Branson & Mehl (partim) : 171, Pl. 5, fig. to only. 1956 Metalonchodina ? sp. Elias: 124, Pl. 5, fig. 3. 1957 Genus Indeterminate Rexroad (partim) : 42, Pl. 4, figs. 19-21 only. 1958 Genus Indeterminate Rexroad : 26, Pl. 5, figs. 1, 2. 1963 Magnilaterella vobusta Rexroad & Collinson : 14, Pl. 2, figs. 4, 5, 9, text-figs. 3, 4. 1964 Magnilaterella vobusta Rexroad & Collinson ; Rexroad & Furnish : 673, Pl. 111, figs. 27-31. 1965 Magnilaterella vobusta Rexroad & Collinson ; Rexroad & Nicoll: 22, 23, Pl. 1, figs. TOLL: MATERIAL. 3 Specimens : figured, X 528, X 529, X 548. RANGE. Scotland Samples DUN 78-79. DeEscrRIPTION. Well preserved specimens from our Scottish faunas are very closely similar to those illustrated and described by Rexroad and Collinson. The inner lateral process is short and stout, and is strongly recurved and very strongly arched. It bears up to 6 denticles, those near the apex being the largest. The posterior bar is small and relatively straight. It is strongly flexed and bears only I or 2 denticles, that nearest the anterior end being the largest. BRITISH AVONIAN CONODONT FAUNAS 149 Magnilaterella sp. Plate 23, fig. 9 MATERIAL. I specimen: figured, X 244. RANGE. Scotland GILM z. DEscrIPTION. A single specimen of doubtful affinities is referred to this genus. It is characterized by the distinctive callus developed on the inner face of the lateral bar and the slit-like excavation developed on both bars. The posterior bar is very short and may not be broken. The lateral bar bears two denticles which are discrete, inclined and sharply pointed ; the bar is broken and is of unknown length. The posterior bar bears a single denticle at its junction with the lateral bar ; the denticle is short but sharply pointed, being only about one sixth to one seventh the length of the posterior bar. Magnilaterella spp. Plate 23, fig. 10 ; Plate 31, figs. 5, 11 MATERIAL. 649 specimens : figured, X 242, X 322, X 323. RANGE. Avon Gorge Z 35-C 24, North Crop CYD 6-3D 17. DESCRIPTION. Fragmentary specimens of Magnilaterella are relatively common in the upper part of the D Zone and elsewhere. Few of them are sufficiently com- plete to enable specific identification, but some of them probably represent new species. We illustrate three extreme forms. Plate 31, fig. 11 (X 322) shows a form with characteristically deep and strong posterior bar, the inner lateral face of which bears a well-developed callus and basal groove, which is thin but conspicuous and long. The apical denticle is very strongly developed, and has four to five times the basal width of other denticles of the posterior bar. The lateral bar is very strongly flexed, and the denticles decrease rapidly in size towards the distal end. Plate 31, fig. 5 (X 323) shows a form characterized by much more slender construc- tion. The apical denticle is elongated and gently curved posteriorly and inwards. It is sharply pointed and its general construction is slender. The callus is con- spicuous, but shallow, and the lateral bar, which lies at about go0° in both a horizontal and vertical plane to that of the posterior bar, has its main flexure at its junction with the posterior bar rather than being continuously recurved. Magnilaterella ? sp. Plate 23, figs. 7a, b MATERIAL. I specimen : figured, X 447. Rance. North Crop ZLA 37. DESCRIPTION. This specimen consists of an antero-lateral and a posterior bar. The major denticle is smaller than the denticles on the posterior bar and lies in 150 BRITISH AVONIAN CONODONT FAUNAS between the planes of the two bars. The anterior bar is lateral and deflected, bearing 3 isolated denticles. The posterior bar bears 3 large, posteriorly inclined denticles. Genus MESTOGNATAHUS Bischoff 1957 1957 Mestognathus Bischoff : 36. TYPE SPECIES. Mestognathus beckmanni Bischoff 1957. DiaGnosis. A canoe-shaped form, with a well-developed platform, tapering to anterior and posterior. The platform ornamented by numerous transverse ridges. A high anterior blade developed on the outer side of the platform ; inner side of the platform, in lateral view, extends further to the anterior, than the outer side of the platform, because of the development of the anterior blade on the latter. A deep trough runs along mid-length of oral surface. Aborally a small narrow basal cavity present. Remarks. The genus Mestognathus Bischoff closely resembles Cavusgnathus Harris & Hollingsworth, but differs from the latter genus in that it has a small narrow basal cavity compared with the wide flaring basal cavity typical of Cavus- gnathus. Mestognathus has not been recorded from North America and makes its first appearance in Europe in Cu II 6/y. In North America Cavusgnathus makes its first appearance at nearly the same horizon and so the two genera may be closely related. Mestognathus beckmanni Bischoff Plate 15, figs. 7a-d 1957 Mestognathus beckmanmi Bischoff : 37, Pl. 2, figs. 4a, b, c, d, 5, 6, 8, 9. 1960 Mestognathus beckmanni Bischoff ; Kronberg, Pilger, Scherp & Ziegler: 14, Pl. 3, figs. Ia, b. 1962 Mestognathus beckmanni Bischoff ; Meischner : text-fig. ro. 1962 Mestognathus beckmanmi Bischoff ; Bartenstein & Bischoff : Tab. 3. MATERIAL. 36 specimens : figured, X 245. Rance. North Crop CYD 7, Avon Gorge C 15—D 26. DESCRIPTION. The carina is restricted to the posterior part of the platform in this species, but may in some cases be extended anteriorly to meet the inner lateral face at a narrow angle. The anterior blade is high and has from 6 to 12 denticles which occupy the anterior margin of the outer side of the platform. The medial trough is deep and very wide, and runs for at least half the length of the platform, being deepest anteriorly. The unit is about four times as long as it is wide, being widest at about mid-length of the platform. In outer lateral view the highest part of the anterior blade is about twice the depth of the posterior platform at mid-point. The anterior blade is characterized in lateral view by the development of from 6 to 12 denticles which are basally fused, only their tips being discrete. They tend to be of variable size and to have bluntly rounded apices with gently convex lateral faces. The largest denticles are the posterior one or two on the blade, especially the most BRITISH AVONIAN CONODONT FAUNAS I5I posterior. This tends to be sub-triangular in form, and is inclined posteriorly, with strongly convex lateral faces and blunt anterior and posterior edges. Its inner lateral face is flatter than its outer. The other denticles stand more or less erect to the bar but their inclination is rather variable. The anterior blade is inclined gently inwards ; there is a tendency for the denticles, to show some reduction in height anteriorly and the anterior blade projects beyond the platform at the anterior end. In oral view a deep trough is developed parallel to the anterior blade, being widest and deepest anteriorly. It shallows towards the position of maximum width of the posterior platform and becomes obsolescent in the posterior half. It is broadly U- shaped. The outer margins of the carina are decorated with feeble to moderate transverse ornament, which tends to be aligned acutely to the length of the unit, forming an arrow-type structure pointing forward, rather than being developed at right angles. There are about 12 of these ridges on the outer side of the platform and about 17 on the inner. They become rapidly obsolescent towards the middle of the platform and are more feebly developed on the inner than on the outer side. There is a variable posterior carina developed in the posterior part of the unit, consisting of a low ridge of only barely distinguishable nodose denticles, but it may be extended anteriorly to meet the antero-lateral inner edge of the platform as a low inconspicuous ridge, dividing the platform into two unequal parts. It runs to the left of the medial trough. The outline of the platform in oral view is such that the anterior two-thirds of the inner lateral margin is straight and the posterior third inclined towards its pointed posterior termination. The outer lateral face is straight in its anterior half and gently concave in its posterior half, the whole appearance of the unit being pinched towards the posterior fifth. The anterior inner lateral edge terminates in an undenticulate projection. The edges of the platform are feebly up- turned. In inner lateral view the antero-inner face of the platform is flat, with sharp oral and aboral lateral edges. The lateral face decreases in width towards the mid- point, beyond which the platform has a thin lateral face which merges with the base. The outer lateral face is characterized by having a flat surface, parallel to the denticles, with a longitudinal ridge developed about the base of them, and then a sloping lateral face which slopes towards the basal cavity below the ridge. In outer lateral view the posterior half has a lateral face, which slopes steadily towards the basal cavity. Anterior blade Outer side of platform Platform Anterior Carine Posterior r ral face Inner lateral fa Trough Fic. 30. Mestognathus sp. showing morphological terms used in the text. 152 BRITISH AVONIAN CONODONT FAUNAS The basal surface is characterized by a restricted median cavity, which is shallow and occupies the anterior half of the platform. It extends anteriorly and posteriorly as a very narrow shallow slit along the unit. Mestognathus bipluti Higgins Plate 25, figs. ra—3c, 8a, b 1961 Mestognathus bipluti Higgins : 216, Pl. ro, figs. 1, 2; text-fig. 4. DiaGnosis. This species is characterized by a short, deep blade which diverges at the anterior end of the unit from the antero-inner lateral edge of the platform. Slender and pointed platform has a more or less prominent median carina. MATERIAL. 3 specimens : figured, X 249, X 248, X 246, X 247. Rance. North Crop CYD 6-CYD 7. DESCRIPTION. This species of conodont has an outline that is reminiscent to some extent of a folsom-point. The inner edge of the platform is straight in the anterior two thirds and then turns rapidly inwards towards the pointed posterior end. The posterior third is also straight and the bend is sharply angular. The outer lateral margin of the platform is straight in its anterior third and up to the end of the anterior blade, but posteriorly it is turned sharply inwards towards the pointed posterior end. The posterior outer lateral face is more or less straight. There is a strongly developed posterior carina, which consists of a series of confluent nodes, and extends about half the length of the platform. It is continued less obviously anteriorly to meet the antero-inner lateral point as a low inconspicuous ridge. There is a narrow deep trough adjacent to the blade and this becomes shallower and obsolescent posteriorly, extending on the outer side of the median carina. The inner lateral portion of the platform adjacent to the carina tends to be flat or feebly con- cave. The margins of the platform are ornamented by relatively strongly developed transverse ridges, which tend to become less conspicuous towards the posterior end. They extend about half the distance from the lateral margins to the carina. The lateral margins themselves are gently up-flexed. The downward and outward curvature of the antero-aboral portion of the blade is a conspicuous feature in oral view, as is the divergence of the anterior blade and the antero-inner edge of the platform to give a branched structure. In aboral view this latter feature is the most conspicuous characteristic of the species. The total length of the branches are a third to a quarter of the length of the platform. The medial cavity is very small and inconspicuous and is only slightly flared. It extends anteriorly and posteriorly as a keeled narrow slit along the median line of the unit. The main cavity is situated near the junction of the blade. In inner lateral view the oral surface of the unit is bluntly serrated and the posterior end is bluntly spatulate. In outer lateral view the aboral margin is straight in the posterior half, but gently concave in the anterior half. In outer lateral view the anterior blade is a very distinctive feature. The posterior denticle is the largest and the blade decreases regularly in depth towards the bluntly spatulate anterior end. BRITISH AVONIAN CONODONT FAUNAS 153 The denticles form a fused series of bluntly pointed confluent denticles, about 5 or 6 in number, grading in the antero-aboral region into minute and inconspicuous confluent denticles. The antero-aboral portion is flexed sharply outwards ; the posterior denticle is inclined slightly posteriorly. The whole posterior outer lateral face of the platform slopes gently inwards to meet the basal slit, giving a boat-like appearance to the unit in lateral view. It is convex to flat in its upper part and may become concave in its postero-aboral portion. In inner lateral view the same feature is seen. The platform is relatively straight in its posterior third, but is regularly concave in its anterior third or half. The inner lateral margin is generally developed at a lower level than the outer lateral margin, and is finely denticulated, the inner anterior edge of the platform bearing rather conspicuous low denticles. The antero- aboral inner edge is strongly convex and is deflected inwards. It is much less deep than the corresponding outer aboral anterior edge. Mestognathus neddensis sp. nov. Plate 15, figs. 4a—6c DERIVATION OF NAME. From the River Nedd, Breconshire. DiacGnosis. Mestognathid with short deep anterior blade, bearing 6 denticles, those at anterior end being only slightly shorter than those at posterior ; their apices are discrete. Anterior blade and inner anterior edge of platform bifurcate at the anterior end of the unit. Posterior platform straight on outer lateral side and gently convex on inner lateral side, posterior inner lateral portion being strongly pinched inwards towards pointed posterior end. Strong posterior carina, consisting of low rounded nodes along posterior half of platform, becoming obsolescent towards anterior inner lateral edge of platform. MATERIAL. 5 specimens : Holotype X 250, Paratypes X 251, X 252 (all figured). TYPE LOCALITY AND HORIZON. North Crop. Sample CYD 6. Rance. North Crop CYD 6-CYD 7. DeEscriPTION. In oral view the unit is elongated and slender. The anterior blade is free for only a very small portion of its length, but the anterior end of the platform is marked by a V-shaped indentation, formed by the junction of the anterior blade and the inner anterior margin of the platform. The blade is conspicuously denticu- lated in oral view and the outer lateral margin of the platform is more or less straight. It is ornamented by a series of transverse denticles which are more strongly developed in the anterior portion than the posterior. The inner lateral platform is gently sinuous, being straight to gently concave in the anterior third and strongly convex in the posterior two thirds. The posterior carina extends beyond the posterior limit of the platform, so the whole appearance of the platform is rather pinched posteriorly. The inner lateral margin of the platform is ornamented by feeble, nodular to trans- verse ridges which become obsolescent towards the anterior part. The posterior half of the platform is marked by a conspicuous carina, consisting of 7 or 8 low rounded fused nodes, and is extended as a rather inconspicuous ridge towards the 154 BRITISH AVONIAN CONODONT FAUNAS anterior inner lateral edge of the unit. There is a narrow V-shaped trough developed adjacent to the blade, running towards the posterior end of the unit on the outer margin of the carina, and becoming shallower and narrower posteriorly. In outer lateral view the blade is conspicuously deeper than the platform. It is of regular depth throughout its length and in some specimens shows a tendency to increase anteriorly in depth. It is very bluntly rounded antero-aborally, and is strongly down-flexed in relation to the blade. Although the junction between the two is curved, the anterior aboral edge of the blade makes an angle of about 45° with the aboral edge of the posterior platform. The oral surface of the blade bears 6 or 7 fused denticles, the apical tips of which are discrete and bluntly rounded. In outer lateral view the posterior platform has a bluntly serrated surface and its outer lateral face slopes down sharply towards the median aboral keel. The posterior end is more or less flat, and the denticles of the posterior median carina tend to be higher in outer lateral view than those on the edge of the platform. The posterior third of the platform is straight, but the anterior part is gently concave. The denticles of the anterior blade are more or less uniform in height, although the most posterior tends in some specimens to be rather larger than the rest. They are more or less erect, though the most posterior denticle may be slightly inclined posteriorly. In inner lateral view the aboral surface of the whole unit appears to be gently convex, except for the rather straight posterior termination. The oral edge is more or less conspicuously serrated by low nodose confluent nodes, and the anterior inner edge is frequently developed into one or two rather conspicuous denticles, its antero- aboral margin being bluntly pointed and making a very prominent bifid junction with the anterior blade. The extension of the posterior carina is a prominent feature in this inner lateral view. The inner oral margin of the platform is strongly convex, but it flattens off along the mid-height of the unit, and the lower part is flat to strongly concave, sloping rapidly towards the elongated aboral keel. In aboral view there is a prominent, but very small, median pit with inconspicuous edges, which is developed near the junction of the blade of the platform. It is biconvex in outline and is elongated antero-posteriorly. A shallow rather flat aboral surface extends posteriorly from it along the unit with an inconspicuous median slit developed towards the posterior end. Anteriorly a thin slit runs towards the junction of the inner anterior edge with the anterior blade. The posterior end of the platform is marked by a more or less vertical face, with rounded posterior aboral margin. The platform deepens towards the anterior inner edge when seen in inner lateral view, and this is a conspicuous feature of the unit. Genus METALONCHODINA Branson & Mehl 1941 TYPE SPECIES. Prioniodus bidentatus Gunnell 1931. Metalonchodina bidentata (Gunnell) Plate 24, figs. 8a-11b 1900 Polygnathus convexus Hinde (partim) : 342, Pl. 9, fig. 8. BRITISH AVONIAN CONODONT FAUNAS 155 1928 Lonchodus convexus (Hinde) Holmes (partim) : 14, Pl. 6, fig. 13. 1931 Prioniodus bidentatus Gunnell 247, Pl. 29, fig. 6. 1933 Prioniodus dactylodus Gunnell 265, Pl. 31, fig. 1. 1941 Metalonchodina bidentata (Gunnell) Branson & Mehl: 106, Pl. 19, fig. 34. 1941 Metalognathus bidentata (Gunnell) Ellison : 116, Pl. 20, figs. 35, 36. 1952 Metalognathus bidentata (Gunnell) Rhodes : 898, Pl. 128 ‘m’. 1957 Metalonchodina bidentata (Gunnell) Bischoff : 37, Pl. 5, figs. 13, 15, 46. 1960 Metalonchodina conflecta Clarke : 17, Pl. 2, fig. 14. 1961 Metalonchodina bidentata (Branson & Mehl) Higgins: PI. 12, fig. 9. 1962 Metalonchodina bidentata (Gunnell) Higgins : Pl. 1, fig. 3. 1964 Lonchodina ? nipponica Igo & Koike : 186, Pl. 27, fig. 20. 1964 Metalonchodina sp. Rexroad & Furnish : 673, Pl. 111, fig. 7. 1965 Metalonchodina fragilis Murray & Chronic : 605, Pl. 73, figs. 19, 20. Metalonchodina bidentata (Gunnell) Collinson & Druce (in press). MATERIAL. 6 specimens : figured, X 253, X 254, X 255, X 256. RANGE. North Crop 3D 10-3D 14/15. DeEscriPTION. The present specimens agree closely with Branson & Mehl’s (1941 : 106) definition of the species. The anterior limb is shorter than the posterior bar and bears a massive denticle or pair of denticles upon it. In aboral view the most conspicuous feature is the very strong lateral flexing below the apex of the two bars. The small and fairly shallow pit is situated in the middle of the strongly laterally expanded aboral surfaces at this point ; the aboral surfaces of each limb being relatively flat or obtusely V-shaped. They are excavated by very narrow shallow slit-like cavities along their lengths. The chief expansion of the base below the apical denticle is concentrated on the inner lateral side and is a very prominent feature of the unit. In inner lateral view the most conspicuous feature of the unit is the enormous size of the denticle developed on the anterior bar. This is about two to three times as wide as any of the other denticles, has straight anterior and posterior edges and is bluntly pointed. It has gently convex inner and outer lateral faces. The anterior edge of the unit is developed into a triangular pointed anterior end. Its aboral margin is straight, and although its junction with the posterior bar is curved, it makes an angle of 80°-g0° with the aboral surface of the latter. The posterior bar bears two or three smaller denticles, sub-circular in cross-section, with inconspicuous anterior and posterior edges, which are inclined anteriorly. Apical denticle 7 ain denticie Inner lateral aboral expansion Anterior limb Posterior bor Aboral margin Fic. 31. Metalonchodina sp. showing morphological terms used in the text. 156 BRITISH AVONIAN CONODONT FAUNAS The apical denticle is smaller than the large denticle on the anterior bar but of similar general form. Its most conspicuous feature is the very strong, internal lateral extension of the aboral portion, to form the inner lateral flange. On the aboral margins both the anterior and the posterior bars are more or less straight. Their most striking feature in inner lateral view is the development of a longitudinal ridge parallel to their bases, which rises higher on the faces towards the apex, and represents the bevelled margin of the flattened aboral surface. In lateral view this latter feature is less conspicuous and the whole unit is flat to feebly convex in general form. REMARKS. This species shows appreciable variation. The specimens illustrated in Pl. 24, figs. 8, 10 and 11 are closely similar. That of Pl. 24, fig. 9, resembles them in overall form but has an additional denticle developed anterior to the main denticle of the anterior bar, and the apical and posterior denticles also tend to be more sub- circular than those of typical members of the species. Similarly, other specimens have two smaller denticles developed anterior to the main denticle of the anterior bar and also have more sub-circular denticles. It may be that these specimens should be regarded as distinct species but they are provisionally included in Metalonchodina bidentata. Genus NEOPRIONIODUS Rhodes & Muller 1956 1956 Neoprioniodus Rhodes & Miller : 698. TYPE SPECIES. Pvioniodus conjunctus Gunnell 1931. Neoprioniodus antespathatus Collinson & Druce Plate 21, figs. Ioa—11b Neoprioniodus antespathatus Collinson & Druce (in press). MATERIAL. 2 Specimens : figured, X 257, X 258. RANGE. North Crop 3D 8-3D 16. DescripTIon. This is a neoprioniodid with a slender anteriorly directed anterior denticle, with sharp anterior edge, blunt posterior edge, and biconvex outline. The posterior bar is slender, decreasing in depth posteriorly, and it has a conspicuously concave junction with the aboral process. Its oral surface bears a series of about 9 denticles, the largest of which are in the anterior half, and which show a broad tendency to decrease in size posteriorly, though this tendency is not conspicuous or regular. The denticles are basally confluent, but are discrete for most of their length. They are of slender general form, with sharp anterior and posterior edges BRITISH AVONIAN CONODONT FAUNAS 157 and gently convex lateral faces. They stand more or less erect or gently posteriorly inclined in relation to the underlying aboral surface of the bar. The posterior bar is gently down-curved, although its distal portion is more or less straight. The aboral projection of the anterior denticle is the most massive feature of the unit. It is about twice as wide in lateral view as the basal part of the anterior denticle itself. Its anterior margin is straight to very gently concave and its anterior aboral termina- tion is bluntly pointed. Its posterior aboral margin is very strongly convex and it decreases in width towards its distal end. The whole effect is of a massive structure. Its lateral faces are more or less flat but the whole unit is feebly curved inwardly. In outer lateral view the whole unit is convex, reflecting the inward recurvature. In aboral view there is a very inconspicuous cavity developed below the apical denticle ; the aboral surfaces of the posterior bar and the aboral process are flat in general form, the inner lateral aboral edge being slightly higher than the lower, and the whole surface is excavated by a minutely narrow and shallow longitudinal groove. The most conspicuous features of this unit are the slender form of the anterior denticle and the posterior bar, in contrast to the massive form of the aboral process, the whole anterior lateral aboral face of which is more or less concave. Anterior denticle Anterior edge Anterior Posterior Posterior bar Aboral Sd process ——— \ # Aboral edge Fic. 32. Neoprioniodus sp. showing morphological terms used in the text. 158 BRITISH AVONIAN CONODONT FAUNAS Neoprioniodus barbatus (Branson & Mehl) Plate 21, figs. 4-7 1934 Prioniodus barbatus Branson & Mehl : 288, Pl. 23, figs. 19, 20. 1934 Prioniodus cornigey E. R. Branson : 329, Pl. 28, fig. 2. 1938 Prioniodus barbatus Branson & Mehl; Branson & Mehl: 144, Pl. 33, fig. 21, pl. 34, figs. 28, 32. 1938 Prioniodus cornigey (?) E. R. Branson ; Branson & Mehl : 143, Pl. 34, fig. 19. 1944 Prioniodus barbatus Branson & Mehl; E. B. Branson : 221, Pl. 39, figs. 28, 32. 1944 Prioniodus corniger (?) E. R. Branson ; E. B. Branson ; 221, Pl. 39, fig. 19. 1949 Prioniodus barbatus Branson & Mehl ; Thomas : 411, Pl. 4, fig. 26. 1949 Prioniodus cornigey E. R. Branson ; Thomas: 411, Pl. 4, fig. 27. 1956 Prioniodina barbata (Branson & Mehl) Bischoff & Ziegler : 160, Pl. 13, figs. 19, 20. MATERIAL. 674 specimens : figured, X 259, X 260, X 261, X 262. RANGE. North Crop KL 13-ZL 9, Avon Gorge K 21-C 16. DescripTION. The anterior denticle is very tall, slender, laterally compressed, and ovate in cross-section. It is continuously and gently recurved toward the posterior, terminating in a fine point. The posterior bar is fairly deep, being deepest at the anterior and shallowing regularly towards the posterior. It bears 9 to 12 tall needle- like denticles, sub-circular in cross-section, which are fused at their bases but free at their tips. In the posterior part there is some twisting of the bar and it is down- curved slightly. The basal cavity is situated on the aboro-posterior side of the anterior denticle, which is produced below the posterior bar to form an aboral process. The complete aboro-posterior surface is excavated, though there is comparatively little flaring of the lips, and the cavity may run for a short distance beneath the posterior bar. In most specimens the aboro-posterior outline of the aboral process is gently convex, but in some specimens a flange tends to develop, making it sigmoidal in outline (6.62 Plvan; fiero): REMARKS. This appears to be a very common Avonian species, especially in the middle of the Z Zone. Neoprioniodus confluens (Branson & Mehl) Plate 21, figs. 2a, b, 8a, b 1934 Prioniodus confluens Branson & Mehl (partim) : 206, Pl. 15, fig. 6, (non Pl. 15, fig. 7=N. alatus). 1934 Euprioniodina prona Huddle (partim) : 52, Pl. 6, fig. 19, (non Pl. 11, fig. 8= Euprioniodina alternata). 1939 Prioniodus alatus Hinde ; Cooper: 404, Pl. 46, figs. 6, 8. 1949 Pyrioniodus aphanes (Cooper) Thomas : 411, Pl. 4, figs. 20, 34. 1949 Prioniodus obtusus Branson & Mehl ; Thomas 408, Pl. 1, figs. 1, 7. 1955 Prioniodus prona (Huddle) Sannemann (partim) : 152, Pl. 3, fig. 1 only. 1957. Prioniodina prona (Huddle) Ziegler in Fliigel & Ziegler : 49, Pl. 4, fig. 6. 1961 Neoprioniodus avmata (Hinde) Scott & Collinson (partim) : 127, Pl. 2, fig. 24, (non Pl. 2, fig. 22=N. armata). BRITISH AVONIAN CONODONT FAUNAS 159 LectotyPeE (here selected). The original of Branson & Mehl : 1934, 206 ; Pl. 15, fig. 6 only, University of Missouri C 365-5. MATERIAL. 672 specimens : figured, X 264, X 263. Rance. North Crop KL 1-ZLA 33, Avon Gorge K 3-C 7. DescripTIon. The anterior denticle is tall and narrows gradually to a pointed extremity. It is produced aborally into an aboral process. The posterior bar, which is straight or gently down-curved, is also deflected through 45° and slightly twisted. It bears a series of erect laterally compressed denticles, which are either fused or are in close proximity. The bar is very long and may possess up to 40 denticles which alternate in size. The basal cavity is situated at the junction of the posterior bar and the aboral process. It has a flared lip to produce a characteristic flange. Remarks. This is one of the most easily recognizable neoprioniodids owing to the large aboral process of mature specimens and the cavity flange. Frequently only the anterior denticle and cavity flange are preserved. Branson & Mehl (1934 : 206) described two co-types of the species Priomodus confluens (Catalogue numbers C 365-5, University of Missouri). These appear to represent different species and we hereby designate the specimen illustrated in Pl. 15, fig. 6, as the lectotype of Neoprioniodus confluens (Branson & Mehl). This is given the same Catalogue Number as the other co-type (C 364-5). One specimen (PI. 21, figs. Ia—c) shows extreme regularity of dentition and it is only tentatively compared with this species. Neoprioniodus conjunctus (Gunnell) Plate 21, figs. 16a-17b, 20a, b 1926 Prioniodus sp. B (Roundy) (partim) : 11, Pl. 4, fig. 12 only. 1931 Prioniodus conjunctus Gunnell : 247, Pl. 29, fig. 7. 1933 Prioniodus cacti Gunnell : 263, 265, 267, Pl. 31, figs. 4 to 5. 1933 Prioniodus sp. Gunnell : 264, 267, Pl. 32, fig. 32. 1941 Prioniodus conjunctus Gunnell ; Ellison : 108-111, 113, 114, Pl. 20, figs. 1-3, 16. 1941 Prioniodus bulbosus Ellison : 108-111, Pl. 20, figs. 4-7. 1944 Prioniodus conjunctus Gunnell; E. R. Branson : 327. 1949 Prioniodus cacti Gunnell ; Youngquist & Downs: 169, Pl. 30, figs. 16, 17. 1953 Prioniodus inclinatus Hass : 87, Pl. 16, figs. 10-14. 1956 Neoprioniodus conjunctus (Gunnell) Rhodes & Miiller : 3. 1957 -Prioniodina bulbosa (Ellison) Bischoff : 46, Pl. 5, fig. 37. 1960 Neoprioniodus brevis Clarke : 13, 14, Pl. 2, fig. 7. 1961 Neoprioniodus inclinatus (Hass) Higgins : 220, Pl. 11, fig. 3. 1962 Neoprioniodus conjunctus (Gunnell) ; Higgins: to, Pl. 1, fig. 2. MATERIAL. 7 specimens : figured, X 265, X 267, X 266. Rance. North Crop 3D 14/15, Avon Gorge Z 35-C 7. DESCRIPTION. The present specimens agree perfectly with Gunnell’s holotype and with Ellison’s (1961) descriptions and illustrations. The massive, blade-like anterior denticle, with the deep posterior bar consisting of confluent, strong denticles, up to about 4 in number, are very conspicuous features of the species. However, the 160 BRITISH AVONIAN CONODONT FAUNAS posterior bar is strongly laterally compressed and is relatively thin, being more or less triangular in section, with the aboral edge being the widest. The lateral faces are flat to feebly concave. The denticles of the posterior bar are strongly laterally com- pressed and are confluent for most of their length. They are bluntly pointed and have more or less sharp anterior and posterior edges, their lateral faces being feebly biconvex. The denticles proper are about twice the length of the posterior bar. The anterior denticle is very strongly developed; it is massive in general form, being about five times the length and two or three times the width of the largest denticles of the posterior bar. It is slightly recurved posteriorly, but its distal portion is more or less straight. It has very sharp anterior and posterior edges and is so strongly compressed in lateral view that it has a sword-like appearance. It is bluntly pointed. Its inner aboral lateral face is very strongly extended inwards, and this is a most conspicuous feature of the unit in lateral view. Its outer lateral face is feebly convex to flat in the lower part and is gently convex in the upper portion. The whole unit is very slightly curved in a horizontal plane, the inner side being feebly concave. In aboral view the most striking feature is the wide flaring of the inner lateral aboral edge around the junction of the anterior denticle and the posterior bar. The outer lateral face is less conspicuously flared. The whole aboral surface below this lateral flexure is excavated, culminating in a deep median pit which is restricted in its area, but extends anteriorly and posteriorly as rather conspicuous longitudinal grooves along the anterior portion of the anterior denticle and along the posterior bar. The posterior aboral edge of the anterior denticle makes an angle of about 120° with the straight edge of the posterior bar. The antero-aboral corner is very slightly convex and the junction with the edge is more or less pointed. Neoprioniodus montanaensis (Scott) Plate 22, figs. 5a—8b 1942 Lochreia montanaensis Scott (partim) : 289, Pl. 29, fig. 9 only, Pl. 40, fig. 12. 1941 Prioniodus barbatus Branson & Mehl; Ellison & Graves (partim) : 3-4, Pl. 1, fig. 25 only. 1953 Prioniodus singulavis Hass : 88, Pl. 16, fig. 4. 1956 Prioniodus cf. singularis Hass ; Elias : 112, Pl. 2, fig. 45. 1956 Prioniodus voundyi var. dividen Elias : 110, Pl. 2, figs. 39-41. 1957 Prioniodina alatoidea (Cooper) Bischoff: 45, Pl. 5, figs. 33, 34, 36. 1957 Prioniodus sp. A Ziegler in Fliigel & Ziegler : 50, Pl. 4, fig. 3. 1958 Neoprioniodus singularis (Hass) Stanley : 471, Pl. 66, figs. 2, 3. 1958 Neoprioniodus sp. A Stanley : 472, Pl. 66, figs. 4, 5. 1961 Neoprioniodus singularis (Hass) Higgins : Pl. 11, fig. 5. 1962 Neoprioniodus singularis (Hass) Higgins: Pl. 1, fig. 8. 1963 Neoprioniodus singularis (Hass) Bouckaert & Higgins : 17, fig. 3. Neoprioniodus singularis (Hass) Collinson & Druce (in press). MATERIAL. 232 specimens : figured, X 268, X 270, X 269, X 271. RANGE. North Crop CYD 6-3D 1g. DESCRIPTION. The most distinctive feature of this species is the long, slender, BRITISH AVONIAN CONODONT FAUNAS 161 blade-like anterior denticle, which is enormously elongated in comparison with its rather slight aboral process. The latter is only about one-sixth to one-seventh the total length of the denticle. The posterior bar is also conspicuous, being short and sharply down-curved. The denticles of the posterior bar show a sharp decrease in length towards the posterior end of the bar. Those adjacent to the anterior denticle tend to be greatly elongated in comparison with those that follow. All are slender, with more or less sharp anterior and posterior edges, and gently convex lateral faces. They are discrete for about half their length and are regularly pointed. The whole unit is more or less strongly curved inwards in a horizontal plane. The anterior denticle is greatly elongated and is very slender in its general form, being bluntly to sharply pointed at its apical tip. It extends as an aboral process only for a short distance, about one-sixth to one-seventh of its total length, below the level of the posterior bar. The anterior and posterior edges are generally straight, though in a few specimens they may be feebly recurved, and in other specimens there is a very slight anterior flexure of the aboral process. The anterior denticle has sharp anterior and posterior edges and gently convex lateral faces. It stands erect to the anterior portion of the posterior bar. The aboral process is more or less sharply pointed and triangular in form, without any conspicuous lateral flaring developed on the inner aboral margin. The anterior denticle is slightly curved inward in its distal third. The denticles of the posterior bar range from Io to 21 in number and show a marked decrease in size posteriorly. The 2 adjacent to the anterior denticle are virtually confluent with it, only their apices being discrete. The remaining denticles of the posterior bar tend to be smaller and to be inclined more sharply posteriorly. They are discrete for about half their total length in complete specimens. The posterior bar shows a marked decrease in depth from the anterior to the posterior end. The posterior terminus is bluntly rounded. It has more or less flat to gently convex lateral faces, and a sharply bevelled aboral margin on both the inner and outer lateral faces. The whole unit is recurved inwardly in a horizontal plane. There is a relatively inconspicuous cavity below the anterior denticle, which extends as a shallow slit along the posterior bar and the antero-aboral process. REMARKS. Hass (1953 : 88) erected the species Prioniodus singularis to include the present specimens. However, because the species was illustrated and described by Scott, even as part of a natural assemblage, it seems to us that his name must have priority. We, therefore, regard Prioniodus singularis Hass (1953 : 88, Pl. 16, fig. 4) as a junior synonym of Scott’s species. Neoprioniodus peracutus (Hinde) Plate 21, figs. 12a—15b 1900 Prioniodus peracutus Hinde (partim) : 343, Pl. 10, fig. 22 only. 1926 Prioniodus peracutus Hinde ; Roundy : 1o, Pl. 4, fig. 6. 1928 Prioniodus pevacutus Hinde ; Holmes: 21, Pl. 3, fig. 38. 1953 Prioniodus ligo Hass: 87, Pl. 16, figs. 1-3. 1957 Neoprioniodus erectus Rexroad : 34, Pl. 2, figs. 23, 25. 162 BRITISH AVONIAN CONODONT FAUNAS 1957 Prioniodina cassilaris (Branson & Mehl) Bischoff : 46, Pl. 5, figs. 27-31. 1960 Neoprioniodus peracutus (Hinde) Clarke : 14, Pl. 2, fig. 6. 1964 Neoprioniodus peracutus (Hinde) Rexroad & Furnish : 674, Pl. 111, fig. 25. MATERIAL. 32 Specimens : figured, X 272, X 273, X 274, X 275. RANGE. North Crop 3D 4-3D 22. DescripTIon. A slender neoprioniodid in which the anterior denticle is continued more or less vertically downward to form the aboral process. There is a slender and highly recurved posterior bar, the straight postero-aboral portion of which makes an angle of about 130° with the posterior edge of the anterior denticle. The posterior bar decreases in depth posteriorly, its posterior termination being bluntly pointed, its antero-aboral surfaces gently concave, and its postero-aboral surface gently convex in lateral view. In outer lateral view its face is flat, and the whole unit is curved slightly inward so that its inner margin is concave. The oral surface of the posterior bar bears about 19 denticles which tend to decrease in height posteriorly. They are basally confluent, but apically discrete, being bluntly pointed, with sharp anterior and posterior edges and convex lateral faces. The denticles tend to be most conspicuously discrete in the anterior third of the bar, those towards the posterior portion being coalesced for the greater part of their length, but being discrete in their apical region. The anterior denticle is slightly offset inwardly from the main line of the posterior denticles. It has sharp anterior and posterior edges, a feebly convex outer lateral face, and a rather flat antero-inner surface which extends downwards into the flat aboral process. The anterior edge of the aboral process is more or less straight, and the posterior aboral edge is regularly but feebly convex, giving the whole aboral extension a slender plough-like appearance. In inner lateral view, the inward deflection and curvature of the anterior denticle are well seen ; the antero-aboral face of the anterior denticle tends to be slightly concave, but otherwise the inner lateral face is more or less flat to feebly convex in its upper portion. Its anterior aboral edge bears two minor irregularities, but these are not sufficiently distinct to be recognized as denticles. The interior aboral edge of the anterior denticle is expanded, but not strongly so, and there is a very shallow longitudinal pit developed which extends along the flattened basal surface of the posterior bar ; the anterior part of the denticle has longitudinal slit-like grooves. Neoprioniodus scitulus (Branson & Mehl) Plate, 22, figs. ga—1ob, 12a, b 1939 Prioniodus peracutus Cooper : 406, Pl. 46, fig. 7. 1940 Prioniodus scitulus Branson & Mehl : 173, Pl. 5, figs. 5, 6. 1947 Prioniodus scitulus Branson & Mehl ; Cooper: 92, Pl. 20, figs. 1-3. 1949 Prioniodus spp. Youngquist & Miller : 62, Pl. ro1, figs. 9, 10, 14. 1956 Prioniodus scitulus Branson & Mehl ; Elias: tog, Pl. 2, figs. 9, 10. 1957 Neoprioniodus scitulus (Branson & Mehl) Rexroad : 35, Pl. 2, figs. 22, 26. 1957 Neoprioniodus striatus (Branson & Mehl) Rexroad : 35, Pl. 2, figs. 11, 12. 1957 Prioniodina cassilaris Branson & Mehl ; Bischoff : 46, 47, Pl. 5, figs. 27-31. BRITISH AVONIAN CONODONT FAUNAS 163 1958 Neoprioniodus scitulus (Branson & Mehl) Rexroad : 23, 24, Pl. 5, figs. 10-14. 1959 Neoprioniodus scitulus (Branson & Mehl) Elias: 151, Pl. 2, figs. 6, 7. 1959 Neoprioniodus cassilaris (Branson & Mehl) Elias : 153, Pl. 2, figs. 20, 21 only. 1961 Neoprioniodus scitulus (Branson & Mehl) Higgins :; 220, Pl. 11, fig. 1. 1961 Neoprioniodus scitulus (Branson & Mehl) Rexroad & Burton : 1155, Pl. 140, figs. 15-17. 1963 Neoprvioniodus scitulus (Branson & Mehl) Bouckaert & Higgins : 17, fig. 3. 1963 Neoprioniodus scitulus (Branson & Mehl) Thompson & Goebel : 12, fig. 3. 1964 Neoprioniodus scitulus (Branson & Mehl) Rexroad & Furnish : 674, Pl. 111, figs. 36, 37. 1965 Neoprioniodus scitulus (Branson & Mehl) Rexroad & Nicoll : 23, 24, Pl. 2, figs. 21, 22. Neoprioniodus scitulus (Branson & Mehl) Collinson & Druce (in press), Pl. 2, fig. 1. MATERIAL. 24 specimens : figured, X 276, X 277, X 278. RANGE. North Crop 3D 2-3D 14/15. DESCRIPTION. This is a variable species which, as Rexroad (1958 : 23) has demonstrated, shows appreciable variation during ontogeny in the relative curvature of the anterior denticle, the length of the aboral projection and the outline of the aboral margin. The basal cavity is also variable, and tends to be filled in during growth, ultimately resulting in a minute pit, with a longitudinal median groove extending anteriorly and posteriorly from it. There are also smaller differences in the form and denticulation of the posterior bar, which are shown by numbers of well- preserved specimens in the present faunas. In younger individuals the posterior inclination of the denticles of the posterior bar tends to be correspondingly greater than that in older individuals, but this, as well as the other variations, seem to fall within the limits of Branson & Mehl’s species. c REMARKS. The variation in “ another prioniodid’’ mentioned by Branson & Mehl (1940 : 174) as including a minute pit and attachment scars on the lateral faces of the anterior denticle, seem to fall within the variation of the present species, rather than representing a distinct species as they suggest. The most striking general features of the present species are the long slender elegant anterior denticle, the rather short finely pointed aboral process, and the relatively slender, straight to slightly curved posterior bar, together with a general lack of flaring in the lateral faces below the anterior denticle. Neoprioniodus spathatus Higgins Plate 21, figs. ga, b 1961 Neoprioniodus spathatus Higgins : 217, Pl. 11, figs. 2, 4, text-fig. 5. MATERIAL. I specimen : figured, X 279. Rance. North Crop 3D 14/15. DEscrRIPTION. The diagnostic feature of this species is the spatulate plough-like form of the aboral process, which projects with conspicuously concave lateral faces and strongly laterally extended basal surfaces. It has a denticulated anterior edge. The anterior denticle is relatively strongly developed. Its inner lateral face is flat to very feebly convex, but its outer lateral face is more strongly convex. It has very sharp anterior and posterior edges and is laterally twisted and slightly inwardly 164 BRITISH AVONIAN CONODONT FAUNAS recurved in its upper portion. In inner lateral view, it is concave in its anterior proximal portion and feebly convex in its posterior proximal portion. It is elongated and more or less sharply pointed, the anterior and posterior edges being straight. The aboral process is strongly developed, with a concave to straight anterior margin, and a continuously convex posterior margin. Its lateral faces are flat in the anterior portion, but the base of the inner lateral side is strongly flared to give a conspicuously spatulate appearance. Its anterior edge has 2 or 3 minute denticles developed on it which are of smaller size than any on the posterior bar. The posterior bar is short and relatively deep. It bears more than 6 denticles, which are more or less erect or only slightly posteriorly inclined to the bar, and which are discrete for at least half their length. They are regularly pointed and have feebly convex lateral faces and sharp anterior and posterior edges. In outer lateral view the whole unit is conspicuously bowed inwards. In aboral view the most conspicuous feature is a continuous slit-like groove, which runs to the anterior aboral point of the anterior aboral process and along its mid-line, being continued as a narrowing slit along the posterior bar. The posterior bar is much thinner than the aboral process but the basal groove is not conspicuously expanded below the process. It is, however, slightly wider behind the posterior part than it is below the anterior. The lateral aboral faces of the aboral process are more or less straight in aboral view, the basal margin being widest below the posterior end of the process and then curving inward sharply towards the posterior bar. The aboral faces are more or less flat. REMARKS. Collinson & Druce (in press) include this species as a junior synonym of N. singularis (Hass). We have only a single specimen in our collections and we are not in a position to determine the range of morphological variation. Neoprioniodus tulensis (Pander) Plate 21, figs. Iga, b 1856 Prioniodus tulensis Pander (partim) : 30, Pl. 2a, fig. 1 only. 1928 Prioniodus tulensis Pander ; Holmes (partim) : 22, Pl. 3, fig. 18 only. 1940 Prioniodus cassilavis Branson & Mehl : 186, Pl. 6, figs. 11, 12, 15, 17. 1950 Prioniodus cassilavris Branson & Mehl ; Youngquist, Miller & Downs: 528, Pl. 67, figs. 23, 24. non 1957 Prioniodina cassilaris (Branson & Mehl) Bischoff: 47, Pl. 5, figs. 38, 39 (=N. pevacutus). 1963 Neoprioniodus tulensis (Pander) Rexroad & Collinson : 18, Pl. 2, fig. 17, 22, 23. MATERIAL. 5 Specimens : figured, X 280. Rance. North Crop CYD 6-CYD 7. Description. The distinctive feature of the present specimens is the long, recurved, bluntly pointed anterior denticle, the broad spatulate form of the aboral process, and the elongated posterior bar, which bears a series of about 15 denticles onits oral surface. These denticles are discrete for most of their length, and decrease in size posteriorly. —— BRITISH AVONIAN CONODONT FAUNAS 165 The anterior denticle is elongated, wide and bluntly pointed. It is gently recurved in its distal half, but its proximal half stands only slightly inclined to the anterior portion of the posterior bar. It has sharp anterior and posterior edges and very feebly convex lateral faces, the outer distal lateral face being almost flat. The aboral process is broad in relation to its length. Its anterior edge is a con- tinuation of the anterior edge of the anterior denticle, and it is more or less straight. Its anterior aboral termination is bluntly rounded and its posterior aboral edge is strongly convex. It has flat lateral faces. The posterior bar is elongated, and has a concave proximal portion and a relatively straight distal portion when seen in outer lateral view. It decreases in depth posteriorly and bears about 15 denticles ; those of the median third tend to be the largest and they decrease posteriorly in size ; they are basally confluent but are discrete for most of their length, with sharp anterior and posterior edges and gently convex lateral faces. There is a tendency in the median part of the bar for a hindeodellid type of denticulation, but this is not a conspicuous feature of the unit. The outer lateral face of the posterior bar is flat and shows a very slight bevelled ridge parallel to its aboral surface. The whole unit is gently incurved in a horizontal plane, so that its inner lateral face is concave. The denticles of the posterior bar stand more or less erect to the bar itself. In inner lateral view the anterior denticle is much more strongly curved and the curvature is especially strongly developed on the posterior proximal lateral face. The inner aboral longitudinal edge of both the aboral process and the posterior bar are sharply bevelled and the inner lateral curvature of both the anterior denticle and the posterior bar are conspicuous. The aboral surface is marked by a shallow pit below the anterior denticle, which is extended posteriorly as a very narrow slit-like cavity. The basal cavity also extends anteriorly as a narrow slit-like process, running along the median part of the anterior aboral surface. The basal cavity itself is not conspicuously laterally expanded. There is a strong bevelled flange on the inner aboral edge of the anterior aboral process. The strongest lateral curvature of the posterior bar occurs in its anterior half, the posterior part being more or less straight. Remarks. The only substantial difference between the present species and NV. scitulus (Branson & Mehl) is the longer posterior bar of the present specimens, which bears a greater number of denticles. There seems to be a morphological discon- tinuity between the two, but we are not certain about this and further study may indicate that the two are morphologically continuous and that N. scitulus should be regarded as a junior synonym of N. tulensis. Neoprioniodus varians (Branson & Mehl) Plate 21, figs. 18a, b 1940 Prioniodus varians Branson & Mehl : 174, Pl. 5, figs. 7, 8. 1941 Prioniodus barbatus Branson & Mehl ; Ellison & Graves : 3, 4, Pl. 1, fig. 27 only. 1957 Prioniodina varians (Branson & Mehl) Bischoff : 49, Pl. 5, fig. 35. 1957 Prioniodina varians (Branson & Mehl) Ziegler im Fliigel & Ziegler : 50. 166 BRITISH AVONIAN CONODONT FAUNAS 1957. Neoprioniodus varians (Branson & Mehl) Rexroad : 35, Pl. 2, fig. ro. 1958 Neoprioniodus varians (Branson & Mehl) Rexroad : 24, Pl. 5, figs. 3, 4 1961 Neoprioniodus varians (Branson & Mehl) Rexroad & Burton: 1155, Pl. 140, figs. 9, 10. 1965 Neoprioniodus vavians (Branson & Mehl) Rexroad & Nicoll: 24, Pl. 2, fig. 18. MATERIAL. 7 specimens : figured, X 281. RANGE. North Crop CYD 7-3D 17. DESCRIPTION. The present specimens have a conspicuous and relatively short anterior denticle, which is very wide at its base in comparison with its length. It is regularly tapered, its anterior and posterior edges being straight, and its distal tip pointed. Its inner lateral face is strongly convex in the proximal portion and less strongly convex in the distal portion. It is extended aborally as a very short aboral process, with a straight anterior edge and a continuously concave posterior edge, which is continuous with the concave margin of the posterior bar when viewed in lateral view. Its inner lateral face is only feebly convex, and there is no sharp inner basal flexure. The posterior bar, when seen in inner lateral view, is continuously and relatively strongly curved downward. It decreases in depth posteriorly and its posterior aboral corner is bluntly rounded. Its lateral face is strongly convex in the anterior half, but flat to feebly convex in the posterior part, its basal margin being slightly bevelled. Its oral surface bears about 16 large denticles, between which there are some smaller “‘ germ’ denticles developed, especially in the anterior third. The denticles as a whole are closely crowded, but the major denticles are generally not confluent with one another. The denticles in the median half of the bar tend to be rather larger in size than the rest. The denticles on the posterior quarter of the bar are the smallest. All the denticles stand more or less erect to the basal surface below them, and have sharp anterior and posterior edges and convex lateral faces. They are short and bluntly pointed. The anterior denticle stands erect to the oral surface of the eee Se bar in contact with it. It is also gently curved inward along its length. In outer lateral view, there is a very conspicuous bevelled edge along the whole of the aboral margin. The outer lateral face of the anterior denticle and the aboral process is more or less flat in the lower proximal portion, but becomes gently convex in the distal two-thirds. The curvature of the posterior bar is very conspicuous, and the bar decreases in depth posteriorly. In lateral view the anterior end of the aboral process is slightly flexed outward in a horizontal plane, and the main part of the posterior bar is gently flexed inward, so that its inner lateral face is concave. There is a deep and obvious basal cavity below the posterior part of the anterior denticle, which decreases in width but is continued as a rather wide extension along both the aboral process and the posterior bar. Neoprioniodus sp. nov. A Plate 22, fig. 14 MATERIAL. I specimen : figured, X 282. BRITISH AVONIAN CONODONT FAUNAS 167 RANGE. North Crop 3D 17. DESCRIPTION. This species is marked by the lack of a large aboral process and the presence of a wide flaring basal cavity. The anterior denticle is strongly laterally compressed, fairly short and recurved in its aboral third. The posterior bar is deep and relatively short, bearing a series of 14 fused, laterally compressed, needle-like denticles, which are inclined posteriorly. In aboral view the pit is large and sub- apical, having flaring lips. It runs along the posterior bar as a narrowing cavity terminating at the posterior extremity of the posterior bar. Neoprioniodus cf. armatus (Hinde) Plate 21, figs. 3a—c 1879 Prioniodus avmatus Hinde (partim) : 360, Pl. 15, fig. 20, non fig. 21. MATERIAL. 3 specimens : figured, X 283. RANGE. North Crop ZLA 14. Description. The anterior denticle is tall and laterally compressed. The anterior edge is feebly concave in lateral view, with a sharp anterior and posterior edge. The blunt aboral surface projects slightly aborally. The posterior bar is denticulate, curved inward, and slightly twisted. The fused denticles are small, more or less erect, number about 11, and decrease in height posteriorly. The cavity is small and situated postero-aborally of the anterior denticle. REMARKS. This form appears to be very close to Neoprioniodus armatus (Hinde 1879, Pl. 15, fig. 20) which is most abundant in the Upper Devonian. This species probably has a long range, and the present specimens may well belong to it but because of their limited occurrence, both stratigraphically and numerically, we have not made a direct assignation. MHinde’s fig. 21 probably represents a different species. Neoprioniodus cf. camurus Rexroad Plate 22, figs. 1a—4b 1957 Neoprionodus camurus Rexroad : 33, Pl. 2, figs. 18-20. MATERIAL. 10 specimens: figured, X 284, X 285, X 286, X 287. RANGE. North Crop 3D 14/15. Description. The distinctive features of this species are the relatively elongated posterior bar, the sharp inner lateral curvature of the bar immediately posterior to the anterior denticle, and the slender anterior denticle and aboral process. The posterior bar is more or less straight in inner lateral view, and is relatively shallow. Its oral surface bears up to 18 denticles, some of which are separated by smaller germ denticles. The denticles are confluent for most of their length, and only their apices are discrete. The apices are sharply pointed with sharp anterior and posterior edges and gently convex lateral faces ; those in the posterior quarter 168 BRITISH AVONIAN CONODONT FAUNAS stand more or less erect to the basal surface of the bar, but those in the anterior three- quarters are inclined slightly anteriorly. The denticles are of variable height but there is no conspicuous increase or decrease in height in either direction. There isa slight tendency for the two denticles immediately posterior to the anterior denticle to be larger than the rest. The anterior denticle, which is not conspicuously large, is flexed sharply inwards, so that its inner lateral edge points inwardly and anteriorly, making an angle of about 140° with the posterior bar. When seen in inner lateral view, looking directly at the junction between the anterior denticle and the posterior bar, the angle between the posterior edge of the aboral process and the posterior bar is about 70°. The anterior denticle is more or less straight, with sharp and straight anterior and posterior edges and gently convex lateral faces. The aboral process is relatively short in comparison with the length of the denticles, with a rather sharp aboral point, and straight anterior and posterior edges. In outer lateral view the most conspicuous feature of the unit is the sharp lateral recurvature at a point about two or three denticles posterior to the anterior denticle. There is a faintly perceptible longitudinal bevelled edge developed, but the whole aboral surface of the unit is rather thin, although it is excavated by a longitudinal slit. There is a shallow, little-flared, posterior cavity below the posterior margin of the anterior denticle. Genus OZARKODINA Branson & Mehl 1933 1933 Ozarkodina Branson & Mehl 51. TYPE SPECIES. Ozarkodina typica Branson & Mehl. Ozarkodina curvata Rexroad Plate 27, fig. 6 1958 Ozarkodina curvata Rexroad : 24, Pl. 4, figs. 1-3. 1961 Ozarkodina cuvvata Rexroad ; Rexroad & Burton: 1156, Pl. 141, figs. 13, 14. 1964 Ozarkodina curvata Rexroad ; Rexroad & Furnish : 674, Pl. 111, figs. Io, 11. 1965 Ozarkodina curvata Rexroad ; Rexroad & Nicoll: 25, Pl. 2, figs. I, 2. Ozarkodina curvata Rexroad ; Collinson & Druce (in press). MATERIAL. I specimen : figured, X 289. RANGE. North Crop CYD 7. DESCRIPTION. The most conspicuous feature of this species is the short, strongly depressed anterior bar, which bears a series of about 4 denticles on its oral edge. These are basally confluent, and only their apices are discrete, being sharply pointed, with gently convex lateral faces. They tend to be recurved parallel to the apical denticle, and show a more or less constant decrease in size anteriorly, those adjacent to the apical denticle being the largest. The anterior bar is relatively deep and relatively straight ; its anterior end is bluntly spatulate and its outer lateral face more or less flat. There is a rather flat bevel visible along the whole aboral edge of the unit, when seen in outer lateral view. The base of the apical denticle is about BRITISH AVONIAN CONODONT FAUNAS 169 two to three times as wide as the largest denticles adjacent to it, and is confluent with them. It is recurved posteriorly but has a more or less straight posterior edge and is bluntly pointed. It has sharp anterior and posterior edges. Its outer lateral face is feebly convex, and the basal margin is sharply, but not greatly, outflexed below it to give a rather inconspicuous navel. The posterior bar is about twice the length of the anterior, but is less deep. It is straight along its aboral margin and the distal end makes an angle of about 90° with the distal end of the anterior bar. The posterior bar decreases in depth posteriorly and bears a series of crowded confluent denticles, more or less of similar size. These number up to about I1 or 12, and have rather sharply pointed free tips. They show no overall trend in size, but the posterior ones tend to be slightly smaller than the rest. Germ denticles are visible between some of them. Those near the anterior end of the posterior bar tend to be inclined posteri- orly, but those towards the distal end of the bar stand more or less erect to the base of the bar itself. The whole posterior bar is sharply inflexed at about its mid-length, so that its inner lateral face is longitudinally concave. The posterior aboral corner of the unit is sharply rounded. In inner lateral view, the inward curvature of the unit is a very conspicuous feature. There is a small basal cavity below the posterior edge of the denticle, around which the basal margins flare slightly. This is continued as a conspicuous but narrow slit along the anterior and posterior bars. Ozarkodina compressa Rexroad Plate 27; fig: 23 1957 Ozarkodina compressa Rexroad : 36, Pl. 2, figs. f, 2. 1958 Ozarkodina compressa Rexroad ; Rexroad: 24, Pl. 6, figs. 1, 2. 1961 Ozarkodina compressa Rexroad ; Rexroad & Burton: 1156, Pl. 141, figs. 16, 17. 1964 Ozarkodina compressa Rexroad ; Rexroad & Furnish : 674, Pl. 111, fig. 9. 1965 Ozarkodina compressa Rexroad ; Rexroad & Nicoll: 24, 25, Pl. 2, figs. 3, 4. MATERIAL. 12 specimens : figured, X 420. Rance. Avon Gorge C 3-S 49, North Crop 3D 14/15-3D 22. DESCRIPTION. The present specimens are broadly similar to those described by Rexroad and other authors, although they differ slightly in that the posterior bar Denticles _- Apical denticle Posterior Anterior Posterior bar Anterior bar Lip of basal cavity Fic. 33. Ozarkodina sp. showing morphological terms used in the text. 170 BRITISH AVONIAN CONODONT FAUNAS tends to be rather more elongate and is slightly twisted. This distinction does not seem sufficient, however, to warrant their recognition as a different species, and in other aspects of their denticulation and general form they closely resemble Ozarkodina compressa. Ozarkodina delicatula (Stauffer & Plummer) Plate 27, figs. 15, 19 1932 Bryantodus delicatulus Stauffer & Plummer : 29, PI. 2, fig. 27. 1932 Bryantodus nasutus Stauffer & Plummer : 29, Pl. 2, fig. 28. 1932 Byryantodus sulcatus Stauffer & Plummer : 30, Pl. 2, figs. 11, 14, 30. 1933 Byryantodus delicatus Gunnell : 267, Pl. 32, fig. 43. 1933 Bryantodus rugosus Gunnell : 269, Pl. 32, fig. 44. 1933 Bryantodus stritatus Gunnell : 268, Pl. 32, fig. 45. 1933 Bryantodus strigillatus Gunnell : 268, Pl. 32, fig. 46. non 1933 Bryantodus delicatus (Stauffer & Plummer) Branson & Mehl: 222, Pl. 16, fig. 19. 1941 Ozarkodina delicatula (Stauffer & Plummer) Ellison : 120, Pl. 20, figs. 40-42, 47. 194% Ozarkodina delicatula (Stauffer & Plummer) Ellison & Graves : 3, Pl. 1, figs. 12-14. 1944 Ozarkodina delicatula (Stauffer & Plummer) E. B. Branson : 327. 1948 Ozarkodina delicatula (Stauffer & Plummer) Youngquist & Heezen: 771, Pl. 118, fig. 6. 1949 Ozarkodina delicatula (Stauffer & Plummer) Youngquist & Downs : 168, Pl. 30, HES) Teese7 non 1949 Bryantodus delicatus (Stauffer & Plummer) Beckmann 161, Pl. 1, fig. 7 ; Pl. 3, fig. 3. 1952 Ozarkodina delicatula (Stauffer & Plummer) Rhodes : 893, Pl. 126, figs. 2, 3. 1957 Ozarkodina delicatula (Stauffer & Plummer) Bischoff : 39, Pl. 1, figs. 25-28. 1958 Ozarkodina compressa Rexroad (partim) : 24. 1961 Ozarkodina delicatula (Stauffer & Plummer) Higgins : 220, Pl. 12, fig. 13. 1961 Ozarkodina delicatula (Stauffer & Plummer) Rexroad & Burton :. 1156, Pl. 141, fig. 12. 1963 Ozarkodina delicatula (Stauffer & Plummer) Bouckaert & Higgins: 17, fig. 3. Ozarkodina delicutula (Stauffer & Plummer) Collinson & Druce (in press). MATERIAL. 27 specimens : figured, X 290, X 2g1. RanGE. North Crop CYD 7-3D 20. DeEscriPTION. This is a relatively variable species with the following character- istics. Anterior and posterior bars are thin, blade-like, straight or continuously gently arched, the anterior tending to be the deeper and the longer. Denticles closely spaced, more or less sub-equal, discrete only at their pointed apical ends. Apical denticle is from one and a half to three times the width of the adjacent denticles. It has a slightly flared basal cavity. The anterior bar is of more or less uniform depth and has a straight to gently concave aboral edge. It bears 12 to 14, strongly laterally compressed denticles, which are confluent for most of their length only their apical tips being discrete. These are sharply pointed, with sharp anterior and posterior edges which are straight. The anterior bar itself is about equal in depth to the length of the denticles. The BRITISH AVONIAN CONODONT FAUNAS 17I denticles at the anterior end of the bar are more or less erect, but those toward the posterior end become increasingly strongly inclined posteriorly. In a few specimens the denticles at the anterior end of the bar are also posteriorly inclined. The lateral faces of the anterior bar are flat to gently convex, the convexity increasing in the posterior half of the bar. The apical denticle is variable in size and in inclination. It is of similar form to the denticles of the anterior bar and its free portion is sharply pointed, with sharp, straight anterior and posterior edges. It is strongly inclined at an angle of up to about 50° to the posterior bar, and is from one and a half to three times as wide and about twice as long as the largest adjacent denticles. In some specimens the denticles of the anterior bar are more widely spaced and appear almost discrete, but in most specimens they are more or less confluent. The posterior bar is depressed with respect to the anterior, and the whole aboral surface is either continuously and gently concave, or both the anterior and posterior bars may be more or less straight and meet at an angle of about 120°. (This is the projected angle made by their straight distal ends in those specimens where the lower surface is strongly arched). The posterior bar bears 10 or more laterally compressed closely spaced denticles, which, although in some specimens they are more or less equal in size, show a marked decrease in size in the posterior quarter of the bar in others. They are generally rather smaller than the denticles of the anterior bar and fewer in number. In some specimens the posterior bar, and to a lesser extent the anterior bar, are strongly flexed inwards. The denticles of the posterior bar are all inclined at about 50° to the posterior bar itself. In aboral view the unit has a rather conspicuously flattened aboral margin, which decreases in width towards the anterior and posterior ends of the unit. There is a continuous longitudinal slit along both limbs, and a slightly flared median cavity below the apical denticle, which is continuous with the slit. The flaring of this cavity is not a conspicuous feature, but the thickened lips of the main longitudinal cavity are more or less conspicuous in aboral view. This species shows some variation in the degree of flexing of the anterior and posterior bars in a vertical plane and in the relative depth and detailed denticulation of the anterior bar. Specimens illustrating various morphological variations are illustrated. Ozarkodina hindei Clarke Plate, 27 figs. 16, 17, 22 1879 Polygnathus dubius Hinde : 363, Pl. 16, fig. 8 only. 1900 Polygnathus dubius Hinde ; Hinde: 341, Pl. 9, fig. 1 only. 1928 Prioniodina (Polygnathus) dubius (Hinde) Holmes : 109, PI. 8, fig. 1 only. 1960 Ozarkodina hindei Clarke : 18, Pl. 3, figs. 1, 6. 1961 Ozarkodina compressa Rexroad ; Rexroad & Burton: PI. 141, fig. 16 only. MATERIAL. 3 specimens : figured, X 294, X 293, X 295. Rance. North Crop 3D 6-3D 12. DEscrRIPTION. The diagnostic features of this species are the very deep and strongly laterally compressed anterior and posterior bars, and the very wide, short 172 BRITISH AVONIAN CONODONT FAUNAS and conspicuously pointed apical denticle. The anterior bar is deeper than the posterior, and carries from 4 to 6 denticles on its oral edge. These are very strongly laterally compressed and more or less sharply recurved, being confluent for the greater part of their length. Their apical halves are discrete, and they are sharply pointed with straight anterior and posterior edges, the anterior edge tending to be sharply deflected at an angle of about 130° at or near the point of confluence with the adjacent denticles, but the posterior edge being straight throughout its length. Germ denticles are visible in places on the anterior bar, especially at its junction with the apical denticle. The most posterior denticle of the apical bar is so coalesced with the anterior edge of the apical denticle that only its highest portion is discrete. The anterior bar tends to show a slight increase in depth anteriorly ; the denticles in the posterior two thirds of the bar are of more or less uniform height. There may, however, be I or 2 much smaller blunt denticles present on the spatulate anterior end. The denticles may curve slightly inwardly in some specimens. The inner lateral face of the anterior bar is more or less flat, but the outer lateral face has a conspicuous, shoulder-like thickening near the base of the denticles. The anterior bar tapers sharply towards the aboral margin. The apical denticle is at least three times as wide as the largest denticles of the anterior and posterior bars. It is very sharply pointed, and is only about twice as long as its basal width. It is recurved posteriorly at an angle of about 60° to the posterior bar, and germ denticles are conspicuous at its base. There is a feebly flaring protrusion of the basal margin below its posterior margin. The posterior bar is shorter and shallower than the anterior, and bears up to 9 denticles of more or less uniform height, basally confluent, but their apices discrete and sharply pointed. They tend to be very slightly smaller than those of the larger series of the anterior bar. The posterior bar thickens towards its aboral surface, which is wide and flat, as an extension of the basal cavity below the apical denticle. It decreases in both width and depth posteriorly, however, and its posterior aboral margin is bluntly rounded. Its inner lateral face is more or less flat and the posterior denticles are gently inclined to the base of the posterior bar. The posterior bar and the anterior bar have relatively straight aboral margins and they make an angle of about 130° with one another in a vertical plane. The whole unit is strongly bowed laterally in a horizontal plane so that it is concave on the inner side, and the denticles are also incurved to a varying degree. This is especially true of the apical denticle. The anterior edge of the anterior bar has an acute angle at the anterior aboral margin and is inclined sharply posteriorly, with a faintly serrated anterior edge in some specimens. In outer lateral view the lateral faces of the unit are flat to gently convex, and the inner curvature is a conspicuous feature. In most specimens there is developed to a varying intensity a bevelled aboral margin, especially conspicuous in the median half of the unit, which includes the posterior part of the anterior bar and the anterior part of the posterior bar. The outer lateral view of the navel below the posterior edge of the apical denticle is distinct and forms a rather flattened apical area. In aboral and outer lateral views the basal cavity is a conspicuous feature, partic- BRITISH AVONIAN CONODONT FAUNAS 173 ularly so in outer view. There is a strong basal expansion below the posterior edge of the apical denticle, and in the anterior third of this, the basal cavity is deepest and widest, forming a biconvex pit. It is extended anteriorly and posteriorly as a shallow slit-like groove, but the posterior extension becomes indistinct near the posterior end of the margin of the expanded base. The anterior extension continues towards but does not quite reach the anterior end of the anterior blade. REMARKS. This species is close to O. compressa Rexroad, but differs from it in the shorter and deeper anterior and posterior bars and the short and relatively very broad apical denticle. Ozarkodina macer (Branson & Mehl) Plate 27, tigs. 7,8 1934 Bryantodus macer Branson & Mehl: 283, Pl. 23, fig. 4. 1934 Ozarkodina elongata E. R. Branson : 313, Pl. 28, fig. 25. ? 1934 Bryantodus scitulus Branson & Mehl: 283, Pl. 23, fig. 5. 1943 Bryantodus equalis Cooper in Cooper & Sloss : 170, Pl. 29, fig. 9. 1943 Bryantodus cf. planus Branson & Mehl ; Cooper im Cooper & Sloss: 170, Pl. 29, fig. 3. 1943 Ozarkodina regulavis Branson & Mehl ; Cooper im Cooper & Sloss : 170, Pl. 29, fig. 12. 1943 Subbryantodus grandis Cooper in Cooper & Sloss : 175, Pl. 29, fig. 19. 1949 Ozarkodina cf. elongata Branson & Mehl ; Thomas: 411, Pl. 4, fig. 28. 1955 Ozarkodina vegularis Branson & Mehl ; Sannemann: 133, Pl. 6, fig. 5 only. 1957 Ozarkodina willsi Rhodes & Dineley : 364, Pl. 38, figs. 1, 5. 1957 Ozarkodina firma (Stauffer) Rhodes & Dineley : 364, Pl. 27, fig. 20. 1957 Ozarkodina delicatula (Stauffer & Plummer) Bischoff : 39, Pl. 1, figs. 25-28. 1957 Ozarkodina voundyi (Hass) Bischoff: 40, Pl. 2, fig. 2 only. 1957 Ozarkodina congesta Stauffer, Bischoff & Ziegler : 75, 76, Pl. 12, figs. 18-20, Pl. 13, fig. 14. 1958 Ozarkodina tortilis Tatge ; Huckriede: 154, Pl. 11, fig. 26 only. 1959 Ozarkodina cf. delicatula (Stauffer & Plummer) Helms : 646, Pl. VI, figs. 14-16. 1959 Ozarkodina cf. regularis Branson & Mehl; Helms: 647, Pl. IV, figs. 13, 14, (non Pl. IV, fig. 15=O. cf. congesta). 1960 Ozarkodina vegularis Branson & Mehl ; Zimmermann : PI. IX, fig. 11 only. 1960 Ozarkodina media Walliser ; Spasov : 68, Pl. 1, fig. 10 only. MATERIAL. 71 specimens : figured, X 304, X 305. Rance. Avon Gorge K 8-Z 38. Description. A gently arched blade with asymmetrical anterior and posterior blades, commonly bearing 5 to 7 straight, posteriorly inclined denticles on the anterior blade, and 8 to 12 straight posteriorly inclined denticles on the posterior blade. The denticles of the anterior and posterior blades may be of uniform eleva- tion, highest near the apical denticle and decreasing in elevation to the extremities of the blades, or they may be of variable elevation. The apical denticle is straight to slightly curved, posteriorly inclined and higher and wider than the blade denticles. The small circular basal cavity is situated beneath the apical denticle. The aboral edge is sharp. 174 BRITISH AVONIAN CONODONT FAUNAS REMARKS. Ozarkodina macer (Branson & Mehl) as here defined, includes a group of ozarkodinids which are characterized by having asymmetrical anterior and posterior limbs. The outline of the denticles of both the anterior and posterior blades is similar in lateral view. O.macer resembles O. cf. congesta in the outline of the blades in lateral view, but in O. macer the anterior and posterior limbs are asymmetrical whereas in O. cf. congesta they are symmetrical. Compared with Ozarkodina macra the blade of Ozarkodina macer is thinner. Ozarkodina macra Branson & Mehl Plate 27, fies. 12, °20, 21 wo) 1931 Bryantodus equalis Cooper : 234, Pl. 28, fig. 9. 1931 Bryantodus subequalis Cooper : 234, Pl. 28, fig. 11. 1934 Ozarkodina macva Branson & Mehl : 192, Pl. 17, fig. 5. 1934 Ozarkodina vegularis Branson & Mehl: 287, Pl. 23, figs. 13, 14. 1938 Ctenognathus firmus Stauffer : 425, Pl. 48, figs. 2, 6, 15. 1955 Ozarkodina rvegularvis Branson & Mehl ; Sannemann : 133, Pl. 6, figs. 3, 7 only. 1956 Ozarkodina rhenana Bischoff & Ziegler : 153, Pl. 14, fig. 19. 1957 Ozarkodina ballai Bischoff & Ziegler : 74-75, Pl. 13, figs. 1, 2. 1957 Ozarkodina macra Branson & Mehl ; Bischoff & Ziegler : 77, Pl. 12, figs. 13a, b, Pl. 13, figs. Ioa, b. 1957 Ozarkodina cf. macya Branson & Mehl ; Bischoff & Ziegler : 78, Pl. 13, fig. 11, Pl. 19, fig. 43. MATERIAL. 36 specimens : figured, X 296, X 298, X 297. RANGE. Avon Gorge K 2-Z 18, North Crop KL 2-KL 16. DESCRIPTION. The aboral edge in lateral view is slightly arched. The anterior and posterior blades are of almost equal length. and bear 8-12 straight, posteriorly inclined denticles, fused for the greater part of their length but free at their tips. The anterior blade is thicker than the posterior blade. The apical denticle is two to three times as wide as the denticles of the anterior and posterior blade. It is inclined to the posterior at an angle of 70°. The small circular basal cavity is situated immediately beneath the apical denticle and the aboral edge is sharp. ~~ ~ ww Ozarkodina parva (Huddle) Plate 27, fig. 18 1934 Bryantodus parvus Huddle : 74, 75, Pl. 4, fig. 9. 1939 Bryantodus orthus Cooper : 385, Pl. 43, figs. 33, 34. 1939 Subbryantodus ? scitulus (Branson & Mehl) Cooper : 417, Pl. 43, figs. 35, 36. MATERIAL. 107 specimens : figured, X 299. RANGE. Avon Gorge K 3-C 7, North Crop KL 2—ZLA 32. DEscRIPTION. The blade is short, thin, symmetrical and slightly arched. The apical denticle is subcentral, flattened, sharp edged and acutely pointed to the poster- ior. The blade denticles are closely appressed and similar to the apical denticle in outline, inclination and insertion. They number 7 to 12 on each side of the apical BRITISH AVONIAN CONODONT FAUNAS 175 denticle, are fused for the greater part of their length, and are highest near the apical denticle. They decrease in height uniformly to the anterior and posterior extremi- ties. The basal cavity is small and thin, and is situated beneath the apical denticle. Ozarkodina plana (Huddle) Plate 27, figs. I-3 1934 Bryantodus planus Huddle : 75-76, Pl. ro, fig. 8. non 1934 Bryantodus planus Huddle ; Branson & Mehl: 284, Pl. 23, fig. 8. 1957 Ozarkodina cf. O. plana (Huddle) Rhodes & Dineley : 364, Pl. 37, fig. 24. 1961 Ozarkodina plana (Huddle) Scott & Collinson : 128, Pl. 2, fig. 8. MATERIAL. 12 specimens : figured, X 300, X 301, X 419. Rance. Avon Gorge K 3-Z 15. DESCRIPTION. The anterior and posterior blades are short, slightly arched, laterally compressed, and very thin. The apical denticle is short, broad at the base, acutely pointed and situated slightly anterior to the basal cavity. The blade denticles are similar in outline to the apical denticle and usually number 4 anteriorly and 6 posteriorly. The basal cavity is small and situated slightly anterior to the apical denticle. Ozarkodina plumula Collinson & Druce Plate 27, figs. 4, 5 Ozarkodina plumula Collinson & Druce (in press). MATERIAL. 4 specimens : figured, X 302, X 303. RANGE. North Crop 3D 12. DescripTion. The diagnostic characteristic of this species is the slender elon- gated anterior bar, bearing a large number of small, posteriorly inclined denticles. The posterior bar is shorter and deeper, and bears a smaller number of conspicuously larger denticles than those of the anterior bar. The apical denticle is only slightly larger than the largest of the posterior bar and the whole unit is more or less con- tinuously recurved. The anterior bar is of slender elongate construction, relatively shallow in depth, and bears a series of up to 12 small confluent denticles, only the apical tips of which are discrete. These are sharply inclined to the anterior bar and tend to decrease in size posteriorly. The apical denticle is only slightly larger than those adjacent to it both in length and in width. It is, however, conspicuously more sharply inclined than most of those of the anterior bar, and in this it parallels the denticles of the shorter posterior bar. It is very strongly laterally compressed, with sharp anterior and posterior edges, and is confluent with the posterior denticles for the greater part of its posterior margin, though its inclination removes most of its anterior edge on the adjacent anterior denticles. The denticles of the posterior bar are similar to, but rather larger than, those of the 176 BRITISH AVONIAN CONODONT FAUNAS anterior. They are about 5 or 6 in number and are strongly laterally compressed with sharp anterior and posterior edges and gently biconvex lateral faces. Their bases are confluent and their sharply pointed apices discrete. The posterior bar is deeper than the anterior, and tends to become shallower towards its posterior end. It is inclined to the anterior bar at an angle which varies from 130°-140°, although the junction between the two is continuously curved, so that the whole aboral margin is concave with more or less straight distal ends. There is a relatively inconspicuous flare on the basal margin below the posterior edge of the apical denticle. The basal cavity is gently flared, being slightly larger than that of many typical ozarkodinids. It is continued as a longitudinal slit along both the anterior and the posterior bars, both of which become narrower towards the aboral margin. The whole unit is more or less straight in a vertical plane. In complete specimens the denticles are seen to be sharply pointed, and the denticles of the posterior bar are discrete for a greater part of their length than those of the anterior bar. The posterior aboral corner of the posterior bar is very strongly rounded and terminates orally in the tip of the posterior denticle. Ozarkodina cf. congesta Stauffer Plate 27, fig. 13 1940 Ozarkodina congesta Stauffer : 427, Pl. 59, fig. 12. 1957 Ozarkodina plana Huddle ; Bischoff & Ziegler 78, 79, Pl. 12, fig. 15a, b. 1959 Ozarkodina cf. vegularis Branson & Mehl ; Helms: 647, Pl. IV, fig. 15 only. MATERIAL. 14 specimens : figured, X 288. Rance. Avon Gorge Z 17-Z 37. Description. A gently arched unit with symmetrical anterior and posterior blades, commonly bearing 7 straight posteriorly inclined denticles, highest near the apical denticle, and decreasing in length uniformly to the anterior and posterior extremities of the blades. The apical denticle is straight to slightly curved, posteriorly inclined and higher and wider than the blade denticles. The small circular basal cavity is situated beneath the apical denticle, The aboral edge is sharp. REMARKS. In the Z beds of the Avon Gorge, specimens of Ozarkodina are found, which are neither identical with one another nor with previously described species. Reference to the literature shows that previous workers, for example Helms (1959) and Bischoff & Ziegler (1957), have often assigned specimens in their studies to species where the holotype bears little resemblance to their specimens. In the present study, the majority of the Z bed ozarkodinids have been referred to two general categories ; O. cf. congesta Stauffer, which has symmetrical anterior and posterior limbs, and Ozarkodina macer (Branson & Mehl) which has asymmetrical anterior and posterior limbs. BRITISH AVONIAN CONODONT FAUNAS 177 Ozarkodina cf. delicatula (Stauffer & Plummer) Plate 27, fig. 14 1932 Bryantodus delicatula Stauffer & Plummer 29, Pl. 2, fig. 27. MATERIAL. 12 specimens : figured, X 292. Rance. North Crop ZLA 31-ZLA 33. DEscrRIPTION. The unit is bowed and slightly curved. Both bars are long. The anterior bar bears about 8 denticles which are sub-equal, laterally compressed, fused at their bases with free chevron tips, and all are inclined posteriorly. The antero- aboral edge is bluntly spatulate. The apical denticle is largest, fairly short, about twice the size of those of the anterior bar, laterally compressed and inclined posteriorly. The posterior bar is of equal length to the anterior bar, but less deep, and shallows posteriorly. The denticles are similar and about 8 in number. The basal cavity is minute and restricted to the aboral region of the apical denticle with sometimes feebly flaring lips. Remarks. Stauffer & Plummer (1932 : 29), described O. delicatula from Penn- sylvanian strata, and it has been recognized in Upper Viséan and Namurian rocks (Bischoff 1957, Higgins 1961). The present specimens appear to be very similar to the type specimens, and it is possible that the species has an even longer range than previously thought. Ozarkodina cf. elegans (Stauffer) Plate 27 ie: 24 1938 Ctenognathus elegans Stauffer : 425, Pl. 48, figs. 9, 12. 1940 Ctenognathus elegans Stauffer ; Stauffer : 422, Pl. 59, figs. 3-5, 8. 1955 Ozarkodina elegans (Stauffer) Sannemann : 133, Pl. 6, fig. 9. 1956 Ozarkodina denckmanni Ziegler : Pl. 7, figs. 1, 2, Pl. 6, figs. 30, 31. 1957 Ozarkodina elegans (Stauffer) Bischoff & Ziegler : 76, Pl. 20, figs. 29-33. 1958 Ozarkodina denckmanni Ziegler ; Bischoff & Sannemann : 99, Pl. 14, figs. 22, 23. 1960 Ozarkodina vegularis Branson & Mehl ; Zimmermann : PI. IX, fig. ro. 1961 Ozarkodina delicatula (Stauffer & Plummer) Rexroad & Burton: 1156, Pl. 141, fig. 12. 1963 Ozarkodina media Walliser ; Spasov & Veselinovic : 246, Pl. 1, fig. 14 only. MATERIAL. 2 specimens : figured, X 109. RANGE. Avon Gorge Z 19-Z 37. DescripPTIon. The anterior blade bears 11 denticles fused to near their tips. The denticles are straight and inclined to the posterior at an angle of 80°. The posterior blade is straight and only half the height of the anterior blade. It bears up to 12 denticles, which are fused for the greater part of their length, but free at their tips. The denticles of the posterior blade are free for a greater part of their length than those of the anterior blade. The denticles of the posterior blade are straight and inclined to the posterior at an angle of 45°. The aboral edge in lateral view, is gently arched. The apical denticle is straight, slightly higher than the posterior 178 BRITISH AVONIAN CONODONT FAUNAS denticle of the anterior blade, and inclined to the posterior at an angle of 70°. Itis also three times the width of the blade denticles. The small circular basal cavity is situated beneath the apical denticle. The aboral edge is sharp. REMARKS. Ozarkodina cf. elegans, as interpreted in this study, is characterized by having longer denticles on the anterior blade than on the posterior blade. Ozarkodina sp. Plate 27, figs. 9-11 MATERIAL. 93 specimens : figured, X 306, X 307, X 308. RANGE. Avon Gorge K 2-S 53. REMARKS. A number of broken specimens which contain part of the anterior, or posterior blades, have been found, but it is impossible to refer them to any species with certainty. Genus PATROGNATHUS gen. nov. DERIVATION OF NAME. From the Latin patey—father. DiaGnosis. Symmetrical platform conodonts, with lanceolate platform and short anterior median blade, generally of five denticles, the most posterior one of which is higher than the others. The platform bears a row of 6 to g nodes on either margin, separated by a central trough. The basal cavity is large, extending almost the complete length of the aboral surface of the platform, asymmetrical and laterally flared. A small posterior blade, composed of two denticles, is developed in a few specimens, but there is no carina extending along the platform. Type SPECIES. Patrognathus variabilis gen. et. sp. nov. DescriPTIOon. As for Patrognathus variabilis sp. nov. REMARKS. Patrognathus is similar to the previously described genera Taphro- gnathus Branson & Mehl, and Stveptognathodus Stauffer & Plummer, but has a wider and more flared basal cavity. Rexroad (1958A) considered Taphrognathus and Streptognathodus to be homoeomorphs, but Lindstrém (1964 : 173) considered Taphro- gnathus to be a synonym of Streptognathodus. The present authors believe Rexroad’s interpretation to be correct, and regard Patrognathus as another broad homoeomorph, which is present at the base of the Tournaisian and possibly in the uppermost Upper Devonian. Glenister & Crespin (1959) reported Taphrognathus from the Upper Devonian strata of the Fitzroy Basin in Australia. The specimens have an anterior blade which is lateral in position and, therefore, appear referable to our new genus Clydagnathus. Likewise Conil, Lys & Mauvier (1964) reported, but did not illustrate, Taphrognathus sp. from the Tny,-Tngp horizons of the Franco-Belgian Province. If the anterior blade is lateral in position, then their specimens should be referred to Clydagnathus gen. nov. Glenister & Klapper (1966, Pl. 94, fig. 3) have found specimens of “ Scaphignathus”’ in Australia identical to our Clydagnathus. In one sample it BRITISH AVONIAN CONODONT FAUNAS 179 occurs 150 ft. below the first appearance of S. aculeatus, but in another it occurs with S. aculeatus and Palmatolepis glabra. Sandberg & Klapper (1967) have also found the genus Clydagnathus in several sections in Wyoming and Montana, and the genus Patrognathus in the Windy Gap Formation of Wyoming, where it is associated with S. sulcatus (see also p. 54) The Lower Devonian Eognathodus Philip differs from Patrognathus in the form of the anterior blade, although the genera resemble one another in overall form. Patrognathus variabilis gen. et sp. nov. Plate 2, figs. 8a—11c DERIVATION OF NAME. From the great variability of this form. Diacnosis. Elongate, symmetrical form, possessing lanceolate platform and medial blade. Carina absent. Posterior denticle of blade twice as large as other blade denticles. Cavity flared, elongate, covering most of platform. Base of cavity and blade grooved. MATERIAL. 625 specimens: Holotype X 311, Paratypes X 519, X 309, X 310 (all figured). TYPE LOCALITY AND HORIZON. Avon Gorge, K Zone. Sample KLz. RANGE. Avon Gorge Samples K 1-K 17, North Crop Samples KL 1-KL 12. DEscRIPTION. The unit is symmetrical, the platform being lanceolate and straight to slightly curved. The blade varies in length, but is commonly a little A. Oral view B. Aboral view High denticle of blade Platform High denticle of blade Anterior Posterior __— Anterior edge “~ Platform denticle ~* Flared basal cavity Position of basal cavity _- High denticle of blade ; Oral edge Anterior edge —_ vad 3 eh Posterior edge \ ~Aboral edge Position of basal cavity C. Lateral view Fic. 34. Patrognathus sp. showing morphological terms used in the text. 180 BRITISH AVONIAN CONODONT FAUNAS shorter than the platform. It is situated medially and bears from 4 to 8 denticles, the posterior-most being twice as large as the remainder. There is a general decrease in size anteriorly, and the denticles are more or less erect. The base of the blade is grooved. Each side of the platform bears a marginal row of laterally elongate nodes, which are transversely paired. These are replaced posteriorly by a single series of medial transverse ridges, composed of two nodes. An additional node is generally developed on the left side of the platform (viewed from the posterior). This addi- tional node, situated at the anterior end of the platform, is developed on the left margin of the platform, irrespective of whether the unit is laterally curved to the right or the left. The number of nodes in each row ranges from 4 to 11. The unit is arched slightly in lateral view and the platform has a nodose edge. In aboral view the cavity is slightly asymmetrically expanded, the inner half being shorter and more inflated. The base of the cavity is grooved. Remarks. Although P. variabilis possesses a variable number of nodes on both the blade and platform, calculations of denticle density of both blade and platform and the construction of a scatter diagram of this information, suggest that this vari- tion is continuous (see Fig. 35). The additional node at the anterior of the inner row of lateral nodes on “right” specimens appears to be constant and implies that paired members of P. variabilis were not symmetrical. Other examples of this asymmetry are to be seen in the genera Cavusgnathus, Scaphignathus, Mestognathus and Pseudopolygnathus. SCATTER DIAGRAM FOR DENTICLE DENSITY OF PATROGNATHUS VARIABLIS. 2o ° 5m Cc o vD o ° w + 9g ° 8 t 0 Ee o &+tot o + Boe + v0 0 OF els v @ eo UD +o 9%o8 2 + 0@ D *-*KL2 22PLOTS 10 ° O*KL3 S4PLOTS 15 20 30 platform denticle density BLADE DENTICLE DENSITY « No OF BLADE OENTICLES LENGTH OF BLADE IN MM PLATFORM DENTICLE DENSITY =No.OF PLATFORM DENTICLES LENGTH OF PLATFORM IN MM Fic. 35. Scatter diagram to show the relationship between the density of denticles on the blade and those on the platform of the species Patrognathus variabilis. BRITISH AVONIAN CONODONT FAUNAS 181 Genus PLECTOSPATHODUS Branson & Mehl 1933 1933 LPlectospathodus Branson & Mehl : 47. TyPE SPECIES. Plectospathodus flexuosus Branson & Mehl. Plectospathodus ? sp. nov. A Plate 25, figs. 8a—9 MATERIAL. 3 specimens : figured, X 312, X 313. RANGE. North Crop ZLA 33. Description. A plectospathodid characterized by a long anterior bar ; denticles free standing, sub-circular in cross-section and posteriorly inclined ; those in the median third the largest. Apical denticle larger than bar denticles, ovate in cross- section, and posteriorly and laterally inclined. Posterior bar about equal in length to anterior bar, twisted and with slight inward curvature, the posterior tip down- flexed. Denticles small, fine, except for terminal denticle, which is as large as apical denticle, and may have small denticles developed on its posterior face. The basal cavity is open, flared on the inner side, with a “ nick’ in the inner lip beneath the apical denticle ; it extends beneath the posterior and anterior bars for a short distance. REMARKS. The genus Plectospathodus has previously been described only from rocks of Upper Silurian and Lower Devonian age, but these specimens agree perfectly with the generic description given by Branson & Mehl (1933A : 47). Plectospathodus ? sp. nov. B Plate 25, figs. 10-12 MATERIAL. 4 specimens : figured, X 427, X 428, X 314. RANGE. North Crop 3D 14/15-3D ro. DESCRIPTION. Very small units consisting of two bars, roundly arched at their junction. Oral edges denticulate. A conspicuous apical denticle. Denticles of Apical denticle Terminal denticle A“ nam Fic. 36. Plectospathodus sp. showing morphological terms used in the text. Anterior bar ~ Posterior bor Basal cavity 182 BRITISH AVONIAN CONODONT FAUNAS variable size, inclined posteriorly ; at or near posterior end of unit a relatively enormous, greatly elongated denticle, slightly greater in basal width than apical denticle. The inner lateral face is generally convex, with a rather flat oral shoulder on which the denticles are developed. The denticulation of the anterior bar consists of a series of rather small inconspicuous basally confluent denticles, all inclined equally posteriorly at an angle of about 45° to the oral edge of the bar. The anterior end is roundly spatulate and there is a very feeble basal flare below the apical denticle. The apical denticle is biconvex in cross-section, with blunt anterior and posterior edges, and is curved slightly inward, as well as being inclined posteriorly. On the posterior bar there is a series of denticles which decrease in size towards the distal end ; they are basally confluent and have sharp free tips, the most posterior, or the one next to it, being much the largest. The posterior portion of the posterior bar is straight-edged, but the posterior aboral corner is bluntly rounded. The whole aboral surface of the unit is gently concave in lateral view and the unit tends to be bowed inwards, as well as the main denticles being rather incurved. In outer lateral view the whole unit is rather flat and is slightly indented below the apical denticle. The basal surface is flared on the inner lateral face below the apical denticle, and there is a broad cavity in this position, which rapidly decreases anteriorly and posteriorly, to be extended along part of both bars as a shallow longitudinal slit. Genus POLYGNATAUS Hinde 1879 1879 Polygnathus Hinde : 359. TYPE SPECIES. Polygnathus dubia Hinde 1879. Polygnathus communis communis Branson & Mehl Plate 12, figs. 2a—5c 1934 Polygnathus communis Branson & Mehl: 293, Pl. 24, figs. 1-4. 1934 Polygnathus communis Branson & Mehl ; E. R. Branson : 308, Pl. 25, figs. 5, 6. 1938 Polygnathus communis Branson & Mehl; Branson & Mehl: 145, Pl. 34, figs. 39-41. 1939 Polygnathus communis Branson & Mehl ; Cooper : 399, Pl. 39, figs. 1, 2, 9, 10, 23, 24. 1939 Polygnathus adola Cooper : 399, Pl. 39, figs. 33-36. 1939 Polygnathus marginata Branson & Mehl ; Cooper: 4o1, Pl. 41, figs. 15, 16. 1944 Polygnathus communis Branson & Mehl ; Branson & Mehl im Shimer & Schrock : 245, Pl. 94, figs. 29-31. 1944 Polygnathus communis Branson & Mehl; E. B. Branson : 208, 221, Pl. 39, figs. 39-41. 1947 Polygnathus communis Branson & Mehl ; Mehl & Thomas: 15, PI. 1, fig. 36. 1949 Polygnathus communis Branson & Mehl; Youngquist & Patterson: 62, Pl. 15, figs. 7; 8: 1949 Polygnathus communis Branson & Mehl ; Thomas: 411, Pl. 3, fig. 70. 1951 Polygnathus communis Branson & Mehl ; Youngquist & Downs: 787, Pl. 111, figs. 4, 5, 19, 20. 1951 Polygnathus communis Branson & Mehl ; Hass: 2538, 2539, Pl. 1, fig. Io. 1956 Polygnathus communis Branson & Mehl ; Bichoff & Ziegler : 156, Pl. 12, figs. 1-3. 1956 Polygnathus communis Branson & Mehl ; Hass : 24, 25, Pl. 2, figs. 3-5. BRITISH AVONIAN CONODONT FAUNAS 183 1957 Polygnathus communis Branson & Mehl ; Bischoff : 42, Pl. 2, figs. 23-27. 1957 Polygnathus communis Branson & Mehl; Ziegler in Fliigel & Ziegler: 46, Pl. 2, fig. 15. 1959 Polygnathus communis Branson & Mehl ; Hass: 390, Pl. 49, figs. 9-11, 13. 1959 Polygnathus communis Branson & Mehl; Helms: PI. 3, fig. 11. 1959 Polygnathus communis Branson & Mehl ; Voges: 288, Pl. 34, figs. 1-7. 1960 Polygnathus communis Branson & Mehl ; Ziegler: PI. 1, fig. 9. 1960 Polygnathus communis Branson & Mehl ; Dvorak & Freyer : 884-888, Pl. 1, figs. 15, 16. 1960 Polygnathus decorosa Stauffer ; Dvorak & Freyer : 882, Pl. 2, figs. 1-2. 1961 Polygnathus communis Branson & Mehl ; Beach : 49, Pl. 6, figs. 1-4. 1961 Polygnathus communis Branson & Mehl ; Scott & Collinson : 130, Pl. 1, figs. 6-10 Pl. 2, fig. 30. 1961 Polygnathus communis Branson & Mehl ; Freyer : 7o. 1962 Polygnathus pura Voges; Miiller : 1388, text-fig. 2a, b. 1964 Polygnathus communis communis Branson & Mehl; Rexroad & Scott: 33, Pl. 2, figs. 17, 18. 1964 Polygnathus communis Branson & Mehl; Higgins, Wagner-Gentis & Wagner : 225, Pl. 5, fig. 30. 1964 Polygnathus communis Branson & Mehl ; Budurov & Tschurner: PI. V, figs. 1a, b, Za, b, £2, 18: 1965 Polygnathus communis Branson & Mehl ; Spasov : 95, Pl. 2, figs. 15, 15a. 1965? Polygnathus communis Ethington : 581, Pl. 67, fig. 7. MATERIAL. 740 specimens : figured, X 346, X 347, X 348. Rance. North Crop KL 3-ZL 10, Avon Gorge K 3-C 9. Description. The platform varies in shape from ovate to lanceolate, but is unornamented except for a medial nodose carina. The platform edges tend to be upturned and thickened. The anterior blade varies in length but is commonly equal to the platform length, bearing from Io to 16 laterally compressed, fused denticles ; the oral outline of the blade is convex. In aboral view the cavity is fairly large, circular, and situated at the junction of the platform and the anterior blade. Insome specimens the cavity appears on the blade. The aboral surface of the unit posterior to the cavity tends to be concave. The cavity is extended as a tapering slit along the anterior blade, to a point just anterior to its mid point. A keel runs from the margin of the main cavity to the posterior tip of the platform ; its aboral surface may bear a fine groove. The aboral surface makes a sharp obtuse angle with the lateral faces of the outer platform margins, giving a chine-like aboral appearance to the unit. REMARKS. Carinate and bifurcate subspecies of Polygnathus communis known from America are not present in our fauna, but the species is very variable throughout the section. A single specimen (Pl. 12, 1a—c) is obviously close to individual speci- mens assigned to this species, but differs in the general form of the oral surface of the platform. The anterior lateral margins of the platform are strongly constricted and upturned, giving almost a Siphonodella-like appearance to the anterior portion. The posterior portion is wide, shallow and bluntly rounded posteriorly, the whole having the general appearance of a shallow spoon. There is no ornamentation and the carina continues as a series of distinct blunted nodes to the posterior end of the 184 BRITISH AVONIAN CONODONT FAUNAS platform, the most posterior node being the smallest of the six exposed on the broken specimen. Polygnathus bischoffi sp. nov. Plate 13, figs. 8a—11¢ 1957 Polygnathus inornata E. R. Branson ; Bischoff: 42, Pl. 2, figs. 17, 18, 20, 21. 1959 Polygnathus cf. flabella Branson & Mehl ; Voges (partim) : Pl. 34, fig. 11 only. 1964 Polygnathus inornata E. R. Branson ; Higgins : 225, fig. 4, Pl. V, fig. 29. DERIVATION OF NAME. After Dr. G. Bischoff. Diacnostis. Arrow-shaped platform ; widest in anterior half, tapering to pointed posterior. Unit usually slightly arched in lateral view. Platform ornamented by delicate ribs, confined to margin. Platform margin upturned in anterior half. Small basal cavity, circular in outline, with thickened lips, situated anteriorly. MATERIAL. 64 specimens : Holotype X 349, Paratypes X 350, X 351, Hypotype X 352 (all figured). TYPE LOCALITY AND HORIZON. South Wales Coalfield. Sample SCC, C Zone, Fall Bay, Gower. Rance. Avon Gorge C 11-C 24. Description. The platform is arrow-shaped, with a straight to slightly curved axis. In lateral view the unit is arched. The platform is widest anteriorly, and at Oral surface _ Platform Anterior blade POSTERIOR ANTERIOR LATERAL VIEW Outer side Ril Platform ' P Cavit Plattorm Corina fhe: a. Inner side Anterior blade ORAL VIEW ABORAL VIEW Fic. 37. Polygnathus sp. showing morphological terms used in the text. BRITISH AVONIAN CONODONT FAUNAS 185 mid-length it is only slightly narrower than at the anterior. The platform is two and a half times as long as wide and tapers to the pointed posterior. The margins of the platform are slightly upturned in the anterior and mid-thirds, and the oral surface is ornamented by a number of transverse ridges, which are more strongly developed at the margin. The margins of the platform are equal in height to the carina and on either side of the carina there is a trough, which is more strongly developed at the anterior. The trough opens tothe anterior. The anterior blade is of the same length as the platform and consists of 6 denticles, which are highest at mid-length. The carina consists of nodes fused for their entire length and extends a short distance beyond the posterior extremity of the platform. The basal cavity; situated in the anterior third of the aboral surface, is small and rounded in outline, with thick lips. In some specimens a groove extends posteriorly from the basal cavity to the posterior extremity of the unit. REMARKS. Compared with Polygnathus inornatus inornatus the platform of P. bischoffi is more elongate, broader in the anterior half and tapering uniformly in the posterior half. The platform also has more convex margins and is arched in lateral view. Polygnathus bischoffi has less strongly developed anterior troughs than Polygnathus inornatus inornatus, because the margins of the platform in the anterior third are not as strongly upturned. Polygnathus bischoffi is characteristic of the C Zone both in the Bristol area and in other parts of the South West Province. It makes its first appearance near the base of the Laminosa Dolomites. Bischoff obtained the specimens of Polygnathus tnornatus which he illustrated from the Cu II Siphonodella Subzone. _ ; P Lan 7 / f Gad ¢ = / _ i j / : = . — / J er ; t f Ber [ 4 ras sy sda ¢ ampouieteon zon = snzeyarey3qoa eyieiasjotopness — Se mapas — mereazeier mpoyrew — ty ode maarutenge = say eupowun = se (eXpiney) *1T=psq9)H oyavodyavetaud euypoyuyad | ty de eaypowren | wineorter “0 “72 wurpoqer9 | | ampind empoynedo enttogers moqnectog | enapdyandeaay> emaeuyzey minwaitea | ——_— | psy snzep>ey » sds enyarastodopnees —— 1 Sresopeu engitushtodopn zed > | stds g enpnecdyudeos | show fe 1 enpoysews sy cape cds emeatoneey se er 2709994 Ae mpoqeatoyiels voryaen maresoreay se puypowtyy arp Epa | ' | — ! | sy cde earpapey | sg *de mmpoyneato ! , o> mpouretoyneds | | ! 1 de eoppoyenyay | Sore | Z and Kk Zones of the North Crop, ZL 1-19, Z Zon eyeieayan mgiewer sia ayeuarep enpreetep sia ty cde 1 epeedyyders os ololk epeaeder (eyvectoeren) F119720957H 23 eeypouesy7 Kes Of species in the Samples IL 1-20, Ik Zone : ayaios}sodenur mpoyestoeds amaetyo expogietoyieds | Chart to show the ran, Sica ace j ] ] | ] moppotyime a 15 eoqnaétosomens | j ; = Toners f | j ———— 1 ragaesalkto : ens | emiraicoy mirmioar enneiitor TG, 50, elie coe TSS ce | pansen cen | Belersrpebert ert alpeprgarcioqrets | auyp03363 7H “19 (#1197 sa -l-t4f4-l--+-—---+4t4-- si Lep9275)K Jeron egies syeurasent so Sr¥epoU mynenie enpown econ snjrents snyrentd enpoure TN a eet : ° o 6 @ = a Pan Penne Gh = 2 << 5 ee taoddagdi bd da aa eae en eA ee 22 2 2 2 2 2 2 Ae #4 | 1 } , a ae eee : : > a, — a a — chp ra —_ 7 9 . } al . — iT a ae a a ieee Tne Qe * o§= ——--- - °4q 7 ¢ : { —_ 4 —— ——— om =h = ne > ; ® ea ab tie Te a a Lee + \ | a — NR. cee ee ettoponpurn ursaea vurpoyuoradng vpunago PT T9poapury, snow -d5 vtTopoopury Ysa snyawusopery anapunfuo> anporuoradony vsso2d09 vurpoyze=9 vaaed erropreqqtH vuraa9ureq wt T9pzuqqmn TAITTTE ETToPIPAgTH +ds curpoyDuoy war3u9pyq Eurpoysuoqea my exA03q vy T9poopuTH snavasya> snyaouenavy yApunoa wurpouok yy snxoawo> snyavulenang sysuoaeq> snyarwopery. vynantd wurpoy30z0 pAeAaTY VTToPospUTT aofyavqonsed wurpoysuoy qyeaqen snpornsuy smuaa vy tspoopuTy Sysuowurau0s vty 9poopuTA syaus8a9qr LTT opoopUTH vanae>95 vp Topoopury *ds vTTopoopurn snavausporsr= snyacuSopoty YoxreT2exed eurpoysuoy by3z0 erTop3eqaTH suvar3s vurporuorag exrenbarqne eurpotuo rz ensopou snpoy3eu9 snaaurqzq snpoyzeuy snaryardsaauv snporuoyzdosy qusyuany euypoysuoy qux0qso Purpoucs ry stnusa euypouod 1 Juosury 109 y4a2x8 enpoyaeuy Ps0q{0q wurpoysuoT J9puIy wurpoysez9, euvatsur33 puypoysuoy xeqdeoa aur ey TpospurH Paepin eLTapospuTH vavauposo7@ curpoquozadng vanov e11opreqqtH snanaeaed snpoyuosadooy, enaeyn=xks snpoysruy ppyuos 14278 snpoyacuy snqnayax snpoyuoyadooy snaapary> enyaeuienany sngeaaundozoy snpoyaeun mmsopousuoa snpoyseu9 sn3Panzzoe9 snpoyseuy Syeuotna euypouo#yy swmyaea snpoyuoyados enaest19p Burpoy: eaeaan> euypoyae%9 v>yasodyaavy wurpo uo yg anyqaed snyavusfoapdy xeqdays 34273 snpoyaeuy caou -dsqne 142278 enpoyacug anjngey39 snpoyapufoyauds Juurny20q anyavusor soy de vp tosaavyyuaey syaiouq CLT opaeqqTH eya91 wuspouod yy sysusuDIu0a snpoyuo radon, syauoina enpoyuoyadooy musqo35 snyanudoandy snpeTq snyaeudoaedy engraaod enuaeuoandy snuyao3 snyjapufoandy ‘1toqdaw> snpoyreutloyauds anjnay20 snpoyavuiloysnds yhaay8 yha278 snpoyrvuy syuxo9yun snyaoudenacy AysuOppoU snyreUudoa am yantdyq. snyavuitoa ny 3D 3p 21 == == = = == = = = =P == 5 == = === == = 3p 19 3p 18 3D 17 3D 16 3D 14/15 3D 13 3D 11 2 5 2 a CONODONT ZONE SAMPLE NUMBER SNUDXeE}21UD SNPOYOUD wv ds csnyyoub)ydoos $NJ2}}2|NS SN}0}sO> snpoyiouBbouiods S}uso2}unN snyyouBopsj> SisuesDp snyyOubopAjD SN}0}SO> $N}0\s0> snpoyioUBboyiodS D}09q OUIpoucbi4 SNIOWIO'N 42 snpoivojsdoaN DIN}SUD'S 42 SnpoyyoUBOY,oOdS $}UJO>}Soda\u0 snpoyioubouiods $Nj0gJ0q snpoj|uoJJdOON $U295249)}J2}0) OU/PO/UO}Jd SN}O{USP}4} SNPOYOUBOUOdS $nj0buoje snpoyyouBoyiods SHINQNS O}}SPOSPUu|H DyUe|ndso> DjjepospujH SN1ODJUSP|SsSOJ> SnpouioUBoy\ods smisngos'S 42 snpoyyouBoyiods SMi0g0] SN10qQo} snyiOUBAIog SnisA2 ‘S}2 SnpouoUboYiOdS $N104}SOJ SniOUJOU! snyyoUBAIOog sisuousemi6 snyuyouBbopfj> SJUNWWOD S}UNWWOD snYyi0UBAjod Suan|iUO> SNPpOoIUdIudOeN Qo1u0A snyyouBoOs10d SM\OUJOUI SNIDUJOU; SNnyiOUBAjOg 2U0Z Sn OdIjep snpoyyouy — $N1D1S02 snj0\s0> snpoyrouBbouiods 2U0Z $NO},UEPIGI S smisnqoy snysnqos's 12°S 2U0Z 010uUN0U! snyiouBAjog — DIlepououdis Samples FAR 4-7, K Zone ORZ 1-A5, Z Zone. Chart to show the ranges of species at Farlow. Fic. 53. snjeptdsnd snyjeusoqedy snusTeos snyqeusojedy snqttjed snyqeusojedy snjzeiqrty snyjeusojzedy shutues snyjeusojedy snpottneyo snyjvusoqedy TT Teqdues snpoyjeus0yjeds eBoTJsodtAseyT PuTpoTUOTIg TuOSUTT TOS TAJZI13 snpoyzeUD snjejnumks snpoyjeuy sn[NotAeu snyzeussnaeg sn[NjIos snpoyqeusoyjeds sNsopououow snpoyjeusy *aou ‘dsqns 1tA}113 snpoyjeuy xeTduts 143113 snpoyjeuy snjeesut{ tq snpoyjeuy sN[N{stio snpoyyeusoyjeds snjejoundomoy snpoyjeuy snjejnuuos snpoyjeug snsopou snpoy eu tAQ113 1A}QI13 snpoyjeug Yy10 Y26 Y29 Y32 W333) Y36 Y41 Y44 Y51 Y¥56 HAWES 3 HAWES 9 HAWES 17 HAWES 19 HAWES 21 HAWES 24 Chart to show the range of selected conodont species in the Yoredale succession. Apatognathid species are shown separately. Samples Hawes 24, Girvanella Bed : Fic. 54. Y 56 Hardraw Scar Hawes 17, Gayle Limestone : Y 50 Limestone IIIA : IVA : Y 33, Limestone IVB: Y 29, Middle Limestone : Hawes 21, Hawes Limestone : Y 10, Three Yard Limestone : Limestone : Y 36, Limestone Y 26, Five Yard Limestone : Y 44 Simonstone Limestone : UND 1, Underset Limestone. ayy i Potele & iets’ _ 5 eters Wee Serre: wtels ape * j Sheil wiry ‘pws ee eee nl 7 a i frary Ro Be! «e. S*64eaeem &6e iia- a rn we i — I t 5 ® 7 : = / Ss —— es a or — ee < « a _——— a ae ooo —_ —E———— —— -_ a { i | > — _ - NS _— ai ———— es = eo ene geene = — -— — — 4 a — ae a ~ a a fo wh moped Le 7 ee «4 a am esas = Bema ——_ ——— Ss) —— a sh py ———— ‘ — - — i} \) ————— ' a 7 _ —— - ——s _ a é - —_—s — . vurzsaeyru%es wurpouo8T] snaesi0d onyanuoacdy sysuoS19q7 PT TopoopUTH y019 wT TopoopuTH a98zaeparaed wurpoysuoy vawqusprq eurpoysuoteay; vanse vTT9pseqqTH Sopyoaeqy snpoopury vinavotTap eurpoys0z9 snap 9zz0do1 snpoopury xApunox eurpovo8ry ueaqsu13 vurpoysucy P20qtoq wuypoysuoT nna Cuo> vuxpoyuoyadoay snavausporsra snyzpusopoyy ersuozep snwaeuopery snusqeo5 snyoufoardy Samples Hosie, Hosie snportneys snyanudoardy enxoauo3 |enyjapudenacg snqn395 snpouavudonaeds snsopou mpoyanu snsopououos =npoyzeuy ‘sneance03 snpoyzeuy m3yaana 142338 snpoyavug Peyuos 76233 enpoyzeus P3r3uspos3 7 eurporuoradng v13v23u0> vypos9a0y Tue; Y9AIVTD PTT oIOIVTIuIOK eucd3a5 vuyporuorazg Hurlet, Hurlet Limestone expmnborqns vurporuoz3g vyn3eazT9p wuypoyaezo ayauqnSure snpoyuoradoay snanopavd enpozuoyadoay: enaeaqit anyapusoaedy nurs’ snyzeuoaedy snapanake snpoyzeuy snqna Aru snyqousnany quosuy1109 14373 enpoyzvuy v>¥asod TAN] Burpoyuosag antia2d snyavufoandy Brwanj wuypoyDu07 Chart to show the ranges of conodont species in the Fife succession. $8-15, Calciferous Sandstone Series PLT9Panaatt STUT PCT Pe tte tee bcd trees eet ten ne ausa201d209 e{1 92020] quHD} n rf H TAT euypouolly - i vyaa0 (-11) eLTopaqati = t won Pr T9paeqaty T ! 1 TePuyulesypoyanz9 ic M™MINIJD9 snpoyuotadooy ! i sy9uUa[Ny snpoyuoradaoy 4 4 u Sn{n32139 snpoyrwuSoyruds = rn o xapdats 143212 enpoyzvuy + n ! Vaay8 34227 enpourvun t i I syu09 yan enyaeustonney 7 + fe yantdyq snyaeuforsm, r | =) | | | oa < wacom < 883 5 55555 2 2 2 2228 gnzed = 2 2 (ove oy ipa) 1 ee ee eo Pag | = op Mii | dead, PP SEW) a § Spe & s ‘ , Dan a e7e7S09 (°H) PL Teprzeqqty sn}tiinj 143113 snpoyzeuy snxo9Au0d snyqeussnaeg sTsus{[n} snpotuotasdoay TASTI TW (°H) PT TeprzeqqTH sn[Nj19s snpoyreusoyjeds sn[noTAeu snyjzeussnae) sue}. eT duod eT Te1ejeT TuUsey ByOID PTT eposputy sinus} eT Tepoaputy ToyxARTO STL eaA7e] tusey TYSTUInNy ePUuTpOYDUOT BJPAIND PUTPOYIezZO *aou *ds eutpotuotig STAVT PUuTpoUos TT sn[njstao snpoyjeusoyjeds P[NIeITTep eutTpoyrezo xeTduts 143113 snpoy.eu9 stjenbaeqns eutpotuotig STIP[NSuts snpotuotizdosay PIIeARUOD eT T2a19},eT tusey STsuss1eqt Bl] epoeputy sninued *N *J2 snpotuotadoay Teputy euTpoyIe zo sn[njtos snpotuotidoay 143113 143113 snpoyjeuy snjeqnumAs snpoyzeuy PQeUeporAITM euTpotuotadng snutua3s snyjeusoqedy PsoOq{oq euTpoudUu0T BIL 103 BIL 102 BIL 101 BIL 100 VEX NGL NGL NGL NGL NGL NGL NGL NGL NGL NGL NGL 12 iU5t 10 NGL NGL 5 4 3 2 i GILM GILM GILM GILM GILM Chart to show the ranges of conodont species in the Midlothian succession. Samples GILM, “ Gilmerton Limestone ”’ : Fic. 56. VEX, NGL, North Greens Limestone : BIL, Bilston Burn Limestone. Lower Vexhim Limestone : stjenboeqns eutpotuotag P[NJEITIT ep euTpoysezo ee S09 (*Y) BT TepzeqqtH TyreToOeIed eutpoyouoT PBsOq[Oq eUuTpoYyouUOT *aou *dsqns snj[nj19s snpoyjeusoyjeds BJsnqol P[][e19}e] tusey snjeiqry snyjeusojedy snsopou snpoyjeu9g ‘gq ‘ds Jo VW ‘Aou usg sn}t1inj 143113 snpoyqeuy TepurTy euTpoyse zo sueTIePA snpotuotidoay sn[notTAeu snyjzeussnaeg epunj qo ePuTpoYyUOT POTISOdTASe]T eUTpoTUOTIg PUTI9IE[TUseM eUTPOUOsTT snpot[neyo snyjeusojedy suejtsuei}] eurpoyouoy JestaeToeied eurtpoyouoy STSUeppou snyjeUusoj sayy tTantdtq snyjeus0jsay snjounfuod snpotuotadosay TesTAeTO snjze[Notusey TYSTWUINZ eUuTpoYyouUoT snutyeos snyjeusojzedy snjeqnwds snpoyzeug snjeoi0d snyjeusojedy stie[nsuts snpotuotadoay snumes snyjeusojedy stutootun snyqeussnaeg TuOSsUTT TOD TA4}113 snpoyQeuUD sn[Njtos snpoujeusoyjeds stsueqTn} snpotuotidoay Tuioqso PuTpouos TT snq{tjed snyjeusojzedy eJeUepPTq EUTPOYIUOTeI AY snjejnuuos snpoyjeuy TApunoa eUuTpoOUOs TT suaqoeTduod eT [oe1eqe{ tuseEy BTAPAJUOD ETT o197e] Lusey ToyxAeTO el e197e] tuseyy TtoT [TW eT Leprzeqqry snjnoried snpotuotidooy sn—njt9s snpotuotadoay STAD] PUTPOUOS TT sn[Njstid snpoyzeusoyjeds snsopououow snpoyjeu9 xe Tduts 143113 snpoujeu9 TAQI13 149119 snpoyqeug snjeeut, iq snpoyjeug DUN 88 DUN 87 DUN 86 DUN 85 DUN 84 DUN 83 DUN 82 DUN 81 DUN 80 DUN 79 DUN 78 DUN 77 DUN 76 DUN 75 DUN 74 DUN 73 DUN 72 DUN 71 DUN 70 DUN 69 DUN 68 DUN 67 DUN 66 DUN 65 DUN 64 DUN 63 DUN 62 DUN 61 DUN 60 DUN 59 DUN 58 DUN 57 DUN 56 DUN 55 DUN 54 DUN 53 DUN 52 DUN 51 DUN 50 Samples Chart to show the ranges of conodont species in the Dunbar succession. FIG. 57. DUN 72-82. Skateraw Limestones : DUN DUN 87, 88, DUN 86, Dryburn Foot Limestone : DUN 50-71, Long Craig Upper Limestone : 84, 85, Chapel Point Limestone : Barnes East Limestone. ULINL. ULINL. ULINL ULINL ULINL. ULINL ULINL: LINL LINE LINE. 3 2 1 GO IN 3 Go IN 2 GO IN 1 GLEN GLEN GLEN, GLEN GLEN GLEN, GLEN GLEN, GLEN GLEN, GLEN GLEN, GLEN GLEN GLEN, GLEN GLE GLE GLEN ADOC ADOC boc Aboc Apoc. ADOC. ADOC. ADOC Aboc. ADOC ADOC Apoc apoc ADOC aboc ADOC. ADoc AoC boc Aboc BRAU BRAU BRAU BRAU BRAU BRAU BRAU BRAU BRAU BRAU 19 18 1 16 15 14 13 12 11 10 He RernHaweacd icornis Apatognathus coronus Cavusgnathus uni ag 9 a Z Gia G2baf2¢¢,52a2 .§ #2 Fe G2.392 233 a2 ef beeeee Seg e -3 ase s orn. e 2a 38 pee eb ee jet ss eegese testi geesee pe kiai leks AAPA SSS OR ee een aS Roe eek ease Pane nOh a aS Ue Breese ssssgess sess eees sess eset et32R8 2333 EEGGTES ZAR GES ES ESSERE SEES SB ESR RS EER EE Seu Sete eRe ete SEs ERE E SESE ES ERE R SRE REESE E38 SPPtSFESESERSLSLSIHSRBAASPZ SSS AZ ARBS BLASS HK S2EERB a _dsecencel ee Be eel ete a Peels... eee eee Sees eas 2 tos sole lele sas loc ce ase --4 Jose Eee eee =U SE ee Pa a T] yaar art to show the 3, 58 nges of conodont species in the Ayrshi here a general absence of conodonts in residues of ‘high ADOG and mples, but ranges of persistent specics are carried through th BRAU Broadstone Limestone; BRAU imestone ; GO IN 1-3 1-7 Upper Linn 10, ADOC 1-20 Doe! x Limestone : LIL Gnathodus nodosus Gnathedus comautatus Ligonodina contraria Hindeodella hibbardi BRITISH AVONIAN CONODONT FAUNAS 243 denticle anteriorly to the anterior arch beneath the anterior bar, and posteriorly to where the posterior bar is broken. REMARKS. This form is unlike any other described conodont genus. Gen. nov. B. sp. Plate 25, figs. 7a, b MATERIAL. 1 specimen : figured, X 410. RANGE. Farlow ORZ 1. DESCRIPTION. This specimen is one of problematical affinities ; its essential features are that it has a conspicuous, elongated, main denticle, which is subtriangular in cross-section, with a more or less sharp anterior edge. Its anterior aboral margin is very flat, but has a narrow slit extending for a minute distance up the median part of the face. It is recurved posteriorly, even though there is no posterior bar. Its base is very thick-lipped and is regularly expanded as a relatively wide and deep cavity. It appears that this anterior denticle is complete, though this is not certain. On the outer lateral face, there is an anterior aboral process which makes an angle of about go° with what would be the line of the posterior bar, and it is also depressed in a vertical plane. Its anterior face is very convex in anterior view, and its anterior distal end is straight-edged, with a sharp antero-aboral corner, but this is fractured in the specimen. Its oral surface bears 3 denticles, of which the two innermost are massive, with bluntly formed lateral edges and strongly convex anterior and posterior faces. The denticle at the distal end is conspicuously smaller than the other two, and the interior denticle, although very broad at the base, divides distally to give 2 separate denticles. There is a tendency for germ denticles to develop between the larger denticles. The posterior lateral face of the anterior aboral process is flat and the base is continuously excavated. RemaArRKS. The fact that this specimen appears essentially complete makes it impossible to assign it to any existing genus. It may, in fact, represent a new one, but it is possible that it is a broken specimen of Hindeodella corpulenta. VII. SUMMARY AND CONCLUSIONS (a) Scope of the present work During the last decade, studies in both Germany and the United States have demonstrated the potential value of conodonts in Carboniferous and Devonian strati- graphical correlation. The present study represents a comprehensive description of the conodont faunas of the British Lower Carboniferous, and a detailed analysis of their stratigraphical distribution. This has been used to erect a zonal scheme, by means of which a more precise correlation has been established between sections in each of the main British Carboniferous depositional provinces than any yet available on the basis of other faunal groups. Intercontinental correlations are also suggested. 244 BRITISH AVONIAN CONODONT FAUNAS (b) Previous research A critical review of previous research on Carboniferous conodont faunas is given, together with a review of the present status of Carboniferous stratigraphical correla- tion (p. 17). (c) Collecting localities Samples have been collected from each of five major depositional areas. This has provided an indication of the degree of variability of conodont faunas both within and between depositional basins. In all some 3% tons of limestone has been processed. Avon Gorge, Bristol Detailed sampling of this area has involved the digestion of some 189 ‘ major’ rock samples, most of them about ro lbs in weight. Every ro ft. of the section was sampled, and these samples were supplemented in critical parts of the succession by others taken at 5 ft. and 2 ft. intervals. The stratigraphy of the collecting areas is described in detail (p. 18). North Crop of the South Wales Coalfield A series of eleven localities in Brecknockshire and Monmouthshire was used to construct a composite Lower Carboniferous section, and small collections were made from Gower and Pembrokeshire. The middle part of the Avonian succession is generally not fossiliferous in this area, but the higher parts of the Dibunophyllum Zone have been used to complement the zonal scheme for the lower part of the section, established in the Avon Gorge. Shropshire The thin development of the Z and K Zones at Farlow and Oreton have yielded well-preserved faunas (p. 25). Yorkshire Sampling of the Yoredale succession in the type area has provided material for a reconnaissance survey of Yoredale conodont faunas. They show close similarities to those of the higher zones from the South Western Province. Scotland Extensive collections have been made from Dunbar, Roxburgh, Midlothian, Fife, Ayrshire and Argyll. All the major limestones in the succession were sampled, some at intervals of six inches, and most yielded well-preserved faunas. (d) Methods of study Most of the 25,000 specimens which form the basis of the study were extracted by digestion of limestone in 8 % acetic acid. Methods of preparation and photography are described. The abundance of conodonts in each sample has been recorded (Figs 59-92). BRITISH AVONIAN CONODONT FAUNAS 245 (e) Stratigraphic ranges The precise ranges of all conodont species recovered are shown by range charts (Figs. 49-58). The ranges of the more stratigraphically useful genera and species are described. Patrognathus gen. nov. is confined to the K Zone. Clydagnathus gen. nov. is found in the K and Lower Z Zones of the North Crop and Shropshire, but is rare in large faunas of the same age from the Avon Gorge. Szphonodella is very rare in the Avonian, being confined to the Upper K Zone (p. 32). Pseudopolygnathus extends from the basal K to the C; Zone. It is represented by numbers of short-lived species and is abundant in the Avon Gorge, but less common in the North Crop (p. 32). Gnathodus is a long-ranging Avonian genus, but individual species are valuable for correlation in the Z, C and D Zones (p. 34). Spathognathodus is equally long- ranging, but several short-lived species are valuable index fossils in various portions of the succession. Polygnathus ranges from the K to the top of the C; Zone, and is represented by a number of species. Mestognathus extends from the C; to the Deg Zone (p. 35), while Cavusgnathus is most characteristic of the Cz, S and D Zones. Taphrognathus is restricted to the Upper Sg Subzone (p. 35) in the south west, but occurs in the C Zone of Roxburghshire. Fourteen conodont assemblage zones are established (£) Geographic variation Our study shows several striking examples of what appear to be geographical differences in contemporaneous conodont faunas. These include representatives of the genera Szphonodella (p. 32), Pseudopolygnathus (p. 32), and Clydagnathus (p. 32) among others. These differences reflect variation not only between faunas separated by intercontinental distances, but also between faunas from the same general depositional basin (e.g. the Avon Gorge and the North Crop). The degree of such geographic variation is shown to be often greater than that generally admitted by most conodont workers, and is an important consideration in stratigraphic correlation. The absence of certain conodont genera and species from some areas may represent either the absence of one or more groups of conodont-bearing animals (conodontifers) of whatever taxonomic level, or the homoeomorphic replacement of certain conodonts within the same broad type of natural assemblage of the cono- dontifers. (g) Correlation within the British Avonian Avon Gorge—North Crop The broad equivalence of Vaughan’s coral—brachiopod zones as recognized in these two areas is supported by a comparison of the conodont faunas. The basal K strata of the North Crop are probably slightly younger than those of the Avon Gorge. The Upper K Zone of the Avon Gorge is equivalent to the uppermost K and basal Z Zones of the North Crop (p. 46). 246 BRITISH AVONIAN CONODONT FAUNAS ° 5 10 15 20 —— titi K20 ea U“f K19 wl Uy K 18-71 Wltsbéd: Hint Rt jpiagh te Iii MAS i | limi 4 @ iD | Ia sil “ ! } i NN Ld aw CT aH ey UH Wy Arathi Ah Hall ie H UW i ait i I | | \ an I Y TJ JM Z fo] 5 Abundance factor = Total no.of specimens _ Total weight of sample Total i in ki Fic. 59. Lithological section of the Cleistopova Zone in the Avon Gorge showing the abundance factor of conodonts in each sample, and the total weight of each sample —K17 were collected in the ri ide section of the 18-K 21 w dissolved in acetic acid. Samples Kr Avon Gorge (ST 556746). Samples K Gorge (ST 557745), see Text-fig. 2 BRITISH AVONIAN CONODONT FAUNAS 7 ° [THA § carat ae Hh \ HHA ait [ I WS Raat id \ | if TH HH HH WSS | ! rH WDWG@ in AVONIAN a ee 8 eet Ce eee eee is ae Rp eRe gl pepe apap ap dpaphp Ap l gpl Appear er ep arene ty APL Abarar er enU eG Cte URAC pee eee ec near EGG | [ PLT A Pd \ \\ i AA a I cir HH Led \ Z ZONE FLALALALAGR ut HH! if ph \ i iy pe iH iced KX c 4) te fe : cit sat x LH Hi Pi fh pape fata ists eebdedbs \ \N o rs rr a a s rr) LL Hay ¢ TAA 4 dj ice SS Abundancefactor = Total no.of specimens Total weight of sample Fic. 60. Lithological section of the Lower and Upper Zaphrentis Zone in the Avon Gorge showing the abundance factor of conodonts in each sample, and the total weight of each sample dissolved in acetic acid. Samples Z 1-Z ro were collected in Quarry 1 (ST 557745), Samples Z 11—Z 20 were collected in the Black Rock Quarry (ST 561747) and Samples Z 21-Z 33 were collected in Quarry 2 (ST 561747). Total weight of mple in kilograms 247 248 2 2 COIN mh C fo} 4 ta Abundance factor = BRITISH AVONIAN CONODONT FAUNAS 60 1 Total no of specimens Total weight of Total weight of sample sample in kilograms Fic. 61. Continuation of the lithological section of the Upper Zaphventis Zone (y Beds) in the Avon Gorge showing the abundance factor of conodonts in each sample dissolved in acetic acid. Samples Z 34—Z 38 were collected in Quarry 2 (ST 558745). BRITISH AVONIAN CONODONT FAUNAS 249 ‘ — Wa 108 =e Y plo eto Mata | =O eo oo Ho a ata Senos \ aie UL tities 7) ONE +] c g B Ae He OSBEEBB8) [ a WC qe s WY, Abundance factor= Lotal no.of specimens Total weight of Total weight of sample sample in kilograms Fic. 62. Lithological section of the Lower Caninia Zone in the Avon Gorge showing the abundance factor of conodonts in each sample dissolved in acetic acid. Samples C 1-C 11 were collected in the Railway Cutting (ST 559745) and Samples C 12-C 25 in Quarry 3 (ST 560744). on see _ ‘ L Ieas ae Ly — a a er es ee KATATA NA 80 ° 5 10 5 20 Abundance factor = Total no of specimens_ Total weight of sample Total weight of sample in kilograms Fic. 63. Lithological section of the Upper Caninia Zone in the Avon Gorge showing the abundance factor of conodonts in each sample dissolved in acetic acid. Samples were collected from the roadside exposure (ST 562746). ive} 0) | 4 I n Ha} > Vz ie) (e) Z (e) 7) e) Z Fy 59] i S Z > n EIB Y iam ie niaaca i ¢ s Fr; : rH gle = aga q gee SS % Ebel aerisscomeabacie i \ i TH nl \ Hs [5 BeSe5 Y an eae tosano G ho ] hae j amas Ze ‘ seSeses LO nh as telat ee tide a rene Lt so ¥ = s8 = = ae sé Abundance factor= Total no.of specimens otal weight of sample sample in kilograms Fic. 64. Lithological section of the Lower and Upper Seminula Zone in the Avon Gorge showing the abundance factor of conodonts in each sample, and the total weight of each sample dissolved in acetic acid. The samples were collected in the Great Quarry (ST 563740). 252 BRITISH AVONIAN CONODONT FAUNAS a V/ 7 WY, _ 100] - | w "Ee Zi <| a ole a 2|2 Co a va Z, Hore monk V4 25 a i a Ssaoeee (C}MOMEONEONS sa TOTOToT Z ° [Oo [olo]{4 ° 20 40 60 80 10 5 Abundance factor- Lotal no of specimens Total weight of Total weight of sample sample in kilograms Fic. 65. Continuation of the lithological section of the upper part of the Seminula Zone in the Avon Gorge showing the abundance factor of conodonts in each sample dissolved in acetic acid. Samples S 22-S 30 were collected from the Great Quarry (ST 563740) and Samples S 31-S 50 from the riverside exposure (ST 562737). BRITISH AVONIAN CONODONT FAUNAS 253 ELST S| AVONIAN | AAS A Lf i! HH Abundance factor - Total no.of specimens Total weight of Total weight of sample sample in kilograms Fic. 66. Continuation of the lithological section of the uppermost part of the Seminula Zone and Concretionary Bed in the Avon Gorge showing the abundance factor of cono- donts in each sample dissolved in acetic acid. Samples S 51-S 72 were collected from the riverside exposure (ST 562737). 254 ‘ 75 ‘ 50 / 25 Fic. 67. AV ONIA N ZaOuN ne: D BRITISH AVONIAN CONODONT FAUNAS 1H t rH a et et 1 —)}) be et ° 20 40 60 80 Abundance factor = [otal no of specimens Total weight of Total weight of sample sample in kilograms Lithological section of the Lower Dibunophylium Zone in the Avon Gorge showing the abundance factor of conodonts in each sample dissolved in acetic acid. Samples D 1-D 9g were collected from the roadside exposure (ST 564737). BRITISH AVONIAN CONODONT FAUNAS 255 ‘ 125 eR ORD ZONE LHL il D IH L H I wi Se 82269248 Ge Gs a Ba) oi 8 LN NYLON USL CoN LN bel_] rer@=ys= an paun| papas cere Ole ce lige UHH . Abundance factor = lotal no. of specimens Total weight of Total weight of sample sample in kilograms Fic. 68. Continuation of the lithological section of the Dibunophyllum Zone in the Avon Gorge showing the abundance factor of conodonts in each sample dissolved in acetic acid. Samples D to D 22 were collected from the roadside exposure (ST 564737). 256 BRITISH AVONIAN CONODONT FAUNAS Fa] PEL H z < AVONI 20 40 60 Abundance factor- Lota! no. of specimens Total weight of sample Total weight of sample in kilograms Fic. 69. Lithological section of the upper beds of the Dibunophyllum Zone in the Avon Gorge showing the abundance factor of conodonts in each sample dissolved in acetic acid. Samples D 23—D 27 were collected from south of Bridge Valley Road (ST 564736). BRITISH AVONIAN CONODONT FAUNAS 257 Z ZONE nN pe Zu dtl = xz n = ° 4! 4 Al I ' ie F110 414 dt | LAL, Pal \r~ é o OrUAo mp taDe0 e l lea dt Leo! bes! A LLM Yl Z Y : a WMA K ZONE =a AVONIAN J i Hy za i= ea ITOUONE \ sa c, 41°58 (oe) id a5 40 9 40 4lo-i(4 9.08 OL El ( é ay Blea Oa ot ge Total no. of specimens Total weight of sample undance factor = ‘ a Total weight of sample in kilograms. DEVONIA Fic. 70. Lithological section of the K Zone of the North Crop of the South Wales Coalfield showing the abundance factor of conodonts in each sample, and the total weight of limestone dissolved. For details of collecting localities see Fig. 7 and also p. 25. 258 BRITISH AVONIAN CONODONT FAUNAS | O syle) Te Z a eraraera a TST oT 6] O oie G G ie : : Cl i i \N S A A aa NJ te i E " \\ AN SH c A Hn au \N \ : a en an NWN Pr orb ore GY pr erh orn Y), eae YY) zia7vft TTT W)éJMéMJaadldédd ee eee ae WY, rea LLL O 10 20 30 40 50 60 70 £80 OO 5 10 15 Abundance factor = [otal no.of specimens Total weight of sample Total weight of sample in kilograms Fic. 71. Lithological section of the Z and Sg Zones of the North Crop of the South Wales Coalfield showing the abundance factor of conodonts in each sample, and the total weight of limestone dissolved. For details of collecting localities see Fig. 7 and also p. 25. BRITISH AVONIAN CONODONT FAUNAS 259 D3 oO Oo ax~iInN< o 3. i | U te] Hi ill cy 3, (Bo ae Oo [9) a< Oo fe} HR Hee U 25 AVONIAN = 2] 2]u2 COUD i slalats ie) 20 40 60 80 (e} 5 10) 15 Abundance factor= Lotal_ no. of specimens Total weight of sample Total weight of sample in kilograms Fic. 72. Lithological section of the Dez Subzone of the North Crop of the South Wales Coalfield showing the abundance factor of conodonts in each sample, and the total weight of limestone dissolved. For details of collecting localities see Fig. 7 and also p. 33. 260 BRITISH AVONIAN CONODONT FAUNAS Fic. 73. = u i Ul TO 198/K Ee TES falta UF ie niita aga I Le ! 4 H EE] ey si EL Abundance factor= lotalno.of specimens Total weight of sample Total weight of sample in kilograms. Lithological section of the D3 Subzone of the North Crop of the South Wales Coalfield showing the abundance factor of conodonts in each sample, and the total weight of limestone dissolved. For details of collecting localities see Fig. 7 and also p. 23. BRITISH AVONIAN CONODONT FAUNAS 261 78 4 ; (tw irs 4, ' , ees eu z < W _ z e Pomel = 645, |O|N 5 > alx 16/2! 251t COVERED SARC NEN '! [Fara [= 4 = X 15 ft COVERED Total no.of specimens Total weight of sample Total weight of sample in kilograms. Abundance factor= DEVONIAN FARLOVIAN Fic. 74. Lithological section of the Cleistopova Zone at Farlow, Shropshire (Map reference SO 642808), showing the abundance factor of conodonts in each sample and the weight of each sample dissolved. 262 BRITISH AVONIAN CONODONT FAUNAS Z ZONE a ox ———_—____— AVONIAN No. of specimens Total weight of Total weight of sample sample in kilograms Abundance = Fic. 75. Lithological section of the Zaphrentis Zone in Oreton Quarry, Shropshire, (SO 648806). o OL C0) —_————————— YOREDALE ° 20 ao 60 60 Abundance factor- Jotalno.of specimens Total weight of sample Total weight of sample in kilograms. Fic. 76. Composite lithological section through the Yoredale Group (Hawes Limestone to base of Simonstone Limestone) in the Gayle Beck—Hawes area (34/864883). BRITISH AVONIAN CONODONT FAUNAS 263 + — YOREDALE GROUP ——» f Abundance factor= Lotal no-of specimens _ Total weight of Total weight of sample sample in kilograms. Fic. 77. Composite lithological section through the Yoredale Group (base of Simonstone Limestone to the top of the Five Yard Limestone inclusive) in the Snaizeholme—Hawes area (34/815840). S. Ls.=Simonstone Limestone : F.Y. Ls.=Five Yard Limestone. ° 5 10 15 g GROUP Ww =) < (2) uw a oO > | COVERED ‘Abundance factor= Total no. of specimens Total weight of sample Total weight of sample in kilograms. Fic. 78. Composite lithological section through the Yoredale Group (top of the Five Yard Limestone to the top of the Underset Limestone inclusive) in the Snaizeholme— Hawes area (34/815840). TIT. Y. Ls.=Three Yard Limestone: U. Ls.=Underset Limestone. a Ht Hi th Le, Is z iil iv] Loe ©] (= ois z ee oe o>) oO |N 8/218 /S}o]> iil " 2 pil HHH Oo Cc [<3 Zz Zz o® (ep) i) ‘A TULL alatetatiitals o_ (= Zz [e)) Oo HARE UIP (< 2 oO N HI ls W z ie) | ol 77) W p3 a) x a UN) () 2 S=eea a =) oO § a 1o) oO z 1) =! ——__——————— LOWER LIMESTONE GROUP Fic. 79. Abundance ftactor= BRITISH AVONIAN CONODONT FAUNAS 40 60 80 Total no.of specimens Total weight of sample UY Yyy Y/ 105 15) 520 WMA WU Uy % WY (0) Wills Y 5 10 +5 20 Total weigpt of sample in kilograms. Lithological section of part of the Lower Limestone Group in the Dunbar area : the Long Craig Upper Limestone, showing the abundance factor for each sample and the weight of each sample dissolved. For localities see p. 30. 265 BRITISH AVONIAN CONODONT FAUNAS \\ eae 2 [este (epee fh rT, Iai apepegagegs ee He Pace eatatge detent ated gti 0 Fe DUNS DUN 79 Total weight of sample in kilograms, = Total no.of specimens Total weight of sample 40 Abundance factor nth es DUN 78 DUN 77 dNOYOD 3NOLSSW!I1 Y¥3MO71 _ = “ : 2 4 = showing the abundance Lithological section of part of the Lower Limestone Group in the Dunbar area : the Scateraw Lower Limestone to the Scateraw Upper Limestone, factor of each sample and the total weight of each sample dissolved. For localities see Fic. 80. Pp. 30. BRITISH AVONIAN CONODONT FAUNAS 266 40 60 80 Abundance factor = Lota! no. of specimens 20 aan | A nl cle RA i i HEE ER RE qh crit : ane 4 HHHR RR EER Sh: glide Hear Hv a EE dNOYS ANOLS3WIT Y3MO71 8 “2 on “& “O ~o Total weight of sample in kilograms. Total weight of sample Lithological section of part of the Lower Limestone Group in the Dunbar area : the Chapel Point Limestone to the Barness East Limestone Fic. 81. showing the abundance , factor of each sample and the weight of each sample dissolved. For localities see p. 30. BRITISH AVONIAN CONODONT FAUNAS 267 U 60 | Paper ST Ota ao U = A) 50 el G @ he fe oO 1} uw 40 ca || Salar Zz!10 7 OC | = 30|m/]un ne \ are ca) = Alas iis, 20 2 w/e 10. a = (@) a =! roy Abundance factor=Total no. of specimens’ Total weight of sample Total weight of sample in kilograms Fic. 82. Lithological succession of part of the Lower Limestone Group in Midlothian : the ‘“‘ Gilmerton’’ Limestone, showing the abundance factor of each sample and the weight of each sample dissolved. This limestone may not be the true Gilmerton Limestone (see p. 50). For localities see p. 30. 268 BRITISH AVONIAN CONODONT FAUNAS 4 | 70 | 3| 2 fe} «1 Ola w W ai Neale 20) wl] w =] w 316 a SE: 01 5 a ee U 10 | ‘ ° 40 60 80 Abundance factor =Lota! no of specimens Total weight of sample Total weight of sample in kilograms Fic. 83. Lithological section of part of the Lower Limestone Group in Midlothian : the North Greens Limestone, showing the abundance factor for each sample and the weight of each sample dissolved. For localities see p. 30. 269 BRITISH AVONIAN CONODONT FAUNAS 15 aT) aa eS pa a) IN or o4or|m n° mM Olan SNOLSASW!I7 NUN : i: NOLS118 SNOLS3WIT w83MO7 ~ 10 80 60 40 20 srl 9-6 a8 oe [o} ~ ” oe & oXc an Seo [o) ros es © w a ° 2 fo} be te a vu 3 3 3 E Ahunidance factor = Lota! no. of specimens the Fic. 84. Lithological section of part of the Lower Limestone Group in Midlothian : Bilston Burn Limestone, showing the abundance factor and total weight of sample dissolved for each sample. For localities see p. 30. BRITISH AVONIAN CONODONT FAUNAS nN | ° — —~+———._ CALCIFEROUS SANDSTONE MEASURES ———* ——] 4 — le i ° = od +—____ LOWER CARBONIIFEROUS ie) 20 40 60 80 O 5 10 15 Abundance factor Seon nose LSpechmens Total weight of sample Total weight of sample in kilograms, Fic. 85. Lithological succession of part of the Calciferous Sandstone Series of East Fife, showing the fossiliferous limestones in the lower part of the succession. Coast section from Hurlet Limestone near Coalfarm to Anstruther (NO 548027). Sample numbers refer to detailed section given by J. W. Kirkby in Geikie (1902), p. 77 ff. BRITISH AVONIAN CONODONT FAUNAS MIDOLE HOSIE LST. 20' ui aay uh OL HURLET LIMESTONE A ee i HHH > LOWER _ LIMESTONE GROUP (eo) Abundance tactor = [otal no.of specimens Total weight of sample Total weight of sample in kilograms. Fic. 86. Continuation of coast exposure of Fig. 85. Lithological section of part of the Lower Limestone Group in East Fife : Hurlet and Hosie Limestones, showing abundance factor for each sample and weight of each sample dissolved. 271 N “ te BRITISH AVONIAN CONODONT FAUNAS GROW SS I | 4h 4 A Al Al i SIMESTON Ey = Fr r ood 414i 4) 4 4 4 il ai aii i 4) 4! 4 i 4 4) di al al i 4 LIMESTONE LOWER Oc KR A Abundance factor - TavelinoroPSPeScume ass Total weight of Total weight of sample _ sample in kilograms Fic. 87. Lithological section of part of the Lower Limestone Group in North Ayrshire : the Dockra Limestone, showing abundance factor for each sample and weight of each sample dissolved. For localities see p. 30. A) W a > < 20] | a nz > y| 10. |WO} Oo retain Ool< yg aale= (re = '1OW)oO 4 ‘ 40 60 Abundance factor= Total no.of specimens uel ht of sample Total weight of sample in kilograms Fic. 88. Lithological section of part of the Calciferous Sandstone Series in North Ayrshire, showing the abundance factor of each sample and the total weight of each sample dissolved. For localities see p. 30. SERIES ————_——_— [: : 2 aS oh o CEMENTSTONE GROUP ——+——_— MAIN ALGAL ‘ Abundance factor = Total weight of sample Total no. of specimens in kilograms Total weight of sample Fic. 91. Lithological section of the Lower Algal Limestone “ Series ’’ of Harden Burn, Roxburghshire, (NY 517907) showing the abundance factor for each sample and the weight of each sample dissolved. 276 BRITISH AVONIAN CONODONT FAUNAS Mid-Avonian unconformity in some places in the North Crop, and the absence of conodonts in others, does not allow comparisons of the middle part of the succession, although the uppermost Z of the Avon Gorge is younger than that of the North Crop. The base of the Dg Subzone corresponds in both the Avon Gorge and the North Crop. Few Dz or Dg conodonts have been recovered from the Avon Gorge (Figs. 67-69). Shropshire The lowest K strata at Farlow appear to be younger than those of the Avon Gorge, or the North Crop. The Shropshire K Zone strata represent a very condensed deposit. The higher part of the K Zone at Farlow is equivalent to the Lower Z of the Avon Gorge. The Z Zone at Farlow represents the Spathognathodus costatus costatus— Gnathodus delicatus Zone. Yorkshire The lowermost Yoredale limestones (the Gayle and the Hawes) have yielded few conodonts. The overlying Hardraw Scar Limestone and Simonstone Limestone fall within the Gnathodus mononodosus Assemblage Zone, and the Middle and Five Yard Limestones within the Gnathodus girtyi collinsont Assemblage Zone. Scotland A correlation is suggested between the Fife, Midlothian, Ayrshire, Dunbar and Glengarnock successions, and between these and the South Western Province. The Scottish sections all fall within the Gnathodus mononodosus or Gnathodus girtyi collinsont Zones, except for the lowest part of the Ayrshire succession and the Lower Algal “ Series’ of Roxburghshire. Details of the correlations are given in Fig. 15. (h) Intercontinental correlation A critical review of North American and European Lower Carboniferous conodont faunas is given (p. 52), and the correlation of these with the British Avonian is summarized in Figs. 12, 16. The K Zone of the Avonian, represented by the two lowest conodont zones and by the lower part of the Spathognathodus cf. S. robustus— S. tridentatus Zone, is probably equivalent to the Lower Hannibal—Upper Chouteau succession of the Mississippi Valley (Cu I-Cu II «). This would imply a very con- siderable unconformity below the “‘ Sedalia Formation ”’ (Lower Cu II $-y) which is correlated with the Polygnathus lacinatus Zone of the Upper Zz Beds. An alternative correlation, based upon the first appearance of Gnathodus delicatus, would equate the Spathognathodus costatus costatus—Gnathodus delicatus Zone of the Middle Z Zone with the Upper Chouteau (Cu II «) (p. 56). The highest Z Zone is equivalent to the Fern Glen and lower part of the Burlington Formations (Middle Cu II 6-y). The C; Subzone of the Avonian is of Upper Cu II B—y—Lower Cu II 3 (Middle and Upper Burlington) age, and the CgS; and Seg Subzones of Upper Cu II 8 age. (Keokuk to Lower St. Louis). The D; Subzone is of Cu III « age, the Dz Subzone of Cu III «Cu III 8 age, and the D3 Subzone of Cu III B-y age. EEGEND* FOR VEIT ROLOGICAL CLASTIC SEDIMENTARY ROCKS ZS S C=, a | ES E = FS FIG. 92. Gravel Conglomeratic arkose Coarse-grained sandstone Conglomeratic sandstone Calcareous sandstone Slightly sandy formation Siltstone Clay Stratified clay Argillaceous formation Thin coal bed Fine clay Shale lenses Silt Carbonaceous shale OTHER SEDIMENTARY ROCKS AND STRUCTURES ] HS 5 4) i] A) Et Limestone Fossil-fragment limestone Detrital limestone Limestone breccia Oolitic limestone Pisolitic limestone Crystalline limestone Sucrose limestone Dolomite Dolomitic limestone Calcareous formation Argillaceous limestone Calcareous lenses Dolomitic lenses SECTIONS GENERAL As] el A) fel Sb A eM ON bel Lithified formation Covered Red beds 25% sand 75% clay Lateral transition Cherty formation Concretions Algae Corals Brachiopods Fossils in general Bryozoa Crinoids Composite legend for the lithological sections shown in the text. BRITISH AVONIAN CONODONT FAUNAS 277 (1) Systematic palaeontology The total fauna described includes some 25,000 identifiable specimens, referable to 167 species. These are described and illustrated, and their precise stratigraphical ranges recorded. Two new named genera, 40 new species and 13 new subspecies are recognized. (j) Detailed lithological sections and abundance figures are included for each part of the succession. Range charts are also provided. VIII ACKNOWLEDGMENTS We are deeply indebted to our colleagues in the Geology Department, University College of Swansea, for help and advice during the course of this study. Mr. T. R. Owen has given us the benefit of his extensive knowledge of the Avonian rocks of South Wales, and has been a particular help to us in planning our collecting in that area. Mr. Brian Simpson has assisted us with various aspects of the technical work involved in the study. We owe a particular debt of gratitude to Mrs. Shirley Osborn and Mr. Michael Reynolds, for their patient help in rock processing, to Miss Sonia Kostromin for her enormous secretarial help, to Mr. Stanley Osborn for his skilful photography, to Mrs. Greir Lewis and Mrs Beryl Fisher who have prepared the text-figures, to Miss Rhiannon Watkins for typing, and to Miss Veronica Arlen and Mr. H. A. H. McKee for their editorial help. We have been greatly helped by the generous advice of a large number of friends in various countries, who have willingly discussed problems of systematics and correlation with us, and have in some cases provided topotype material for com- parison. We particularly wish to thank Dr. Gunther Bischoff of Gewerkshaft Elwerath Erdolwerke, Hannover, Dr. Charles W. Collinson of the Illinois Geological Survey, Dr. Raphael Conil of the Catholic University of Louvain, Professor Brian F. Glenister of the University of Iowa, Professor F. Hodson of Southampton University, Dr. John Huddle of the U.S.G.S., Washington, Dr. Huw Jenkins of Sydney Univer- sity, Dr. Gilbert Klapper of Pan American Petroleum Corporation, Tulsa, Oklahoma, Dr. M. Lys of the Institut Francais du Pétrole, Dr. S. C. Matthews of the University of Bristol, Dr. Klaus-Dieter Meischner, of the University of Gottingen, Dr. D. Moore of Southampton University, Dr. Carl Rexroad of the Indiana Geological Survey, Dr. James W. Scatterday of the State University of New York at Geneseo, Dr. Trevor Walker of Long Beach College, California, Mr. R. B. Wilson of the I.G.S., Edinburgh, and Dr. Wilh Ziegler of the Geologisches Landesamt Nordrhein-West- falen. We are also grateful for the financial support which made this study possible. The Department of Scientific and Industrial Research, and its successor, the Science Research Council, made a grant to F. H. T. Rhodes, to support a programme of research, of which this study forms a major part. This grant provided support for E. C. Druce, and R. L. Austin received a D.S.I.R. Studentship. We are also grateful for the support in the form of accommodation, apparatus, materials and technical help provided by the University College of Swansea. 278 BRITISH AVONIAN CONODONT FAUNAS The completion of much of the present paper has also involved help from other sources which we wish to acknowledge. During 1965-66 F. H. T. Rhodes held a National Science Foundation Senior Visiting Scientist Fellowship at Ohio State University. The award of this Fellowship, and the warm hospitality provided by the Geology Department at Ohio State are acknowledged with deep gratitude, as is the typing assistance of Miss Emily Laws. R. L. Austin gratefully acknowledges the facilities and assistance provided at the University of Southampton during the past two years, and especially the con- tributions of Mrs. B. Gilkes and Mrs. A. Dunkley. The publication of the present paper owes much to the generous encouragement and help of Dr. H. W. Ball, Dr. W. T. Dean, Mr. E. F. Owen and Mr. H. G. Owen of the Palaeontology Department of the British Museum (Natural History). IX. REFERENCES ABDVSSELAMOGLY, S. 1963. Nouvelles observations stratigraphiques et palaeontology sur les terrains palaeozoiques affleurant a L’Est du Bosphore. Bull. Miner. Res. Explor. Inst., Ankara, No. 60. ARMSTRONG, W. G. & TarRLo, L. B. H. 1966. Amino-acid components in fossil calcified tissues. Nature, Lond., 210 : 481-482. Austin, R. L. & Bassett, M.G. 1967. j io f op Oe @¢ eure) wy at ha a 4 an edt a oe ortam @ Meee BOR ralig 400-96 . iy ) et el atgenn ly “oe begin eatidgrared dager a | oar Be “> ™ oo i? reer’ ¢ owe ome eee ee, on ee eee | Oo LIf ume (Poa heen, Bat : | > eclieeew?l wa.) Vout he) 2a 46 ’ ; ‘gat. etal}? Cia), tat ‘* Ti t oeediiande: oer, ©, 908 ope pe ve pele . > tet 2 OP Re <5 wheat : + b> Gn am ie) vorrei sy eee y Pers Gomme a tn T area se! va~. be _ $9 7 _ a ~~ ‘ _ = “TT Lee | ore i a. on 7 of ai Ae ~ - 1» 7 f e- i. : Z ns oa moa ty te - sil we ib ae ce ~ ae a. ee ee | Ag 's ™S Lh. Pe. PS ono he. mse is . i, wi Z es ey fo Piae,. (G4 ; oa» — ° _ 9 ge” -o* i _ a : -_ Lae > eee yen Geb oy oor) eae Ba 7 gues 1 a t 29) oh om erie e oe tan ie te, Oo bck iin oe é é aale > ie LES » 9 a oe L << Te ss oa 7 - = Des = mid eS : ed -_ -_ an a 4 a 7 4 T* NN = — Oe ag , PLATES BAM Er All specimens coated and magnified x 31.5 Fics. I, 2, 5,6. Spathognathodus plumulus plumulus sp. nov. 1a. Outer lateral view of holotype X 476. 1b. Oral view of holotype X 476. tc. Aboral view of holotype X 476. 2a. Outer lateral view of paratype X 379. 2b. Oral view of paratype X 379. 2c. Aboral view of paratype X 379. 5. Outer lateral view of paratype X 380, posterior portion missing. 6. Outer lateral view of juvenile paratype X 381, anterior aboral portion of blade missing. Fics. 3, 4. Spathognathodus plumulus nodosus subsp. nov. 3a. Outer lateral view of paratype X 383, posterior portion missing. 3b. Oral view of paratype X 383. 3c. Aboral view of paratype X 383. 4a. Outer lateral view of holotype X 382, posterior portion missing. 4b. Oral view of holotype X 382. 4c. Aboral view of holotype X 382. Fics. 7, 8. Spathognathodus plumulus shirleyae sp. et subsp. nov. 7a. Outer lateral view of paratype X 385, posterior portion missing. 7b. Oral view of paratype X 385. 8a. Outer lateral view of holotype X 384. 8b. Oral view of holotype X 384. 8c. Aboral view of holotype X 384. Fics. 9-13. Clydagnathus cavusformis gen. et sp. nov. g. Oral view of paratype X 72. 10. Oral view of paratype X 73. Ita. Outer lateral view of holotype X 75. 11b. Inner lateral view of holotype X 75. t11c. Oral view of holotype X 75. 11d. Aboral view of holotype X 75. 12a. Outer lateral view of paratype X 71. 12b. Inner lateral view of paratype X 71. 12c. Oral view of paratype X 71. 12d. Aboral view of para- type X 71. 13a. Outer lateral view of paratype X 74, posterior portion missing. 13b. Inner lateral view of paratype X 74. 13c. Oral view of paratype X 74. 13d. Aboral view of paratype X 74. Bull. By. Mus. nat. Hist. (Geol. Suppl.) 5 PLATE 1 PEATE 2 All specimens coated and magnified x 31.5 Fic. 1. Clydagnathus gilwernensis gen. et sp. nov. a. Oral view of holotype X 78. b. Outer lateral view of holotype X 78. c. Inner lateral view of holotype X 78. d. Aboral view of holotype X 78. Fics. 2, 3, 5. Clydagnathus unicornis gen. et sp. nov. 2a. Oral view of holotype X 79. 2b. Outer lateral view of holotype X 79. 2c. Inner lateral view of holotype X 79. 2d. Aboral view of holotype X 79. 3a. Oral view of paratype X 8o. 3b. Outer lateral view of paratype X 80. 3c. Inner lateral view of paratype X 80. 3d. Aboral view of paratype X 80. 5a. Oral view of paratype X 81. 5b. Inner lateral view of paratype X 81. Fic. 4. Clydagnathus gen. et sp. nov. A a. Oral view of specimen X 82. b. Outer lateral view of specimen X 82. c. Inner lateral view of specimen X 82. d. Aboral view of specimen X 82. Fics. 6, 7. Clydagnathus darensis gen. et sp. nov. 6a. Oral view of holotype X 77. 6b. Outer lateral view of holotype X 77. 6c. Inner lateral view of holotype X 77. 6d. Aboral view of holotype X 77. 7a. Oral view of paratype X 76. 7b. Outer lateral view of paratype X 76. 7c. Inner lateral view of paratype X 76. 7d. Aboral view of paratype X 76. Fics. 8-11. Patrognathus variabilis gen. et sp. nov. 8a. Oral view of paratype X 310. 8b. Lateral view of paratype X 310. ga. Oral view of paratype X 519. 9b. Aboral view of paratype X 519. 9c. Lateral view of paratype X 519. toa. Oral view of paratype X 309. t1ob. Aboral view of paratype X 309. toc, Lateral view of paratype X 309. 11a. Oral view of holotype X 311. 11b. Aboral view of holotype X 311. tic. Lateral view of holotype X 311. Fic. 12. Scaphignathus ? sp. B a. Oral view of specimen X 533. b. Inner lateral view of specimen X 533. c. Aboral view of specimen X 533. Fic. 13. Scaphignathus ? sp. A a. Oral view of specimen X 532. b. Inner lateral view of specimen X 532. c Aboral view of specimen X 532. Bull. By. Mus. nat. Hist. (Geol. Suppl.) 5 SPO.5 ‘tasare 4 LAs Aa 4 . _ AY ern Ot 1808 ye i ae ee ak dem BE = Ra! 2 ~— ee 8a 8b ‘ +e ee _ PLATE 3 All specimens coated and magnified x 31.5 Fics. 1-4. Spathognathodus crassidentatus (Branson & Mehl) ta. Inner lateral view of specimen X 463. 1b. Aboral view of specimen X 463. 2a. Inner lateral view of specimen X 460. 2b. Oral view of specimen X 460. 3a. Inner lateral view of specimen X 461. 3b. Aboral view of specimen X 461. 4a. Inner lateral view of specimen X 462. 4b. Aboral view of specimen X 462. Fics. 5-8. Spathognathodus anteposicornis Scott 5a. Inner lateral view of specimen X 540. 5b. Oral view of specimen X 540. 6a. Inner lateral view of specimen X 543. 6b. Aboral view of specimen X 543. 7a. Inner lateral view of specimen X 541. 7b. Aboral view of specimen X 541. 8a. Inner lateral view of specimen X 542. 8b. Oral view of specimen X 542. Fics. 9-12. Spathognathodus tridentatus (E. R. Branson) ga. Inner lateral view of specimen X 395. 9b. Oral view of specimen X 395. 9c. Aboral view of specimen X 395. 10a. Inner lateral view of specimen X 396. 1o0b. Oral view of specimen X 396. toc. Aboral view of specimen X 396. 11a. Inner lateral view of specimen X 397. 1b. Oral view of specimen X 397. 11c. Aboral view of specimen X 397. 12a. Inner lateral view of specimen X 394. 12b. Oral view of specimen X 394. 12c. Aboral view of specimen X 394. Fics. 13-15. Spathognathodus costatus costatus (E. R. Branson) 13a. Inner lateral view of specimen X 456. 13b. Aboral view of specimen X 456. 14a. Inner lateral view of specimen X 166. 14b. Oral view of specimen X 166. 15a. Inner lateral view of specimen X 455. 15b. Oral view of specimen X 455. Fics. 16-18. Spathognathodus costatus sulciferus (Branson & Mehl) 16a. Inner lateral view of specimen X 459. 16b. Oral view of specimen X 459. 17a. Inner lateral view of specimen X 458. 17b. Aboral view of specimen X 458. 17c. Oral view of specimen X 458. 18a. Aboral view of specimen X 457. 18b. Inner lateral view of specimen X 457. 18c. Oral view of specimen X 457. Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5 PLATE 3 PLATE 4 All specimens coated and magnified x 31.5 Fics. 1-4. Spathognathodus bischoffi sp. nov. 1a. Oral view of paratype X 399. 1b. Aboral view of paratype X 399. Ic. Outer lateral view of paratype X 399. Id. Inner lateral view of paratype X 399. 2a. Oral view of paratype X 400. 2b. Aboral view of paratype X 400. 2c. Outer lateral view of paratype X 400. 2d. Inner lateral view of paratype X 400. 3a. Oral view of paratype X 398. 3b. Aboral view of paratype X 398. 3c. Outer lateral view of paratype X 398. 3d. Inner lateral view of paratype X 398. 4a. Oral view of holotype X gor. 4b. Aboral view of holotype X 4or. 4c. Outer lateral view of holotype X 401. 4d. Inner lateral view of holotype X 4or. Fics. 5-8. Spathognathodus ziegleri sp. nov. 5a. Oral view of paratype X 437. 5b. Aboral view of paratype X 437. 5c. Outer lateral view of paratype X 437. 5d. Inner lateral view of paratype X 437. 6a. Oral view of paratype X 402. 6b. Aboral view of paratype X 402. 6c. Outer lateral view of paratype X 402. 6d. Inner lateral view of paratype X 402. 7a. Oral view of paratype X 404. 7b. Aboral view of paratype X 404. 7c. Outer lateral view of paratype X 404. 7d. Inner lateral view of paratype X 404. 8a. Oral view of holotype X 403. 8b. Aboral view of holotype X 403. 8c. Outer lateral view of holotype X 403. 8d. Inner lateral view of holotype X 403. Fics. 9-11. Spathognathodus pulcher Branson & Mehl — ga. Oral view of specimen X 386. gb. Aboral view of specimen X 386. 9c. Lateral view of specimen X 386. toa. Oral view of specimen X 513. 1o0b. Aboral view of specimen X 513. 1oc. Lateral view of specimen X 513. toc. Lateral view of specimen X 513. tI1a. Oral view of specimen X 512. 11b. Aboral view of specimen X 512. 11c. Lateral view of specimen X 512. Fic. 12. Spathognathodus sp. A a. Oral view of specimen X 405. b. Aboral view of specimen X 405. c. Lateral view of specimen X 405. Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5 Ic oaeehs Set ‘Id PLATE 5 All specimens coated and magnified x 31.5 Fics. I, 3, 5-8. Pseudopolygnathus vogesi sp. nov. ta. Aboral view of holotype X 155. 1b. Oral view of holotype X 155. 1c. Lateral view of holotype X 155. 3a. Aboral view of paratype X 504. 3b. Oral view of paratype X 504. 3c. Lateral view of paratype X 504. 5a. Oral view of paratype X 507. 5b. Aboral view of paratype X 507. 5c. Lateral view of paratype X 507. 6a. Oral view of paratype X 505. transitional to Ps. expansus. 6b. Aboral view of paratype X 505. 6c. Lateral view of paratype X 505. 7a. Aboral view of paratype X 501. 7b. Oral view of paratype X 501. 8a. Aboral view of paratype X 506. 8b. Oral view of paratype X 506. Fics. 2, 4. Pseudopolygnathus expansus sp. nov. 2a. Aboral view of paratype X 482. 2b. Oral view of paratype X 482. 2c. Lateral view of paratype X 482. 4a. Oral view of holotype X 483. 4b. Aboral view of holotype X 483. 4c. Lateral view of holotype X 483. Fics. 9-13. Pseudopolygnathus dentilineatus E. R. Branson ga. Aboral view of juvenile specimen X 478. 9b. Oral view of juvenile specimen X 478. gc. Lateral view of juvenile specimen X 478. 10a. Aboral view of juvenile specimen X 477. 1ob. Oral view of juvenile specimen X 477. toc. Lateral view of juvenile specimen X 477. 11a. Oral view of specimen transitional from Spathognathodus X 479. 11b. Aboral view of specimen transitional from Spathognathodus X 479. 11c. Lateral view of specimen transitional from Spathognathodus X 479. 12a. Aboral view of specimen X 480. 12b. Oral view of specimen X 480. 12c. Lateral view of specimen X 480. 13a. Aboral view of adult specimen X 481. 13b. Oral view of adult specimen X 481. 13c. Lateral view of adult specimen X 481. Fics. 14-16. Pseudopolygnathus multistriatus Mehl & Thomas 14a. Oral view of specimen X 486. 14b. Aboral view of specimen X 486. 14c. Lateral view of specimen X 486. 15a. Aboral view of specimen X 487. 15b. Oral view of specimen X 487. 15c. Lateral view of specimen X 487. 16a. Oral view of specimen X 485. 16b. Aboral view of specimen X 485. 16c. Lateral view of specimen X 485. Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5 PLATE 5 PLATE 6 All specimens coated and magnified x 31.5 Fic. 1. Pseudopolygnathus cf. fusiformis Branson & Mehl a. Aboral view of specimen X 552. b. Oral view of specimen X 552. Fic. 2. Pseudopolygnathus multistriatus Mehl & Thomas a. Oral view of specimen X 484. b. Aboral view of specimen X 484. c. Lateral view of specimen X 484. Fic. 3. Pseudopolygnathus sp. A. a. Oral view of specimen X 515. b. Aboral view of specimen X 515. c. Lateral view of specimen X 515. FIGs. 4, 5, 7, 10-12. Pseudopolygnathus primus Branson & Mehl 4a. Aboral view of specimen X 546. 4b. Oral view of specimen X 546. 4c. Lateral view of specimen X 546. 5a. Aboral view of specimen X 497. 5b. Oral view of specimen X 497. 7a. Aboral view of specimen X 499. 7b. Oral view of specimen X 499. 7c. Lateral view of specimen X 499. 10a. Aboral view of specimen X 500. tob. Oral view of specimen X 500. toc. Lateral view of specimen X 500. 11a. Aboral view of specimen X 549. I1b. Oral view of specimen X 549. t11c. Lateral view of specimen X 549. 12a. Aboral view of specimen X 498. 12b. Oral view of specimen X 498. t12c. Lateral view of specimen X 498. Fic. 6. Pseudopolygnathus postinodosus sp. nov. a. Aboral view of holotype X 496. b. Oral view of holotype X 496. c. Lateral view of holotype X 496. Fic. 8. Pseudopolygnathus dentilineatus E. R. Branson a. Aboral view of specimen X 438. b. Oral view of specimen X 438. c. Lateral view of specimen X 438. Fic. 9. Spathognathodus sp. nov. a. Oral view of specimen X 518. b. Aboral view of specimen X 518. c. Lateral view of specimen X 518. Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5 PLATE 6 PLATE 7 All specimens coated and mangified X 31.5 Figs. 1-5. Spathognathodus elongatus (Branson & Mehl) 1a. Lateral view of specimen X 472. 1b. Oral view of specimen X 472. 2. Lateral view of specimen X 474. 3. Aboral view of specimen X 472. 4a. Lateral view of specimen X 473. 4b. Aboral view of specimen X 473. 5a. Lateral view of specimen X 475. 5b. Aboral view of specimen X 475. Fics. 6,7. Spathognathodus cf. robustus (Branson & Mehl) 6a. Lateral view of specimen X 388. 6b. Oral view of specimen X 388. 6c. Aboral view of specimen X 388. 7a. Lateral view of specimen X 387. 7b. Oral view of specimen X 387. 7c. Aboral view of specimen X 387. Fic. 8. Spathognathodus sp. B a. Lateral view of specimen X 406. b. Oral view of specimen X 406. c. Aboral view of specimen X 406. Fics. 9-11. Spathognathodus coaptus (Branson & Mehl) ga. Lateral view of specimen X 454. 9b. Aboral view of specimen X 454. 9c. Oral view of specimen X 454. Ioa. Lateral view of specimen X 453. t1ob. Aboral view of specimen X 453. toc. Oral view of specimen X 453. Ita. Lateral view of specimen X 436. 11b. Aboral view of specimen X 436. t11c. Oral view of specimen X 436. Fics. 12-14. Spathognathodus cf. cyrius (Cooper) 12a. Lateral view of specimen X 471. 12b. Oral view of specimen X 471. 12c. Aboral view of specimen X 471. 13a. Lateral view of specimen X 470. 13b. Oral view of specimen X 470. 13c. Aboral view of specimen X 470. 14a. Lateral view of specimen X 469. 14b. Oral view of specimen X 469. 14c. Aboral view of specimen X 469. Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5 PLATE 7 PLATE 8 All specimens coated and magnified x 31.5 Fics. 1-4. Spathognathodus cf. campbelli Rexroad 1a. Lateral view of specimen X 451. 1b. Aboral view of specimen X 451. 1c. Oral view of specimen X 451. 2a. Lateral view of specimen X 435. 2b. Aboral view of specimen X 435. 2c. Oral view of specimen X 435. 3a. Lateral view of specimen X 452. 3b. Oral view of specimen X 452. 3c. Aboral view of specimen X 452. 4a. Lateral view of specimen X 450. 4b. Oral view of specimen X 450. 4c. Aboral view of specimen X 450. Fic. 5. Gnathodus simplicatus sp. nov. a. Lateral view of paratype X 88. b. Oral view of paratype X 88. c. Aboral view of paratype X 88. Fic. 6. Gnathodus cuneiformis Mehl and Thomas a. Lateral view of specimen X98. b. Oral view of specimen X98. c. Aboral view of specimen X 98. Fics. 7, 8, 12, 13. Spathognathodus cf. cristulus Youngquist & Miller 7a. Lateral view of specimen X 554. 7b. Oral view of specimen X 554. 7c. Aboral view of specimen X 554. 8a. Lateral view of specimen X 555. 8b. Oral view of specimen X 555. 8c. Aboral view of specimen X 555. I2a. Lateral view of specimen X 556. 12b. Oral view of specimen X 556. 31a. Lateral view of specimen X 557. 13b. Oral view of specimen X 557. Fics. 9-11. Spathognathodus scitulus (Hinde) ga. Lateral view of specimen X 391. 9b. Lateral view of specimen X 391. 9c. Oral view of specimen X 391. 9d. Aboral view of specimen X 391. tIoa. Lateral view of specimen X 392. 1ob. Lateral view of specimen X 392. toc. Oral view of specimen X 392. tod. Aboral view of specimen X 392. Ita. Lateral view of specimen X 393. 11b. Lateral view of specimen X 393. tic. Oral view of specimen X 393. 11d. Aboral view of specimen X 393. Fics. 14-18. Spathognathodus cristulus Youngquist & Miller 14a. Lateral view of specimen X 466. 14b. Lateral view of specimen X 466. 15a. Lateral view of specimen X 467. 15b. Lateral view of specimen X 467. 15c. Oral view of specimen X 467. 15d. Aboral view of specimen X 467. 16a. Lateral view of specimen X 468. 16b. Lateral view of specimen X 468. 16c. Oral view of specimen X 468. 16d. Aboral view of specimen X 468. 17a. Lateral view of specimen X 464. 17b.Lateral view of specimen X 464. 17c. Oral view of specimen X 464. 17d. Aboral view of specimen X 464. 18a. Lateral view of specimen X 465. 18b. Lateral view of specimen X 465. 18c. Oral view of specimen X 465. 18d. Aboral view of specimen X 465. Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5 PLATE 8 2a 18c PLATE 9 All specimens coated and magnified x 31.5 Fics. 1-4. Pseudopolygnathus nodomarginatus (E. R. Branson) 1a. Oral view of specimen X 491. 1b. Aboral view of specimen X 491. Ic. Lateral view of specimen X 491. 2a. Oral view of specimen X 489. 2b. Aboral view of specimen X 489. 3c. Lateral view of specimen X 489. 3a. Oral view of specimen X 490. 3b. Aboral view of specimen X 490. 3c. Lateral view of specimen X 490. 4a. Oral view of specimen X 488. 4b. Aboral view of specimen X 488. 4c. Lateral view of specimen X 488. Fics. 5-8. Polygnathus lobatus lobatus Branson & Mehl 5a. Oral view of specimen X 378. 5b. Aboral view of specimen X 378. 5c. Lateral view of specimen X 378. 6a. Oral view of specimen X 376. 6b. Aboral view of specimen X 376. 6c. Lateral view of specimen X 376. 7a. Oral view of specimen X 377. 7b. Aboral view of specimen X 377. 7c. Lateral view of specimen X 377. 8a. Oral view of specimen X 440. 8b. Aboral view of specimen X 440. 8c. Lateral view of specimen X 440. Fic. 9. Polygnathus lobatus inflexus subsp. nov. a. Oral view of holotype X 375. b. Aboral view of holotype X 375. c. Lateral view of holotype X 375. Fic. Io. Cavusgnathus ? sp. nov. A. a. Oral view of specimen X 70. b. Aboral view of specimen X 70. c. Inner lateral view of specimen X 70. d. Outer lateral view of specimen X 70. eR ‘S866 Aplin 08 “ Saray § -w ( ios =} WN a ie} o oF Ss w i S = a SS 1 isa) S = Q PLATE to All specimens coated and magnified x 31.5 Fics. 1-3. Polygnathus inornatus vexatus sub. sp. nov. ta. Oral view of holotype X 358. 1b. Aboral view of holotype X 358. 1c. Lateral view of holotype X 358. 2a. Aboral view of paratype X 359. 2b. Oral view of paratype X 359. 2c. Lateral view of paratype X 359. 3a. Oral view of paratype X 551. 3b. Aboral view of paratype X 551. 3c. Lateral view of paratype X 551. Fics. 4-6. Polygnathus inornatus inornatus Branson & Mehl 4a. Aboral view of specimen X 353. 4b. Oral view of specimen X 353. 4c. Lateral view of specimen X 353. 5a. Aboral view of specimen X 355. 5b. Oral view of specimen X 355. 5c. Lateral view of specimen X 355. 6a. Oral view of specimen X 354. 6b. Aboral view of specimen X 354. 6c. Lateral view of specimen X 354. Fics. 7-9. Polygnathus inornatus rostratus subsp. nov. 7a. Aboral view of holotype X 530. 7b. Oral view of holotype X 530. 7c. Lateral view of holotype X 530. 8a. Aboral view of paratype X 357. 8b. Oral view of paratype X 357. ga. Aboral view of paratype X 356. 9b. Oral view of paratype X 356. 9c. Lateral view of paratype X 356. Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5 PLATE 10 PLATE 11 All specimens coated and magnified x 31.5 Fics. 1-4. Polygnathus lacinatus asymmetricus subsp. nov. ta. Aboral view of paratype X 360. 1b. Oral view of paratype X 360. tc. Lateral view of paratype X 360. 2a. Aboral view of paratype X 363. 2b. Oral view of paratype X 363. 2c. Lateral view of paratype X 363. 3a. Aboral view of holotype X 361. 3b. Oral view of holotype X 361. 3c. Lateral view of holotype X 361. 4a. Aboral view of paratype X 362. 4b. Oral view of paratype X 362. 4c. Lateral view of paratype X 362. Fics. 5-7, 11. Polygnathus lacinatus prelobatus subsp. nov. 5a. Oral view of paratype X 372. 5b. Aboral view of paratype X 372. 6a. Oral view of paratype X 374. 6b. Aboral view of paratype X 374. 7a. Oral view of paratype X 373. 7b. Lateral view of paratype X 373. I1a. Oral view of holotype X 371. 11b. Aboral view of holotype X 371. 11c. Lateral view of holotype X 371. Fics. 8-10. Polygnathus lacinatus lacinatus Huddle 8a. Oral view of specimen X 370. 8b. Lateral view of specimen X 370. 9a. Oral view of specimen X 369. 9b. Aboral view of specimen X 369. 9c. Lateral view of specimen X 369. toa. Aboral view of specimen X 368. t1ob. Oral view of specimen X 368. toc. Lateral view of specimen X 368. Fics. 12-15. Polygnathus lacinatus circaperipherus subsp. nov. 12a. Aboral view of paratype X 367. 12b. Oral view of paratype X 367. 12c. Lateral view of paratype X 367. 13a. Aboral view of paratype X 365. 13b. Oral view of paratype X 365. 13c. Lateral view of paratype X 365. 14a. Aboral view of holotype X 364. 14b. Oral view of: holotype X 364. 14c. Lateral view of holotype X 364. 15a. Oral view of paratype X 366. 15b. Aboral view of paratype X 366. 15c. Lateral view of paratype X 366. fx) a QD 3 MAR 1969 Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5 PLATE 31 j ‘ hut i) +a A "ee , é re as i ) 4 , . oe AAs 4, Pedy fy, > 1 hey é Th) ne ; nal | a i a ‘ew bal ly j oh! ra aon me sl , are I - ar ee Ane ey ayia | , s if { , ! if We My a i "y ; a) ae Ml | ; ” | | - wy ; vif nh i i ‘ oO 1 ON x 4 : ; " th a is {f il = 7 7 ° 7 \ — | ; ~ — | | | | " 4 \ An a | | - ij { ~ 3 | | | | = & ~ : F i \ f ~~. | a | ~ a ‘ Vc oe x 5 My oe | : — i . ‘ wy L ~ x: ‘ is } wie is a nd ‘ i ‘ i} f @ 1 Hh Retes, eh bl plgaete etree are aT: vd eied Spe et yh ewe yor, a plea stglared ei