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Z CO Z CO Z 00 Z ^ E 2 ZTOO^SX E ^ E < X CO o Z _ ^ _ r _ > ' 2 > ' S N' > ^ , 1-103. and kremp, g. 1954. Die Gattungen der palaozoischen Sporae dispersae und ihre Stratigraphic. Geol. Jb. 69, 111-84. 1955. Die Sporae dispersae des Ruhrkarbons, ihre Morphographie und Stratigraphie mit Ausblicken auf Arten anderer Gebiete und Zeitabschnitte: Teil I. Palaeontographica, 98 B, 1-136. 1956. Idem, Teil II. Ibid. 99, 85-191. schopf, J. m., wilson, l. r., and bentall, r. 1944. An annotated Synopsis of Palaeozoic fossil spores and the definition of generic groups. Rep. Invest. III. St. Geol. Surv., 91, 72 pp. sen, j. 1964. The megaspores of the Ayrshire coalfield and their stratigraphic value. Micropaleon- tology, 10, 97-104. smith, d. l. 1962. Three fructifications from the Scottish Lower Carboniferous. Palaeontology, 5, 225-37. smith, a. h. v. and butterworth, m. a. 1967. Miospores in the coal seams of the Carboniferous of Great Britain. Spec. Paper Palaeont. 1. spinner, e. 1965. Westphalian D megaspores from the Forest of Dean Coalfield, England. Palaeontology, 8, 82-106. 24 PALAEONTOLOGY, VOLUME 10 STAPUN, f. l. 1960. Upper Mississippian plant spores from the Golata formation, Alberta, Canada. Palaeontographica, 107 B, 1-40. streel, 1964. Une association de spores du Givetien inferieur de la Vesdre a Goe (Belgique). Ann. Soc. geol. de Belgique , 87, 1-30. Sullivan, h. J. 1964m Miospores from the Lower Limestone Shales (Tournaisian) of the Forest of Dean Basin, Gloucestershire. C.R. 5e Congr. Av. Etud. Strat. curb. Paris, 3, 1249-59. 19646. Miospores from the Drybrook Sandstone and associated measures in the Forest of Dean Basin, Gloucestershire. Palaeontology, 7, 351-92. winslow, m. r. 1959. Upper Mississippian and Pennsylvanian megaspores and other plant micro- fossils from Illinois. Bull. III. St. geol. Surv. 86, 102 pp. ■ 1962. Plant Spores and Other Microfossils from Upper Devonian and Lower Mississippian Rocks of Ohio. Prof. Pap. U.S. geol. Surv. 364, 93 pp. zerndt, j. 1934. Les Megaspores du bassin houiller polonais, 1. Acad. Pol. Sci. Lett. Trav. Geol. 1, 1-55. 1937. Idem, 2. Ibid. 3, 1-78. Manuscript received 3 November 1965 MAVIS A. BUTTERWORTH, University of Aston Gosta Green, Birmingham 4 EDWIN SPINNER Department of Geology, University of Sheffield, Mappin Street, Sheffield 1 THE INTERPRETATION OF SIZE-FREQUENCY DISTRIBUTIONS IN MOLLUSCAN DEATH ASSEMBLAGES by A. HALLAM Abstract. It has been widely assumed that water currents play a major role in determining the shape of the size-frequency distributions of molluscan and brachiopod shells in death assemblages, by the selective removal of small-size grades. To test this assumption, the commonest bivalve and gastropod species in two transported death assemblages, one fossil and one forming at present, have been subjected to size-frequency analysis. The interaction of varying growth and mortality rates among living bivalves is discussed and the results of experi- mental work on shell fragmentation presented. It is concluded that the size-frequency distributions of the death assemblages under consideration primarily reflect growth and mortality rates, modified somewhat by the selec- tive destruction of smaller shells. The invocation of size sorting appears to be unnecessary, and this postulated process has still to be demonstrated as a significant factor in controlling the shape of size-frequency distribu- tions. A recent palaeoecological paper by Fagerstrom (1964) contains the following state- ment (p. 1202): ‘Large areas of the sea floor are swept by relatively weak currents of low competence. In these areas the small empty shells of the uncemented benthonic and pelagic species are removed by currents; the residue consists mostly of large shells which, upon burial, become residual fossil communities. The effect of this selective removal of larger numbers of small, empty shells is to change right-skewed (i.e. positively skewed) size-frequency distributions of unwinnowed populations to distributions that are bell- shaped or normal. . . . The location of the mode depends largely on the competence of the current.’ These assertions express a common belief in the importance of size sorting by water currents, which was reinforced by the theoretical work of Boucot (1953) and Olson (1957). This belief lacks, however, a sound basis in empirical observations and has been contested for particular instances by Craig and Hallam (1963) and Broadhurst (1964). A primary object of this paper is to investigate the validity of Fagerstrom ’s ideas with reference to two concentrations of molluscan shells (or shell beds), one forming at the present, the other fossil, which have been undoubtedly affected by strong current acti- vity. Both beds contain the young and adult shells of a large number of species of widely varying size. If size sorting is as important a factor as has been claimed it should have had a major effect on the size distributions. The influence on size-frequency distributions of varying growth and mortality rates and of selective fragmentation of shells is also considered. DESCRIPTION OF SHELL CONCENTRATIONS Newport Bay, southern California The lower terrace in the upper part of the bay contains an extremely fossiliferous Upper Pleistocene shell bed. Approximately fifty species, predominantly bivalves and gastropods, occur in a matrix of shell fragments and coarse sand with scattered stone [Palaeontology, Vol. 10, Part 1, 1967, pp. 25-42.] 26 PALAEONTOLOGY, VOLUME 10 cobbles, encrusted with serpulids, bryozoans, and barnacles. Most of the shells are fresh and well-preserved but a few apparently reworked shells occur, notably a species of Cardita. A sample was collected from a part of the shell bed several yards in area and 2 ft. deep. This sample was subsequently screened through a 1-mm. mesh sieve and complete shells separated from fragmentary material by hand picking. The commonest bivalves of large size were Tivela stultorum, Clinocardium nuttali, Chlamys hastatus hericius , and Pseudochama exogyra , but small-sized species are much more abundant. Disarticulation was complete. The numbers of right and left valves were compared for two of the commonest occurring species, both of the genus Donax, and also for a species of Tellina(i). There were 408 left and 426 right valves of Donax gouldi. The corresponding figures for D. californica are 255 and 211 and for Tellina( ?) sp. 107 and 86. Application of the Chi-Square (x2) test showed that there is a significant difference at the 5% level in the case of Donax californica. Separate plots of the size frequency distributions of both right and left valves of the Donax species give similar results. Therefore in the case of the other bivalve species selected for study, the two valves have not been separated. Only ten species of bivalves and gastropods were sufficiently abundant in the sample to give satisfactory size- frequency histograms (text-fig. 1 ). Measurements of the maximum dimension were made to the nearest millimetre but are given in terms of pairs of millimetres, as in Craig and Hallam (1963). In the comparison of size-frequency distributions of species of widely varying size the straightforward plotting of numbers against length in millimetres is not entirely satisfactory. To bring such distributions more into line, it is better to express size as a percentage of the maximum. In text-fig. 2 the measurements have been grouped into six frequency classes, the class interval being defined for each sample as one-sixth of the maximum value observed in the sample. This method of plotting demands large samples of given species, since otherwise major inaccuracies might arise in determining the maximum size. Another disadvantage is that large species are represented by cruder histograms than small ones. Clearly, grouping into such frequency classes should only be used to supplement histograms of the more orthodox kind. Text-figs. 1 and 2 indicate that the histograms may be divided into three groups: (a) those with a strong positive skewness ( Clinocardium , Chlamys, Chione ); ( b ) those with a moderate positive skewness (both Donax species, Tellina, Crucibulwn) ; (c) those that are more or less symmetrical ( Olivella , Nucula, Crassinella). It is likely, however, that the distributions of the last two bivalves are distorted, since a large proportion of these minute shells must have escaped through the 1-mm. mesh sieve. The purpose in plotting histograms in these cases will become apparent later. Tivela and Pseudochama were at least as abundant as Chlamys and Clinocardium in the largest size grades of the shell bed but were poorly represented in the sample because of a paucity of small shells. Gosford Bay, East Lothian, Scotland A sample containing at least twenty-five species of bivalves and gastropods was col- lected from an area of several square yards near high-tide mark in the middle of Gosford Bay. The rich shell accumulation at this level of the beach, containing much broken shell material, occurs in a matrix of medium sand with small pebbles of basalt derived from A. HALLAM: MOLLUSCAN DEATH ASSEMBLAGES 27 nearby reefs. As before, the sample was sieved (this time with a 2-mm. mesh sieve) and complete shells separated from fragments and grouped into species. text-fig. 1. Size-frequency distributions of molluscan species from Newport Bay assemblage. Size (in mm.) along abscissa. Disarticulation of the bivalves was complete, with the exception of a few young speci- mens of Mytilus eclulis. The distribution of numbers of left and right valves among the commonest species is as follows: Left valves Right valves Cardium edule 57 64 Macoma baltica 31 29 Mytilus edulis 200 218 Venus fasciata 33 30 28 PALAEONTOLOGY, VOLUME 10 Application of the Chi-Square (x2) test revealed no significant difference for any of these species. Text-fig. 3 gives the size-frequency distributions of the commonest species in the sample, with the exception of Littorina littorea. This was excluded because of the diffi- culty of effecting a rigorous separation from two other Littorina species, L. saxatilis and L. neritoides. L. littorea is undoubtedly by far the most abundant of the three, however. text-fig. 2. Size-frequency distributions of the same species as in text-fig. 1, plotted in terms of six frequency classes. and an approximate idea of its size-frequency distribution can be obtained from text- fig. 8, in which all three species are grouped together. All species are plotted in terms of maximum size except for Ensis siligma. This species is so much larger than the others in the sample that it was convenient to plot width rather than length. These two measures are related by an approximate ratio of 1 : 7. In text-fig. 4 these data are plotted as in text-fig. 2, and the same treatment is applied to previously published size-frequency data on Cardium and Mytilus collected from similar death assemblages (Craig and Hallam 1963). Numbers being smaller than in the Newport Bay sample, it is not surprising that the histograms are less regular. Nevertheless, it is apparent that moderate positive skewness A. HALLAM: MOLLUSCAN DEATH ASSEMBLAGES 29 is again dominant, with Macoma and Ensis approaching most closely to a symmetrical shape. The Mytilus sample of Gosford Bay differs from those of Fernie Ness and Craigelaw Bay principally in the greater proportion of small forms. The Littorina histograms differ from all others in being clearly bimodal. It is instructive to plot the position of the histogram modes for both samples against number of the frequency class in text-figs. 2 and 4. Text-fig. 5 shows that there is a maxi- text-fig. 3. Size-frequency distributions of molluscan species from Gosford Bay assemblage. Size in mm. mum at the fourth and a slight rise towards the first such class. Except for the anomalous Littorina distribution, there are no modes at the fifth or sixth. To summarize the principal size-frequency characteristics in the two samples, strong positive skewness and sym- metrical distributions are less common than moderate positive skewness, and negative skewness is absent. The anomalous bimodal distribution of Littorina littoralis in the Gosford Bay sample is readily explained by the occurrence of a living community of this species a few yards away on a rocky reef. Unlike the other species in the sample, most Littorina shells have been transported very little distance, and the death assemblage evidently reflects the sudden death of a large number of individuals of more than one age group. Both shell assemblages were clearly transported to their present positions by water movements and laid down in highly disturbed conditions. The data presented here do not support the contention that size sorting is the primary agent in shaping the 30 PALAEONTOLOGY, VOLUME 10 size-frequency distributions. Symmetrical bell-shaped distributions are exceptional and the hypothesis of size sorting offers no explanation of the widely differing size distribu- I2J4S6 12 3 4 5b text-fig. 4. Size-frequency distributions of the same species as in text-fig. 3, plotted as in text-fig. 2. 10 -| Frequency Class text-fig. 5. Plot of modal against number of frequency class, of species inNewportandGosford Bay assemblages. Explana- tion in text. A. HALLAM: MOLLUSCAN DEATH ASSEMBLAGES 31 tions of species of similar size in the same sample, such as the Gosford Bay Macoma and Venus, and the Newport Bay Tivela and Clinocardium, nor for the very similar size distributions of certain small and large species of the same sample. It does not seem plausible to attribute the rarity or absence of small shells of large species to removal by currents when shells of other, small species occur in abundance in the same sample. This is strikingly true of both samples. In that from Newport Bay, minute species of Nucula and Crcissinellci occur in huge quantities within the size grades 1-5 mm, which are thinly represented in some of the larger species. Similarly, although the Gosford Bay sample contains abundant shells of less than 10 mm length there is a complete absence of the large and elongate Ensis species in this size grade, even when only width measurements are taken into account. (The data are even more striking, of course, if length is considered.) Interpretation of the size-frequency distributions is impossible without an adequate understanding of the interaction of varying growth and mortality rates, and attention must now turn to this topic. GROWTH AND MORTALITY RATES IN LIVING BIVALVES Data on growth and mortality rates are much more abundant for bivalves than gastro- pods and attention will be confined here to the former. Such data as exist give no reason for supposing that gastropods are appreciably different in these respects. Growth rates. The annual growth of bivalve shells can be determined by growth-ring analysis, each ring corresponding to a year. The reliability of this technique has been established by direct observation by many workers (e.g. Weymouth 1923, Weymouth et al. 1925, Orton 1926, Newcombe 1935, Mason 1957). Complications due to distur- bance rings can usually be eliminated by taking average results from large samples. Data for a number of representative bivalves have been plotted in text-fig. 6. This should be studied in conjunction with Table 1, which gives the source of the information for each species. It will be seen that in general there is a steady decline in rate of growth with age, though it never completely ceases during life. Careful work by Weymouth et al. (1931) on the Pacific razor clam Siliqua patu/a has shown that the growth cannot be expressed accurately by a simple exponential function. Such a function fails to account both for the characteristic sigmoid shape of the growth curve, with a point of inflection near the origin, and for the growth of the oldest clams, which is greater than calculated. Growth 7. Venus mercenaria 8. Siliqua patula, Alaska 9. Pecten maximus 10. Tivela stultorum 1 . Cardinal edule 2. Cardium edule 3. Venus gallina 4. My a arenaria 5. Mytilus edulis 6. Cardinal corbis table 1 (Orton 1926) (Vogel 1959) (Vogel 1959) (Newcombe 1935) (Savage 1956) (Weymouth and Thompson 1931) (Hopkins 1930) (Weymouth et al. 1931) (Mason 1957) (Weymouth 1923) 11. Siliqua patula, California ( Weymouth et al. 1931) 12. Mytilus calif ornianus (Coe and Fox 1944) 32 PALAEONTOLOGY, VOLUME 10 is, indeed, an exponential function of time, but the exponent is a changing one, decreasing with time in an exponential fashion. The inflection appears in fact to have no indepen- dent biological significance. It is likely that the study of Weymouth and his co-workers has a fairly general application to bivalves, since sigmoidal growth curves are not un- common. text-fig. 6. Simplified graphical plot of growth data for twelve species of bivalves. See Table 1 . Another point brought out in this important study is that in low latitudes a relatively high growth rate is combined with relatively early death. In high latitudes growth is slower because of lower temperatures and hence lower metabolic rates, but longevity and the ultimate size attained are greater. Intermediate latitudes show correspondingly intermediate growth and mortality characteristics. The bearing of data of this type on the problem of stunting has already been discussed elsewhere (Hallam 1965); it remains to be noted here that where growth-ring analysis is feasible, there seems to be a promising prospect of working out palaeotemperature gradients if fossil material is collected from the same horizon over a large area. Much more work is required, however, on other Recent species to determine whether these relationships have a general application. Mortality rates. It is quite evident that larval mortality in bivalves must be enormous but, as pointed out by Craig and Hallam (1963), this can be disregarded by palaeoecologists, A. HALLAM: MOLLUSCAN DEATH ASSEMBLAGES 33 who are only concerned with fossilizable material. Therefore the only relevant mortality rates are those following the successful settling of spat. Data are unfortunately scant as yet, but examination of the literature and correspondence with marine biologists has revealed one case where there is sufficient information available for the construction of an adequate life table and survivorship curve. The Californian Pismo Clam, Tive/a stultorum, has considerable economic importance and hence has received detailed study over a long period. Biological knowledge of this species was summarized by Fitch (1950), who gave mortality data based on a census taken over several years. A life table has been constructed (Table 2) with these basic data, using a method of calculation proposed Age Age as % deviation from mean length of Number dying in age interval out Number sur- viving at be- ginning of age interval out of 1,000 Mortality rate per thousand alive at be- ginning of in- Expectation of life, or mean lifetime re- maining to those attaining age intervals (years) life of 1,000 born born terval (years) X r X dx (r 1000 qx e* 0-1 -100 550 1,000 550 2-07 1-2 -52 202 450 449 1-87 2-3 -3 72 248 290 1 99 3-4 +45 60 176 341 1 60 4-5 + 93 60 116 517 118 5-6 + 142 38 56 678 0-90 6-7 + 192 13 18 722 0-75 7-8 + 237 5 5 1,000 0-50 by Deevey (1947). From this a survivorship curve has been constructed (text-fig. 7). The mortality rate in the first year of growth is moderately high (55%). It then declines to 30% by the third year. The sharp increase in mortality rate after the fourth year is due to human predation, as the clams attain marketable size. Without the interference of man, the Pismo Clam may occasionally reach the considerable age of 35 years or more, that is, about 800% positive deviation from the mean life span of the clam population subjected to the census. There is a moderate amount of information available on mortality rates within the first year of growth of bivalve species and some instances will be given of this. Hancock and Simpson (1961) recorded a mortality rate of 66% for a population of Cardium edule, taken from one October to the next. Ansell (1961) determined a rate of 40% for Venus stricitida in Karnes Bay, Millport. Weymouth et a/. (1925) studied the mortality of Siliqua patida following a heavy spatfall in the summer of 1923. The mortality rate from August to December was approximately 66% but a heavy winter storm caused widespread destruction, and the mortality rate calculated from August to February was 98%. Ford (1925) also recorded a high mortality rate of 89% from July to February for a Spisida elliptica population in Plymouth Sound. Outsell (1930) observed that mortality in the bay scallop of American Atlantic shores is normally very high at sizes less than 10 mm. At times of extremely high spatfall, the mortality can be enormous. Thus Smidt (1951) recorded a case of Mya arenaria in the Danish Waddensee, in which, of 43,000 estimated 0 44 "iG D 34 PALAEONTOLOGY, VOLUME 10 spat successfully settled in June, none was left in the following October. Wilson (1965) gave further examples of very high first-year mortality. The data of Craig and Hallam (1963) suggest fairly low first-year mortality for a population of Mytilus edulis and fairly high mortality for a population of Cardium edule. text-fig. 7. Survivorship curve for the Pismo Clam, Tivela stultorum. Information is sparse on mortality rates after the first year. The data on Tivela stultorum suggest a gradually declining rate which might have continued for a considerable period but for the interference of man. The Venus striatula population studied by Ansell ap- parently had a rate of about 33% in the second and third years. In the case of the scallop Placopecten magellanicus the annual rate may drop as low as 10% after several years of growth (Merrill and Posgay 1964). On the other hand, Weymouth et al. (1931) deduced a gradually increasing mortality rate after the first year of growth of Si/iqua patula. It A. HALLAM: MOLLUSCAN DEATH ASSEMBLAGES 35 appears that, after the heavy first-year mortality in the case they studied, the rate dropped to negligible proportions for the next year or two, before increasing subsequently. Clearly, in view of the present state of knowledge, it would be unwise to risk broad generalizations, apart from the presumption that first-year natural mortality is usually higher than in subsequent years, at least when spatfall is heavy. This is not surprising, since young bivalves are more prone to removal from the sediment by strong water movements. This renders them more vulnerable to predators or to the vicissitudes of the physical environment. Winter storms may therefore take a heavy toll. Certain predators such as flatfish only attack young and comparatively small bivalves of a given species, though others, such as carnivorous gastropods, are less discriminating. The latter, however, do not destroy the shells. The importance of population density is not yet clearly established. Intensive competition for food should result in high mortality, but whereas some data appear to support this, it is seemingly contradicted in other cases (Savage 1956, Ansell 1961). In view of the wide fluctuations that take place in living populations, deductions of fossil mortality rates will depend on the elimination as far as possible of other variables. The next section deals with one of these. EXPERIMENTS ON SHELL BREAKAGE As both shell assemblages contain large proportions of fragments one is naturally led to investigate the possibility that certain size grades are more susceptible to destruction by physical agents than others (though obviously many fragments must be the result of fish and bird predation). If so this will clearly have a modifying effect on the size- frequency distributions. Experiments on shell breakage were undertaken with four of the commonest species in Gosford Bay, the bivalves Cardium edule, Mytilus edulis, and Venus fasciata, which between them represent a wide range in shape, and the gastropod Littorina littorea. The bivalve samples were collected over a wide area and no significance should be read into the size-frequency distributions portrayed in text-fig. 8. The Littorina sample, on. the other hand, comes from the analysed assemblage, from which it was excluded because of the likely presence of small quantities of two other species of similar shape. The sample is readily acceptable for the experimental work, however. The shells of each species, following size measurements, were in turn subjected to rapid tumbling in a closed container using a Turbula mixer-pulsator. Periodic inspection was undertaken to determine when a substantial proportion of the shells had been fragmented. Shell destruction proved easily determinable with the bivalves, whose numbers were considerably reduced after a few minutes. The gastropods proved far more resistant because of the greater strength of coiled and relatively thick shells as opposed to shallow convex valves. The criterion used to determine destruction was punc- ture of the early whorls or complete removal of the apertural lip (clearly the criterion of destruction need only be consistent for one observer). Even this relatively modest damage took several hours to be accomplished, with tumbling at the same speed as with the bivalves. The results (text-figs. 8 and 9) show pronounced differences between the behaviour of the bivalve and gastropod shells. The smaller shells of the bivalves are clearly more 36 PALAEONTOLOGY, VOLUME 10 susceptible to destruction in the experimental conditions, presumably because of their thinner shells. This is most strikingly shown in the case of the weakest shells, those of Venus fasciat a. As illustrated in text-fig. 8, the histogram mode of the ‘survivors’ has shifted appreciably to the right and the shape has changed from symmetrical to nega- tively skewed. In the case of Mytilus and Cardium the modes have shifted only slightly to the right but all Mytilus shells less than 19 mm. and Cardium shells less than 12 mm. ® 10 20 30 40 50 60 text-fig. 8. Size-frequency distributions of intact molluscan shells before (N 1 ) and after (N2) breakage experiments. Size in mm. long have been destroyed. With Littorina, in contrast, the smaller shells appear to be the more resistant. It will be seen from text-fig. 8 that the mode was unchanged after several hours and the general shape of the size-frequency histogram not appreciably altered. It would have been futile to attempt to simulate natural conditions in the sea and it may be objected that small shells, with their different hydrodynamic properties, would not be subjected to crushing between larger shells as in the conditions of the experiment. In the absence of precise information on the actual mechanism of post-mortem shell fragmentation on the shore or elsewhere this can neither be refuted nor accepted. There is, however, some empirical evidence to suggest the existence of a selective fragmentation process among bivalves in natural conditions comparable to that observed in the experi- ments. In a study of the production of Mactra stultorum in the western part of the A. HALLAM: MOLLUSCAN DEATH ASSEMBLAGES 37 Dogger Bank, Birkett (1959) paid attention to the quantity of dead shells in the samples collected on successive cruises, showing an interest (exceptional among marine biolo- gists) in the rate at which such shells break up once they have become empty. Data from Birkett’s table 3 have been used in text-figs. 8 and 9. The larger histogram of text-fig. 8 represents a collection made in October 1958 and the smaller histogram one made in the following May, 218 days later. The numbers of unbroken shells were considerably re- duced during this period, with the smaller, thinner shells being more readily destroyed, just as in the experiments described. No doubt winter storms played a major role in this o 10 20 30 40 50 60 60 1 Littorma 100] . ^ , Moclro I . Vx so -| . . 40 - 40 T t ; I r—~ r r— 1 0 10 20 30 o 5 10 15 20 100 - Venus 80 1 ' 0 S 10 15 20 25 30 text-fig. 9. Data of text-fig. 8 plotted as percentages of broken shells of given species at different sizes. destruction. To Birkett it was evident that the smallest length classes of Mactra could not have survived for more than a few weeks in the ground. Schafer (1962, p. 550) con- firmed that a large proportion of bivalve shells do not survive in the North Sea beyond a few months after they become empty. Evidently, given conditions of agitated water, the factor of differential break-up of bivalve shells of different size grades cannot readily be discounted. INTERPRETATION OF SIZE-FREQUENCY DISTRIBUTIONS It was demonstrated in a previous study (Craig and Hallam 1963, text-fig. 8) that, given linear growth, constant mortality can be represented by a size-frequency histogram of the death assemblage rising at an increasing rate towards the origin, the mode being determined only by the size of the class interval chosen, while a constantly increasing mortality rate could give rise to an approximately normal distribution. Slight modifica- tions result from the more realistic application of growth rate declining with time. Thus the normal distribution may become negatively skewed. It is obvious that age-frequency data, and hence approximate mortality rates, can only be derived from size-frequency 38 PALAEONTOLOGY, VOLUME 10 data provided the average growth rate of the assemblage under consideration can be worked out from growth rings. Unfortunately, this is not a practicable proposition for many molluscs, including most of the species under consideration. Reasonable approxi- mations are obtainable, however, if realistic models of growth and mortality rates are constructed from existing data. Three model bivalve growth curves are presented in text-fig. 10, one representing simple linear growth, which is approximated by some bivalves for parts of their life history; the second a growth characterized by a slow (approximately exponential) rate of change, half the maximum size (attained at 10 years) being achieved at 3| years; and text-fig. 10. Three growth models for bivalves ; case 1, simple linear growth; case 2, slow exponential decline; case 3, rapid exponential decline. the third a growth characterized by a rapid rate of change, half the maximum size being reached at 2 years. These curves are, of course, simplifications but are satisfactory for the present purpose. The three curves seem to embrace reasonably adequately the docu- mented cases of bivalve growth curves illustrated in text-fig. 6. Producing a realistic mortality model is far more difficult, because of the lack of data and the wide fluctuations in mortality rate that are known to occur. It is considered soundest here to construct a model closely approximating to the mortality rates worked out for Tivela stultorum in the previous section, but taking into account that mortality among the first-year population is likely to be highest in the second half year of growth because of winter storms and cold spells. This can be achieved by taking 50% as the mortality rate for the first half-year, 80% for the next, 50% for the following two half- years, and 40% each subsequent half-year. This gives a 55% mortality rate for the first year, 45% for the second, and 36% for the third. Such a mortality distribution must indeed approximate a large number of actual cases, judging from the data which exist. In text-fig. 1 1 size-frequency distributions are given using this mortality model and the three growth models of text-fig. 10. The influence of widely varying initial growth rates is clearly shown and needs no comment, but it should be observed that each curve has a long tail to the right. Such tails are the inevitable result of mortality rates which do not increase notably with time, and is almost certainly the normal situation. A. HALLAM: MOLLUSCAN DEATH ASSEMBLAGES 39 Returning now to the two shell assemblages illustrated in text-figs. 1 to 4, it becomes readily apparent that the general shapes of the size-frequency histograms must be pri- marily due to the interaction of fairly normal growth and mortality rates. Those with strong positive skewness signify high juvenile mortality rate, with a subsequent decline, while the few with symmetrical distributions could signify a condition of increasing mortality with time, or a high initial growth rate, or a combination of the two (obviously, independent growth data are required to decide between these alternatives). text-fig. 11. Size-frequency distributions derived from the three growth models of text-fig. 10 and a mortality model described in the text, based on data from Tivela stultorum. There is a strong suggestion that there has been selective removal of small shells, how- ever, in at least some cases, because the approximate mortality rates that may be de- duced from the histograms do not appear to correspond sufficiently closely with the more directly derived data reviewed earlier, which indicate high rates of juvenile mortality as the common condition. This difference is brought out clearly in text-fig. 5. In the case of the bivalves at least (to which may be added with reasonable confidence the thin- shelled limpet Crucibulum , though not the coiled gastropods Olivella and Littorina ), there is a ready explanation available, namely selective fragmentation in an agitated aqueous environment. While such fragmentation has in all likelihood removed a con- siderable proportion of the smaller shells, it is unlikely that it has succeeded in doing more than altering the degree of skewness. It certainly cannot explain the rarity of small specimens of, for instance, Pseudochama and Tivela in the Newport Bay sample, which must be largely attributable to low juvenile mortality. Nor can it account for the virtual absence of small Ensis shells in the Gosford Bay sample. This must principally 40 PALAEONTOLOGY, VOLUME 10 be due to an exceptionally high initial growth rate compared with the smaller-sized species, together with only slight mortality during the first few months of growth. Lack of information about mortality in the period just after settling of spat, and about growth rates in specific cases, provide limits to the confidence of interpretation. None of this proves, of course, that size sorting has played no role whatever, but its invocation appears unnecessary and the burden of proof in these and similar cases rests squarely upon those who would insist upon its importance. It is not sufficient to reiterate the obvious, that shells of different size and thickness have different hydro- dynamic properties. In regimes subjected to tidal action, for instance, oscillating currents are likely to return what they have removed, and the net effect may be negligible. Even in cases in which a size-sorting effect has been experimentally demonstrated, the results may not be readily predictable. Thus Lever et al. (1964) found that large valves of Donax vittatus are actually transported more readily than small valves. DISCUSSION Although information is unfortunately insufficient for the rigorous disentanglement of the several variables involved, it can be claimed with reasonable confidence that the present study lends little support to the hypothesis that size-frequency distributions of transported and highly disturbed shell assemblages primarily reflect size sorting, but are rather the result of the interaction of normal growth and mortality rates, somewhat modi- fied in all probability by the selective destruction of smaller shells. The Newport Bay Pleistocene assemblage may represent a strandline accumulation like the Gosford Bay assemblage, and consists of fossils which in life inhabited inter- tidal or shallow subtidal waters. Accumulation on the strandline is, together with the formation of lag concentrates in channels, by far the most important way of forming transported shell concentrations around our present shores. It is apparent from the work of Schafer and others that the duration of complete shells in a disturbed aqueous environment is limited to brief periods in most cases, and assemblages such as those described are most probably the result of only a few years of growth; in the case of species with small fragile shells they may represent only one year of growth. In reply to the contention that because most strandline accumulations are destroyed quickly they are insignificant in the fossil record it may be pointed out that they have a chance of preservation comparable with ripple marks or similar ‘ transient ’ sedimentary structures. A certain proportion of such shell beds must be preserved following ultimate burial of a sedimentary accumulation of the appropriate type. Fossils are often concentrated, of course, as a result of slow sedimentation. Condensed shell beds formed in this way should exhibit wider scatter in the size-frequency distribu- tions of their component species, because of the mixing of forms which grew at varying speeds at widely differing times. Diagenetic solution of small, thin shells is more likely to be of importance in this type of shell bed than any other. If the selective destruction of small, thin shells in agitated water is a major factor then argillaceous deposits should contain higher proportions of juveniles than arenaceous ones. Black shales usually signify deposition in stagnant or near-stagnant water in which water disturbance was at a minimum. Such deposits frequently contain minute shells of given species which have been widely interpreted, with some justification, as stunted adults (Hallam 1965). A. HALLAM: MOLLUSCAN DEATH ASSEMBLAGES 41 A condition of declining mortality rate with age, combined with lack of selective destruc- tion, may give rise to a strong juvenile peak and a very small number of much larger adults. Unless large samples are collected, of the order of hundreds of specimens for each species, these adults may easily be missed. It is clearly desirable to undertake thorough size-frequency analyses of a number of species in a fauna when stunting is suspected. Acknowledgement. I am indebted to Dr. G. Y. Craig for his helpful comments. REFERENCES ansell, a. d. 1961. Reproduction, growth and mortality of Venus striatula (da Costa) in Karnes Bay, Millport. J. mar. biol. Ass. U.K. 41, 191-215. birkett, l. 1959. Production in benthic populations. Internat. Council for Exploration of Sea: Near Northern Seas Committee, no. 42, 1-12. boucot, a. J. 1953. Life and death assemblages among fossils. Am. J. Sci. 251, 25-40. broadhurst, f. m. 1964. Some aspects of the palaeoecology of non-marine faunas and rates of sedi- mentation in the Lancashire Coal Measures. Ibid. 262, 858-69. coe, w. r. and fox, d. l. 1944. Biology of the California sea mussel ( Mytilus calif ornianus). III. Environmental conditions and rate of growth. Biol. Bull. mar. biol. Lab., Woods Hole, 87, 59-72. craig, G. y. and hallam, a. 1963. Size-frequency and growth-ring analyses of Mytilus edulis and Cardium edule, and their palaeoecological significance. Palaeontology, 6, 731-50. deevey, e. s. 1947. Life tables for natural populations of animals. Q. Rev. Biol. 22, 283-314. fagerstrom, J. a. 1964. Fossil communities in paleoecology : their recognition and significance. Bull, geol. Soc. Am. 75, 1197-216. fitch, J. e. 1950. The Pismo Clam. Calif. Fish Game, 36, 285-312. ford, e. 1925. On the growth of some lamellibranchs in relation to the food supply of fishes. J. mar. biol. Ass. U.K. 13, 531-59. gutsell, J. s. 1930. Natural history of the bay scallop. Bull. Bur. Fish. Wash. 46, 569-627. hallam, a. 1965. Environmental causes of stunting in living and fossil marine benthonic invertebrates. Palaeontology, 8, 132-55. Hancock, d. a. and simpson, a. c. 1961. Parameters of marine invertebrate populations. In: The Ex- ploitation of Natural Animal Populations. Ed. e. d. le cren and m. w. holdgate, Oxford. hopkins, H. s. 1930. Age differences and the respiration in muscle tissues of mollusks. J. exp. Zool. 56, 209-39. lever, j., van den bosch, m., cook, h., van DiJK, t., thiadens, a. j. h., and thijssen, r. 1964. Quanti- tative beach research: III. An experiment with artificial valves of Donax vittatus. Neth. Jnl Sea Res. 2, 458-92. mason, J. 1957. The age and growth of the scallop, Pecten maximus ( L . ) , in Manx waters. J. mar. biol. Ass. U.K. 36, 473-92. Merrill, a. s. and posgay, J. A. 1964. Estimating the natural mortality rate of the Sea Scallop ( Placo - pecten magellanicus). Bull. Int. Comm. North West Atlantic Fish. Res. 1, 89-106. newcombe, c. l. 1935. Growth of Mva arenaria L. in the Bay of Fundy region. Can. J. Res. 13, D, 97- 137. olson, e. c. 1957. Size-frequency distributions in samples of extinct organisms. J. Geol. 65, 309-33. orton, J. h. 1926. On the rate of growth of Cardium edule. Part 1 . Experimental observations. J. mar. biol. Ass. U.K. 14, 239-79. savage, r. e. 1956. The great spatfall of mussels ( Mytilus edulis L.) in the River Conway estuary in Spring, 1940. Fishery Invest., Load., Ser. 2, 20, 7. H.M.S.O. schafer, w. 1962. Aktuo-Paldontologie nacli Studien in der Nordsee. Frankfurt a. M. smidt, e. l. b. 1951. Animal production in the Danish Waddensee. Meddr Kommn Danm. Fisk.-og. Havunders., Ser. Fisk, 2, no. 6. vogel, k. 1959. Wachstumsunterbrechungen bei Lamellibranchiaten und Brachiopoden. N. Jb. Geol. Paldont., Abh. 109, 109-29. 42 PALAEONTOLOGY, VOLUME 10 Weymouth, F. w. 1923. The life history and growth of the pismo clam ( Tivela stultorum Mawe). Calif. Fish Game Commiss., Fish. Bull. 7. mcmillin, h. c. and holmes, h. b. 1925. Growth and age at maturity of the Pacific razor clam, Siliqua patula (Dixon). Bull. Bur. Fish., Wash. 41, 201-36. and rich, w. h. 1931. Latitude and relative growth in the razor clam, Siliqua patula. J. exp. Biol. 8, 228-49. and Thompson, s. h. 1931. The age and growth of the Pacific cockle ( Cardium corbis Martyn). Bull. Bur. Fish., Wash. 46, 633-41. Wilson, J. b. 1965. The palaeoecological significance of infaunas and their associated sediment. Unpubl. Ph.D. Thesis, Univ. Edinburgh. A. HALLAM Grant Institute of Geology, King’s Buildings, West Mains Road, Edinburgh 9 Manuscript received 18 November 1965 ON THE STRUCTURE AND PHYLOGENETIC RELATIONSHIPS OF THE FERN RADSTOCKIA KIDSTON by THOMAS N. TAYLOR Abstract. Raclstockia kidstonii sp. nov. is described from compression specimens contained in ironstone con- cretions discovered at the Mazon Creek (Illinois) locality. The botanical affinities are suggested as being close to marattiaceous ferns. The genus Radstockia Kidston (1923) was originally described on the basis of Upper Carboniferous fertile fern-like foliage initially designated as Schizostachys spheno- pteroides Kidston (1888) and Hymenotheca beyscldagi Potonie (1890). Forms placed in the genus are characterized by elliptical fructifications that display a superficial seg- mented appearance. In R. sphenopteroides the fructifications are described and illus- trated as being borne either sessile or on short stalks along non-foliar laterals. They may occur singly, in pairs, or in definite clusters at lower levels on the frond. Two foliar specimens referable to the genus Radstockia contained in an ironstone concretion collected at the famous Mazon Creek locality represent the material described in this account. Several additional specimens collected from the same locality and pre- sently deposited in the palaeontological collections at the Chicago Natural History Museum and Illinois State Museum at Springfield were also examined. The present contribution is concerned with the description of a new species and the interpretative problems which it presents. SYSTEMATIC DESCRIPTION Genus radstockia Kidston 1923 Radstockia kidstonii sp. nov. Plate 6, figs. 1-4; Plate 7, figs. 2, 3, 5 Diagnosis. Foliar units at least bipinnate, rachis straight, longitudinally striated; foliar laterals alternate, lanceolate to oblong-lanceolate, free on lateral margins. Fructifica- tions elliptical, 2-0 mm long and 1-0 mm wide, pendant and partially embedded in abaxial surface of foliar units; spores spherical, 40-60 p; exine thin, levigate. Holotype. Plate 6, fig. 1. Peabody Museum of Natural History; Yale University, Paleobotanical Collections, No. 1004. Type Locality. Mazon Creek, Will County, Illinois (U.S.A.). Stratigraphic occurrence. Francis Creek Shale, Carbondale Formation, Kewanee Group. Age. Middle Pennsylvanian. (Palaeontology, Vol. 10, Part 1, 1967, pp. 43-46, pis. 6-7.] 44 PALAEONTOLOGY, VOLUME 10 DESCRIPTION OF SPECIMENS, AND DISCUSSION The nodule contains portions of two foliar segments (PI. 6, fig. 1); one specimen shows features of more distal parts, while the second displays characters at more proxi- mal frond levels. From the limited extent of the two specimens it is impossible to deter- mine the branching level represented by the material, although the parallel relationship exhibited between the two foliar parts (PI. 6, fig. 1) suggests that at least secondary pinnae are represented. Because of the uncertainty, however, the branching foliar axes will be referred to arbitrarily as ultimate, penultimate, and antepenultimate throughout the description that follows. Foliage. The larger, more distal foliar specimen consists of an antepenultimate axis approximately 9-5 cm. long bearing 1 5 alternately arranged penultimate axes (pinnatified pinnules) (PI. 6, fig. 1). These pinnules are broadly lanceolate to oblong-lanceolate and are constricted where they are attached to the primary (antepenultimate) rachis (PI. 6, fig. 3). Margins are deeply lobed and free from surrounding foliar units (PI. 7, figs. 2-3). The rachis is straight and characterized by longitudinal striations (PI. 6, figs. 1-3) that may represent vascular strands or accompanying sclerenchyma fibres. The second foliar unit displays features of lower frond levels and consists of a pri- mary axis bearing 7 alternately arranged penultimate axes (PI. 6, fig. 1). Each of these in turn gives rise to small ultimate axes (pinnules). Lower units of this foliar segment bear alternately arranged, decurrent, obovate pinnules, each of which is subdivided into 3-6 spatulate lobes (PI. 6, fig. 2). Lobes are uniform in size and each bears a single fructifica- tion on its abaxial surface. Each penultimate axis is supplied by a single prominent vein that departs from the primary rachis, enters the foliar unit, and is further subdivided into smaller veinlets. Whether the individual veins continue to the margin of the lamina cannot be deter- mined from the material. No pinnule lobe contains more than a single vein. At some levels of the specimen it appears that both fertile and sterile pinnules are present. This, however, is not the case when one carefully removes the matrix surround- ing these units. From the present material on hand it appears that fructifications were produced on all of the foliar units. Fructifications. The fructifications of R. kidstonii consist of elliptical bodies partially embedded in the abaxial surface of marginal foliar lobes (PI. 6, fig. 4; PI. 7, figs. 2-3). Each unit measures approximately 2-0 mm long and 1 -0 mm wide in its greatest dimen- sion. Externally each fertile structure is marked by a single conspicuous longitudinal EXPLANATION OF PLATE 6 Figs. 1-4. Radstockia kidstonii. 1, One half of ironstone concretion showing upper (left) and lower (right) portions of two leaves; X 1. 2, Pinna showing lobed configuration of individual pinnules x 3; note striated rachis and pinna base. 3, Fertile pinna near tip illustrating marginal position of synangia, X 3-5. 4, Surface view of two synangia showing linear arrangement of sporangia, X 22. EXPLANATION OF PLATE 7 Figs. 1, 4. Mamttia alata. 1, Fertile pinnule; nearly all of the sporangia at the right have dehisced, while those at the left are still intact, x6. 4, Fertile pinna, x3; compare with Plate 6, fig. 3. Figs. 2, 3, 5. Radstockia kidstonii. 2, Single pinnule showing marginal position of the synangia, x 13. 3, Tip of fertile pinna showing partial fusion of sporangia (arrow), X 12. 5, Spore showing numer- ous folds of the thin-walled exine, X 1000 (Slide No. 17). Palaeontology, Vol. 10 PLATE 6 TAYLOR, Carboniferous fern Radstockia PLATE 7 Palaeontology, Vol. 10 TAYLOR, Carboniferous fern Raclstockia T. N. TAYLOR: THE FERN RADSTOCKIA KIDSTON 45 furrow that appears to divide the entire unit (PI. 6, fig. 4). Arising at right angles from this median cleft are smaller furrows that give the entire unit a segmented appearance. Because of the almost complete replacement of the original organic material nothing is known of the structure of the fructifications. In his description of/?, sphenopteroides , Kidston (1923) regarded the entire unit as a single sporangium. According to this interpretation the longitudinal and transverse furrows that mark the surface represent features involved in sporangial dehiscence. An examination of the Mazon Creek specimens produced evidence for another inter- pretation. This author regards the fructifications of R. kidstonii as clusters of partially fused sporangia in a linear arrangement. Figure 3 (PI. 7) shows one of these synangia slightly flattened in a lateral plane and illustrates the partial fusion (arrow) of the individual sporangia. Additional support for this point of view can be obtained from the nature of the longitudinal furrow on the surface of each fructification. Figure 4 (PI. 6) clearly demonstrates that the furrow is in fact a suture formed by the linear arrangement of the individual sporangia, and is not itself a structural feature of a sporangium. Spores. Isolated spores and fragments of spore masses were obtained by chipping away several synangia and subsequently macerating these in dilute hydrochloric acid. Spores of R. kidstonii are spherical, smooth-walled, and range in size from 40 to 60 p.. In the fossilized condition (PI. 7, fig. 5) they are distinctly flattened and appear circular to sub- circular in outline, but they are typically distorted owing to the numerous folds of the very thin spore wall. Haptotypic features are absent. If encountered in the dispersed state, spores of R. kidstonii would most closely correspond to forms presently placed in the genus Laevigatosporites (Schopf, Wilson, and Bentall 1944). Discussion. At present the systematic position of R. kidstonii is debatable. There are, however, several striking similarities to be found between R. kidstonii and certain genera placed in the Marattiaceae, both fossil and living. The discussion that follows serves to illustrate several of these comparisons, while at the same time demonstrating the unique position presently occupied by this form. In its linear soral organization R. kidstonii differs markedly from other fossil forms regarded as having marattiaceous affinities (e.g. Astero theca , Ptychocarpus, Sco/ecop- teris). There are, however, several linear soral arrangements in forms of approximately the same age as R. kidstonii. Pecopteris marattiatheca Grand’Eury (1877, pp. 77-78, pi. 7, figs. 6, k-o ) is charac- terized by linear synangia partially embedded in the abaxial surface of pecopterid foliage. Each fertile unit consists of eight partially fused sporangia which are believed to have opened by an apical pore. No information is provided about the spores. Two other forms displaying the linear soral arrangement are Danaeites Goeppert (1836, pi. 19, figs. 4-5) and Parapecopteris Grand’Eury (1890, pi. 5, figs. 2-5). In Danaeites saraepontcmus Stur (1885, fig. 33) each synangium is composed of 8-16 ovoid sporangia organized in two series on the lower surface of pecopterid foliage. In Parapecopteris neuropteroides , on the other hand, the pinnules are described as intermediate between pecopterid and neuropterid types. Here, as in Danaeites , the synangia are partially em- bedded in the lamina and located along the lateral pinnule veins. It should be noted that in a recent paper Danaeites sciraepontanus and Parapecopteris neuropteroides are regarded by Corsin (1951) as synonyms. 46 PALAEONTOLOGY VOLUME 10 Superficially the petrifaction genus Eoangiopteris Mamay (1950, p. 440, pi. 9, figs. 47-53) resembles R. kidstonii in the organization of the sorus. Unlike the synangiate condition of R. kidstonii, the fructifications of Eoangiopteris consist of clusters of 5-8 free sporangia. Moreover, the sorus is borne on a small fleshy receptacle on pecopterid foliage. Spores are reported as spherical (45-60 p), thick walled, and conspicuously pitted on the exine. In addition to the similarities shared with several fossil forms, R. kidstonii closely resembles such living members of the Marattiaceae as Marattia alata (PI. 7, figs. 1, 4) and M. excavata. In these forms the synangia are borne on small fleshy receptacles along the veins. No indusium is present (which may or may not be the case in R. kidstonii ). At maturity the synangium splits into two valves (PI. 7, fig. 3), each sporangium subsequently forming a pore at its tip. At present comments concerning evolutionary trends within the Marattiaceae are provisional at best. Notwithstanding, the marginal synangial position illustrated by R. kidstonii may be regarded as additional support for the ideas presented by Mamay (1950) concerning the ‘phyletic slide’ of the fructification to a superficial position on the lamina. According to this interpretation the coenopterid fern Chorionopteris with synangia attached to the tips of marginal pinnule lobes illustrates a condition that may have been found in the prototype of the Marattiaceae. In this series the ‘phyletic slide’ of the synangium (illustrated by forms both actual and hypothetical) culminates with the fructification in a superficial position. Whether R. kidstonii represents an intermediate form in the ‘shift’ of the sorus from a marginal to superficial position on the lamina is still a matter of conjecture. The dis- covery of additional more complete specimens, hopefully displaying structural features of the fructification, should help to answer this question. Acknowledgement. This research was supported by a National Science Foundation Grant (GB 1435) to T. Delevoryas and a similar NSF Grant (GB 4325) to the author. REFERENCES corsin, p. 1951. Etudes des Gites mineraux de la France. Bassin houiller de la Sarre et Lorraine. I. Flore fossile. Fasc. 3-4. Les Pecopteridees, 175-370. goeppert, h. r. 1836. Die fossilen Farrenkrauter (Systema filicum fossilium). Nova Acta Leopotdina 17, 1-486. grand ’eury, c.-f. 1877. Memoire sur la flore carbonifere du Departement de la Loire et du centre de la France. Mem. Acad. Sci. Inst. Fr. 24, 1-624. 1890. Geologie et Paleontologie du bassin houiller du Gard. St. Etienne, 1-354. kidston, r. 1888. On the fossil flora of the Radstock Series of the Somerset and Bristol Coal Field (Upper Coal Measures). Trans. R. Soc. Edin. 33, 335N17. 1923. Fossil plants of the Carboniferous rocks of Great Britain, pt. 4. Mem. geol. Surv. G.B. 2, 277-375. mamay, s. H. 1950. Some American Carboniferous fern fructifications. Ann. Missouri Bot. Gard. 37, 409-76. potonie, h. 1890. Uber einige Carbonfarne. Jb. Preuss. geol. Landesanst. (1889), 21-27. schopf, J. M., wilson, L. R., and bentall, r. 1944. An annotated synopsis of Paleozoic fossil spores and the definition of generic groups. Rep. Inst. III. St. geol. Surv. 91, 1-73. stur, d. 1885. Die Carbon-Flora der Schatzlarer Schichten I. Fame der Carbon-Flora der Schatzlarer Schichten. Abh. geol. Bundesanst., Wien. 11, 1-418. T. N. TAYLOR Department of Biological Sciences, University of Illinois at Chicago Circle, Chicago, Illinois, U.S.A. Manuscript received 23 November 1965 NEW TRILOBITES FROM THE TREMADOC SERIES OF SHROPSHIRE by r. hutchison and J. k. ingham Abstract. A new locality in the Shineton Shales of the Cardington district is referred to the Clonograptus tenellus Zone. The fossils are compared with related and similar forms previously known from the Wrekin district. The fauna includes three new species of trilobites — Asaphoon pithogastron gen. et sp. nov., Dichelepyge phylax sp. nov. and Myindella crux gen. et sp. nov. D. phylax represents the first recognition of Dichelepyge out- side South America. Myindella crux suggests that the Family Myindidae is closely related to the Hapalopleuridae and should therefore be included in the Suborder Trinucleina. The specimens here described were collected by one of us(R. H.) from a greyish-green, nodular, micaceous siltstone seen in a small exposure of about 2 ft of Shineton Shales in Heath Brook, 1,100 yd. south-east of Cardington church (Grid Ref. 51259440) and 4 miles ENE. of Church Stretton. The beds are disturbed and their exact stratigraphical position is obscure but they most probably lie within the Clonograptus tenellus Zone (Stubblefield and Bulman 1927, p. 110) as they contain the zonal graptolite and an assemblage of trilobites which has its closest counterpart in the C. tenellus Zone of the Wrekin district (see table). In a short description of the Cardington outcrops Stubblefield and Bulman (p. 116) suggested that the Transition Beds, which underlie the C. tenellus Zone, are also present in the area in view of the association of C. tenellus (Linnarsson), Dictyonema flabelli- forme (Eichwald) and Shumardia curt a Stubblefield on specimens in the Sedgwick Museum, Cambridge. Neither of the two new genera — Asaphoon and Myindella — is as yet known outside the Cardington district but Myinda Stubblefield (in Stubblefield and Bulman, p. 130), a genus closely related to Myindella , was described from the C. tenellus Zone of the Wrekin district. The discovery of Dichelepyge , Harrington and Leanza, 1952, in the Shineton Shales provides a further link between the Tremadoc Series in Europe and Argentina. D. phylax sp. nov. is the only known European species referable to the genus. The specimen described as Hysterolenus tornquisti Moberg ?var. (Stubblefield in Stubble- field and Bulman, pp. Ill, 118, 137; pi. 4, fig. 8) from the C. tenellus Zone of the Wrekin district is undoubtedly conspecific with the new form. In Table 1 the fauna collected from the locality is compared with allied, identical, and possibly identical forms, together with their stratigraphical ranges in the Wrekin district, as listed by Stubblefield and Bulman. SYSTEMATIC DESCRIPTIONS The terminology used is that of Harrington and others (in Moore 1959, pp. 038-0126). Glabellar furrows are numbered forwards from the occipital furrow. All specimens are deposited in the Hunterian Museum of the University of Glasgow. [Palaeontology, Vol. 10, Part 1, 1967, pp. 47-59, pi. 8. 48 PALAEONTOLOGY, VOLUME 10 Suborder asaphina Salter 1864 Superfamily asaphacea Burmeister 1843 Family asaphidae Burmeister 1843 Genus asaphoon gen. nov. Type species. Asaphoon pithogastron sp. nov. Derivation of name, asaphes (Gr.) = indistinct, obscure+oo/; (Gr.) = egg. Diagnosis. Small asaphid trilobite with highly convex glabella and long preglabellar field. ?Four pairs of short, indistinct lateral glabellar furrows and a posteriorly situated glabellar tubercle present. Occipital ring crescentic. Fixigenae possess small, convex, poorly defined paraglabellar areas. Palpebral lobes long. Pygidium with entire margin and concave border. Pygidial axis has seven annulations and pleural regions are crossed by seven pleural furrows which do not reach the margin. Faint interpleural furrows present. Discussion. No other described asaphid trilobite has palpebral lobes as proportionally long or a glabella so convex as Asaphoon. The swollen nature of the glabella, however, HUTCHISON AND INGHAM: TRILOBITES FROM THE TREMADOC SERIES 49 may be a feature of youth. Ptychopyge Angelin 1854 shows some similarities in possess- ing a long preglabellar field and in the presence, behind the palpebral lobes, of small nodes resembling the convex paraglabellar areas in Asciphoon. Although possessing such general asaphid characteristics as the course of the anterior branches of the facial suture and in having a glabellar tubercle near the occipital furrow, the new genus is so different in detail from other asaphid genera that it is impossible to place it in any of the recognized subfamilies within the Asaphidae. Table 1 LIST OF SPECIES FROM THE NEW LOCALITY NEAR CARDINGTON INCLUDING NEW FORMS DESCRIBED IN THIS PAPER RANGES OF ALLIED (A) OR IDENTICAL (1) FORMS PREVIOUSLY RECORDED FROM THE SHINETON SHALES OF THE WREKIN DISTRICT (after Stubblefield & Bulman, 1927) c 0 N | G 1 c o X U ■a CD C o c O i— c o N J3 G Q u *o CD -O o a. o o CD 0 N G G a G I 1 S [Arenaceous Beds Agnostid 3 agnostids recorded X X X X Asophoon p/thogostron gen. et sp. nov. ? Beltel/o sp . Drche/epyge phy/ox sp. nov. 1 Hystero/enus tdmgu/st i Moberg ?var. X L/Chopyge cf .CUSp/dOtO Callaway ? 1 L. CUSp/dOtO Callaway X Mocropyge sp . ?l M. chermi Stubblefield X X ? MyindellO crux gen. et sp. nov. A Mytndo uriconn Stubblefield X Plolype/toides croft ii (Callaway) 1 Symphysurus croft// (Callaway) X X X Ade/ogroptus ? sp. ?l ? Bryogroptus cf. fiunnedergens/s Moberg X X C/onogroptus teneUus (Linnarsson) 1 C. tene/lus (Linnarsson) X X C. fenel/us co/lovei Elies & Wood 1 C. tene/lus var. col love / Elies & Wood X X Lingu/e/Jo cf . n/cho/soni Callaway ?l L. nicholsoni Callaway X X X X X X Hyolithus sp . 3 hyolithids recorded X X X Asaphoon pithogastron gen. et sp. nov. Plate 8, figs. II, 13, 14; text fig. 2. Derivation of name . pithogastros (Gr.) = potbellied. Holotvpe. Hunterian Museum A5807a, b (PI. 8, fig. 11) internal and external moulds of a cranidium. Paratypes. HM. A5809 (PI. 8, fig. 14); HM. A5810a, b (PI. 8, fig. 13). Other material. One damaged pygidium HM. A5808. Description. Holotype cranidium subtriangular in outline, a little broader than long (sag.) in the ratio 7 : 6. Glabella almost twice as long (sag.) as broad, inflated, egg-shaped with frontal lobe bluntly rounded and posterior margin slightly overhanging occipital furrow. Maximum width (tr.) a little in front of the middle of the glabella. At least three pairs of short, equally spaced lateral glabellar furrows present. The first pair are the deepest, situated at about one-third the length of the glabella from its posterior margin and directed slightly backwards. The second and third pairs of furrows are a little longer and more transverse than the first pair but they are very weakly impressed. There is an indication of a fourth, anterior pair of glabellar furrows represented only by faint indentations on the sides of the glabella about three-quarters the length of the glabella from its posterior margin. A large median tubercle is present near the posterior margin of the glabella. The axial and preglabellar furrows are not deeply impressed, the glabella C 4466 E 50 PALAEONTOLOGY, VOLUME 10 being defined primarily by the steepness of its sides. Occipital furrow arched backwards, sharply defined, its depth being exaggerated by the steepness of the glabellar margin. Occipital ring crescentic in outline, its sagittal length being about one-eighth the length of the glabella. It is slightly broader (tr.) than the maximum width of the glabella and is text-fig. 2. Partial reconstruction of Asaphoon pithogastron gen. et sp. nov. Approx. X 18. EXPLANATION OF PLATE 8 Figs. 1-5, 7. Myindella crux gen. et sp. nov. 1, HM. A5802, X 12. Latex cast of holotype cranidium, an external mould. 2, 3, HM. A5805a and b, X 8. Internal mould and latex cast of external mould of paratype thorax/pygidium. 4, HM. A5803b, X 8. Latex cast of external mould of cranidium. Para- type. 5, As for fig. 1 . Oblique frontal view X 8. 7, HM. A5804, X 8. Latex cast of external mould of poorly preserved incomplete individual showing the nature of the marginal suture and a suggestion of the presence of a lower lamella. Paratype. Figs. 6,8-10, 12, 15, 16. Dichelepyge phylax sp. nov. 6, HM. A5772b, x 9. Latex cast of external mould of holotype cranidium. 8, HM. A5781a, X 6. Internal mould of incomplete pygidium associated with damaged thoracic segments, showing two pairs of marginal spines. Paratype. 9. HM. A5784, X 9. Internal mould of pygidium with four thoracic segments. Paratype. 10, HM. A5776, x6. Internal mould of almost complete individual. Paratype. 12, HM. A5785, X 6. Internal mould of hypostome. Paratype. 15, HM. A5779a, X 9. Internal mould of left librigena showing long genal spine. 16, HM. A5770, x 9. Latex cast of external mould of incomplete cephalon and thorax showing the course of the facial suture. Paratype. Figs. 11, 13, 14. Asaphoon pithogastron gen. et sp. nov. 11, HM. A5807b, X 12. Latex cast of external mould of holotype cranidium. 13, HM. A5810a, X 8. Internal mould of badly damaged incomplete individual showing shape of librigena and traces of anterior thoracic segments. Paratype. 14, HM. A5809, x 8. Internal mould of pygidium. Paratype. Palaeontology, Vol. JO PLATE 8 HUTCHINSON and INGHAM, Tremadocian trilobites HUTCHISON AND INGHAM: TRILOBITES FROM THE TREMADOC SERIES 51 defined laterally by shallow furrows which continue the curve of its posterior margin and run obliquely forward to meet the posterior border furrows of the fixigenae. The posterior margin is interrupted laterally by a pair of short, shallow, transverse furrows which have the effect of giving a slight independent convexity to the outer portions of the predominantly flat occipital ring. Preglabellar field long (sag.), almost half the length of the glabella, slightly concave with a narrow, upturned anterior border defined by a shallow border furrow. Palpebral portions of fixigenae of moderate width (tr.); posterior portions wide (tr.), curving backwards a little distally. Posterior borders defined by weak border furrows which die out laterally. Small, convex paraglabellar areas lie close to the posterior part of the glabella in the angles formed by the axial furrows and the posterior border furrows. They are ill-defined both laterally and frontally. Palpebral lobes are long, narrow, slightly elevated, and crescentic in shape. Anteriorly they begin opposite the ?fourth pair of glabellar furrows and extend backwards to a level a little to the rear of the preoccipital glabellar furrows. Their length (exsag. ) is a little more than half the length of the glabella. Palpebral furrows shallow. Palpebral lobes continue anteriorly into short, gently convex eye ridges which are terminated by the axial furrows a little in front of the ?fourth pair of lateral glabellar furrows. Anterior branches of facial suture diverge at first at about 40°, then curve gradually inwards to meet dorsally at an angle of 135°. Posterior branches of facial suture curve gently outwards and backwards. Librigenae, known only from a poorly preserved individual (HM. A5810a, b, PI. 8, fig. 13), are broad, flat and produced into rather stout genal spines which are at least as long as the palpebral lobes. Hypostome unknown. Thorax also known only from the fragmentary evidence of HM. A5810a, b. Number of segments unknown. Axis occupies about one-quarter the total thoracic width. Pleurae very poorly preserved but each pleura ends in a short, backwardly directed point and is apparently crossed obliquely by a moderately deep pleural furrow. Pygidium semicircular to paraboloid in outline. Axis convex, narrow, occupying a little less than one-quarter the maximum pygidial width anteriorly. Axial furrows con- verge posteriorly at 30°. The axis does not quite reach the posterior border which, however, is crossed by a narrow post-axial ridge. Seven well-defined axial rings and terminal piece present. Pleural fields with a gently convex inner portion and a concave border. Anterior margins straight proximally but curving backwards distally. Six pairs of distinct, and one posterior pair of faint pleural furrows curve gently outwards and backwards from the axis, not reaching pygidial margin but dying out on the concave border. Faint interpleural furrows discernible on the three anterior pairs of pleural ribs. Doublure not seen. The flattened and incomplete pygidium in HM. A5810a, b (PI. 8, fig. 13) differs from HM. A5809 (PI. 8, fig. 14) in that a seventh pair of faint, backwardly directed pleural furrows is visible. This is probably not a significant difference. Surface of cranidium and pygidium smooth. Measurements (in mm.). HM. A5807b (external mould) Length of cranidium 2-30 Max. width of cranidium 3 00 Width of cranidium at palpebral lobes 1-95 Length of glabella 1-40 PALAEONTOLOGY, VOLUME 10 52 Measurements Cm mm.). Max. width of glabella Length of preglabellar field and anterior border Length (exsag.) of palpebral lobes 0-80 0-65 0-75 HM. A5809 (internal mould) Length of pygidium Max. width of pygidium Anterior width of axis Length of axis (including articulating half-ring) 1- 55 2- 45 0-60 1-20 Superfamily ceratopygacea Linnarsson 1869 Family ceratopygidae Linnarsson 1869 Genus dichelepyge Harrington and Leanza 1952 Type species. Dichelepyge pasquali Harrington and Leanza 1952, p. 203, by original designation. Dichelepyge phylax sp. nov. Plate 8, figs. 6, 8-10, 12, 15, 16; text-fig. 3. 1927 Hysterolenus tornquisti Moberg ?var. ; Stubblefield in Stubblefield and Bulman, p. 1 37, pi. 4, fig. 8. non 1898 Hysterolenus tornquisti Moberg, pp. 318-23, pi. 17, figs. 1-9. Derivation of name, phylax (Gr.) = jester, referring to the impression given of a grinning face on the cranidium. Holotype. HM. A5772a, b (PI. 8, fig. 6) internal and external moulds of a cranidium. Paratvpes. HM A5781a, b (PI. 8, fig. 8); HM. A5784 (PI. 8, fig. 9); HM. A5776 (PI. 8, fig. 10); HM. A5785 (PI. 8, fig. 12); H.M. A5770 (PI. 8, fig. 16). Other material. Two incomplete individuals, three cranidia, three librigenae, one hypostome, one thoracic fragment HM. A5773a, b to HM. A5775a, b, HM. A5777a, b, HM. A5778a, b, HM. A5779a, b (PI. 8, fig. 15), HM. A5780a, b, HM. A5782, HM. A5783, HM. A5786a, b. Diagnosis. Dichelepyge with anterior branches of facial suture diverging. Glabella with median tubercle. Pygidium with a rounded posterior margin and axis consisting of only three rings and a terminal piece. Pleural portions of thoracic segments relatively short (tr.). Description. Cephalon only weakly convex, broadly semicircular in outline, with long genal spines. Glabella, in holotype cranidium, weakly convex, raised a little above level of fixigenae and defined by broad, shallow, axial furrows gradually converging forwards. Length (sag.) of glabella about two-thirds median length of cephalon; basal width almost one-quarter the maximum width of the cephalon between the genal angles. Anteriorly the glabella is broadly rounded and laterally it is slightly constricted at the level of the first pair of glabellar furrows. Three pairs of lateral glabellar furrows present. First pair bifurcated, the posterior branches being very deep adaxially and directed obliquely backwards but not reaching occipital furrow. Anterior branches very short and indistinct. Second pair of lateral glabellar furrows consist of shallow, transverse pits situated at half the glabellar length, not reaching axial furrows. Anterior pair of furrows are rather longer and although reaching the axial furrows are extremely shallow at this point. A large median glabellar tubercle is situated at the level of the first glabellar furrows. Occipital furrow broad (tr.), deepest distally. Occipital ring gently convex transversely and gently HUTCHISON AND INGHAM: TRILOB1TES FROM THE TREMADOC SERIES 53 arched backwards, its posterior margin slightly flattened mesially. Median length (sag), about one-sixth the glabellar length, becoming narrower (exsag.) laterally. Length (sag.) of preglabellar field equal to about one-quarter the length of the glabella, gently convex (sag., exsag.), passing forwards insensibly into a broad, shallow, border furrow whose anterior margin ends abruptly. Narrow anterior border with slightly raised posterior ridge and anterior portion declined forwards. Palpebral areas of fixigenae narrow (tr.), with palpebral lobes near to glabella. Posterior portions wide, roughly quadrilateral text-fig. 3. Reconstruction of Dichelepyge phylax sp. nov. Approx. X8. in shape, extending laterally for a distance equal to two-thirds of the basal glabellar width. Palpebral lobes short and narrow, strongly crescentic, beginning at a level just to the rear of the anterior pair of glabellar furrows and extending backwards almost to the level of the first glabellar furrows. Palpebral furrows shallow. Short eye ridges run obliquely forwards in continuation of the lobes. Posterior border furrows shallow, well- defined but dying out laterally. Posterior borders narrow proximally, expanding a little distally where, on its posterior margin, each bears a small socket for the articulation of the first thoracic pleura. Facial suture seen most clearly in HM. A5770 (PI. 8, fig. 16). Anterior branches diverge at first at about 90°, then curve gradually forwards and inwards to cross the anterior border very obliquely, becoming confluent on the dorsal surface a very short distance from the anterior margin. Posterior branches of facial suture curve gently backwards and outwards from the palpebral lobes, then turn sharply backwards and finally curve outwards again to cut the posterior margin of the cephalon a short distance beyond the articulating sockets on the posterior borders. Librigenae large and almost flat, produced into long, narrow, slightly outwardly directed genal 54 PALAEONTOLOGY, VOLUME 10 spines which extend backwards for a distance at least equivalent to the median length of the cranidium. Lateral borders narrow, slightly elevated and gently concave in cross- section. Posterior borders ill-defined. Three very narrow, concentric grooves cross the librigenae parallel to the lateral borders. Innermost groove very faint. In addition, a broad, shallow groove set further from the border (PI. 8, figs. 15, 16) may be an im- pression of the inner margin of the cephalic doublure. Eyes narrow, crescentic, convex in cross-section, bounded below by a shallow furrow. Hypostome almost as wide as long, with strongly convex median body. Anterior border flat, short (sag.), crescentic in shape, becoming a little longer (exsag.) laterally where it is continued into prominent, backwardly truncated anterior wings. Anterior margin of hypostome strongly curved. Lateral notches right-angled. Lateral and posterior borders narrow except postero- laterally where the borders expand into small, rounded projections. Border furrow deepest opposite this pair of structures. Lateral margins straight, subparallel. Posterior margin curved backwards. Thorax of six segments, rather shorter than the median length of the cranidium. Axis occupies a little more than one-quarter of the total thoracic width anteriorly. Narrow axial furrows converge gradually backwards as far as the fourth segment, beyond which they curve inwards more strongly. Axial rings decrease in length (sag.) progressively from front to back, moderately arched (tr.), strongly curved forwards distally, less so mesially. A faint transverse groove on each ring (PI. 8, fig. 16 (external mould)) is prob- ably an impression of the anterior margin of the articulating half-ring belonging to the segment behind. Small slit-like apodemal pits are situated in the lateral portions of the ring-furrows. Proximal portion of each pleura swollen anteriorly. A sigmoidal furrow crosses from the antero-proximal corner of the pleura behind the swelling to separate off a narrow (exsag.) posterior portion which itself expands a little distally, and even less so proximally, to form two small articulating sockets. The proximal socket, which is less obvious than the distal one, is situated adjacent to the axial furrow. It is clearly visible on the first thoracic segment of HM. A5770 (PI. 8, fig. 16). A shallow furrow in front of the pleural swelling defines a small anterior process which fits into the outer articulating socket of the segment in front. Another small process, not seen, is presumably present proximally. Each pleura is produced distally into a fairly flat, pointed, blade- like pleural tip, not in contact with adjacent segments. On the anterior segments the pleural tips are curved gently backwards but on successive segments the curvature is progressively more marked so that on the sixth segment the points are directed posteriorly. A shallow furrow on each pleural tip runs close to the posterior margin. Pygidium, excluding spines, paraboloid in outline. Maximum width equal to about twice the median length. Convex axis occupies about one-quarter the width of the pygi- dium anteriorly and extends backwards for half its median length. Axial furrows deep, converging posteriorly at about 45° at first, then becoming subparallel. Axis ends bluntly but faint continuations of the axial furrows continue on to border. Three axial rings, similar to those of the thorax, and a terminal piece present. Pleural regions gently convex proximally, with a broad concave border which is longest (sag.) posteriorly. Two pairs of narrow interpleural furrows extending faintly on to the concave border alternate with three pairs of shorter, but deeper, pleural furrows. A number of very fine, concentric, but sinuous, grooves are present on the pygidial border. Two pairs of lateral border spines present. Anterior pair short, blade-like, similar to the spines of the HUTCHISON AND INGHAM: TRILOBITES FROM THE TREMADOC SERIES 55 last thoracic segment, but recurved. Posterior pair long and slender, gently curved, reach- ing backwards for a distance equivalent to a little more than the median length of the pygidium. Surface of test fairly smooth except for the postero-mesial part of the glabella, the posterior portions of the fixigenae, the occipital ring and the axial rings, all of which are finely granular. Measurements of type specimens (in mm.). EM. = external mould, IM. = internal mould. HM. A5772b HM. A5770 HM. A5776 HM. A5781a HM. A5784 EM. EM. IM. IM. IM. Width of cephalon at genal angles 5-80 (est.) Length of cranidium Max. width of crani- 4-40 3 00 3-50 (est.) dium (est.) Width of cranidium 5-55 3-60 at palpebral lobes Width of cranidium 3-15 2-20 (est.) across preglabellar field 3-80 2-80 (est.) Length of glabella with occipital ring Basal width of 3-30 215 2-65 glabella Length of palpebral 2-25 1-40 (est.) 1 80 lobes Median length of thorax Max. width of 0-65 0-50 2-70 thorax (est.) 5-40 5-70 Anterior width of thoracic axis Median length of 1 80 pygidium excluding articulating half- ring Max. width of 1 65 2-60 1-80 pygidium Anterior width of 3-50 (est.) 4-60 3-55 pygidial axis 0-85 1-20 (est.) 0-75 Length of hypostome HM. A5785 (IM.) 3 00; max. width 3T5 (est.) Discussion. Dichelepyge pasquali Harrington and Leanza (1952, p. 203, pi. 1, figs. 3-6; 1957, p. 184, figs. 97, 98, 1 a-d), from the Kainella meridionalis Zone of the Lower Tremadoc of Salta Province in the Eastern Cordilleras of Argentina, is the only other species in the genus. It is of approximately the same age as the Shropshire specimens of D.phylax sp. nov. and is very similar to the new form. Both species possess two pairs of marginal pygidial spines (a generic character) but there are several striking differences in proportion, the most noticeable of which is in the size of the pygidium. In D. pasquali the median lengths of pygidium and cranidium are approximately equal, whereas in D. phylax the median length of the pygidium is only about half that of the cranidium. The pygidial axis is longer, narrower, has more axial rings in the South American 56 PALAEONTOLOGY, VOLUME 10 species (seven, compared with three in D. phy/ax ), and the pygidial margin is flattened mesially, that of D. phylax being rounded. The holotype of D. pasquali , a cranidium, seems to have suffered slight crushing which may account for the more forward position of the eyes and the transverse fold in front of the glabella. Nevertheless, the anterior branches of the facial suture are less divergent than in D. phylax and there is no median glabellar tubercle. Also, the posterior portions of the fixigenae are much wider (tr.) in D. pasquali and as it is this part of the cephalon which articulates with the thoracic pleurae, the proximal, articulating portions of the latter are also much wider (tr.) than in the Shropshire form. Finally, in D. pasquali, the free, blade-like extremities of the pleurae are proportionally longer, particularly on the four posterior segments. Suborder trinucleina Swinnerton 1915 Family myindidae Hupe 1955 Genus myindella gen. nov. Type species. Myindella crux sp. nov. Diagnosis. Myindid with carinate glabella and three pairs of short lateral glabellar fur- rows. Distinct paraglabellar areas present. Preglabellar field short, with transfrontal ridge. Cephalon with marginal suture has narrow elevated border surrounding pitted genal region and long genal spines. Border furrow with single row of larger pits. Eye ridges club-like. Occipital and axial rings with large median tubercle or spine. Thorax/ pygidium with narrow axis, narrow (exsag.), transverse, furrowed pleurae and small, triangular terminal piece. Number of segments unknown. Discussion. Myindella agrees with Myinda Stubblefield (in Stubblefield and Bulman 1927, p. 130) in the general plan of the cranidium, similar eye ridges and transfrontal ridge and the number of glabellar furrows. Also, the occipital ring in Myinda uriconii (op. cit., p. 131, pi. 4, fig. 3) may possess a median tubercle. The two genera differ in that Myindella has a more transverse cephalon and much shorter (sag.) preglabellar field and transfrontal ridge, a carinate glabella with depressed lateral portions, and para- glabellar areas. In addition, the genal region internal to the border is pitted in Myindella and the row of large pits in the border furrow is not present in Myinda. Hupe (1955, pp. 149, 155) included the Myindidae in his Utioidae because of the [quite different] preglabellar structures shown by Inouyia Walcott and allied genera, but Whittington (in Moore 1959, pp. 0167, 0512) listed the family under ‘Order Uncertain’. Harrington and Leanza (1957, p. 209) noted that Araiopleura Harrington and Leanza displays certain similarities to Myinda and that Myinda may belong to the Hapalopleuri- dae. The new myindid material described here strengthens the view that the Hapalopleuri- dae and the Myindidae are related but there are sufficient differences between them to warrant the retention of the Myindidae as a separate family within the Trinucleina. Major differences between the two families include the presence of opisthoparian facial sutures and lack of a transfrontal ridge and distinct cephalic border in hapalopleurid genera. Similarities are seen in the general shape of the cephalon, glabella, and eye ridges. Also, the multisegmented post-cephalic exoskeleton with no obvious distinction between thorax and pygidium, so characteristic of the Hapalopleuridae and Alsata- spididae, is also found in Myindella and therefore presumably in Myinda. The presence of a row of large pits in the cephalic border furrow of Myindella, together with the HUTCHISON AND INGHAM: TRILOBITES FROM THE TREMADOC SERIES 57 marginal suture and an indication of a lower lamella (see below), suggests a relation- ship with the Dionididae and the Trinucleidae. The carinate glabella and axial tubercles or spine bases of Myindella may also be important in this respect as both are seen in some trinucleid genera (e.g. Reedolithus and some species ofTretaspis). The post-cephalic segments in general configuration also recall those of Lloydolithus as figured by Whittard (1958, pi. 11). text-fig. 4. Reconstruction of Myindella crux gen. et sp. nov. Approx. X 15. Myindella crux gen. et sp. nov. Plate 8, figs. 1-5, 7; text-fig. 4. Derivation of name, crux (Gr.) = cross, referring to the cross-shaped arrangement of ridges on the cephalon. Holotype. HM. A5802 (PI. 8, figs. 1, 5) external mould of incomplete cranidium. Paratypes. HM. A5805a, b (PI. 8, figs. 2, 3); HM. A5803a, b (PI. 8, fig. 4); HM. A5804 (PI. 8, fig. 7). Other material. Isolated thoracic segments HM. A5806a, b. Description. Cephalon twice as wide (tr.) as long, roughly semicircular in outline, some- times a little flattened frontally and antero-laterally, as in the holotype. Genal angles produced into long, stout, and slightly curved genal spines having a triangular cross- section. In the holotype, the glabella, occupying about two-thirds the median length of the cephalon and one-fifth its maximum width, is roughly parallel-sided, a little convex laterally and bluntly rounded in front. A high median crest runs forwards from the occipital furrow, but becomes reduced and finally disappears about two-thirds the length of the glabella from its posterior margin. Laterally the glabella is somewhat depressed where it bears three pairs of short, transverse, weakly impressed, and equidistant lateral glabellar furrows. Axial and preglabellar furrows shallow. Occipital furrow shallow 58 PALAEONTOLOGY, VOLUME 10 mesially but deep abaxially where it contains a pair of deep apodemal pits. Occipital ring strongly convex (tr.), arched backwards and narrow (exsag.) abaxially, bearing a prominent median tubercle or spine base. Preglabellar field flat, extending forwards for a distance equal to about one-third the length of the glabella, crossed sagittally by a narrow, sharply defined, and convex (tr.) transfrontal ridge which links the frontal lobe of the glabella wth the narrow anterior border. Genal areas quadrant-shaped, flat, with narrow lateral borders. Shallow border furrows contain a row of relatively large, rather irregularly distributed pits, there being fifteen to twenty pits between the transfrontal ridge and the genal angles on each side of the cephalon. Posterior borders broad (exsag.), expanding abaxially, highest along the posterior margin and declined forwards. Posterior border furrows shallow but sharply defined frontally. No dorsal facial suture. Marginal suture present, becoming dorsal only at the genal angles, the genal spines thus belonging to a ventral lamella. Specimen HM. A5804 (PI. 8, fig. 7), although poorly preserved, shows evidence of the existence of a lower lamella as in trinucleids and dionidids. The cranidium and lower lamella have parted along the marginal suture and the former has moved forwards a little relative to the latter, clearly showing the separation between the genal spines and the postero-lateral corners of the cranidium. The row of pits in the marginal furrow of the cranidium is discernible but close behind is a ridge which seems to be an impression on to the cranidium of a ventral structure, possibly a row of pits similar to those on the dorsal surface and originally having been opposed to them. Con- vex eye ridges extend outwards and a little backwards from the postero-lateral corners of the frontal glabellar lobe to the centre of the genal areas. They are very sharply defined and expand somewhat abaxially. There is no indication of a lens-bearing surface. Small, gently convex paraglabellar areas present opposite the preoccipital glabellar lobes. Genal areas, internal to border furrows and with the exception of the eye ridges and paraglabellar areas, are covered with small, shallow pits. Eye ridges have small granules adaxially. Hypostome unknown. Post-cephalic exoskeleton not known in its entirety and proportions belonging to thorax and pygidium impossible to ascertain due to the similarity of the segments through- out its length. Specimen HM. A5805a, b (PI. 8, figs. 2, 3) may represent a pygidium but the margin is not entire and each segment is very similar to others associated with a cephalon (HM. A5804, PI. 8, fig. 7). Pygidium may, therefore, be represented by the small, triangular terminal piece. Total number of segments unknown. Axis convex, occupying a little more than one-fifth the width of the thorax frontally. Each axial ring bears a median tubercle or spine base smaller than that borne by the occipital ring. Each pleura is narrow (exsag.) and straight for most of its length and has a very distal fulcrum and a rounded termination. A deep pleural furrow runs from the axis parallel to the anterior and posterior margins of the pleura, maintaining its depth almost to the ter- mination of the segment. Posteriorly the segments become progressively shorter (tr.). The postcephalic exoskeleton is terminated by a small, transverse, triangular plate on to which the axis continues to the posterior margin; an indication of segmentation is present on the pleural portions. Measurements (in mm.) (all external moulds). HM. A5802 HM. A5803b Max. width of cephalon 5 00 (est.) 5 00 Median length of cephalon 2 50 2-20 HM. A 5 804 4-50 (est.) 215 HUTCHISON AND INGHAM: TRILOBITES FROM THE TREMADOC SERIES 59 Basal width of glabella 100 100 (est.) Median length of glabella 1-55 1 -35 Length of preglabellar field Anterior width of thorax 0-45 0-50 (est.) 3-65 Anterior width of axis 0-75 Dimensions of specimen HM. A5805b (PI. 8, fig. 3) Median length 1-15 Maximum width 3-05 Acknowledgements. The authors would like to thank Sir James Stubblefield and Professor T. Neville George for kindly reading the manuscript and offering much useful advice and helpful criticism. REFERENCES angelin, n. p. 1854. Palaeontologica Scandinavica. Academia Regia Scientarium Suecanae ( Hoi - miae ), 2, i-ix, 21-92, pis. 25-41. Harrington, h. j. and leanza, a. f. 1952. La classification de los ‘Olenidae’ y de los‘Ceratopygidae\ Revta. Asoc. Geol. Argent. 7, (3), 190-205, 1 pi. • 1957. Ordovician trilobites of Argentina. Univ. Kansas (Lawrence), Dept. Geol. Spec. Pub. 1, 1-276, 240 figs. hupe, P. 1955. Classification des trilobites. Annls. Paleont. (Paris), 41, 91-235, figs. 93-247. moberg, J. c. 1898. En trilobit fran Skanes Dictyograptusskiffer. Geol. For. Stockh. Fork. 20, 317-24, pi. 17. moore, R. 1959. Treatise on Invertebrate Paleontology, Part O Arthropoda 1, i-xix, 01-0560. Stubblefield, c. J. and bulman, o. M. b. 1927. The Shineton Shales of the Wrekin district. Q. Jl geol. Soc. Lond. 83, 96-146, pi. 3-5. whitt ard, w. f. 1958. The Ordovician trilobites of the Shelve Inlier, west Shropshire, Part 3. Palaeon- togr. Soc. [Monogr.] R. HUTCHISON Ministry of Mines and Power, Geological Survey Division, P.M.B. 2007, Kaduna South, Nigeria J. K. INGHAM Hunterian Museum, University of Glasgow, Glasgow, W.2 Manuscript received 24 November 1965 VARIATION AND ONTOGENY OF SOME OXFORD CLAY AMMONITES: DISTIC HO CERA S BICOSTATUM (STAHL) AND HORIOCERAS BAUGIERI (D’OR BIGNY), FROM ENGLAND by D. F. B. PALFRAMAN Abstract. Variational and ontogenetic studies of Distichoceras bicostatum (Stahl) and Horioceras baugieri (d’Orbigny) have shown identity in their early stages. Variation in protoconch size is consistent and small, as is the diameter of the nepionic construction. Divergence in shell form occurs only at the onset of maturity, which in H. baugieri begins at about 8-10 mm. and in D. bicostatum at about 30-35 mm. It is concluded that the two ‘species’ are a sexually dimorphic pair. The name D. bicostatum has priority. Neither Distichoceras bicostatum (Stahl) nor Horioceras baugieri ( d’Orbigny) appears to be plentiful in this country. Among the author’s collection of several thousand am- monites from the Oxford Clay of Woodham, Bucks. (Arkell 1939 and Palframan 1966), only eight belonged to these species. From a locality not recorded in the literature as having typical Oxford Clay facies, but mentioned by Arkell (1945) as having crushed ammonites in a shale of Coronatum age, at Peckondale Hill, near Malton, Yorkshire (Grid. Ref. 745686), the author collected more than a thousand ammonites from the Athleta/Lamberti Zones of the Oxford Clay and found only three specimens of these species. The actual proportion of the ammonite fauna these two species occupy is generally not given, but from the numbers or frequency mentioned in the literature it would appear that they are at best rare and, more often, extremely rare. Preservation. Almost all the specimens examined from the Oxford Clay of Eye, Woodham, Oxford, Dauntsey, and Tidmoor Point are preserved as internal pyrite moulds; in no specimen has the original shell been preserved. Some specimens from these localities and all those from Peckondale Hill are internal moulds of limonite. Because of the presumed physico-chemical factors which influenced preservation of many Oxford Clay ammonites, rarely are pyritic moulds to be found with a diameter greater than 2-3 cm. A notable exception to this is one superbly preserved phragmocone of Distichoceras bicostatum (Stahl), OUM J25688, from the Oxford Clay of Tidmoor Point, Dorset, which has a diameter of 5 cm. The body chamber, however, is almost entirely lacking (see PI. 9, fig. If). Several small ammonites from the Oxford Clay, which are almost certainly the juvenile stages of D. bicostatum, have been found and it is these which furnish most of the information relating to the early ontogenetic stages mentioned here. The later ontogenetic stages, especially those of maturity, are largely based on specimens from the Hackness Rock of the Yorkshire Coast. Specimens from this bed are usually preserved to diameters of 4-7 cm. and are internal moulds composed of hard, slightly oolitic, limestone; in a very few cases tiny patches of shell material have been preserved, which appear to retain their original structure. The ammonites from the Hackness Rock often lacked body chambers and almost all had indifferently preserved inner whorls. [Palaeontology, Vol. 10, Part 1, 1967, pp. 60-94, pis. 9-13.] D. F. B. PALFRAMAN: SOME OXFORD CLAY AMMONITES 61 Within the 70 ft. of Oxford Clay exposed at Woodham, Bucks., is a one-foot thick band of compact marly limestone, the ‘Lamberti Limestone’ of Arkell (1939 — see this work for details of the exposure). The ammonites from this bed are generally poorly preserved internal moulds composed of the same material as the surrounding matrix and often crushed. The shell is commonly represented by a fine, powdery, black film covering the mould. Septa are, however, frequently preserved as relatively resistant calcite. The inner whorls of these ammonites are often broken, lacking or preserved as featureless recrystallized calcite, entirely unsuitable for ontogenetic studies. From the clays beneath the Lamberti Limestone are the familiar pyritic nuclei of about 2 cm. diameter. Material. Altogether some 63 specimens belonging to these two species have been examined, 56 from England and 7, for comparative purposes, from Europe. They are recorded from the following localities: Specimen Locality Number Sex Bed/Horizon Collector 1. Yorkshire a. Scarborough BM 39525 9 ‘Kellaway Rock’, Callovian W. Bean BM 50622 9 Kellaways Rock, Callovian J. Morris BM 89044 $ Kellaways, Rock Callovian J. S. Bowerbank BM C69282 9 Scarborough Grey Limestone (Lamberti Zone) L. F. Spath SM J5618-21 4 9 9 Kellaways Rock J. Leckenby SM J47113 9 Kellaways Rock b. Gristhorpe Bay SM J5622 9(?) Kellaways Rock J. Leckenby SM J5623 9 Kellaways Rock c. Peckondale Hill LU 263-4 2 9 9 Oxford Clay D. F. B. Palt'raman LU 265 <3 Oxford Clay D. F. B. Palframan 2. Eye, near Peter- borough BM Cl 5708-1 BM C 1 57 1 2 j 2 3 3, 2jj l 9(?) J Oxford Clay E. T. Leeds 3. Woodham, OUM J 14560 3 Oxford Clay R. A. Monkhouse Bucks. OUM J20851-3 3 9 9 Oxford Clay, Lamberti Zone W. J. Arkell OUM J20854 9(?) Oxford Clay, Lamberti Zone W. J. Arkell OUM J25677-) OUM J25684 j 4 ). A slight thickening of the ribs in mid-flank gives a third variation of lateral ornament, as shown by specimen SM J47113, that of a bullate spiral (PI. 11, fig. 7 a). 01 1-0 10 70 DIAMETER(mm) — text-fig. 5. Graph showing the relationship between Diameter and Height of Distichoceras bico- slatum (Stahl) $ and $. Dashed lines connect recordings made on the same specimen. Inset, the same graph plotted on a linear scale, showing the plot of the approximate best-fit line. The arrowed points ds cj and ds ? represent the position of the mean diameter at which septation ceased in mature speci- mens of male and female respectively. Two rather delicate forms of ornament seen only on one juvenile specimen, OUM J25684, are spiral striae and small crescentic pits. The spiral striae are strongest near the umbilical shoulder becoming progressively weaker ventrally and fading altogether in the ventro-lateral region. On the mid-flank of the same specimen is a spiral series of small, shallow, convex, crescentic pits (PI. 11, figs. 3c, d). D. F. B. PALFRAMAN: SOME OXFORD CLAY AMMONITES 69 Remarks. The spiral striae and crescentic pits, just mentioned, may be impressions of shell ornament or, possibly, impressions of muscle attachments. Ribbing. The earliest development of ribbing is at a diameter of about 12-13 mm. (OUM J20854, see PI. 9, fig. 8). Each ventro-lateral spine is associated with a looped rib with no independent ribs between (PI. 9, fig. Id). The looped ribs are rursiradial (PI. 9, figs. 7/and 8; PI. 11, fig. 7 a; and PI. 12, figs. 3, 5, 6b, la, 8 b, and 9a), though in the early stages of specimen OUM J25688 (PI. 9, fig. Id) only feebly so. In a few cases infrequent, single (non-looped) ribs are connected with individual ventro-lateral spines (PI. 12, fig. 6b) and in one case there are independent ribs not connected with ventro- lateral spines (PI. 12, fig. la). These cases are almost certainly ‘normal exceptions’ within the species under consideration. In the later stages of phragmocone growth the ribs of A text-fig. 6. Ornamentation in Distichoeeras bicostatum (Stahl), a, juvenile male(?) from the Lamberti Zone, Tidmoor Point, Dorset, England, showing three narrow fillets with wide grooves between: OUM J25687. B, juvenile male from the Athleta/Lamberti Zone, Wood- ham, Bucks., England: OUM J14560. The point a: marks the position of the last suture. The sinuous elevation may represent a muscle-scar (see also PI. 9, fig. la). Both figs. X 5. the ventral flank and the ventro-lateral spines become somewhat degenerate. The spines become indistinct and the ribs at this stage do not appear to be looped or intimately associated with the spines (PI. 9, figs. If and h). Ribbing on the ventral flank is never very strong and is best seen under low-angled lighting. Rib strength may be weak (SM J 562 1 , PI. 11, fig. 8 a) to relatively strong (BM C69282, PI. 13, fig. 2). In the early growth stages ribbing is almost entirely confined to the ventral portion of the flanks: in one observed case, OUM J20854, ribbing is also present on the lower, or dorsal, portion of the flank at a diameter of about 13 mm. (PI. 9, fig. 8). From the material studied this certainly appears to be atypical, most specimens do not develop this inner ribbing until a much later stage in their ontogeny. Generally, in mature individuals, this feature develops on the final quarter whorl of the phragmocone (PI. 11, fig. 8u). On the dorsal portion of the flank the ribbing is quite strongly prorsiradial, but towards a mid-flank position becomes rectiradial or even rursiradial (PI. 9, fig. 8 and PI. 11, fig. 8 a). These lower ribs are usually separated from the upper by some form of spiral ornament situated on the mid-flank. They are related to the upper ribs in their 70 PALAEONTOLOGY, VOLUME 10 early development, in that each lower rib is opposite an upper looped rib. Towards the adoral end of the mature phragmocone, where the ventro-lateral spines become degenerate and in consequence the upper ribs are not looped, the lower and upper ribs are paired. This is more easily observed when the spiral ornament, which separates the upper and lower ribs, fades towards the end of the phragmocone and the ribs are text-fig. 7. Cross-sections through Distichoceras bicostatum (Stahl), a, juvenile from the Athleta( ?) Zone, Eye, near Peterborough, England: BM Cl 5712. Specimen entirely septate; note the tabulation of the venter on the final preserved whorl, b, male from the Athleta/Lamberti Zone, Woodham, Bucks., England: OUM J25680. Drawn at D = 12-4 mm. (maximum septate diameter of adult), c, juvenile female(?) from the Athleta/Lamberti Zone, Woodham, Bucks., England: OUM J25681. Drawn at D = 11 1 mm. d, juvenile female from the Elackness Rock, Scarborough, Yorks., England: BM 89044. Section through immature phragmocone. Figs, a, b, and c, X 10, fig. d, X 3. continuous across the whole flank (PI. 12, fig. 3). The rib-type of the phragmocone immediately before the body chamber in mature specimens is convex to biconcave or sinuous (Arkell 1957a, p. L89). Sutures Sutural ontogeny. The sutural ontogeny of D. bicostatum $ is best illustrated diagram- matically (text-fig. 8). The succession of sutures (A-X) comprising the sutural ontogeny D. F. B. PALFRAMAN: SOME OXFORD CLAY AMMONITES 71 of text-fig. 8, is determined solely by increasing order of the diameter at which the sutures were drawn (from several different specimens). Because of individual variation and growth-rates, adjacent sutures (in text-fig. 8) drawn at similar diameters but from different specimens may not in fact reflect a true sutural ontogeny and would better con- form by being reversed (as S and T in text-fig. 8). It should also be noted that text-fig. 8 is a composite sutural ontogeny of both supposed males and females of D. bicostatum, the presumed sex of each specimen from which a suture was drawn being denoted in the text-fig. caption. The addition of new sutural elements occurs at the umbilical seam, ‘U-type ontogeny’ of Schindewolf (1954). Remarks. As the works of Schindewolf (1954, 1960, 1962, and 1963) have shown, there is a basic pattern according to which the sutural ontogeny of Jurassic ammonites can seemingly be predicted. This is, briefly, the formation of a septum closing the proto- conch (proseptum) which at its margin gives rise to the prosuture with a predominantly large ventral saddle. This first-formed suture is very different from all succeeding sutures which are simply elaborations on the second-formed suture (primary suture). The primary suture is composed of more or less equally sized elements, the lobes being: external (or ventral), lateral, U2, Ul5 and dorsal. This is the quinquelobate basic suture of Schindewolf (1954). D. bicostatum $ conforms to this pattern as shown by Schinde- wolf (1963, p. 407, fig. 228) and herein text-fig. 8. Sutural variation. In order to assess qualitatively the sutural variation at a prescribed diameter, the most ornate and variable elements of the suture (ventral and lateral lobe and first and second lateral saddles) from three randomly chosen specimens were drawn at a diameter of about 38 mm. Sutural differences either side of the venter in any single specimen are extremely small and such differences are, in part, influenced by the position of the ventro-lateral spines or interference by earlier formed septa (see text-fig. 9). Differences between the sutures of the three specimens are more marked and are prob- ably influenced by the absolute diameter at which they were drawn (in text-fig. 9, a is drawn at a smaller diameter, 38 mm., than c, 38-5 mm.). Remarks. Another factor which may influence the variation seen is that of absolute size of the phragmocone of the adult specimen. Ventral tubercles on the phragmocone of Creniceras renggeri (Oppel) d and $ do not develop until the last quarter whorl of the phragmocone in mature specimens irrespective of the size of the phragmocone (Palframan 1966). As Makowski (1962) has pointed out, the diameter at which certain features develop is dependent on the stage of growth of an individual and not its size. This may also be true of sutures which have a level of complexity, or development, for a prescribed diameter which is influenced by the ultimate size of the phragmocone of the mature specimen. In other words, a small mature specimen of an ammonite species may have slightly more advanced sutures at any prescribed diameter than a larger speci- men of the same species at the same diameter. Even so the final sutures of the smaller specimen will almost certainly be less complex than the final sutures of the larger specimen. A third factor influencing sutural differences may well be one of evolution as the material examined here almost certainly extends over two ammonite zones (Athleta and Lamberti). Finally, the variation may be in part geographic. The sutures of specimen OUM J25684 from Woodham, Bucks., here considered as D. F. B. PALFRAMAN: SOME OXFORD CLAY AMMONITES 73 being a juvenile form of D. bicostatum ?, are irregularly spaced (see PI. 11, figs. 3c and d). This spacing may be due to any one, or a combination, of several factors which may affect the growth-rate: (a) relative abundance/scarcity of food, (b) variable salinity or temperature of the sea-water, (c) disease, (d) periods of reproductive activity. The number of sutures on the final preserved whorl of the specimen in question is eight com- pared with twelve for other specimens of a similar size: BM C28325 (PI. 9, fig. lc) and OUM J25681 (PI. 11, fig. 4a). Two pairs of adjacent sutures on specimen OUM J25684 are closely spaced, at diameters of about 7 mm. and 10 mm. respectively. The range of sutural approximation observed for ten specimens of Horioceras baugieri (d’Orbigny) (which in this paper is considered as being D. bicostatum <3) is 8-7 mm. to 16-7 mm. It may be that the specimen in question (OUM J25684) has changed sex during life as do some living molluscs. The latter explanation is considered unlikely, though as this feature has not been seen in other specimens studied here, the explanation of the phenomenon is itself, no doubt, unusual. The mature phragmoeone. Sutural approximation and degeneration is regarded as a feature of maturity throughout this paper, along with other points generally considered as denoting maturity and listed by Callomon (1957). These are: uncoiling of the body chamber at the umbilical seam, modification of ornament, and the development of apertural modification such as lappets, rostra, and constrictions. The mean diameter at which septation ceases in mature specimens was found to be 39-5 mm. with a range of 3T5 to 49-7 mm. A phragmoeone of D. bicostatum $ figured by R. Douville (1914, PI. 5, figs. 20 and 20 a) at ‘grandeur naturelle’, has a diameter of about 70 mm. The author has seen a plaster cast of this specimen in L’Ecole des Mines, Paris and verifies the size. From the composite phragmoeone ontogeny constructed it is estimated that from the prosuture to the beginning of the body chamber in D. bicostatum $ there are 1-lb com- plete whorls. On no phragmoeone did the author see original shell material. BODY CHAMBER The following description of the body chamber rests almost entirely on two specimens, one from the Hackness Rock of Scarborough, Yorks. (BM 50622), the other from the Lamberti Limestone of Woodham, Bucks. (OUM J20851); the former being complete, the latter with a damaged aperture. text-fig. 8. Sutural ontogeny of Distiehoceras bicostatum (Stahl), a, prosuture, BM Cl 5712, female(?), D = 0-24 mm. X 136; b, prosuture, OUM J25687, male(?), D = 0-29 mm. X 120; c, primary suture, OUM J25681, female(?), D = 0 29 mm. X 120; d, primary suture, OUM J25687, male(?), D = 0-31 mm. X 115; E, female(?), OUM J25681, D = 0-61 mm. xlOO; F, female(?), OUM J25681, D = 0-77 mm. X 91 ; g, male( ?), OUM J25687, D = 1-01 mm. X 71 ; h, female, OUM J25688, D = 2-21 mm. X 38; i, female( ?), OUM J25681, D = 2-92 mm. x34; J, female(?), OUM J25681, D = 417 mm. X23; k, male, OUM J25677, D = 4-75 mm. Xl8; l, juvenile, OUM J25686, D = 5 04 mm. Xl7; m, male( ?), OUM J25679, D = 5-4mm. Xl7; n, juvenile, OUM J25682, D = 5-8 mm. X 16; o, female(?), OUM J25681, D = 6-3 mm. x 14; p, juvenile, OUM J25683, D = 6 8 mm. Xl3; Q, female, OUM J25688, D = 7-3 mm. x 12; r, male, OUM J25677, D = 8-2 mm. x 10; s, female!?), OUM J25681, D= 101mm. X8-3; T, male, OUM J25680, D= 110 mm. x81; u, female!?), OUM J25685, D = 15 5 mm. X5-7; v, female, OUM .125688, D= 160 mm. X5-6; w, female, OUM J25688, D = 26 5 mm. X2-9; x, female, OUM J25688, D = 45 mm. X T6. For localities and horizons see chart in text. The order of succession (a-x) is determined solely by the increasing diameter at which each suture was drawn. 74 PALAEONTOLOGY, VOLUME 10 General growth The umbilical wall retains its steepness and the umbilical seam begins to uncoil but not markedly (PI. 9, fig. 7/and PI. 13, figs, la and 2): this is best shown graphically (text- text-fig. 9. Sutural variation in Distichoceras bicostatum (Stahl). Females: a, OUM J25688 at D = 38 mm. from the Lamberti Zone, Tidmoor Point, Dorset, England; b, BM 39525 at D = 38-2 mm. from the Hackness Rock, Scarborough, Yorkshire, England; c, BM 50622 at D = 38-5 mm. from the Hackness Rock, Scarborough, Yorkshire, England. The positions of spines (dot-dash lines) and adjacent sutures (dashed lines) are clearly marked. All figs. X 5. D. F. B. PALFRAMAN: SOME OXFORD CLAY AMMONITES 75 fig. 4). The W/D and HH/D ratios show negative allometry in the final growth stages of the body chamber (text-figs. 3 and 5). With only one complete specimen as evidence, the body chamber extends for a little more than half a whorl, bringing the total number of whorls from the proseptum to an estimated 7|-8|. Ornament Ribbing. Many of the morphological features of the phragmocone are lacking or de- generate on the body chamber. The venter, though remaining tabulate, loses the ventro- lateral spines and ventral ridge, the transformation occurring either immediately before the end of the phragmocone (see PI. 9, fig. lb) or on the earliest part of the body chamber (see PI. 13, figs. 1 b-c and 3). As a result of the degeneration of the ventro- lateral spines, the ribs are no longer looped and, due to the absence of the lateral orna- ment, continue uninterrupted to the umbilical shoulder where they fade. The ribs of the body chamber are of the same form as those of the phragmocone, essentially sinuous (see PI. 12, fig. 3 and PL 13, fig. 1 a). Ribbing on the early part of the body chamber is fairly dense, becoming more distant and finally dense again near the peristome (see PI. 1 3, figs. \a and 3). The ribbing of specimen OUM J20851 is strong on the ventro-lateral area, weakening on the flanks, and not extending as far as the umbilical shoulder. Parallel to the ribs and best seen on the ventro-lateral area are fine growth lines (see PI. 13, fig. 1 a). In the final growth stages ribbing becomes denser; the peristome assumes the outline of the rib-form but with slightly greater ventral prorsiradiation, forming a small rostrum to an otherwise simple peristome (BM 50622 see PI. 13, figs. 1 a, d). On the same speci- men the ribbing crosses the venter of the body chamber, but is weaker ventrally than ventro-laterally (see PI. 13, fig. 1 b). Lateral ornament. The spiral or lateral ornament, which generally fades towards the end of the phragmocone, is retained almost to the end of the body chamber in the form of a rather indistinct fillet in specimen BM 50622 (see PI. 13, fig. 1 a), but in this case does not interrupt the lateral ribbing. Remarks. No consistent (thus discounting the lateral fillet/groove) morphological fea- ture was seen which could be interpreted as a muscle scar, nor is there a feature which the author considered to be an annulus (Crick 1898). The latter feature may, however, have been masked by the vagaries of preservation. The annulus has been noted in other oppelid ammonites (Crick 1898 and Palframan 1966), but in these cases the mode of preservation was different, usually as internal pyritic moulds. All the material examined has been in the form of internal moulds ; in the case of speci- men BM 50622, patches of shell material remain. These are probably inner shell layers and show feather structure (see PI. 13, fig. \e), a feature which has been recorded on other oppelid ammonites (Arkell 1957u and Holder 1955). These patches of shell, even in the ventro-lateral and ventral regions, show precisely the same ornament as is shown by the internal mould and include such features as the weak lateral fillet and fading ventral ridge. As far as the author is able to determine there do not appear to be any significant differences, in the early stages of ontogeny, between specimens of D. bieostatum $ from the localities previously listed, nor between preparations of the juvenile stages of undoubted specimens of this species and a collection of nuclei which is identical with 76 PALAEONTOLOGY, VOLUME 10 the early stages of both D. bicostatum (= D. bicostatum $ ) and Horioceras baugieri (d’Orbigny) (= D. bicostatum J) as is shown in Table 1. The later growth stages de- scribed here depend almost entirely on specimens from the Hackness Rock of the York- shire coast, but a large specimen from Tidmoor Point, Dorset, and three large specimens from Woodham, Bucks., agree very closely in all respects with those from Yorkshire. VARIATION AND ONTOGENY OF HORIOCERAS BAUGIERI (d’orbigny) (It is considered in this article that Horioceras baugieri (d'Orbigny) is the male of a dimorphic pair and is here referred to as Distichoceras bicostatum (Stahl) $.) Family oppeliidae Bonarelli 1894 Subfamily distichoceratinae Hyatt 1900 [= BONARELLIDAE Spatll 1925] Genus horioceras Munier-Chalmas 1892, Type species. Ammonites baugieri d'Orbigny 1842-9. Distichoceras bicostatum (Stahl) S Plate 9, figs. 2 a-b, 3a-b, 4, 5 (7)a-b, 6( ?) ; Plate 10, figs. 1 a-d, 2 a-c, 3 a-c, 4 a-c; Plate 11, figs, 1, 2, 6: Plate 12, figs. 1, 2, 4; text-figs. 1 ( ?), 3-5, 6, 7(1), 8, 10, 11. 1842-51 Ammonites baugieri ; d’Orbigny, p. 445, pi. 158, figs. 5-7. 1852 Ammonites bidentatus ; Quenstedt, p. 367, pi. 28, fig. 8. 1858 Ammonites bidentatus ; Quenstedt, p. 531, pi. 70, fig. 10. 1886-7 Ammonites bidentatus ; Quenstedt, p. 736, pi. 85, figs. 16-22, 24. 1898 Distichoceras baugieri', Crick, p. 100, pi. 20, fig. 8. 1914 Oppelia (Horioceras) baugieri (pars); Douville, R., p. 16, fig. 10, pi. 5, figs. 17, 21, 21 b, 22, 22 a. EXPLANATION OF PLATE 10 Distichoceras bicostatum (Stahl) Fig. 1. Male from the Oxford Clay of Eye, near Peterborough, England: BM Cl 5710. Mature phrag- mocone with a quarter of a whorl of body chamber, a, side view, note lateral groove; b , ventral view, note degeneration of the ventral ridge and relative increase in spine size adorally; c, ventral view; d, preparation of the phragmocone (cf. Plate 9, figs. 1 c and la). Fig. 2. Male from the Athleta/Lamberti Zone of Woodham, Bucks., England: OUM J25680. Mature specimen showing one-third of a whorl of body chamber, a, side view, note approximation of sutures and uncoiling of the body chamber at the umbilical seam; b, ventral view of body chamber, note the complete loss of the ventral ridge and the enormity of the ventro-lateral spines; c, ventral view, the most adapical part shows the presence of the ventral ridge. Inset x 1. Fig. 3. Male from the Athleta/Lamberti Zone, Peckondale Hill, near Malton, Yorkshire, England: LU 265. Mature specimen with a third of a whorl of body chamber, a, side view, note sutural approximation and small crescentic pits on the flank; b, apertural view; c, ventral view. Fig. 4. Male from the Athleta/Lamberti Zone of Woodham, Bucks., England: SM J34090. Almost complete adult specimen with a little more than half a whorl of body chamber, a, side view, note the complete fading of the spines on the body chamber, the presence of spiral ornament, and the uncoiling of the body chamber at the umbilical seam; b, ventral view, note the absence of the ventral ridge; c, apertural view, note the presence of the ventral ridge. Inset X 1. All figures X 3 unless otherwise stated. Specimens have been whitened with ammonium chloride. Photographs by the author, all un-retouched. Palaeontology, Vol. 10 PLATE 10 4a 4b 4c PALFRAMAN, Distichoceras from the Oxford Clay D. F. B. PALFRAMAN: SOME OXFORD CLAY AMMONITES 77 1927-33 Horioceras baugieri ; Spath (part vi, 1933), p. 668, pi. 125, figs. 13, 14. 1957 Horioceras baugieri; Arkell, Kummel and Wright, p. L279, figs. 327, 3 a. 1963 Horioceras baugieri; Callomon, p. 42, fig. 9m. 1963 Horioceras baugieri; Schindewolf, p. 406, figs. 229, 230. General remarks and diagnosis. Mature specimens of D. bicostatum $ do not appear to grow beyond a maximum diameter of 2-3 cm., in consequence they are often preserved almost entire as internal pyritic moulds in the Oxford Clay at many localities. Because of its relatively small size it does not appear to be preserved in either the Lamberti Limestone of Woodham, Bucks., or the Hackness Rock of Yorkshire. In both these strata the inner whorls of most ammonites seem to be either poorly preserved, recrystal- lized and structureless, or entirely lacking beneath a diameter of 2-3 cm., which means that the chances of preservation of D. bicostatum $ are extremely slender. The basic shape of D. bicostatum is rather eclipsed by the enormous ventro-lateral spines which develop on the last whorl of mature specimens. It is, however, moderately involute with a whorl width the diameter and a whorl height about half the diameter. The umbilicus is small but widens appreciably, due to uncoiling at the umbilical seam, on the body chamber of adult specimens. The innermost whorls are smooth; the last whorl of the phragmocone develops ventro-lateral spines and a ventral ridge. The latter fades at the end of the phragmocone as the spines become relatively larger. The body chamber is initially spinose but towards the end is smooth and terminated by a lappeted peristome. PROTOCONCH Only one protoconch from D. bicostatum has been obtained; its dimensions are very similar to those of D. bicostatum $. Altogether five protoconchs from the species under consideration have been obtained (from males and females): the size range is as follows: D, 0-24 to 0-30 mm., W, 0-40 to 0-48 mm. (see Table 1). Text-fig. 1 is drawn from D. bicostatum <^(?), OUM J25687, showing the nature of the prosuture and general shape. Remarks. The range in protoconch size though small is greater than that recorded for another oppelid ammonite species, Creniceras renggeri (Oppel) (Palframan 1966). However, the species examined here has been collected from a much wider stratigraphical and geographical range than the localized C. renggeri (op. cit.), and this almost certainly influences the observed variation. PHRAGMOCONE Early whorls and general growth pattern From the proseptum the first whorl of growth is smooth and depressed and terminated by the nepionic constriction. In specimen BM C28329 the nepionic constriction does not occur until a little after one whorl of growth, at a diameter of 0-57 mm. The dia- meter at which the nepionic constriction occurs ranges, in D. bicostatum d, from 0-48 to 0-57 mm. The nepionic constriction is strongest ventrally and ventro-laterally, weakening on the flanks and fading completely near the umbilical seam (cf. text-fig. 2). No morphological feature is present in the early whorls until a diameter of between 5-7 mm. The extremely wide and depressed whorl outline of the protoconch (cf. text-fig. 1) 78 PALAEONTOLOGY, VOLUME 10 alters markedly within the space of one whorl of growth (cf. text-fig. 2) and rapidly becomes subquadrate at a diameter of about 2 mm. Beyond this size the flanks flatten and begin to converge towards the venter. Ventral tabulation occurs at a diameter of about 5-7 mm., almost immediately before the first true ornament, and continues to the end of the phragmocone (see text-fig. 7a-b). From a diameter of about 1 mm. to near the adoral end of the phragmocone the W/D, U/D, and HH/D ratios remain almost constant, reflecting more or less isometric growth. Throughout there is no marked umbilical shoulder and the umbilical wall is consequently rounded. Remarks. Two measurements of the diameter of the nepionic constriction, one from D. bicostatum $ and another from a juvenile specimen, are recorded and both fall within the range of the same measurement of D. bicostatum S (see Table 1). Ornament At a diameter of 5-7 mm. the whorls, which up to this stage are smooth, develop orna- ment of the following nature: ventro-lateral spines, a ventral ridge, and lateral ornament. The ventro-lateral spines and ventral ridge usually begin together, as shown by speci- men BM C28329 (see Table 1), or the ventral ridge may develop at a slightly later growth stage than the spines. The lateral ornament usually begins at about the same diameter as the ventro-lateral spines and may precede them (PI. 9, fig. 6), begin at the same diameter (PI. 9, fig. 3a), or succeed the ventro-lateral spines (PI. 11, fig. 2). Ventro-lateral spines. The ventro-lateral spines of D. bicostatum S are identical in EXPLANATION OF PLATE 11 Distichoceras bicostatum (Stahl) Fig. 1. Juvenile! ?) male, from the Oxford Clay of Summertown, Oxford, England: BM C10638. The specimen may be adult, but the final sutures do not appear to be approximated. The body chamber (final half whorl) is, however, beginning to uncoil at the umbilical seam. Side view showing about five complete whorls; the protoconch is absent. Fig. 2. Male from the Lamberti Zone, Tidmoor Point, Dorset, England: BM C28327. Mature speci- men with one-eighth of a whorl of body chamber. Side view, note sutural approximation. Fig. 3. Juvenile female(?) from the Athleta/Lamberti Zone, Woodham, Bucks., England: OUM J25684. Immature phragmocone. a, ventral view (venter poorly preserved); b, apertural view; c, side view, note the irregular spacing of the sutures; d , as c, enlarged ( X 5) to show the spiral striae and sculpturing of the flanks. Fig. 4. Juvenile female(?) from the Athleta/Lamberti Zone of Woodham, Bucks., England: OUM J25681. Immature phragmocone. a, side view; b, ventral view, note the continuous ventral ridge; c, apertural view. Fig. 5. Juvenile female(?) from the Athleta/Lamberti Zone of Peckondale Hill, near Malton, York- shire, England: LU264. Immature phragmocone. a, side view; b, ventral view, note the continuous ventral ridge. Fig. 6. Male from the Oxford Clay, near Chippenham, Wiltshire, England: BM 37755. Side view, the final five-eighths of a whorl is body chamber. Fig. 7. Female from the Hackness Rock of Scarborough, Yorkshire, England: SM J47113. Immature (?)phragmocone. a, side view; b, ventral view. Both X 1. Fig. 8. Female from the Hackness Rock, Scarborough Castle Rock, Yorkshire, England: SM J5621. Mature!?) phragmocone. a, side view; b, ventral view. Both X 1. All figures X 3 unless otherwise stated. Specimens have been whitened with ammonium chloride,, except fig. 6 which has been whitened with magnesium oxide. All photographs by the author, all un- retouched. Palaeontology, Vol. 10 PLATE 11 PALFRAMAN, Distichoceras from the Oxford Clay D. F. B. PALFRAMAN: SOME OXFORD CLAY AMMONITES 79 their early developmental stages to those of D. bicostatum $ at a similar growth stage. They are small, rounded, alternate either side of the venter and the same density per whorl. After about half a volution of development, or one-eighth of a whorl before the beginning of the body chamber in adult specimens, the spines attain a relatively much larger size (see PI. 10, figs. 1 a, d, 2a, 3 a, and 4 a). At this stage the ventro-lateral spines become more angular and distant and instead of remaining on the ventro-lateral area, the median aspect of the spine bases extends on to the venter proper. Ventral ridge. In consequence of the encroachment of the ventro-lateral spines on to the venter, the ventral ridge, which up to this stage remains clearly visible, completely dis- appears (see PI. 1 0, figs. 1 b, 2c, and 4c) . F rom its development to its degeneration the ventral ridge is commonly straight unlike that of D. bicostatum $ which, though often straight at small diameters, has a tendency to be wrinkled on the final whorl of the phragmocone. Lateral ornament. At no stage on a single observed specimen were there ribs to be seen : lateral ornament, however, is a common feature generally taking the form of either a fillet or groove or even a combination of these. Lateral grooves situated on the mid- flanks are undoubtedly more common than fillets. Grooves vary from narrow and dis- tinct (see PI. 9, fig. 6) through to shallow and less obvious (see PI. 9, fig. 3 a and PI. 10,. figs, la and b). In the case of specimen BM C15710, the broad lateral groove is flanked by levee-like elevations. Only one specimen (OUM J25687 was observed to have a com- bination of spiral grooves and fillets. They are very feeble and do not show up photo- graphically even using a low-angled light source (see PI. 9, fig. 5 a and text-fig. 6a). Some specimens are perfectly smooth (see PI. 10, fig. 2 a and PI. 11, fig. 1) or with very feeble spiral fillets (see PI. 10, fig. 4c). On the flanks of the final phragmocone whorl of a well- preserved specimen (OUM J23247) is a series of very fine striae, similar in nature to those already described for specimen OUM J25684 ( D . bicostatum $, cf. PI. 11, fig. 3d). Small, shallow, convex, crescentic pits are to be seen on the flanks of some specimens (see PI. 9, fig. 4 and PI. 10, fig. 3a). The pits begin either immediately before or shortly after the commencement of ventro-lateral spines and extend on to the body chamber. Remarks. It is considered that the spiral fillets and grooves may be related more to the internal moulds of the specimens studied, by way of soft-part attachment areas, than true reflections of shell ornament. The same may well be true of the crescentic pits situated on the flanks. Sutures Sutural ontogeny. The prosuture of D. bicostatum <$ is very different from all succeed- ing sutures, but almost identical to the prosuture of D. bicostatum $ (see text-fig. 8a and b). Extremely close similarity is also true of the primary suture of the supposed sexual dimorphs (see text-fig. 8c and d). Successive sutures develop new elements which are added in the umbilical region, U-type ontogeny, and become progressively more frilled and complex towards the adoral end of the phragmocone (see text-fig. 8). Sutural variation. Sutural variation at a prescribed diameter, here arbitrarily chosen at about 9 mm., from randomly chosen specimens on which the sutures at this diameter are not degenerate, is seen to be small (text-fig. 10). The elements of the suture considered are the ventral and lateral lobe and the first and second lateral saddles. These are the most complex sutural elements at any diameter. 80 PALAEONTOLOGY, VOLUME 10 Remarks. The variation recorded may be due to any of the factors previously mentioned as influencing the sutural variation of D. bicostatwn In addition, the relatively large spines of D. bicostatum S and the degeneration of the ventral ridge at about this diameter may have an even greater sutural influence at both and intra- and inter-individual level, than in D. bicostatwn $. Spath (1938), in his study of liparoceratid ammonites, recorded marked discordances between the form of adjacent sutures and also within the same suture on either side of the venter. Wide sutural variation was also demonstrated by Arkell (19576) between otherwise identical specimens of the two species Morrisiceras morrisi (Oppel) and Clydoniceras discus (Sowerby). No such marked differences are recorded here for either D. bicostatwn £ or $ in which even the most marked variation is very small and of the same order as that displayed by Creniceras renggeri (Oppel) S and £ (Palframan 1966). The mature phragmocone. Sutural approximation and degeneration, already considered here as a feature of maturity, can clearly be seen in many specimens (see PI. 10, figs. 2 a and 3 a and PI. 11, fig. 2). The diameter of its occurrence is from 7-17 mm. (see Table 1), with a mean of 12-2 mm. Remarks. The six specimens (BM 37755, BM C10646, OUM J23246-7, BM C10644-5) now recorded in Table 1 (column M.S.D.(A)) were not discovered by the author until after the completion of text-figs. 3, 4, and 5 on which the mean diameter at which septa- tion ceased in adult specimens (ds) is denoted as being 10-9 mm. However, as no measure- EXPLANATION OF PLATE 12 Distichoceras bicostatum (Stahl) Fig. 1 . Male from the Oxford Clay, Summertown, Oxford, England: BM C10646. Side view, the final half whorl is body chamber. Note the ornamented spines of the body chamber. X 3. Fig. 2. Male from the Lamberti Beds, Trockau, Bavaria: BM C40982. Side view, showing lappet. X 3. Fig. 3. Female from the Hackness Rock, Scarborough Castle Rock, Yorkshire, England: SM J5619. Mature specimen with one-third of a whorl of body chamber. Side view, note the ribbing on to the lower flank of the body chamber. Fig. 4. Male from the ‘Brown Jura 3, Beuren, Wiirttemberg’, Germany: BMC 73644. Side view of almost complete adult with two-thirds of a whorl of body chamber. The adapertural body chamber termination is constricted and bears the beginnings of a lappet, x 3. Fig. 5. Female from the Lamberti Limestone, Woodham, Bucks., England: OUM J20852. Badly crushed mature phragmocone. Side view. Fig. 6. Female from the Hackness Rock, Scarborough, Yorkshire, England: BM 39525. Mature specimen with about one-sixteenth of a whorl of body chamber, a, ventral view, note the weakening of the ventral ridge and the ventro-lateral spines towards the body chamber; b, side view, note the lateral fillet fading adorally. Fig. 7. Juvenile! ?) female from the Hackness Rock, Scarborough Castle Rock, Yorkshire, England: SM J5620. Phragmocone only, a, side view, note the presence of some non-looped ribs; b, ventral view. Fig. 8. Female from the Hackness Rock, Scarborough, Yorkshire, England: BM 89044. Mature phragmocone. a , ventral view, showing well-developed ventral ridge; b, side view, showing well- developed looped ribs and lateral groove; c, cross-section of immature phragmocone. Fig. 9. Female from the Hackness Rock of Gristhorpe, Yorkshire, England: SM J5623. Mature! ?) specimen with one-eighth of a whorl of body chamber, a, side view; b, ventral view. All figures x 1 unless otherwise stated. Specimens have been whitened with ammonium chloride, except figs. 1, 2, 4 which have been whitened with magnesium oxide. Photographs by the author, all un- retouched. Palaeontology . Vol. 10 PLATE 12 PALFRAMAN, Distichoceras from the Oxford Clay D. F. B. PALFRAMAN: SOME OXFORD CLAY AMMONITES 81 ments of these six specimens were plotted on any of the three graphs they are accurate as they stand. No single phragmocone is sufficiently entire or well preserved to count the number of whorls. It is estimated, however, that from the proseptum to the end of the phragmocone in mature specimens there are betewen 5J and 5f complete whorls. text-fig. 10. Sutural variation in Distichoceras bicostatum (Stahl). Males: a, OUM J25680 at D = 9-2 mm. from the Athleta/Lamberti Zone, Woodham, Bucks., England; b, BM 05710 at D = 8-5 mm. from the Athleta(?) Zone, Eye, near Peterborough, England; c, SM J34090 at D = 8-9 mm. from the Athleta/Lamberti Zone, Woodham, Bucks., England. The position of the spines is clearly marked (dot-dash lines). All figs, x 20. BODY CHAMBER Though no complete body chamber was examined among British specimens, several individuals had sufficient preserved to enable an over-all description to be undertaken. In most of these cases, however, preservation is not good. Specimens from Germany help considerably in the description of the peristome and in determining the length of the body chamber of adults. General growth General whorl shape of the body chamber differs little from that of the mature phrag- mocone. The angle made by the flanks on the former, however, is more acute (cf. text-fig. G C 4466 82 PALAEONTOLOGY, VOLUME 10 7b and see PI. 10, figs. 3b and 4c). The W/D and HH/D ratios decrease significantly in the late stages of growth (see text-figs. 3 and 5), the latter being accompanied by a complementary increase of the U/D ratio (see text-fig. 4). The whorl width is the first dimension to show negative allometry, at a mean diameter of about 10-11 mm. Uncoil- ing of the body chamber at the umbilical seam, a feature of maturity, begins at a mean diameter of about 14— 16 mm., becoming very marked in adults after half a whorl of body chamber growth (see PI. 10, figs. 2a, 3 a, and 4a). Ornament Ventro-lateraJ spines. The enormous ventro-lateral spines are undoubtedly the most marked characteristic of the body chamber. They show positive allometry towards the end of the phragmocone and continue to increase relatively for about of a whorl on to the body chamber. The largest spines, measured radially, are in the order of 2-3 mm. They are generally rectiradial (PI. 10, figs. \a, la, 3a, and 4a), but may be feebly rursi- radial (PI. 11, fig. 6) and are much more distant than on the phragmocone. On the venter the alternating spine bases overlap the median line; a ventral view at this stage is reminiscent of a coarsely set saw (see PI. 10, figs. 2b 2c, 3c, and 4b). The spines extend for about a whorl before dying out completely, having reached an acme -J— of a whorl of body chamber growth in adults. The venter and ventro-lateral areas are smooth in the final stages of growth, the former being gently rounded (see PI. 10, figs. 4b and 4c). Remarks. D "Orbigny ( 1 842-51) first figured and described the species Ammonites Baugieri (= Horioeeras baugieri = D. bicostatum <$), which, though incomplete, has a maximum diameter of 36 mm. (d "Orbigny ibid., pi. 158, fig. 5). The last figured whorl shows the spines at first becoming relatively larger, reaching an acme, and finally fading completely to give rise to a smooth venter and ventro-lateral areas. On the same plate (ibid., fig. 6) is figured an apertural view of the same (?) specimen, which shows the ammonite to be completely septate. Other illustrations of apertural views of ammonite specimens are figured by d "Orbigny (1842-51), which in side view are uncoiling at the umbilical seam and/or presenting highly modified ornament in the late stages of the outer whorl and EXPLANATION OF PLATE 13 Distichoceras bicostatum (Stahl) Fig. 1. Female from the Hackness Rock, Scarborough, Yorkshire, England: BM 50622. Complete adult, a, side view, note degenerate and approximated sutures, ribbing on the lower flank of the body chamber, and uncoiling of the body chamber at the umbilical seam; b , ventral view of the body chamber, note the absence of the ventral ridge and ventro-lateral spines and the continuous ribbing over the venter; c, apertural view, note the presence of both ventral ridge and ventro-lateral spines; d, side view showing the outline of the peristome; e, side view (reverse side of a) showing feather structure in original shell (x 3). Fig. 2. Female from the 'Scarborough Grey Limestone ’(?) (probably the Hackness Rock), Scar- borough, Yorkshire, England; BM C69282. Adult specimen with one-sixth of a whorl of body cham- ber. Side view showing well-developed fillet on the phragmocone which fades on the body chamber. Fig. 3. Female from the Lamberti Limestone of Woodham, Bucks., England: OUM J20851. Side view of slightly crushed adult specimen with half a whorl of body chamber. Spines and looped ribs fade on the body chamber. All figures X 1 unless otherwise stated. Specimens have been whitened with ammonium chloride. All photographs by the author, all un-retouched except fig. 1 d. Palaeontology, Vol. 10 PLATE 13 PALFRAMAN, Distichoceras from the Oxford Clay D. F. B. PALFRAMAN: SOME OXFORD CLAY AMMONITES 83 which are drawn as still being septate. The author considers that these septa are imaginary rather than real and that d'Orbigny’s figures (op. cit. — also reproduced by Arkell, Kummel, and Wright 1957, p. L280, figs. 327, 3 a and 3b) are of a large mature specimen with perhaps the final half whorl being body chamber. The same figures also show the ventro-lateral spines of the last half whorl are notched by radial grooves which begin near the spine base: similar grooves have been seen on only one English specimen (BM C10646) from Summertown, Oxford (PI. 12, fig. 1). Lateral ornament. Lateral ornament is generally present, as indicated by d’Orbigny (1842-51), in various forms. A feeble fillet present on the phragmocone of specimen SM J34090, persists on to the body chamber (see PI. 10, fig. 4 a) as does the lateral groove of specimen BM C28327 (see PI. 11, fig. 2). The poor preservation of body chambers, however, probably masks some of these delicate features. The small crescentic pits described as occurring on the phragmocone of specimen LU 265 continue on to the body chamber for about one-sixth of a whorl before completely fading (see PI. 10, fig. 3a). Remarks. As was suggested previously these pits may represent internal moulds of shell processes to which muscular attachment of the adapical soft parts of the creature was made. Adult peristome Quenstedt (1852, 1858, and 1886-7) figured several specimens of Ammonites biden- tatus (= D. bicostatum 3); in the two later works (ibid.) are figured adult specimens with apertural modifications (1858, pi. 70, fig. 10; 1886-7, pi. 85, figs. 17 and 18). One of these figured specimens (1886-7, pi. 85, fig. 17) has an unusually wide umbilicus which differs significantly from specimens examined here (see text-fig. 4). The second figure on the same plate (op. cit., fig. 18) has an umbilicus similar in size to those the author has examined from England: the unusually wide umbilicus mentioned may be due to preser- vation (the specimen appears to have been crushed) or to inaccurate drawing. The diameter of the phragmocone of these specimens is 11-12 mm., which falls within the range of material here examined, and have a maximum diameter of 18-5 to 22 mm. The final one-third of a whorl of body chamber is spineless and terminated by an ornate peristome. Immediately preceding the peristome is a feeble constriction which appears to be most marked ventrally. The actual peristome is slightly flared, the flaring weaken- ing as it passes adorally on to a large spoon-shaped lappet (Quenstedt 1886-7, pi. 85, figs. 17 and 18 and herein text-fig. 11, inset). The point of contact between the lappet and body chamber is narrow, the lappet becoming wider, relative to the median plane, and rounded adorally. An apertural view (see text-fig. 11, inset 18/?) shows that the lappets, which are concave relative to the median plane, converge adorally but do not quite meet. These complete specimens have a body chamber of between §-§ of a whorl in length. Two almost complete German specimens, BM C40982 from Trockau, Bavaria, and BM 73644 from Beuren, Wurttemberg, show that the body chamber comprises about two-thirds of a whorl. The interpretation of the crushed Bavarian specimen is somewhat tenuous, especially as the phragmocone is represented as an external mould only. However, there appears to be evidence of sutures, on this external mould, two-thirds of a whorl behind the peristome. Both these specimens have a constricted peristome (PI. 12, figs. 2, 4); one of them (BM C40982, PI. 12, fig. 2) bears a lappet which is in agreement, in both 84 PALAEONTOLOGY, VOLUME 10 shape and size, with those illustrated by Quenstedt (1886-7 table 85, figs. 17, 18; reproduced herein text-fig. 11, inset). The most complete English specimens examined by the author, SM J34090 and BM 37755, have a little more than half a whorl of body chamber (PI. 10, fig. 4 a and PI. 11, fig. 6) and show the spines completely fading adorally as on Quenstedt ’s complete figured specimens (op. cit.) and a German specimen illustrated herein (PI. 12, fig. 4). A fairly accurate estimate of the total number of whorls in complete mature specimens, counting from the proseptum, is between 5f-6J. Shell and muscle scars No shell has been seen on specimens of D. bicostatum S examined in the preparation of this paper: it is therefore impossible to describe any relationship between it and the internal moulds studied. Remarks. Despite the lack of shell certain characteristics, which may be associated with the attachment of soft parts to the shell, have been noted. The muscle attachments recorded by Crick (1898) on two specimens of'Distichoceras BaugierV (= D. bicostatum S) is parallel and near to the umbilical seam of the body chamber, swinging across the flank on to the venter near the junction between the body chamber and the phragmocone: no such attachment has been seen on material investigated here. The lateral ornament of the flanks, already described, may be associated with muscle attachment. In one juvenile specimen (OUM J 14560), which has a quarter of a whorl of body chamber preserved, a sinuous elevation is present on the flank of the body chamber about one-eighth of a whorl from the last septum. This is strongest adorally on the mid-flank, weakening adapically towards the venter and umbilical seam (see PI. 9, fig. 2 a and text-fig. 6b), and may have been a temporary area of muscle attachment, which, had the creature grown, may have subsequently been infilled with secreted shell material. The ‘attach- ment’ is strongest in precisely the same position, mid-flank, as a series of pits already men- tioned on specimen LU 265 (see PI. 10, fig. 3a). It is also noteworthy that these pits do not continue beyond one-eighth of a whorl of the body chamber of the mature specimen where the soft parts of the creature may have been adapically attached. DISCUSSION ON SEXUAL DIMORPHISM Historical outline Dimorphism in ammonoids has been recorded from the Devonian, the Jurassic, and the Cretaceous, though not all authors have necessarily considered this dimorphism to be sexual, Arkell (1957a) and Birkelund (1965) to mention but two. De Blainville (1840) appears to be the first author to mention sexual dimorphism in ammonites but gave no specific examples. The earlier workers, on the whole, preferred to compare only the adult stages of supposed sexual dimorphs, in which the small form with an ornate peristome was considered as being the male, the female being large and with a simple peristome (Munier-Chalmas 1892). Shortly after the turn of the century the theory of sexual dimorphism in ammonites sank into relative obscurity only to be rejuvenated within the last ten years, due largely to the efforts of Callomon (1955, 1957, and 1963) and Makowski (1962). D. F. B. PALFRAMAN: SOME OXFORD CLAY AMMONITES 85 The last decade has seen a new approach to the problem, the inner whorls of supposed dimorphs are more closely examined and comparisons with living cephalopods more strongly sought. Statistical techniques appear to substantiate the theory (Makowski 1962 and Palframan 1966) rather than destroy it and, as Callomon (1963, p. 51) says: ‘ . the evidence on which it [the theory of sexual dimorphism] is based has grown rather than melted away, and in many Jurassic ammonites is now very strong. ’ It seems by analogy with many living cephalopods that the smaller dimorph is the male, the larger the female. This is the most popular interpretation among current workers who accept the theory of sexual dimorphism, as it appears to have been in the past. Remarks. A point, which to the author’s knowledge is not recorded in the literature, concerns the rate of evolution and its correlation with sexual reproduction with reference to ammonites. Species which reproduce sexually are likely to produce offspring showing wider variation than those reproducing asexually. ‘The great advantage resulting from this power of recombination explains why species with separate sexes have evolved further [than those which have not]’ (de Beer 1959, p. 39). Few would disagree that the general rate of ammonite evolution appears to have been extremely fast. So fast, in fact, that their evolution is sometimes spoken of as orthogenetic or even typogenetic. Simpson (1953) indicates that guide genera of ammonites have evolved much faster than many vertebrates. However, the rate of ammonite evolution though probably related to sexual reproduction is not necessarily to be correlated with sexual dimorphism of hard parts. Comparison of the ‘ species' examined It has been assumed that sexual dimorphs of the same species will have identical early growth stages and certain similarities in later growth stages. This is, therefore, a brief summary of the foregoing description of the two ‘species’ (sexual dimorphs) here con- sidered. The protoconchs and diameter of the nepionic constriction are fairly consistent in size. Lack of material does not permit a statistical analysis of the early ontogenetic stages; however, as well as consistent size these early stages show consistent shape of protoconch and whorl outline. At a diameter of about 5-7 mm., both supposed sexual dimorphs show ventral tabu- lation almost immediately followed by the development of ventro-lateral spines, a ventral ridge, and lateral ornament. These features are identical in both dimorphs by way of position, size, frequency, and variation. Differences between the dimorphs begin at a diameter of about 10 mm.; the larger dimorph continues to grow almost isometrically until considerably larger than this diameter, but the small form shows marked changes. These are a relative increase in the size of the ventro-lateral spines followed by degenera- tion of the ventral ridge near the junction of the phragmocone and body chamber. The spines reach maximum size after £ of a whorl of growth of the body chamber and then fade completely leaving the final growth stages smooth. In the larger form the ventro-lateral spines reflect isometric growth throughout: both these and the ventral ridge degenerate near the transition from phragmocone to body chamber in mature individuals. The venter remains tabulate to the end of the body chamber, but, as distinct from the small form, is weakly ribbed. Ribbing is not known in the small form but 86 PALAEONTOLOGY, VOLUME 10 its earliest appearance in the large form is usually at greater diameters than are ever attained by the small form. Growth of both forms is identical up to a diameter of about 10 mm.; at this stage of TABLE 1 Table of diameters. Under each column appears the catalogue numbers of each specimen fol- lowed by the diameter of the feature recorded in the side heading. The diameters are expressed in milli- metres. The three columns: Juvenile, <$, and $ correspond to: juvenile forms (sex indeterminate), males and females respectively of Distichoceras bicostatum (Stahl). The side headings: M.S.D.(A) and M.D.(A) correspond to: maximum septate diameter of adult shells and maximum diameter of adult shells respectively. In the side heading 'Protoconch’, measurements of the width (in mm.) have been added. Asterisks denote uncertainty in either measurement and/or interpretation. Juvenile Male Female Protoconch BM Cl 57 12 — D = 0-24 W = 0-40 BM C28328 — D = 0 29* W = 0-45* BM C28330 — D - 0 30 W = 0-45 OUM J25687 — D = 0 29* W = 0-48* OUM J25681 — D = W = Nepionic constriction BM C28330 — 0 52 OUM J25687 — 0-48* BM Cl 0638 — 0-51 BM C28329 — 0-57 OUM J25681— 0-49 Fillet/Groove begins OUM J25686— 6-3 OUM J25677 — 5 0 OUM J25679 — 7-5 OUM J25688— 6.3 Ventral Ridge begins BM C28328 — 6-2 BM C28330 — 6-3 BM C28329 — 6-2 OUM J25687 — 6-6* LU 265—7-1 SM J34091 — 7-4 BM C28327— 7-5 OUM J25688— 6-3 Spines begin BM Cl 57 1 2 — 5-2 OUM J25683— 5-4* OUM J25682 — 5-8 OUM J25684 — 6 0* BM C28328 — 6-2 BM C28330— 6-3 OUM J25686 — 7-7 OUM J 14560— 5-3 OUM J25687 — 5-6* OUM J23246— 5-8* BM C28329 — 6-2 OUM J25677 — 6-3 OUM J25679— 6-9 LU 265—7 1 BM C10638— 7-3 BM Cl 5709— 7-3 BM C15710— 7-3 OUM J25680 — 7-3* SM J34091 — 7-4 BM C28327— 7-5 OUM J 23 247 — 9 8* OUM J25681 — 5-8 OUM J25688— 6-3 LU 264—6-3 BM C28325— 7-3 LU 263—7-5 Ventral Ridge ceases BM C28327 — 8-3 OUM J25679 — 9-3 BM C10638— 9-3 SM J34090 — 9-7 OUM J25680— 9-8 LU 265—10-5 BM C15710 — 12-2 OUM J23246 — 12-5 OUM J23247— 12-5 D. F. B. PALFRAMAN: SOME OXFORD CLAY AMMONITES 87 Juvenile Mate Female M.S.D.(A) BM 37755 — 6-8* BM C28327 — 8-7* OUM J25677 — 9-2 OUM J25679 — 9 3* LU 265 — 11 6 BM C10638 — 11-6 OUM J25680 — 12-4 SM J 34090 — 12-6 BM C10646— 13 0* BM C15710 — 13-2 OUM J23246— 13-8 BM C10644 — 16-0* BM C10645— 16 0* OUM J23247— 16-7 BM 89044—31-5 SM J5623— 31-8 SM J5619 — 33 0 SM J5621 — 36-4 OUM J20851— 40* OUM J20852— 40* OUM J20853— 40* BM 39525—40-5 BM 50622—40-5* BM C69282 — 44-5 SM J5618— 45-7 OUM J25688 — 49-7 Spines cease BM 37755—11-0 SM J34090 — 17-1 M.D.(A) BM 50622—68 OUM J20851 — 70* development growth of the smaller form is influenced by the onset of maturity. It is noteworthy that both large and small forms change their growth-rate, for the features measured (W/D, U/D, and HH/D), at almost identically the same relative growth stage. This change of growth rate is most marked in both forms in the early stages of body chamber development. Suturally both forms are identical at comparable diameters from the prosuture to a diameter of about 10 mm. (cf. text-fig. 8). The sutures of the large form are more complex than those of the small form only at greater septate diameters than are re- corded for the latter. Both forms show little sutural variation within themselves at a prescribed diameter. The body chamber of both forms uncoils at the umbilical seam and in both cases is slightly more than half a whorl in length: that of the large form is terminated by a simple peristome, that of the small form is lappet-bearing. The largest of the small forms, which has about 6| complete whorls, is very much smaller than the smallest of the large forms which has about 8 complete whorls. Previous consideration of the dimorphic pair Munier-Chalmas (1892) was the first author to pair Distichoceras with Horioceras. In both cases he erected the genera basing them on Ammonites bipartitus Zieten 1830 (= A. bicostata Stahl 1824) and A. Baugieri d’Orbigny, respectively. The smaller form, Horioceras, was considered as being the male, Distichoceras being the female, by Munier-Chalmas (op. cit.), and Rollier (1913). Spath (1928, p. 92), though believing in the contemporaneity and concomitance of the two forms, considers the idea of the pair being sexually dimorphic as unlikely: ‘Munier-Chalmas, Rollier and H. Douville . . . even held that they [ Distichoceras and Horioceras ] were merely male and female of the same species, but there is little concrete evidence in favour of this view. ’ In the same mammoth work (Spath 1927-33) he goes on to call Horioceras the ‘companion genus’ of Bonarellia (= Distichoceras ) (1933, part vi, p. 668) and later mentions 88 PALAEONTOLOGY, VOLUME 10 ‘the inseparable companions Horiocerasbaugieri and Bonarelliabicostata [= Distichoceras bicostatum ]’ (1933, p. 843). Arkell (1939, p. 167), while considering two tiny nuclei of Distichoceras bicostatum, with a diameter of 8 mm. and 9 mm. respectively, points out that they are ‘. . . at a stage indistinguishable from Horioceras baugieri (d’Orbigny)’. Though Arkell had clearly observed dimorphism in Mesozoic ammonites . especially in the Middle and Upper Jurassic . . (1957a, p. L87), he did not necessarily consider it as sexual in nature and suggested that ‘. . . the theory of sexual dimorphism [in ammonites] can only be shelved as unproved’ (1957a, p. L90). text-fig. 11. Reconstruction of the sexually dimorphic pair: Distichoceras bicostatum (Stahl). $ based on specimen BM 50622 from the Hackness Rock, Scarborough, Yorkshire, England. $ based on specimens OUM J25680 and SM J34090 from the Athleta/Lamberti Zone, Woodham, Bucks., England, BM C40982 from Beuren, Bavaria, Germany and Quenstedt 1886-7, table 85, figs. 17 and 18 (see inset). All figs. X 1. The author has found it impossible to express a precise ratio of large to small forms of D. bicostatum from each bed and/or locality, in part due to the small number of individuals available, in part due to incomplete preservation. It is considered here, how- ever, that the ratio does not exceed 2:1-1 :2. R. Douville (1913) has shown that the two genera Distichoceras and Horioceras are contemporaneous at Dives, northern France, and that the ratio Distichoceras : Horioceras is about 2-3 : 1 . STRATIGRAPHICAL DISTRIBUTION The subfamily Distichoceratinae Hyatt arose from the Hecticoceratinae Spath during the early Middle Callovian (Arkell, Kummel, and Wright 1957 and Schindewolf 1963). The earliest record of D. bicostatum is from the Athleta Zone. Europe England. In England D. bicostatum appears to be restricted to the Athleta and Lamberti Zones. The Hackness Rock of the Yorkshire Coast (= upper part of the Kellaways D. F. B. PALFRAMAN: SOME OXFORD CLAY AMMONITES 8^ Rock, or Kelloway Rock, of some authors, but, which according to Arkell 1933, 1936, 1939, and 1945 and Sylvester-Bradley 1953, comprises the Athleta and Lamberti Zones only) has yielded undoubted female specimens of D. bicostatum, which, with other species,, is ‘peculiar’ (Leckenby 1859, p. 7) to this bed. Other species listed by Leckenby (1859) from this bed are ‘ Ammonites athleta and Am. Lamberti'. Leckenby also found 'Am. Baugieri' from a locality near Gristhorpe Bay, Yorkshire, and writes: ‘The . . . two species [A. bipartitus and A. Baugieri ] agree exactly with the figures of d’Orbigny.’ Arkell mentions a crushed ‘ IHorioceras sp. ’ from the Oxford Clay, Mariae Zone, of the Yorkshire Coast (1939, p. 197). The specimen was not collected by Arkell and, as his question mark infers, there is some doubt about identification. Crushed, ventrally spined oppelid ammonites can be confusing to identify; a case in point will be men- tioned later. Inland, a second Yorkshire exposure has yielded D. bicostatum, both male and female. This is situated in typical Oxford Clay with familiar limonitic-pyritic ammonite nuclei, at Peckondale Hill, near Malton (Grid. Ref. 745686). From a temporary adjacent ex- posure, investigated by Wilson (1936), the following ammonites were found: ‘ Querist ed- toceras lamberti, Q. henrici, IQ. williamsoni and Peltoceras sp. indet. ’ (fauna identified by Arkell 1939, p. 197). The fauna of Peckondale Hill is richer in species with a predomi- nance of Kosmoceras and Quenstedtoceras species, especially Q. lamberti. The beds exposed at this locality comprise the lower part of the Oxford Clay in this area (Huddle- ston 1878 and Wilson 1936) and, to judge from the fauna, belong to the Athleta and Lamberti Zones. Further south at Eye, Peterborough, five specimens of D. bicostatum were collected by E. T. Leeds (BM collection). The label accompanying the specimens makes no mention of the horizon from which they were collected : it seems, however, that the highest beds of the Oxford Clay of the area belong to the Lamberti Zone, no trace of a Mariae fauna being recorded (Neaverson 1925). One is therefore led to consider the specimens in question to be older than Mariae Zone age. From Woodham, Bucks., have been collected at least twenty-three specimens of D. bicostatum, the majority (twelve) by W. J. Arkell. Of these, seven came from his bed C (Arkell 1939, p. 167) and ranged in size from 16-70 mm. The remaining five speci- mens are small pyritic nuclei 8-1 1 mm. in diameter found loose in the pit. Arkell ten- tatively regards them as also having come from his bed C (the Lamberti Limestone), partially on the basis that ‘Unlike most other ammonites in bed C, the inner whorls of this species are pyritized’. The author has examined four of the seven specimens col- lected by Arkell from bed C; of these the smallest (OUM J20854 — see PI. 9, fig. 8) is wholly septate and entirely pyritic with an estimated diameter of 15-16 mm. The other three (OUM J20851-3) are internal moulds of marly limestone with a size range of 40-70 mm. (see PI. 12, fig. 5 and PI. 13, fig. 3): their internal whorls are also of marly limestone. This leads the author to consider that ‘. . . the inner whorls of this species are pyritized’ (Arkell 1939) is a not very accurate generalization. The author’s own col- lecting at Woodham, however, did not produce a single specimen of this species in situ in the true clays. Of the eight small pyritic nuclei the author found loose in the pit, most had adherent matrix of typical Oxford Clay and some had individual camarae completely filled by clay: none had adherent particles of marly limestone. Without being categorical, the author considers the majority of these pyritic nuclei may have come from the clays 90 PALAEONTOLOGY, VOLUME 10 (mainly Athleta Zone) beneath the Lamberti Limestone, from which a fauna showing similar preservation has been collected. On this basis the author is aware that the nuclei may almost equally well have come from the clays (Mariae Zone) overlying the Lamberti Limestone, but from other stratigraphical considerations this is thought to be unlikely but by no means certain. With some degree of reservation the author has given the hori- zon of these nuclei, found loose, as Athleta/Lamberti Zone. A single specimen of D. bicostatum S (collected by C. W. Wright) has been found from a temporary exposure in Oxford: accompanying it was a fauna of undoubted Lamberti Zone ammonites (Arkell 1938). From this exposure were found some 250 ammonites, emphasizing the rarity of the species. Five specimens, four males and one female D. bicostatum (BM C10638, BM C10644-6, and OUM J20325 respectively), from Summertown, Oxford, may have come from the Lamberti Zone or possibly even older horizons (Arkell 1947#); the latter is labelled ‘Lamberti Zone’. To the south of Oxford, from Cowley, came two male specimens of D. bicostatum (recently catalogued as OUM J23246-7). The only information on the accompanying label is the word ‘Cowley’, which is largely situated on the Upper Oxford Clay possibly of Mariae age ( Arkell 1947#). The only localities between Oxford and Dorset to yield D. bicostatum are Dauntsey, Wiltshire, and ‘ Nr Chippenham, Wilts. ’ ; (the latter locality may also be Dauntsey as the two are separated by only a few miles: both collections were made by W. Buy). From the former locality have come three poorly preserved specimens (BM 27411 and BM C72580-1) and are labelled ‘Athleta Zone’. One of these (BM 2741 1) is a female as are probably the other two. A single male (BM 37744) came from the latter locality; the horizon is not recorded. Progressing further south to the most southerly outcrop of the British Oxford Clay, at Tidmoor Point, Dorset, is one of the best documented exposures of the uppermost Callovian. The clays here are almost entirely Lamberti in age with possibly whisps of Athleta and Mariae faunas. D. bicostatum (both male and female according to the author’s interpretation) is recorded from this locality by Spath (1927-33) and Arkell (1939): four specimens collected by M. R. House substantiate this. Despite the apparent rarity of the species, D. bicostatum is known throughout the out- crop of Upper Callovian rocks of England. To judge from the literature the species is known from a great deal of Europe, Asia, and Africa: a brief stratigraphical and geo- graphical distribution follows: France. Auberville, Normandy (Lamberti Zone, D. bicostatum) (Mercier 1936); Marnes-de-Dives (Athleta Zone(?), D. bicostatum and Horioceras baugieri) (Raspail 1901); Villers-sur-Mer, Normandy (Athleta Zone, D. bicostatum and H. baugieri ) (R. Douville 1904 and 1914); Brigon (Upper Athleta Zone, D. bicostatum ) (Thiery and Cossman 1907); Oiron and Niort, near Thouars ( D . bicostatum and H. baugieri) (d’Orbigny 1842-51); Jura Mountains (Athleta Zone, Distichoceras and Horioceras) (Arkell 1956); Franche-Compte, Haute-Saone ( D . bicostatum and H. baugieri) (Maire 1908, 1932, and 1938). Germany. Reutlingen, Wiirttemberg (Upper Callovian, D. bicostatum and H. baugieri) (Schindewolf 1963); Schwabian Jura (Braune Jura, D. bicostatum and H. baugieri) (Quenstedt 1852, 1858, and 1886-7). D. F. B. PALFRAMAN: SOME OXFORD CLAY AMMONITES 91 A collection of some 263 ammonites, recorded by Model and Model (1937) from Trockau, Bavaria, came from beds which appear to comprise the Coronatum to Mariae Zones (Spath 1949). The beds composed mainly of clays and numbered 1 (lowest) to 8 (highest), total about 4 m. and clearly represent a condensed sequence. Information from the ‘ Fossilliste’ (Model and Model 1937, p. 635) shows that the number of speci- mens of the Distichoceratinae is small: ‘ Subbonarellia (1), BonareUia ( Distichoceras ) (2), Horioceras (6). ’ Spath, who examined the Model collection, maintains that the speci- men of Subbonarellia ‘. . . is . . . a Distichoceras (“ BonareUia") . . . marked as coming from bed 6’ (Spath 1949, p. 426). He continues: ‘An example of “ BonareUia bipartita ” (Zieten) . . . presumably came from bed 6. . . . Another example of a Distichoceras and six specimens labelled Horioceras “ baughieri ” (d'Orbigny) are compressed on slabs of clay and not marked as coming from a particular bed. ’ Having examined two of these specimens (BM C40979-80), which are here interpreted as being females of Distichoceras bicostatum (Stahl), the present author is of the opinion that probably all three specimens, ‘ Distichoceras (“ BonareUia ”), “ BonareUia bipartita ” and Distichoceras ’, are females of the species D. bicostatum. The six specimens of ‘ Horioceras “ baughieri require careful consideration. They are crushed, apparently mature individuals, generally with poorly preserved phragmocones or with the phrag- mocone lacking. One of these specimens (BM C40927) is undoubtedly Creniceras renggeri (Oppel): the phragmocone is feebly ribbed, without ventral spines and has the suture of C. renggeri, which is substantially different from that of D. bicostatum <$. The same specimen has a narrow umbilicus and the body chamber carries a long, slender lappet: it is almost identical to the specimen of C. renggeri from the Oxford Clay of Yorkshire figured by Palframan (1966, PI. 52, fig. 8). Four of the other specimens of ‘ Horioceras “ baughieri from Bavaria cannot be interpreted reliably: two (BM C40926 and BM C40929), have long, slender lappets and may be C. renggeri. The final specimen (BM C40982) is crushed. The body chamber bears a short, broad lappet and the peristome is constricted (PI. 12, fig. 2). The phragmocone is lacking, but an external mould of this in the clay, shows that the umbilicus is in keeping with sizes recorded from D. bicostatum the author is very grateful to Dr. M. R. House. My sincere thanks go to Mr. J. M. Edmonds of the University Museum, Oxford, for allowing access to the Arkell Library and for the loan of specimens. Dr. M. K. Howarth of the British Museum, Natural History, loaned specimens in his care and kindly gave permission to break up certain specimens. The author is also indebted to the curators, Mr. A. G. Brighton of the Sedgwick Museum, Cambridge, and Mr. R. J. King of the Department of Geology, University of Leicester, for the loan of specimens. A grant from the Science Research Council is grate- fully acknowledged. REFERENCES arkell, w. J. 1933. The Jurassic System in Great Britain. Clarendon Press, Oxford. 1936. The Ammonite Zones of the Upper Oxford Clay of Oxford, and the Horizons of the Sowerbys’ and Buckman's Types. Q. JI. geol. Soc. Lond. 92, 146-87. 1938. The Geology of the Site of the Bodleian Extension in Broad Street. Oxoniensia, 3, 1-5. 1939. The Ammonite Succession at the Woodham Brick Company’s Pit, Akeman Street Station,. Buckinghamshire, and its bearing on the Classification of the Oxford Clay. Q. Jl geol. Soc. Lond„ 95, 135-222. 1945. The Zones of the Upper Jurassic of Yorkshire. Proc. Yorks, geol. Soc. 25, 339-58. 1947a. The Geology of Oxford. Clarendon Press, Oxford. D. F. B. PALFRAMAN: SOME OXFORD CLAY AMMONITES 93 arkell, w. j. 19476. The Geology of the country around Weymouth, Swanage, Corfe and Lulworth. Mem. geol. Surv. G.B. — — 1956. Jurassic Geology of the World. Oliver and Boyd, London. 1957#. Introduction to Mesozoic Ammonoidea. In Treatise on Invertebrate Paleontology, ed. R. C. Moore, (L) Mollusca 4. Univ. Kansas Press. L81-L129. 19576. Sutures and Septa in Jurassic Ammonite Systematics. Geol. Mag. 94, 235—48. — kummel, b., and wright, c. w. 1957. Mesozoic Ammonoidea. In Treatise on Invertebrate Paleon- tology, ed. R. C. Moore, (L) Mollusca 4. Univ. Kansas Press, L80-L81 and L129-L437. Basse, e. 1934. Etude du Sud-Ouest de Madagascar. Mem. Soc. geol. Fr. ser. A, 24, 1-157. beer, g. de 1959. A Handbook on Evolution. British Museum (Natural History), London, 1-130. birkelund, t. 1965. Ammonites from the Upper Cretaceous of West Greenland. Meddr Gronland, 179, No. 7, 1-192. blainville, m. h. d. de. 1840. Prodrome d'une monographie des ammonites. Extrait du Supplement du dictionnaire des Sciences naturelles , Bertrand, Paris, 1-34. branco, w. 1879-80. Beitrage zur Entwickelungsgeschichte der fossilen Cephalopoden. Palaeonto- graphica, A26, 15-50. 1880-1. Beitrage zur Entwickelungsgeschichte der fossilen Cephalopoden. Ibid. A27, 11-81. callomon, J. h. 1955. The ammonite succession in the Lower Oxford Clay and Kellaways Beds at Kidlington, Oxfordshire, and the zones of the Callovian stage. Phil. Trans. R. Soc. B239, 215-64. • 1957. Field meeting in the Oxford Clay of Calvert and Woodham brick pits, Buckinghamshire. Proc. Geol. Ass. 68, 61-64. — — 1963. Sexual dimorphism in Jurassic ammonites. Trans. Leicester lit. phil. Soc. 57, 21-56. crick, g. c. 1898. On the Muscular Attachment of the Animal to its Shell in some Fossil Cephalo- poda (Ammonoidea). Trans. Linn. Soc. Lond. ser. 2, Zoology, 7, 71-113. 1899. Note on Ammonites calcar Zieten. Geol. Mag. 36, 554-8. 1902. Additional note on Ammonites calcar Zieten. Ibid. 39, 47—48. douville, r. 1904. Sur la coupe du Jurassique Moyen de la plage de Villers-sur-mer (Calvados). Bulk geol. Soc. France, ser. 4, 4, 106-12. 1913. Esquisse d'une classification phylogenetique des Oppeliides. Ibid. 8, 56-75. 1914. Etudes sur les Oppeliides de Dives et Villers-sur-mer. Mem. Soc. geol. Fr. 48, 1-26. gerard, c. and contaut, H. 1936. Les Ammonites de la zone a Peltoceras athleta du Centre-Ouest de la France. Ibid., n.s. xiii, 29, fasc. 2-3. grossouvre, a de. 1891. Sur le Callovien de l’Ouest de la France et sur sa faune. Bull. Soc. geol. Fr., ser. 3, 19, 247-62. holder, h. 1955. Die Ammoniten-Gattung Taramelliceras im Sudwestdeutschen Unter- und Mittel- malm. Palaeontographica, 106A, 37-153. Huddleston, w. h. 1878. The Yorkshire Oolites. Part III. Proc. Geol. Ass. 5, 407-94. jeannet, a. 1951. Die Eisen- und Manganerze der Schweiz: Stratigraphie und Palaeontologie des oolithischen Eisenerzlagers von Herznach und seiner Umgebung. Beitr. Geol. Schweiz, ser. XIII, 5, 1-240. leckenby, j. 1859. On the Kelloway Rock of the Yorkshire Coast. Q. Jl geol. Soc. Lond. 15, 4-15. loczy, l. v. 1915. Monographie der Villanyer Callovien-Ammoniten. Geol. Hungarica, 1, fasc. 3-4, 255-502. maire, v. 1908. Contribution a la connaissance de la Faune des Marnes a Creniceras renggeri, dans la Franche-Compte septentrionale. Premiere partie: Le Callovien et l’Oxfordien inferieur a Authoison ( Haute-Saone). Bull. Soc. grayloise d'Emul. 11, 143-74. 1932. Notes complementaires sur le Gisement d’Oxfordien inferieur d’Authoison. Gray, 1-23. 1938. Sur quelques especes Oxfordiennes rares ou nouvelles. Bull. Soc. geol. Fr., ser. 5, 8, 43-61. makowski, h. 1962. Problem of Sexual Dimorphism in Ammonites. Palaeont. pol. 12, 1-92. mercier, j. 1936. Sur la position stratigraphique de Creniceras renggeri Oppel en Normandie. Extrait Bull. Soc. linn. Normandie, ser. 8, 9, 28-29. model, r. and model, e. 1937. Die Lam6erl/-Schichten von Trockau in Oberfranken nebst einem Anhang: Castor-Pollux-Zone und Obductus-Lager. Jb. preufi. geol. Landesanst. BergAkad. 58, 631-65. 94 PALAEONTOLOGY, VOLUME 10 munier-chalmas, e. c. p. a. 1892. Sur la possibility d'admettre un dimorphisme sexuel chez les Ammonitedes. Bull. geol. Soc. Fr. ser. 3, 20, clxx-clxiv. neaverson, e. 1925. The Zones of the Oxford Clay near Peterborough. Proc. Geol. Ass. 36, 27-37. orbigny, A. D. d’. 1842-51. Paleontologie fra utilise. Terrains jurassiques. 1 : Cephalopodes. Paris, 1-642. palframan, d. f. b. 1966. Variation and Ontogeny of some Oxford Clay Ammonites: Taramelliceras richei (de Loriol) and Creniceras renggeri (Oppel), from Woodham, Buckinghamshire. Palaeonto- logy, 9, 290-311. quenstedt, f. a. 1852. Handbuch der Petrefactenkunde. Tubingen. 1858. Der Jura. Tubingen. 1886-7. Die Ammoniten des Schwdbischen Jura. Band 2: Der Braune Jura ( and Atlas). Stuttgart. raspail, J. 1901. Contribution a l’etude de la falaise jurassique de Villers-sur-mer (Suite), Coupe de la falaise jurassique au promontoire d’Auberville. Feuille jeun. Nat., ser. 4, 365, 145-72. rollier, L. 1913. Sur quelques Ammonoides jurassiques et leur dimorphisme sexuel. Arch Sci. phys. nat. ser. 4, 35, 263-88. schindewolf, o. h. 1 954. Status of Invertebrate Palaeontology, 1953, VIII. On development, evolution and terminology of the ammonoid suture line. Bull. Mas. comp. Zool. Harv. 112, 217-37. 1960. Studien zur Stammesgeschichte der Ammoniten. Lief. I, Abh. math.-naturw. Kl. Akad. Wiss. Mainz, NR. 10, 635-745. 1962. Studien zur Stammesgeschichte der Ammoniten. Lief. II, Ibid. NR. 8, 425-572. 1963. Studien zur Stammesgeschichte der Ammoniten. Lief. Ill, Ibid. NR. 6, 285-432. simpson, G. G. 1953. The Major Features of Evolution. Columbia. spath, l. f. 1924. On the Blake Collection of Ammonites from Kachh, India. Mem. geol. Surv. India Palaeont. indica, N.s. ix, 1, 1-29. 1926. Notes on Yorkshire Ammonites. X. On some Post-Liassic Ammonites and a new species of Bonarellia. Naturalist, 321-26. 1927-33. Revision of the Jurassic Cephalopod Fauna of Kachh (Cutch). Mem. geol. Surv. India Palaeont. indica, N.s. ix, 2, parts i-vi, 1-945. 1938. Ammonites of the Liassic Family Liparoceratidae. British Museum (Natural History), London. 1949. On a Collection of Divesian (Mesoxfordian) Ammonites from Franconia. Ann. Mag. nat. Hist. 26, 422-31 . stahl, c. f. 1824. Ubersicht fiber die Versteinerungen Wurttembergs. KorrespBl. des Wiirttemb. Landwirtsch. Ver. vi, 7, 29-35 and 47-51. sylvester-bradley, p. c. 1953. A Stratigraphical Guide to the Fossil Localities of the Scarborough District. The Natural History of the Scarborough District, i, 19-48. thiery, p. and cossman, M. 1907. Note sur le Callovien de la Haute-Marne et specialement sur un gisement situe dans la commune de Bricon. Vesoul, 1-75. westermann, G. e. G. 1958. The Significance of Septa and Sutures in Jurassic Ammonite Systematics. Geol. Mag. 95, 441-55. wilson, v. 1936. The Upper Jurassic Rocks of the Country between Malton and Castle Howard, East Yorkshire. Proc. Geol. Ass. 47, 254-64. zieten, c. h. von 1830-3. Die Versteinerungen Wiirttembergs. Stuttgart. D. F. B. PALFRAMAN, Department of Geology and Mineralogy, University Museum, Oxford Present Address: Department of Geology, The University, Southampton Manuscript received 29 November 1966 FOSSIL MICROPLANKTON IN DEEP-SEA CORES FROM THE CARIBBEAN SEA by DAVID WALL Abstract. Quaternary fossil microplankton is described from three piston cores taken in the Caribbean Sea. Two cores were from the abyssal plain of the Yucatan Basin in the western Caribbean and the third from the Cariaco Trench, a deep-water depression lying within the continental shelf off Venezuela. This microplankton includes five new genera and eighteen new or reclassified species of dinoflagellates. Its stratigraphic distribution is outlined and its origin and ecology is discussed. Investigation of the organic microplankton in Quaternary marine deposits was neglected for decades while research into Palaeozoic, Mesozoic, and Tertiary micro- plankton progressed. The belief that hystrichospheres were extinct arose because the apparent absence of living forms from modern plankton was accentuated by the diffi- culties involved in sampling Holocene or Pleistocene marine deposits. Similarly, the phylogenetic relationships between fossil dinoflagellates and living dinoflagellates re- mained unknown partly because the Quaternary constituted a palaeontological hiatus for microplankton. Recently, certain problems concerning the nature and distribution of living and fossil microplankton throughout the Quaternary were examined with encouraging results. Evitt and Davidson (1964) and Wall (1965) demonstrated that microplankton (including ‘hystrichospheres’) with archeopyles were the resting spores (cysts) of dinoflagellates, thus unfounding the ‘extinction hypothesis’ and removing a major objection against recognition of the valid existence of Quaternary microplankton. In the fields of syste- matics and stratigraphy, Rossignol’s pioneer work (Rossignol 1961, 1962, 1964) on the Quaternary of Southern Israel and the Nile Delta demonstrated the abundance of micro- plankton in these deposits and exemplified its value in subsurface correlations. Similarly, West (1961) also encountered numerous microplankton in his study of the marine Early Pleistocene in Norfolk, England. This paper represents an initial extension of microplankton studies into the realm of marine geology. It describes microplankton from three Kullenberg piston cores taken in the Caribbean Sea during R/V Atlantis cruises A-240 in 1957 and A-254 in 1960. Two of these cores (A254/330 and A254/327) came from the abyssal plain of the Yucatan Basin situated south of Cuba and the third (A240/18) came from the Cariaco Trench, a deep-water trench located within the limits of the continental shelf north of the Venezuelan coast (Table 1; text-fig. 1). The general topography of the Caribbean Sea floor including its northernmost basin, the Yucatan Basin, was described by Wust (1963, p. 166). Core A254/330 was taken in the centre of the Yucatan abyssal plain and core A254/327 along its north-easterly extension towards the continental rise south of the Isla de Pinos and Gulf of Batabano. The geology of the Cariaco Trench was described by Athearn (1965) and its hydro- graphy and stagnation discussed by Richards and Vacarro (1956) and Heezen, [Palaeontology, Vol. 10, Part 1, 1967, pp. 95-123, pis. 14-16.] 96 PALAEONTOLOGY, VOLUME 10 Menzies, Broecker, and Ewing (1958) respectively. Core A240/18was taken in the eastern deep-water basin of the trench. LITHOLOGICAL DESCRIPTIONS OF THE CORES Core A254/330. This core comprises a light grey (N7) lutite from 34-5 cm. to its base at 605 cm. Above there are thin (1-8 cm.) alternating bands of yellowish grey (5Y 7/2), table 1. Locations, depths, and lengths of cores. Core Latitude Longitude Depth in metres Length in centimetres A254/330 19° 35' N. 84° 5L W. 4,430 605 A254/327 20° 45' N. 83° 00' W. 4,355 499 A240/18 10° 30-8' N. 64° 40' W. 1,344 952 85° 80° 75° 70° 65° 90° 85° 80° 75° 70° 65° 60° text-fig. 1 . Location of cores. light olive grey (5Y 6/1), and grey (N3, N5) lutites. Foraminifera are only abundant above 34-5 cm. and the sediments are extremely fine-grained in their absence. The basal grey lutite is highly calcareous (60-70% CaC03) and contains calcitic dust, some fora- minifera and microforaminifera, rhabdoliths, coccoliths, and discoasters, the latter in a poor state of preservation. Samples: 4, 10, 18,27,40, 150, 180, 240, 355, 455, and 600 cm. Core A254/327. From the surface to 397 cm. excepting a thin light brown (5YR 6/4) lutite band between 9 and 16 cm., this core comprises a loosely compacted, light grey, coarse globigerina-pteropod ooze almost entirely composed of foraminifera and ptero- pods with fine shell debris including gasteropods and lamellibranch sprat, rare ostra- cods and, near the base in particular, frequent pieces of carbonized wood. From 397 cm. to the base at 499 cm., there is a series of lutite bands. These are greenish grey (5GY 7/1) D. WALL: FOSSIL MICROPLANKTON FROM THE CARIBBEAN SEA 97 down to 439 cm. and light yellowish grey (5Y 7/1) below. They are silty between 450 and 477 cm. Other fine silt laminae occur at 402, 407-10, and 424 cm. Samples: 2, 11, 16, 40, 125, 180, 250, 350, 390, 400, 411, 420, 434, 443, 459 cm. Core A240/18. This core is a greyish olive silt and clay succession, mostly unlaminated but with restricted zones containing laminated bands, each only a few centimetres thick, at over twenty levels. Foraminifera were abundant only at 195 cm. This and other cores from the Cariaco Trench were described by Athearn (1965, figs. 4-6). Samples: 25, 80, 175, 275, and 380 cm. The numerical colour code is from the Geological Society of America Rock Colour Chart. CYST-THECA RELATIONSHIPS AND TAXONOMY Fossil dinoflagellates are studied to trace the phylogeny of the group and facilitate its stratigraphic applications. In my opinion both purposes are served best by retaining the existing taxonomic system for the fossils even though the possibility of combining cer- tain fossil and modern categories has arisen recently. The fossil taxonomy cannot be abandoned for practical reasons (Deflandre 1964, p. 5029; Evitt and Davidson 1964, p. 10) but it can be improved by more precise morphological observations. They will increase the value of stratigraphic and phylogenetic studies. If, for practical reasons, two systems of classification must coexist their mutual rela- tionships need to be understood. Eventually most Pleistocene and some late Tertiary cysts will be correlated with their parental thecae; how then will the two systems compare? Initial indications are that the scope of a fossil genus (e.g. Hystrichosphaera) will be coincident with that of a subgeneric thecate group (e.g. the‘Spinifera’ group of Gonyau- lax). If this applies to other groups as seems probable from research on modern cysts, then the scope of a fossil genus is narrower than the thecate genus which in this sense is polyphyletic. The phylogeny of a thecate subgeneric group will be traced through the fossil record by the history of a cyst genus with its constituent species. Conversely, prior knowledge of a cyst-theca relationship could aid in formulation of a fossil genus. Perhaps eventually the scope of modern dinoflagellate genera can be revised to coincide more precisely with the fossil scheme. Cysts of modern dinoflagellates are seldom common in plankton, but they are not so rare as once believed; over fifty types with archeopyles have now been isolated from Woods Hole plankton. One serious hazard to successful correlation of the two systems is the case where a fossil genus envelops a wide morphological range of species with variable archeopyles, poten- tially belonging to several different thecate genera or species-groups. The two largest microplankton genera, Hystrichosphaeridium (Deflandre 1937) Eisenack 1958 and Baltisphaeridiwn (Eisenack 1958) Downie and Sarjeant 1963, are heterogeneous in this context. They were established before the taxonomic value of the archeopyle and other dinoflagellate cyst characters was realized. Now they need to be restricted as their species are re-interpreted and reclassified. For example, Baltisphaeridium (type species: B. longispinosum Eis., a Lower Palaeozoic species with a circular pylome) is a genus for acanthomorphitid acritarchs (Downie, Evitt, and Sarjeant 1963, p. 7) and should not include dinoflagellate cysts. Again, Hystrichosphaeridium should be restricted to include C 44fifi H 98 PALAEONTOLOGY, VOLUME 10 only species with tubular, plate-centred processes and apical archeopyles comparable with the type species, H. tubiferum (Ehrenberg 1838) Deflandre 1937. To rectify this situa- tion necessitates the creation of new genera: the disadvantage is more names to manipu- late, but the advantage of an increased understanding of the chronological, phylogenetic, and ecological distribution of microplankton is considerable. This taxonomic trend is clearly foreshadowed by Evitt’s (1961, 1963) reviews. Consequently, three new genera are created for species previously allocated to Baltisphaeridium and Hystrichosphaeri- dium. They are diagnosed with particular reference to their archeopyles, spine structure, and arrangement. TABULATION PATTERNS AND TAXONOMY Detailed tabulation patterns were determined for all Caribbean species with sutural septa. The constant similarity of their plate-area patterns was surprising. Species belong- ing to different genera ( Hystrichosphaera , Leptodiniwn , or Gonvaulacysta) according to pre-existing criteria had identical plate patterns (text-fig. 2). The formula was always gonyaulacid, 3-4', Oa, 6", 6g, 5-6"', lp, 1"". While tabulation is a useful and often diagnostic character, obviously in this case ornamentation must assume a role of equal importance if these genera are to remain separated. LEPTO DINIUM KLEMENT VERSUS GO NYAULACYSTA DEFLANDRE There is no basic difference between the tabulation patterns of Hystrichosphaera,, Gonyaidacysta, or Leptodiniwn. Allowing for the fact that we are dealing with cysts re- flecting the tabulation of their parental thecae in differing degrees of perfection (especially in the ventral area), members of all three genera exhibit orthodox gonyaulacid tabulation. But ornamentation can serve as a basis for separation if Leptodiniwn is reserved for species possessing only low, narrow sutural septa of more or less equal height but lacking either the plate-cornered spines of Hystrichosphaera or the more elaborate crispate or otherwise serrated septa of Gonyaidacysta. There is a case for combining Leptodiniwn and Gonyaidacysta , but for the reasons expressed above, phylogeny and stratigraphy may benefit by their continued separation. For example, only species of Leptodiniwn as defined here (and not Gonyaidacysta) occur in the Quaternary which emphasizes the comparatively distant relationship between Gonyaidacysta and extant Gonyaidax. In fact, Gonyaidacysta as currently defined (Deflandre 1964, p. 5030) includes only extinct species represented by their cysts. The same argument applies to use of the broader diagnoses of Baltisphaeridium and Hystrichosphaeridiwn when dealing with Quaternary microplankton. Use of these names implies that species comparable with their respec- tive species exist as living or post-Tertiary organisms which to the extent of existing knowledge is incorrect. SYSTEMATIC DESCRIPTIONS Class DINOPHYCEAE Order peridiniales Family gonyaulacaceae Lindemann Genus hystrichosphaera (O. Wetzel) Deflandre 1937 D. WALL: FOSSIL MICROPLANKTON FROM THE CARIBBEAN SEA 99 Revised diagnosis. Ovoid to circular dinoflagellate cysts with sutural septa and spines developed from the outer of a two-layered cell wall reflecting a tabulation of 3-4', Oa, 6", 6g, 5-6"', lp, 1"". Archeopyle dorsal and precingular (3"), precingular plate-area 6" triangular. Spines not extensively united distally. Hystrichosphaera furcata (Ehr.) O. Wetzel 1932 Plate 14, figs. 1,2; text-fig. 2 Description. The test is ovoid with broadly rounded apices; circular in polar view. The girdle is narrow, descending and displaced by slightly more than its width ventrally; V" text-fig. 2. Tabulation model for Quaternary species of Hystrichosphaera and Leptodinium. a. b, c, Complete development as seen in H. bentori, H. membranacea sp. nov., H. tertiaria var. obliqua nov., L. paradoxum sp. nov., and L. sphaericum sp. nov. in apical, antapical, and ventral projections, d, e, f, Incomplete development as seen in H. furcata, H. hyperacantha, H. bulloidea, H. mirabilis, H. scabrata sp. nov., Nematosphaeropsis batcombiana, and some specimens of L. paradoxum. a.s., anterior sulcal; r.a., right accessory; r.s., right sulcal; l.s., left sulcal; p.s., posterior sulcal. the longitudinal furrow is weakly inclined, narrow anteriorly, only extending on to the epitheca for a short distance but broadening posteriorly. The tabulation (3-4', Oa, 6", 6g, 5-6'", lp, 1"") reflected primarily by very low sutural septa which are no more than traces between spine bases. In the apical series there are two pentagonal dorsal plate-areas and two smaller, linear ventral areas; the septum separating the latter is small and variously developed. The precingular areas are subrectangular except for plate-area 6" which is triangular. The archeopyle is developed from plate-area 3". The postcingular plates are also subrectangular apart from the first which, when visible, lies to the left of the furrow and is a weak linear structure comparable with that found in extant Gonyaulax. The 100 PALAEONTOLOGY, VOLUME 10 posterior intercalary area is small, anterior to the large, subrectangular antapical area. Spines are the dominant ornamentation and are situated at the corners of plates in most instances but can occur in between along the sutures. Septa are not usually well developed. The most complex spines, which are initially trifurcate and secondarily bifurcate, are found along the girdle, at the head of the furrow, around the posterior intercalary plate and at the dorsal antapical points. In these positions, two parallel branchlets of a spine may be directed along the course of a suture-trace. Intratabular areas are more or less smooth. Dimensions. Maximum test size 43-62 p. Remarks. This is a conspicuous member of almost every core sample examined, and there can be little doubt that this long-ranging species not only survived into but proli- ferated during the Pleistocene. Hystrichosphaera hyper acantha Deflandre and Cookson 1955 Plate 14, fig. 3; text-fig. 2 Remarks. The distinction between this species and H.furcata concerns the stronger de- velopment of two spines inserted along the longitudinal sutural traces between plate- area corners and the weaker tabulation pattern seen in H. hyper acantha. Every transitional stage between the restriction of spines to plate-area corners and a maximal development of two ‘intercalary’ spines (with a minute bifurcation beyond the main bifurcation) along the longitudinal suture-traces has been observed in specimens of Hystrichosphaera from the Yucatan Basin. Thus it is debatable whether H. hyperacantha is not a robust variety of H. furcata rather than a separate species. For statistical purposes at least, this species was grouped with H. furcata until further studies have been possible. Hystrichosphaera bulloidea Deflandre and Cookson 1955 Text-fig. 2 Remarks. This species is extremely common in the marine Quaternary of the Caribbean. It is similar to H. furcata but is smaller, its test rarely exceeding 40 p. It is a variable species with respect to the length of its spines and the development of septa. A culture of EXPLANATION OF PLATE 14 Figs. 1-16. Hystrichosphaera spp. 1-2, H.furcata (Ehr.) Wetzel, A254/330, depth 600 cm. 1, dorsal. 2, ventral; test only 48 p. 3, H. hyperacantha Dell, and Cooks., A254/330, depth 455 cm.; test only 50 p. 4, H. bentori Rossignol, A254/327, depth 408 cm.; ventral; test only 55 p. 5, 6, H. mirabilis Rossignol. 5, A254/330, depth 600 cm.; test 58 p. 6, A254/327, depth 420 cm., test 53 p. 7-9, H. nodosa sp. nov., Holotype, A240/18, depth 25 cm.; test 57 p. 7, dorsal. 8, apical. 9, ventral. 10-13. H. scabrata sp. nov., Holotype, A254/330, depth 150 cm.; test 55 p. 10, dorsal. 11, ventral. 12, apical. 13, antapical. 14, 15, H. membranacea Rossignol comb. nov. A254/330, depth 180 cm., test 56 p. 14, antero-ventral. 15, postero-ventral. 16. H. tertiaria Eis. and Gocht var. obtiqua var. nov., type specimen, A254/327, depth 400 cm.; test 44 p. Fig. 17. Nematosphaeropsis batcombiana Dell, and Cooks., A254/330, depth 240 cm.; test 42 p. Figs. 18, 19. Leptodinium aculeatum sp. nov. 18, Holotype, A254/327, depth 459 cm.; test 36 p. 19, A254/330, depth 27 cm., apical; test 36 p. Fig. 20. Leptodinium patulum sp. nov., Holotype, A254/330, depth 355 cm.; test 59 p; dorsal. Palaeontology, Vol. 10 PLATE 14 WALL, Quaternary microplankton D. WALL: FOSSIL MICROPLANKTON FROM THE CARIBBEAN SEA 101 Gonyaulax scrippsae Kofoid was started from a specimen of H. bulloidea suggesting this theca-cyst relationship, but confirmation by repetition has not been demonstrated. Hystrichosphaera bent or i Rossignol 1962 Plate 14, fig. 4; text-fig. 2 1961 Hystrichosphaera bentori Rossignol, pi. 1, figs. 7, 8. 1962 Hystrichosphaera bentori Rossignol, p. 132. 1963 Hystrichosphaera bentori', Rossignol, pi. 1, figs. 13-15, text-fig. 17. 1964 Hystrichosphaera bentori', Rossignol, p. 84, pi. 1, figs. 3, 7, 8, pi. 3, figs. 2, 3; text-fig. a-f. Remarks. This species, which has been shown to be the cyst of Gonyaulax digitale (Pouchet) Kofoid by Evitt and Davidson (1964, p. 5) and Wall (1965, p. 312), has a reflected tabulation typical of the genus Hystrichosphaera. It is relatively infrequent in Caribbean deep-sea cores. Hystrichosphaera mirabilis Rossignol 1962 Plate 14, figs. 5, 6; text-fig. 2 1962 Hystrichosphaera mirabilis Rossignol, p. 162. 1963 Hystrichosphaera mirabilis Ross.; Rossignol, pi. 2, figs. 16-21. 1964 Hystrichosphaera mirabilis Ross.; Rossignol, p. 86, pi. 2, figs. 1-3, pi. 3, figs. 4, 5. Remarks. This is a common species in the marine Quarternary of the Caribbean cores examined. The spines are densely set along the sutures and are briefly bifurcate or trifurcate distally. There is a conspicuous sutural flange bordering the margins of the antapical area. The tabulation is 3-4', Oa, 6", 6g, 5-6"', lp, 1"", and the archeopyle is precingular (3"). Its shape is similar to the archeopyle of H. furcata but it is easily de- formed. Several specimens from the Cariaco Trench were observed possessing an inner capsule whose wall was composed of a refractive, yellowish substance; they were com- parable with specimens previously described by Rossignol (1963), but the inner capsule was thinner. Hystrichosphaera nodosa sp. nov. Plate 14, figs. 7-9; text-fig. 2 Holotype. Plate 14, figs. 7-9; test 57 X 48 ft, specimen 39/5, Core A240/18, depth 25 cm., Cariaco Trench (10° 30-8' N. 64° 40' W.). Diagnosis. A species of Hystrichosphaera with much reduced spines forming small sclerotia at the plate-area angles. Dimensions. Test 31 X 28 ft to 62 x 52 ft. 20 specimens. Occurrence. Yucatan Basin and Cariaco Trench, uncommon. Description. The test is ovoid with weakly truncated apices. The plate-areas are defined by distinct but low (1 ft or less) sutural septa and are typical in number and arrange- ment for the genus. The characteristic processes are restricted to the corners of plate- areas. They are small, either bifurcate or trifurcate and recurve strongly towards their 102 PALAEONTOLOGY, VOLUME 10 own bases or lie along the test surface so that there appears to be a small pad or sclero- tium of tissue at each junction. Only rarely do the spines project more than a few microns above the test wall. The species forms a typical 3" archeopyle and has a weakly inclined furrow. Remarks. This species gives the impression that as a cyst it was closely pressed against its parental thecal covering and that the spines were unable to develop fully, but it is not necessarily an immature form. Hvstrichosphaera scabrata sp. nov. Plate 14, figs. 10-13; text-fig. 2 Holotype. Plate 14, figs. 10-13; test 55x50 /a, spines 12-5 p, specimen 17/4, Core A254/330, depth 150 cm., Yucatan Basin (19° 35' N. 84° 51'W.). Diagnosis. A species of Hvstrichosphaera with microgranular sutural septa, membranous processes and a broad posterior ventral area. Dimensions. Test 48-55 p, processes 10-17 p. Numerous examples. Occurrence. Common in Cores A254/330 and A254/327, rarer in the Cariaco Trench. Description. The theca is ovoid with broadly rounded apices and divided into epithecal and hypothecal hemispheres by a narrow descending girdle displaced by its own width ventrally. The test wall is thin, its outer layer forming microgranular sutural septa. Their outline in optical section is undulate and their height equivalent to one-third of the test diameter. These septa unite at the corners of plate-areas to form spine-like processes with trifurcate or further subdivided tips with strongly divergent angles. Its tabulation is typical for the genus, 3-4', Oa, 6", 6g, 5-6'", lp, and 1"", and the plate pattern as for H. furcata and H. bentori. A complex process occurs at the head of the longitudinal fur- row, above which, the two ventral apical plate areas (T, 4') are situated; they may be in- completely separated. The furrow is weakly inclined and has at least four constituent platelet-areas. Usually, however, only the posterior sulcal platelet is obvious. In the postero-ventral area the posterior intercalary plate-area is well developed and almost as broad as the furrow itself at this point. The archeopyle is typical (3") and weakly rounded. Hvstrichosphaera membranacea Rossignol comb. nov. Plate 14, figs. 14, 15; text-fig. 2 1964 Hystrichosphaera furcata var. membranacea Rossignol, p. 86, pi. 1, figs. 4, 9, 10; pi. 3, figs. 11, 12. Holotype. Rossignol 1964, p. 86, pi. 1, fig. 4, Ashkelon, Israel; Recent. Test 57x 50 p. Description. The test is circular, ovoid, or weakly elongated (broader than high). Its surface is scabrate to microgranular and ornamented by membranous sutural septa which are stronger where they fuse at the corners of plate-areas. Distal projections arising from the septa are trifurcate or more complex at plate corners but bifurcate in between. There is a strong antapical dorsal and lateral flange around plate-area V" that is equal in height to one-third of the test diameter. The tabulation and plate pattern is typical for D. WALL: FOSSIL MICROPLANKTON FROM THE CARIBBEAN SEA 103 the genus. The archeopyle is dorsal and precingular (3") and the furrow is weakly in- clined and broader posteriorly. It is possible to recognize anterior, right accessory, right and left and posterior sulcal platelet-areas within the furrow; of these, the right sulcal is very small. Remarks. This uncommon species differs from Hystrichosphaera mirabilis by lacking strong rows of spines over its test; instead its processes are weak and membranous. It differs from H. scabrata sp. nov. by possessing a strong antapical flange. This appears to be a distinctive form which ranges back into the Miocene and worthy of elevation to specific status. Some small Tertiary specimens resemble H. bulloidea but lack two dorsal antapical spines seen in that species. Hystrichosphaera tertiaria Eisenack and Gocht 1960 var. obliqua var. nov. Plate 14, fig. 16; text-fig. 2 Type specimen. Plate 14, fig. 16; test 44x40 p, spines c. 12 /x, specimen 17B/1, Core A254/327, depth ’ 400 cm., 20° 45' N., 83° 00' W. Description. The test is ovoid, sometimes with a rudimentary apical boss, has a smooth to weakly microgranular wall, and is divided by an equatorial, narrow, descending girdle. Its tabulation is 4', Oa, 6", 6g, 6"', lp, V" and the arrangement of plate-areas is identical with that seen in H.furcata and H. bentori. The longitudinal furrow is narrow anteriorly but widens posteriorly and is oblique, while the girdle is quite strongly dis- placed about it. The spines are characteristic: the most complex closely resemble those of H. tertiaria as figured by Eisenack (1954, pi. 9, figs. 1-4, text-fig. 3) under the synonym H. cf. furcata. They are trifurcate with secondary branchlets which tend to remain parallel and often are connected by delicate membranes as they flare. Such spines are restricted to plate-area corners but bifurcate spines occasionally ornament longitudinal septa. The two dorsal antapical spines are particularly prominent as an aid to identification. Dimensions. Test only 40-50 /x, spines 10-12 p. 6 specimens measured. Occurrence. Relatively uncommon. Core A254/327, Yucatan Basin. Remarks. This variety differs from the typical form of H. tertiaria Eisenack and Gocht in being smaller (less than 50 /x), but has the characteristic spines and general appearance of the former. (The plate-pattern of H. tertiaria is considered to be gonyaulacid (text-fig. 2a, b) and not as originally stated by Eisenack and Gocht (1960, p. 515): this reinterpreta- tion is based upon the original illustrations and examples from cores A254/330 and A254/327.) Hystrichosphaera bentori is closely related but can be distinguished by its stronger apical boss and more numerous processes. Genus nematosphaeropsis Deflandre and Cookson 1955 Nematosphaeropsis balcombiana Deflandre and Cookson 1955 Plate 14, fig. 17 Remarks. This is a persistent but relatively infrequent species in the Caribbean marine Quaternary from the Yucatan Basin and Cariaco Trench. It is recognizable by its outer 104 PALAEONTOLOGY, VOLUME 10 trabeculum of parallel strands suspended above sutural septal traces by spines at the corners of plate-areas. Its tabulation and archeopyle are similar to those of Hystricho- sphaera furcata. There may be two varieties in the Pleistocene : one form possesses a relatively small, globular central body, whose diameter is around 25 p and whose spines are equal to a radius; the other is more robust and has an ovoid central body with a maximum length around 40 p and has spines equivalent to one-third of this dimension. Both range from the Miocene or earlier into the Holocene. Genus leptodinium Klement 1960 emend. Revised diagnosis. Ovoid, spherical, or polyhedral tests ornamented with more or less level, low sutural septa (but not with spines), developed from the outer of a two-layered wall, reflecting a tabulation of 3-4', Oa, 6", 6g, 5-6"', lp, 1"". Girdle spiral, ventral sulcus only just extending on to the epitheca and in contact with I'. Archeopyle dorsal and precingular (3"). Apical or antapical projections essentially absent. Remarks. Development of a linear, gonyaulacid first postcingular plate-area in cysts is variable and unreliable as a criterion for separating Leptodinium from Gonyaulacysta, but the characteristic sutural septa and lack of apical structures in Leptodinium are distinctive. Leptodinium aculeatum sp. nov. Plate 14, figs. 18, 19; text-figs. 3c, d Holotype. Plate 14, fig. 18; test 36 X 29 p, specimen 7/8, Core A254/327, depth 459 cm., Yucatan Basin (20° 45' N. 83° 00' W.). A B C D text-fig. 3. Tabulation schema for Leptodinium spp. a, b, L. paradoxum sp. nov., ventral variation c, d, L. aculeatum sp. nov., ventral and apical, a, anterior; ac, accessory; m, median; p, posterior ventral platelet areas. Diagnosis. A relatively small, ovoid species with a relatively wide girdle zone and exten- sive ventral area; test hyaline with sutural septa most strongly developed in the posterior intercalary area; precingular plate-area 6" very narrow. Dimensions. Test only 28-38 p long; septa up to 9 5 p high. Over 100 specimens. Occurrence. Yucatan Basin; Pleistocene, and Holocene. Description. The test is ovoid and divided into more or less equal epithecal and hypo- thecal regions by a relatively wide, weakly descending girdle, displaced by its own width ventrally. It is ornamented by hyaline, sutural septa whose maximum elevation (equiva- D. WALL: FOSSIL MICROPLANKTON FROM THE CARIBBEAN SEA 105 lent to one-quarter of the diameter) is found at the corners of plate-areas and along the left margin of the ventral area, especially near the posterior intercalary area; in between the septa are lower. At the equator the septa are inclined so that the girdle plate-areas widen distally. The tabulation is 3-4', Oa, 6", 6g, 5'", lp, 1"". There are two pentagonal dorsal apical plate-areas (2', 3') and two minute median ventral areas (1 4'). Precingular areas 1" to 5" are subrectangular, the sixth is linear and narrow; plate-area 3" forms a trapezoidal archeopyle. There are five subrectangular postcingular areas, T" and 5"' being smaller than the others; the adjacent posterior intercalary plate-area is small and the outer test wall may be completely separated from the inner at this point. There is a single small, subquadrangular antapical area. The longitudinal furrow occupies almost the entire length of the ventral area, extending well into the epitheca. it occupies approximately one-third of the equatorial diameter and widens slightly posteriorly. Leptodinium patulum sp. nov. Plate 14, fig. 20; Plate 15, figs. 1-4; text-fig. 4 Holotype. Plate 15, figs. 1, 2; text 50x 55 /a, specimen 10/8, Core A254/330, depth 355 cm., Yucatan Basin (19°35'N. 84° 51' W.). Diagnosis. An ovoid species of Leptodinium ornamented with low, level sutural septa forming a plate-area pattern characteristically reduced on the ventral surface. Test rarely less than 40 p. Dimensions. Test only 38-62 /x long, 34-55 /x broad; septa 2-5 to 7 /x high. Over 50 specimens. Occurrence. Yucatan Basin, relatively infrequent; known from the Middle Miocene to Holocene. Description. The test appears weakly ovoid in lateral view and circular in polar view. Its surface is smooth to weakly microgranular and bears a pronounced reflected tabula- tion defined by low, level sutural septa approximately equivalent to one-tenth of the test diameter in height. The formula is 4', Oa, 6", 6g, 5"', lp, V". The test is divided into A B C text-fig. 4. Tabulation of Leptodinium patulum sp. nov. a, apical; b, antapical; c, ventral. epithecal and hypothecal regions by a relatively narrow, weakly descending girdle; dorsally the girdle plate-areas are complete, but only the uppermost of the delimiting septa are present along two cingular plate-areas on the ventral surface adjacent to the furrow. The epitheca lacks intercalary plate-areas. The apical series comprises two large pentagonal dorsal plate-areas (2' and 3') and a smaller, median ventral, compound 106 PALAEONTOLOGY, VOLUME 10 plate-area representing 1' and 4'; here there is no complete division into two plate-areas but there is a significant re-entrant angle in the septum separating this areas from 3'. There are five discrete, subrectangular precingular plate-areas; 3" forms a conspicuous dorsal archeopyle with its borders slightly within the septa. The sixth precingular plate- area is not differentiated from the anterior sulcal platelet-area with which it forms a compound area in the mid-ventral equatorial region. The remainder of the furrow extends posteriorly and is almost entire; median and posterior platelet-areas are only indicated by rudimentary septal ingrowths. Similarly, the septum separating the relatively larger posterior intercalary plate-area from the furrow may be developed only partially. The remainder of the hypotheca comprises five large, subrectangular plate-areas and one quadrangular antapical (1""). Remarks. The characteristic tabulation of this species differentiates it clearly from any previously described. Leptodinium paradoxum sp. nov. Plate 15, figs. 5-8; text-figs. 2, 3a, b Holotvpe. Plate 15, fig. 5; test only 31 X 26 /a, specimen 8/6, Core A254/330, depth 40 cm., Yucatan Basin (19°35'N., 84° 51' W.). Diagnosis. A very small ovoid species with a tabulation 3-4', Oa, 6", 6g, 5-6"', lp, V", defined by low sutural septa which are sometimes reduced in the ventral area. Test not exceeding 40 p. Dimensions. Test only 29-38 p; septa around 3 p. Over 50 specimens. Occurrence. Yucatan Basin; known range of Middle Miocene to Holocene. Description. The test is ovoid to polyhedral and divided equatorially into epithecal and hypothecal regions by a relatively wide, descending girdle displaced by its own width ventrally. The longitudinal furrow broadens on to the hypotheca and is weakly inclined. The sutural septa are hyaline and very low (equivalent to approximately one-tenth of a diameter) ; the test varies from smooth to microgranular. The apical plate series comprises two pentagonal dorsal areas and a linear, median compound ventral area which may be EXPLANATION OF PLATE 15 Figs. 1-4. Leptodinium patulum sp. nov. 1, 2, Holotype, A254/330, depth 355 cm.; test 59 p, apical and postero-ventral. 3, A254/330, depth 27 cm.; test 58 p, ventral. 4, A254/330, depth 150 cm., test 60 p, antero-ventral. Figs. 5-8. Leptodinium paradoxum sp. nov. 5, Holotype, A254/330, depth 40 cm.; test 31 p, antapical. 6, A254/330, depth 240 cm. ; test 30 p, apical. 7, 8, Upper Miocene, near Guadalupe Island, both tests 36 p and ventral views showing complete and incomplete plate-patterns. Figs. 9, 10. Leptodinium strialatum sp. nov. 9, Holotype, A254/330, depth 355 cm.; test 36 p. 10, A254/330, depth 180 cm.; test 36 p, ventral. Figs. 11-15. Leptodinium sphaericum sp. nov. 11, 12, Holotype, A254/330, depth 10 cm.; test 50 p, dorsal and apical. 13-15, A254/330, depth 240 cm.; test 55 p, dorsal, antero- and postero-ventral. Figs. 16, 17. Lingulodinium machaerop/iorum Defl. and Cooks., comb, nov., 16, A254/327, depth 434 cm.; test only 44 p. 17, A254/330, depth 600 cm.; test 40 p. Figs. 18-20. Hemicystodinium zoharyi Rossignol comb, nov., A254/330, depth 600 cm.; test only 65 p. Optical, polar, and lateral views. Palaeontology, Vol. 10 PLATE 15 WALL, Quaternary microplankton D. WALL: FOSSIL MICROPLANKTON FROM THE CARIBBEAN SEA 107 divided longitudinally to form two areas (T and 4'). Precingular areas 1" to 5" are sub- rectangular, 3" being an archeopyle; 6" is triangular and either incompletely separated from the furrow or possessing a concave outer margin. The furrow may be divided into three platelet-areas by very reduced septa. The girdle plate-areas are rectangular ; sections of the septa outlining 5g and 6g may be missing. There are usually five postcingular areas but in some specimens there are six due to the additional presence of a small linear first post-cingular area, V". There is a small posterior intercalary area and a quad- rangular antapical area. Remarks. L. paradoxum sp. nov. recalls L. patulum sp. nov. in some details of its tabula- tion but is smaller. It differs from L. aculeatum sp. nov. in outline and in configuration of the sixth precingular area. Leptodinium strialatum sp. nov. Plate 15, figs. 9, 10; text-fig. 5 Holotvpe. Plate 15, fig. 9; test only 36 x 29 p, specimen 11/1, Core A254/330, depth 355 cm., Yucatan Basin (19° 35' N., 84° 51' W.). Diagnosis. A small species of Leptodinium with relatively broad, weakly radially striate sutural septa reduced in the ventral area. text-fig. 5. Tabulation of Leptodinium strialatum sp. nov. a, apical; b, antapical; c, ventral; d, dorsal; e, right lateral. Dimensions. Test only 26-38 p, septa 5-10 p. Over 50 specimens. Occurrence. Yucatan Basin; known range from Middle Miocene to Holocene. Description. The test is ovoid with broadly rounded apices and smooth to weakly microgranular. It is ornamented by relatively broad sutural septa (equivalent to between one-fifth and a quarter of the equatorial diameter) with weak radial striations. These indi- cate a tabulation of 3-4', Oa, 6", 6g, 5"', 1 p, 1 whose basic pattern follows that of Lepto- dinium aculeatum sp. nov. and L. paradoxum sp. nov., but in L. strialatum the septa are 108 PALAEONTOLOGY, VOLUME 10 so reduced in several places that there are large, open compound areas on the test. These include two conspicuous longitudinal ventral areas where the cingular plates 6g and lg are so reduced that the girdle is scarcely recognizable between the pre- and post-cingular series. The cingular areas on the dorsal surface also are reduced, only area 4g being complete and visible below the precingular archeopyle (3"). There is no longitudinal septum between the archeopyle and the fourth precingular area. The structure of the ventral region is not easily discernible but there appear to be one or two minute ventral apical plates (T and 4'), a small anterior sulcal platelet, and a reduced sixth precingular plate-area. In this region the girdle appears to be displaced by its own width. The longitudinal furrow, too, is poorly defined ; its left margin is very weakly developed in particular, but posteriorly there is a conspicuous posterior sulcal platelet- area and a posterior intercalary area. Below these there is a square antapical area. Remarks. Pentadinium laticinctum Gerlach 1961 is similar in overall appearance but is considerably larger and different in details of tabulation. Leptodinium sphaericum sp. nov. Plate 15, figs. 11-15; text-fig. 2 a-c Holotype. Plate 15, figs. 11, 12; test only 50x43 ju, specimen 29/2, Core A254/330 depth 10 cm.. Yucatan Basin (19° 35' N., 84° 15' W.). Diagnosis. A spherical to polyhedral species with very low sutural septa defining a tabu- lation 4', Oa, 6", 6g, 6"', lp, 1""; test with a small apical boss. Size approximately 40-58 p. Dimensions. Test 43-58 /x including apical boss; septa around 3 p. 9 specimens. Occurrence. Yucatan Basin; Pleistocene and Holocene. Description. The test is spherical to polyhedral and has a small blunt apical boss. Its surface is weakly microgranular and ornamented by very low sutural septa, only a few microns high. Its tabulation is 4', Oa, 6", 6g, 6"', lp, 1"". The girdle is narrow, descend- ing, composed of rectangular plate-areas and divides the test equatorially into equal epithecal and hypothecal regions; ventrally the girdle is displaced by slightly more than its own width. The longitudinal furrow is quite strongly inclined and comprises five platelet-areas, namely, anterior, right accessory, right and left sulcal, and posterior sulcal; of these, the right sulcal is very small while the posterior sulcal is large. There are two pentagonal dorsal apical areas and two linear median anterior ventral areas in the apical series. The precingular series comprises six areas, of which the third forms an archeopyle and the sixth is triangular with a concave left margin. There are six post- cingular areas, T" being a small linear structure on the left margin of the sulcus; the other areas are subrectangular. The posterior intercalary area is relatively large and anterior to a quadrangular antapical area (1""). Remarks. An identical cyst was isolated from a plankton haul in the North Atlantic (40° 00' N., 71° 15' W.) in July 1963 at a depth not greater than 100 metres. It had colourless cell contents and no archeopyle but otherwise was identical with fossil speci- mens from the Yucatan Basin. The shape of polyhedral varieties superficially resembles that of Gonyaulax polyedra Stein but in other details these species are quite different. D. WALL: FOSSIL MICROPLANKTON FROM THE CARIBBEAN SEA 109 Genus lingulodinium gen. nov. Type species. Lingulodinium machaerophorum Deflandre and Cookson 1955 comb. nov. Diagnosis. Spherical to ovoid dinoflagellate cysts which, after dehiscence, possess a large, compound epithecal archeopyle representing the loss of either four or five precingular plate-areas. The remainder of the epitheca forms an elongate angular projection or lingula; this corresponds to several (apical, intercalary, and one precingular) plate-areas. The test wall is microgranular to microreticulate and ornamented with numerous intra- tabular spines. Lingulodinium machaerophorum Deflandre and Cookson 1955 comb. nov. Plate 15, figs. 16, 17; text-fig. 6 1955 Hystrichosphaeridium machaerophorum Deflandre and Cookson, p. 274, pi. 9, figs. 4, 8. 1961 Hystrichosphaeridium ashdodense Rossignol, pi. 1, fig. 9. 1962 Hystrichosphaeridium ashdodense Ross.; Rossignol, p. 132, pi. 2, fig. 2. 1964 Baltisphaeridium machaerophorum Dell, and Cooks.; Rossignol, p. 90, pi. 2, fig. 14, pi. 3, figs. 20, 21. Description. The test is spherical but rarely found whole. Upon dehiscence it develops a large compound precingular archeopyle, so all that remains of the epitheca is a narrow, elongated, angular projection, attached to the hypotheca ventrally. The archeopyle, in its text-fig. 6. Comparison of Gonyaulax polyedra Stein with Lingulodinium lmchaero- phorum Defl. and Cooks., comb. nov. A, epithecal tabulation of G. polyedra, Woods Hole, August 1965; b, plate equivalence of the archeopyle (shaded) in L. machaero- phorum-, c, lateral view of L. machaerophorum (spines omitted). most entire form, represents the loss of five precingular plate-areas (1" to 5") but it may represent only four plates (2" to 5") or very rarely, only the dorsal precingular plate 3". The test is microgranular and bears numerous (15 to 20 in optical section), flexuous, hollow spines of variable length. Their bases are circular and minutely striated; their distal extremities are flexuous, closed, and bear spinules. There is a tendency towards flattening of the spines. Size. Test 36 to 50 p. Remarks. This fossil species is almost certainly the cyst of Gonyaulax polyedra Stein, since it compares closely with the cysts described by Erdtman (1954, fig. 3b) and Evitt and Davidson (1964, p. 4, pi. 1, fig. 13). The archeopyles of the fossils have been inter- preted on this assumption. In its early stages of development, the archeopyle may appear 110 PALAEONTOLOGY, VOLUME 10 as a simple 3" structure (see Rossignol 1964, pi. 3, fig. 21) which is comparable with that found in other cysts of Gonyciulax. L. machaerophorum is a common species both in the Yucatan Basin and Cariaco Trench cores and appears to attain its acme in the Quater- nary. It certainly occurs in the Miocene, but apparently less abundantly. Records of older occurrences should be re-evaluated with particular attention to spines and archeopylar structure before the first appearance of this species is established. These structures should serve to distinguish this from other species such as Baltisphaeridium hirsutum Ehr. Family incertae sedis Genus hemicystodinium gen. nov. Type species. Hemicystodinium zoharyi Rossignol 1962. Diagnosis. Spherical to ovoid dinoflagellate cysts which dehisce equatorially to form hemispheres; rims of the hemispheres with a small projection or indentation and slight displacement at the mid-ventral point. Ornamentation variable, from microreticulate to spinose; spines, when present, variable in length and predominantly simple. Elements of ornamentation randomly disposed or intratabular. Hemicystodinium zoharyi Rossignol 1962 comb. nov. Plate 15, figs. 18-20 1962 Hystrichosphaeridium zoharyi Rossignol, p. 132, pi. 2, fig. 10. 1964 Hystrichosphaeridium zoharyi Rossignol 1962; p. 88, pi. 2, figs. 4, 9, 10, 11. Description. Test hemispherical, the mid-ventral point marked by a small subrectangular projection and displacement of the rim. Test smooth to microreticulate, spine bases weakly striate. Spines numerous, length variable, all but a few simple and capitate, the others bifurcate. Remarks. The parallel alignment of spines in the equatorial region reflects the position of a girdle and the mid-ventral projection or sulcal notch probably indicates the former position of the anterior limit of the longitudinal furrow. This is a common species in the Yucatan Basin and Cariaco Trench where both varieties described by Rossignol (1964* p. 88) are represented abundantly. Genus operculodinium gen. nov. Type species. Operculodinium centrocarpum Deflandre and Cookson 1955 comb. nov. Diagnosis. Spherical to ovoid cysts possessing simple, dorsal precingular archeopyles (reflecting plate 3"), and lacking polar structures. A weakly defined girdle and ventral sulcal depression often present. Cell wall double, the inner thin and the outer thicker and microgranular or microreticulate. Elements of ornamentation variable, from small cones to long spines but all with circular, minutely striated bases and often capitate extremities. Spine arrangement intratabular with several spines to each plate-area, commonly arranged immediately within the reflected plate-area margins. Remarks. Members of this genus differ from species of Apteodinium Eisenack 1958 and D. WALL: FOSSIL MICROPLANKTON FROM THE CARIBBEAN SEA 111 Trichodinium Eisenack and Cookson 1960 by lacking polar projections and possessing spines. Several members were allocated previously to the acritarch genus Baltisphaeridium but this is inadmissible for forms possessing archeopyles and other dinoflagellate cyst characteristics. Operculodinium centrocorpum Deflandre and Cookson 1955 comb. nov. Plate 16, figs. 1, 2, 5 1953 Hystrichosphaeridium sp. a Cookson, p. 115, pi. 2, figs. 26, 27. 1953 Hystrichosphaeridium sp. b Cookson, p. 115, pi. 2, fig. 28. 1955 Hystrichosphaeridium centrocarpum Deflandre and Cookson, p. 272, pi. 8, figs. 3, 4. 1959 Hystrichosphaeridium centrocarpum Defl. and Cooks.; Maier, p. 314, pi. 28, fig. 9. 1961 Baltisphaeridium centrocarpum Defl. and Cooks.; Gerlach, p. 192, pi. 28, fig. 9. 1963 Baltisphaeridium centrocarpum Defl. and Cooks. ; Brosius, p. 44, pi. 6, fig. 6, text-fig. 8 a, 6. Description. The test is almost spherical and densely ornamented with slender radiating spines whose length (8— 1 6 /x) varies between approximately one-fifth and one-quarter of the cell diameter. The dorsal precingular archeopyle is large and subtrapezoidal. The outer cell wall is microgranular and the immediate spine bases are conical with minute striations. The spine tips bear small hooklets which are visible only at high magnifica- tions. The spines are aligned in the girdle region but there is no distinct ventral sulcus. The spine arrangement is intratabular, most spines lying alongside the sutural lines. Dimensions. Caribbean specimens vary from 40 to 56 p for the test alone. Miocene specimens may be much larger, with diameters approaching 90 p. Operculodinium israelianwn Rossignol 1962 comb. nov. Plate 16, figs. 3, 4 1962 Hystrichosphaeridium israelianum Rossignol, p. 132, pi. 2, fig. 3. 1964 Baltisphaeridium israelianum Ross.; Rossignol, p. 91, pi. 2, fig. 12, pi. 3, figs. 13, 14. Remarks. Specimens similar to those described by Rossignol are common in the Yucatan Basin and Cariaco Trench cores. Their spines vary from three to six microns and are equivalent to approximately one-tenth or less of the test diameter which ranges from 40 to 65 p. A narrow girdle and small mid-ventral depression are visible sometimes. The dorsal archeopyle is trapezoidal and precingular. Caribbean and Mediterranean speci- mens examined consistently have very short spines with weakly capitate tips and in these respects differ from the description given by Rossignol (1964, p. 91). O. israelianum is fundamentally similar to O. centrocarpum according to these observations and only distinguishable by its smaller spines relative to the test size but this is a consistent feature. Operculodinium psilatum sp. nov. Plate 16, figs. 6-8 Holotype. Plate 16, figs. 6-8; test 58x56 p, spines 2 p, specimen 23/4, Core A240/18, depth 175 cm., Cariaco Trench, (10° 30-8' N., 64° 40' W.). Description. The test is ovoid and without polar structures. The wall is smooth, with a tectate appearance and has sparse, extremely small and delicate spines which are scarcely 112 PALAEONTOLOGY, VOLUME 10 visible at low magnifications except as darker spots on the test wall. There is a very well defined, narrow equatorial girdle, which is displaced slightly at the mid-ventral point. Below it there is a smaller sulcal depression with an ellipsoidal scar. The archeopyle is trapezoidal, precingular, and dorsal. Dimensions. Test dimensions 50-60 p maximum. Numerous examples. Occurrence. Particularly abundant in the Cariaco Trench core A240/18, less abundant in the Yucatan Basin cores. Remarks. The minute spines and well-developed girdle distinguish this species from O. israelianum. Operculodinium giganteum sp. nov. Plate 16, figs. 9, 10 Holotvpe. Plate 16, figs. 9, 10; test 84x72 p, spines 3 p, specimen 55/1, Core A254/327, depth 420 cm. Yucatan Basin (20° 45' N., 83° 00' W.). Diagnosis. A very large, polyhedral species bearing numerous short capitate spines and possessing traces of tabulation. Dimensions. Test only 74-86 p, maximum dimensions, spines 2-4 p. 10 specimens. Occurrence. Yucatan Basin, Core A254/327, relatively rare. Description. The test is polyhedral with broadly truncated extremities. The wall is micro- reticulate or microgranular and bears numerous tiny spines. Some of these are aligned either side of suture-like lines on the test and appear to reflect a gonyaulacid tabulation where there is a small posterior intercalary plate-area and a subrectangular 6" plate-area. Full details were not determined. The girdle is equatorial, narrow, and descending and the furrow is also very narrow and marked by two parallel rows of spines. The archeopyle is dorsal and precingular (3"). The spines have conical bases and capitate tips. Genus tectatodinium gen. nov. Type species. Tectatodinium pellitum sp. nov. EXPLANATION OF PLATE 16 Figs. 1, 2, 5. Operculodinium centrocarpum Defl. and Cooks., comb, nov., A254/330, depth 180 cm.; test only 54 p. Figs. 3, 4. Operculodinium israelianum Rossignol comb, nov., A254/330, depth 180 cm.; test 53 /x. Figs. 6-8. Operculodinium psilatum sp. nov. Holotype, A240/18, depth 175 cm.; test 58 /x; dorsal, lateral, and ventral views. Figs. 9, 10. Operculodinium giganteum sp. nov., Holotype, A254/327, depth 420 cm.; test 84 p; lateral and ventral. Figs. 11, 12. Tectatodinium pellitum gen. et sp. nov. 11, Middle Miocene, near Guadalupe Island, test 50 p. 12, Holotype, outer continental shelf near Beirut, Lebanon; test 52 p. Figs. 13, 14. Chytroeisphaeridia cariacoensis sp. nov., A240/18, depth 380 cm. 13, Paratype, test 40 p. 14, Holotype, test 52 p. Figs. 15, 16. Tuberculodinium vancampoae Rossignol comb. nov. 15, A254/327, depth 459 cm., over-all 101 p. 16. A254/330, depth 600 cm., over-all 95 p. Palaeontology, Vol. 10 PLATE 16 WALL, Quaternary microplankton D. WALL: FOSSIL MICROPLANKTON FROM THE CARIBBEAN SEA 113 Diagnosis. Spherical to ovoid dinoflagellate cysts without apical, antapical, or any other form of projections. Test wall double (resembling tectate pollen), the outer layer being thicker and less compact or homogeneous than the inner. Test penetrated by a large dorsal precingular archeopyle representing the loss of one plate. A girdle or ventral sulcus rarely present. Remarks. This genus is intended for smooth-walled microplankton resembing leiospheres but differing by possessing simple, dorsal precingular archeopyles which denote dino- flagellate affinities. It differs from Operculodinium gen. nov. in the absence of spinose ornamentation and from Pyxidiel/a Cookson and Eisenack 1958 by being less elongate and possessing a precingular archeopyle. Tectatodinium pellitum sp. nov. Plate 16, figs, 11, 12 Holotype. Plate 16, fig. 12; test 52 x 50 p, wall 5 p thick, specimen 23A/4, 33° 34-5' N., 35° 12' E. Description. The test is ovoid and thick-walled. The latter is double-layered, the inner being thin and homogeneous, the outer thicker and spongy; apparently it is formed by numerous, finely interwoven fibrils so that in optical section the focus is indistinct. In surface view the test appears microgranular. There is a large, dorsal, trapezoidal archeo- pyle but no girdle or ventral sulcus. Dimensions. Test 40-55 p, wall thickness 3-7 p. Numerous examples. Occurrence. Relatively uncommon, Yucatan Basin and Cariaco Trench; known range of Miocene to Holocene. Remarks. Rossignol (1964, p. 92) invalidly classified Pleistocene forms which apparently belong to this species as Leiosphaeridia scrobiculata Deflandre and Cookson 1955. The latter species had been transferred previously to Pyxidielia by Cookson and Eisenack (1958, p. 52) while the genus Pyxidielia had been placed with the Dinophyceae by Downie, Evitt, and Sarjeant (1963, p. 13). Live specimens from the Woods Hole region have been induced to excyst and although the parental dinoflagellate has not been identi- fied, the dinophycean affinities of this cyst seem beyond doubt. Family peridiniaceae Lindemann Genus chytroeisphaerjdia Sarjeant 1962 Chytroeisphaeridia cariacoensis sp. nov. Plate 16, figs. 13, 14 Holotype. Plate 16, fig. 14; test 52 p, archeopyle 20 x 28 p, specimen 4 1/3, Core A420/18, depth 380 cm., 10° 30-8' N„ 64° 40' W. Diagnosis. A spherical dinoflagellate cyst with a large elongate hexagonal dorsal inter- calary archeopyle. Dimensions. Test 36-55 p diameter. Numerous examples. Occurrence. Abundant in the Cariaco Trench, relatively rare in the Yucatan Basin. O 4468 I 114 PALAEONTOLOGY, VOLUME 10 Description. The test is spherical, often with sharp secondary folds bordering depressions, and penetrated by a hexagonal dorsal, intercalary archeopyle. This is elongated equatori- ally, its width being almost equal to twice its height, while its size (around 16 x 28 p) and shape are constant. Other splits occur in the test but do not reflect a tabulation. The wall is thin and may enclose an inner capsule with either a minutely thin, hyaline wall or a waxy yellow refractive wall. There are often small, granular inclusions within the cell lumen. Unmacerated cysts are characteristically brown but they become paler after oxidation. Comparison. Chytroeisphaeridia simplicia Wall 1965 differs by having an asymmetrical, hexagonal archeopyle with a length: breadth ratio of 1 : 1. The natural affinities of both species lie with Peridinium, and the archeopyle represents the loss of a dorsal intercalary plate. Family incertae sedis Genus tuberculodinium gen. nov. Type species. Tuberculodinium vancampoae Rossignol 1962 comb. nov. Diagnosis. Test discoidal, with two cell wall layers, the outer supported above the inner by numerous short, stout, tuberculate projections. Dorsal surface with a large compound archeopyle which probably corresponds to a combination of precingular and inter- calary plates. Tuberculodinium vancampoae Rossignol 1962 comb. nov. Plate 16, figs. 15, 16 1962 Pterospennopsis van campoae Rossignol, p. 134, pi. 2, fig. 1. 1964 Pterospennopsis van campoae Ross.; Rossignol, p. 90, pi. 2, figs. 17, 18; pi. 3, fig. 15. Holotype. Rossignol 1964, p. 90, pi. 2, fig. 17; Pleistocene, Ashdod, Israel. Description. The test is discoidal with two cell wall layers, the outer separated from the inner by numerous short, stout, hollow, tuberculate processes. These are circular in surface view, but in lateral views their shapes vary from spherical to figure-of-eight- shaped while the distal extremity of a process may flare and merge with the outer wall layer. The archeopyle is large and polyhedral; it has one long straight side and approxi- mately eight shorter sides roughly arranged about an arc. It probably represents both dorsal precingular and intercalary plates, in which case the whole test is flattened dorso- ventrally. There are sometimes weak traces of a girdle, longitudinal furrow, and a slight posteroventral sulcal depression on the surface opposite to the archeopylar opening, which support this interpretation. Over-all variations observed in the structure of this species include loss or partial detachment of the outer layer and the presence of an inner capsule with a refractive, yellowish wall. Occurrence. Relatively uncommon but persistent, Yucatan Basin and Cariaco Trench. Dimensions. Over-all size from 62 to 113 /u., maximum dimensions. Discussion. This species does not have the structure of Pterospennopsis and, in con- sideration of the presence of an archeopyle, must be regarded as a dinoflagellate cyst : D. WALL: FOSSIL MICROPLANKTON FROM THE CARIBBEAN SEA 115 therefore it is removed from Pterospermopsis to a new genus. As a dinoflagellate cyst it possesses an unusual appearance and its natural affinities remain quite obscure. Its known stratigraphic range is from Miocene to Holocene. STRATIGRAPHIC DISTRIBUTION OF MICROFOSSILS Core A254/330. (Text-fig. 7.) Over thirty species were found in this core; sixteen occurred at every horizon examined and the remainder were distributed sporadically throughout. H. furcata H bulloidea 'sT'H. zoharyi 0 israelianum H. mira bil i s P->0 centrocarpum L. aculeatum L. machaerophorum text-fig. 7. Relative frequency distribution of common microplankton species in core A254/330. Microplankton was most abundant at 240 cm. and had a minimum at 27 cm. judging by the numbers counted in approximately equal samples. In the thick grey lutite sequence below 34-5 cm. the composition of the assemblages was relatively constant; Hystricho- sphaera species (in particular H. furcata and H. bulloidea) accounted for 59 to 64%, Lingulodinium gen. nov. for 9 to 14%, species of Leptodinium for less than 3%, and species of Hemicystodinium and Opercuiodinium together for 22 to 28% of the assemblages. Above 34-5 cm., the composition of assemblages varied as lithology became variable. At 27 cm. Leptodinium aculeatum sp. nov. formed 44%; here there was a decline in other genera rather than any overwhelming increase in Leptodinium. From 1 8 cm. to the surface there was a gradual restoration to abundance of Hystrichosphaera, Hemi- cystodinium gen. nov., Lingulodinium, and Opercuiodinium gen. nov. Foraminifera indicate that the whole sequence in this core is Pleistocene. Globo- quadrina hexagona Natland and G. conglomerata Schwager are sporadic throughout, while the former associates with a relative abundance of Globorotalia menardii menardii D. WALL: FOSSIL MICROPLANKTON FROM THE CARIBBEAN SEA 117 and small numbers of G. menardii flexuosci in the upper 34-5 cm. According to data by Ericson, Ewing, Wollin, and Heezen (1961, pp. 260, 268) and Ericson, Ewing, and Wollin (1964), these foraminifera indicate that the entire core is older than the main Wisconsin (Wurm) Glaciation (LG1 2-3). Possibly the upper 20 cm. represent the Wisconsin (Wurm) Jnterstadial (LG1 1/2), from c. 20 cm. to 34-5 cm. represents the early Wisconsin Glaciation (LG1 1) and the thick greylutite below is a Sangamon (Riss- Wurm) Interglacial deposit. This assumes that the diagnostic foraminifera are in situ. There is evidence of some reworking at most levels; redeposited Pliocene foraminifera ( Globigerinoides fistidosa Schubert and G/obigerina digit at a) occur at depths of 27, 10, and 4 cm., although as extremely rare forms, and a few scattered Pliocene discoasters including D. challenged, D. pentaradiatus, and D. brouweri occur at all levels. All these forms cited as reworked Pliocene species are extinct in the Pleistocene according to Ericson, Ewing, and Wollin (1963). Core A254/327. (Text-fig. 8.) This core contains the same species as core A254/330. They also are continuously distributed throughout the column but there are fewer species and specimens in the coarse, thick globigerina-pteropod ooze that comprises most of the core than in the basal lutite sequence. Microplankton decreases from 208 specimens/gm. to 91/gm. at progressively younger horizons within the basal lutites. The globigerina- pteropod ooze above has a maximum of 16/gm. although a lutite band within it at 9 to 1 6 cm. has 9 1 / gm. There is a pollen and spore maximum at 434 cm. with 232 grains/gm. due to an abundance of bisaccate pollen and fern spores. The proportional composition of microplankton in the samples from the basal lutites is more or less constant. Hystri- chosphaera species comprise 54 to 68%, Lingulodinium comprises 6 to 11%, and Hemi- cystodinium and Operculodiniwn together comprise a minimum of 12 to 20% of the assemblages. Leptodinium is abundant only at one level (411 cm.) where it forms 18% of the assemblage. The relative paucity of microplankton in the globigerina-pteropod ooze makes percentage determinations unreliable. Foraminiferal analyses indicate that the upper 16 cm. including the thin brown lutite band are post-glacial sediments with an abundance of Globigerinoides rubra, some specimens of Globorotalia menardii and G. menardii tumida. Below this to its base at 397 cm. the underlying globigerina-pteropod ooze contains colder water foraminifera (G. truncatulinoides, G. crassiformis, G. dutertrei) and comparatively few warmer water species and can be considered as Wisconsin (Wurm) in age. The presence of abundant displaced terrestrial and shallow water neritic organisms in this layer can be correlated with glacial lowering of sea level over the Gulf of Batabano platform (see Bandy 1964, p. 1672) during this time. The basal lutites do not contain sufficient foraminifera for dating but on the basis of their high microplankton content they can be regarded provisionally as warmer water deposits representing the Wisconsin Interstadial (LG l 1 /2). Core A240jl8. Fifteen species were observed in five spot samples from this core. Micro- plankton was abundant but always accompanied by large quantities of kerogenic material. Between 413 and 630 specimens per gramme were recorded in the upper three samples (25, 80, 175 cm.), excluding some very small forms. The common species were Chytroei- spliaeridia cariacoensis sp. nov., Hystrichosphaera mirabilis, H. bul/oidea, Operculodiniwn israelianum, and O. psilatum sp. nov. In contrast with Yucatan Basin cores, Leptodinium was absent. All the samples are post-glacial in age. 118 PALAEONTOLOGY, VOLUME 10 CONCLUSIONS Piston cores from the ocean floors can provide valuable information concerning Quaternary microplankton. This preliminary study describes the microplankton from two piston cores taken in the Yucatan Basin abyssal plain and one from the Cariaco Trench in the Caribbean Sea. It differs from earlier Quaternary studies (listed in Downie and Sarjeant 1964, pp. 73, 74), which were confined mostly to deltaic or lagoonal en- vironments, by examining a totally marine succession, but it supplements them in demonstrating how widespread and abundant microplankton is in the Quaternary. text-fig. 8. Microplankton distribution in core A254/327. The species content of Quaternary assemblages from widely separated geographical provinces may be very similar as illustrated by comparison of Caribbean and Mediter- ranean analyses. The minimum of 25 species recorded from the Caribbean includes 11 of the 14 species described by Rossignol (1964) from the Mediterranean. Moreover, Leptodinium aculeatum sp. nov., L. patulum sp. nov., L. sphaericum sp. nov., Hystri- chosphaera bulloidea, and species of Chytroeisphaeridia were found recently in samples dredged from the outer continental shelf near Lebanon (R/V Chain Cruise 43, Station 78 at 33° 24-5' N., 35° 12' E.). This new record of these species occurring in the Mediterranean makes agreement between species lists representing the two provinces complete excepting only a few rare varieties. The cumulative results of all the currently available analyses indicate that the follow- ing microplankton are characteristic of the Quaternary. 1. Tabulated spiny cysts belonging to Hystrichosphaera and Nematosphaeropsis. 2. Tabulated cysts with level sutural septa and without spines or polar projections, allocated to Leptodinium. D. WALL: FOSSIL MICROPLANKTON FROM THE CARIBBEAN SEA 119 3. Non-tabulated cysts with precingular archeopyles; these may have a simple archeopyle (3") and possess radial spines ( Operculodinium gen. nov.) or lack spines ( Tectatodinium gen. nov.) or alternatively they may have a compound archeopyle representing the loss of several precingular plates and have radial spines ( Lingulodiniwn gen. nov.). 4. Non-tabulated, smooth-walled dark brown cysts of Peridinium varying in shape from spherical to peridinioid and possessing dorsal intercalary (sub-apical or apical) archeopyles which are basically hexagonal in shape: the spherical fossil forms have been allocated to Chytroeisphaeridia while the peridinioid forms are without names at present, but are most closely comparable with Deflandrea. 5. Unclassified small, unornamented cysts around 30 ^ in size with apical archeopyles; these are extremely common in some Pleistocene samples but have not been formally described at present. 6. Strongly tuberculate forms with compound archeopyles, called Tubercidodinium gen. nov. 7. Hystrichokolpoma. 8. A few species of the acritarch genus Cymatiosphaera. 9. The problematical form Concentricystes, which is quite common in deep-sea sedi- ments as well as in neritic or epicontinental deposits. Members of the first five groups commonly dominate Pleistocene assemblages; representatives of the other groups are less common. Hystrichokolpoma is the only genus with restricted stratigraphic occurrence; it has not been found in deposits younger than early Sicilien. Stratigraphic comparison with late Tertiary microplankton recorded from the Mio- cene and Oligocene of Germany by Eisenack (1954), Maier (1959), Gerlach(1961), and Brosius (1963) and from the Miocene of Australia by Deflandre and Cookson (1955), reveals that many Tertiary species do not survive into the Pleistocene. These include Gonyaulacysta tenuitabulata Gerlach, Hystrichosphaera cornuta Gerlach, Cordosphaeri- dium inodes (Klumpp) Eisenack, C. diktyoplokus (Klumpp) Eisenack, C. divergens Eisenack, C. floripes (Deflandre and Cookson) Eisenack, C. microtriaina (Klumpp) Eisenack, Hystrichosphaeridium alcicornu Eisenack, H. asperum Maier, H. grallaeforme Brosius, H. leptodermwn Maier, H. salpingophorum Deflandre, H. simplex (White) Deflandre, H. stellatum Maier, H. tubiferum (Ehrenberg) Wetzel, H. xipheum (Maier) Sarjeant, Tenua liystrix Eisenack, Rottnestia borussica (Eisenack) Cookson and Eisenack, Thalassiphora pelagica (Eisenack) Eisenack and Gocht, Pentadinium laticinctum Ger- lach, and Palmnickia lobifera Eisenack, in addition to older Tertiary genera with numerous species such as Deflandrea (s'.s'.) and Wetzeliella. However, most species found in the Pleistocene also occur in Miocene or older strata: at present only the following Pleisto- cene species have not been found in older strata: Hystrichosphaera bentori Rossignol, Leptodinium aculeatum sp. nov., L. sphaericum sp. nov., Hemicystodinium zoharyi Rossig- nol, Operculodinium psilatum gen. et. sp. nov., O. giganteum gen. et sp. nov. All the other Quaternary species described here occur in Miocene strata in the Caribbean region. Unfortunately, very little is known about Pliocene microplankton that would permit any worthwhile comparisons with either the Miocene or Pleistocene. 120 PALAEONTOLOGY, VOLUME 10 DISCUSSION Morphological and biological studies (Evitt and Davidson 1964; Wall 1965) demon- strate that Quaternary microplankton assemblages almost entirely comprise the resting spores (cysts) of thecate dinoflagellates. For example, Hystrichosphaera bentori , H. furcata, H. mirabilis, H. bulloidea, Nematosphaeropsis balcombiana, Lingulodinium machaerophorum nov. comb., Opercidodinium centrocarpum nov. comb., Tectatodinium pellitum n. gen. et sp., and a number of Chytroeisphaeridia species all have been isolated from Atlantic marine plankton in the Woods Hole region. The study of living material is a new concept in hystrichosphere research which is relevant especially to Quaternary ecology, but as yet undeveloped. Nevertheless, the elemental origin of the thanato- coenose from a phytoplanktonic community is established in principle and the biological function of microplankton becomes a little clearer. Species of Gonyciulax, Peridinium , and Protoceratium emerge as the prime cyst-producers and factors influencing their spore production and marine distribution account for the presence or absence of a fossil cyst-species in the Quaternary sediments of a region in the first instance. Beyond these, factors concerning productivity, sedimentation, and fossilization determine the abun- dance of microplankton, as they do for other pelagic microfossils. A few palaeoecological observations based upon fossil sequences are possible. Neritic and epicontinental assemblages in the Quaternary appear liable to considerable and rapid fluctuations in composition involving a small number of common species, especially where there are non-marine intercalations. Individual assemblages are often poor in species. Conversely, known deep-sea assemblages are comparatively stable in composi- tion but richer in species. Isolated species are not restricted to either neritic or open oceanic environments but many appear to be incapable of survival in brackish or fresh water. Thus in the eastern Mediterranean epicontinental province, Rossignol (1962) envisaged two main associations alternating throughout the lower Pleistocene; these also were recognizable in samples dredged from the outer continental shelf off Lebanon. One association was dominated by Hystrichosphaera furcata, H. bentori, and Lingulo- dinium machaerophorum (synonym: Hystrichosphaeridium ashdodense Ross.) and the other by Hemicystodinium zoharyi (synonym: Hystrichosphaeridium zoharyi Ross.). Also in the Caribbean Cariaco Trench, the few assemblages examined were dominated by different species, namely, Hystrichosphaera mirabilis, Chytroeisphaeridia cariacoensis sp. nov., and Opercidodinium israelianum comb. nov. In contrast, Yucatan Basin abyssal lutite assemblages frequently were dominated by Hystrichosphaera bulloidea with H. furcata a common associate and the proportional representation of these and other species remained constant within narrow limits throughout the observed sequences. The only exception was an increase of Leptodinium aculeatum sp. nov. in thin bands within both cores. Of the parameters influencing the distribution of microplankton, salinity, temperature, and light variations are probably most significant, but the extent of their influence is not well known. Rossignol (1962) suggested that subnormal salinities caused by increased freshwater run-off favoured the development of a Hemicystodium zoharyi association in the Mediterranean Pleistocene and that the alternating Hystrichosphaera furcata, H. bentori, Lingulodinium machaerophorum association accumulated under conditions of normal salinity for the area and time. Temperature-induced fluctuations have not D. WALL: FOSSIL MICROPLANKTON FROM THE CARIBBEAN SEA 121 been identified positively, but judging by Yucatan Basin cores there are two methods of approach which merit further investigation. First, the maximal absolute abundances of microplankton expressed in terms of specimens per gramme of lutite may indicate the warmer climatic intervals, and secondly, an increase of Leptodinium aculeatum sp. nov. may be indicative of climatic change. Useful knowledge of the present-day distribution of dinoflagellate cysts for comparison with layers in cores is almost non-existent and should be acquired. Again, the possibly disturbing influence of turbidity currents on the composition of microplankton assemblages in the deep-sea also requires further investigation. The presence of microplankton in the deep-sea raises several problems. Judging by the amount of known reworking as indicated by displaced foraminifera and discoasters, less than 5% of the microplankton in the Yucatan Basin lutites are redeposited (this is not true for the coarse globigerinapteropod ooze in core A254/327 which shows excessive quantities of terrigenous and neritic material probably displaced from the Gulf of Batabano platform). Also, diagnostic Miocene or older Tertiary species are absent from these lutites and it appears that most of the cysts accumulated by settling from the euphotic zone. Yet it is difficult to envisage survival of an excysted protoplast at such depths (over 4,000 m.), especially since excystment may be regulated in part by seasonal temperature fluctuations. Settling of cysts to these depths apparently constitutes a loss to the organism, but it is estimated provisionally from fossil analyses plus sedimentation data available for the Caribbean area (Van Andel, Postma and Kruit 1954; Muller 1959; Ericson, et al. 1961) that at least ten times and up to a thousand times more cysts accumu- late upon shelf structures than in the deep-sea plains, so that the loss is small. Special flotation aids, for example longer spines, may be a feature of oceanic cysts; short- spined varieties of Hystrichosphaera bentori appear most frequently close to shore, in the harbour at Woods Hole for instance. These problems require further investigation. This preliminary study can only outline a few taxonomic and distributional aspects concerning microplankton in the Quaternary. The fields of research suddenly opened by the discovery of living and submarine fossil specimens remain essentially unexplored. Acknowledgements. This research was supported by Grant GB-2881 of the National Science Founda- tion of America and Cont. NONR-2196 from the United States Office of Naval Research. The Carib- bean cores were taken and made available by J. Zeigler and W. A. Athearn (who acknowledge Cont. NONR-2196) and the Mediterranean sample provided by R. L. Chase who acknowledges Cont. NONR-4029 and NSF GP-2370. Special thanks are due to Dr. Tsunemasa Saito of Larnont Geo- logical Observatory who supplied invaluable data of foraminiferal analyses. REFERENCES athearn, w. d. 1965. Sediment Cores from the Cariaco Trench, Venezuela. Rep. Woods Hole oceonogr. Instn. Ref. No. 65-37, 1-20, 6 figs. 1 pi. (Unpublished manuscript.) bandy, o. l. 1964. Foraminiferal Biofacies in Sediments of Gulf of Batabano, Cuba, and their Geo- logic Significance. Bull. Am. Ass. Petrol. Geol. 48, 1666-79. brosius, m. 1963. Plankton aus dem nordhessischen Kasseler Meeressand (Oberoligozan). Z. dt. geol. Ges. 114, 32-56. cookson, i. c. and eisenack, a. 1958. Microplankton from Australian and New Guinea Upper Meso- zoic sediments. Proc. R. Soc. Viet. 70, 19-79. deflandre, g. 1937. M icrofossiles des silex cretaces II. Flagelles incertae sedis. Hystrichosphaeridees. Sarcodines. Organismes divers. Annls paleont. 26, 51-103. 122 PALAEONTOLOGY, VOLUME 10 deflandre, G. 1964. Remarques sur la classification des Dinoflagelles fossiles, a propos d’Evittodinium, nouveau genre cretace de la famille des Deflandreaceae. Acad. Sci. Paris, C.R. 258, 5027-30. • and cookson, i. c. 1955. Fossil microplankton from Australian late Mesozoic and Tertiary sediments. Amt. J. Mar. Freshw. Res. 6, 2, 242-313. downie, c., evitt, w. r., and sarjeant, w. A. s. 1963. Dinoflagellates, hystrichospheres and the classi- fication of the acritarchs. Stanford Univ. Pubs., Geol. Sciences, 7 (3), 1-16. ■ — — and sarjeant, w. a. s. 1963. On the interpretation and status of some Hystrichosphere genera. Palaeontology, 6, 83-96. -1964. Bibliography and index of fossil dinoflagellates and acritarchs. Mem. geol. Soc. Atro 94, 1-180. New York. eisenack, a. 1954. Mikrofossilien aus Phosphoriten des samlandischen Unter-Oligozans und fiber die Einheitlichkeit der Hystrichosphaerideen. Palaeontographica, ser. A, 105, 49-95. ■ 1958. Mikroplankton aus dem norddeutschen Apt nebst einigen Bemerkungen fiber fossile Dino- flagellaten. Neues Jb. Geol. Paldont., Abb. 106, 383-422. and cookson, i. c. 1960. Microplankton from Australian Lower Cretaceous sediments. Proc. R. Soc. Viet. 72, 1-11. and gocht, h. 1960. Neue Namen ffir einige Hystrichospharen der Bernsteinformation Ost- preuBens, Neues Jb. Geol. Paldont., Mh. 11, 511-18. erdtman, g. 1954. On pollen grains and dinoflagellate cysts in the Firth of Gullmarn, S.W. Sweden. Botan. Not. Jg., Lund (1954), 103-11. ericson,d. brewing, M.,and wollin, g., 1963. Pliocene-Pleistocene Boundary in Deep-Sea Sediments. Science, 139, 3556, 727-37. 1964. The Pleistocene Epoch in Deep-Sea Sediments. Ibid. 146, 3645, 723-32. — - — and heezen, b. d. 1961. Atlantic Deep-Sea Sediment Cores. Bull. geol. Soc. Amer. 72, 193-286. evitt, w. r. 1961. Observations on the morphology of fossil dinoflagellates. Micropaleontologv, 7, 385— 420. 1963. A discussion and proposals concerning fossil Dinoflagellates, Hystrichospheres and Acritarchs. Proc. natn. Acad. Sci. U.S.A. 49, 158-64, and 298-302. and davidson, s. e. 1964. Dinoflagellate Studies I. Dinoflagellate Cysts and Thecae. Stanford Univ. Pub!., Geol. Sciences, 10, 3-12. gerlach, E. 1961. Mikrofossilien aus dem Oligozan und Miozan Nordwestdeutschlands, unter besonderer Berficksichtigungder Hystrichosphaerideen undDinoflagellaten. Neues Jb. Geol. Paldont., Abb. 112, 143-228. heezen, b. c., menzies, r. j., broecker, w. s., and ewing, m. 1958. Date of Stagnation of the Cariaco Trench, Southeast Caribbean. Bull. geol. Soc. Am. 69, 1579 (abs.). klement, K. w. 1960. Dinoflagellaten und Hystrichosphaerideen aus dem Unteren und Mittleren Malm Sfidwestdeutschlands. Palaeontographica, ser. A 114, 1-104. maier, d. 1959. Planktonuntersuchungen in tertiaren und quartaren marinen Sedimenten. Neues Jb. Geol. Paldont., Abb. 107, 278-340. muller, J. 1959. Palynology of Recent Orinoco delta and shelf sediments. Micropaleontologv, 5, 1-32. Richards, f. a. and vacarro, r. f. 1956. The Cariaco Trench, An Anaerobic Basin in the Caribbean Sea. Deep Sea Res. 3, 214—28. rossignol, m. 1961. Analyse pollinique de sediments marins quaternaires en Israel. I. Sediments recents. Pollen el Spores, 5, 301-24. 1962. Analyse pollinique de sediments marins guaternaires en Israel. II. Sediments pleistocenes. Ibid. 4, 121-48. • 1963. Apergus sur le developpement des Hystrichospheres. Bull. Mus. Hist. nat. Paris, ser.2, 55, 207-12. 1964. Hystrichospheres du Quaternaireen Mediterranee orientale, dans les sediments pleistocenes et les boues marines actuelles. Rev. Micropaleont. 7, 83-89. van andel, t., postma, H., and kruit, c. 1954. Recent sediments of the Gulf of Paria (Reports of the Orinoco Shelf Expedition; Vol. I). Verb. K. Nederl. Akad. Wetenscb., ser. 1, 20, 1-245. wall, d. 1965. Modern hystrichospheres and dinoflagellate cysts from the Woods Hole region. Grana palynologica, 6, 297-314. D. WALL: FOSSIL MICROPLANKTON FROM THE CARIBBEAN SEA 123 west, r. g. 1961. Vegetational history of the Early Pleistocene of the Royal Society borehole at Lud- ham, Norfolk. Proc. R. Soc. B, 155, 437-53. wust, g. 1963. On the stratification and the circulation in the cold-water sphere of the Antillean- Caribbean Basins. Deep-Sea Res. 10, 165-87. DAVID WALL Woods Hole Oceanographic Institution, Manuscript received 30 November 1965 Massachusetts, U.S.A. CONODONTS OF THE GENUS APATOGNATHUS BRANSON AND MEHL FROM THE YOREDALE SERIES OF THE NORTH OF ENGLAND by W. J. VARKER Abstract. The paper describes six species of conodonts assigned to the genus Apatognathus Branson and Meh 1934, from the Yoredale Series of the Askriggand Alston Blocks in northern England. A? chaulioda. A? cuspidata , A? librata. A? petila, and A? scalena are new species, whilst A? gemina (Hinde) is redescribed. The previously recorded occurrences of the genus are listed along with a consideration of possible homeomorphy. The orienta- tion of the genus is reorganized and the distribution of the Yoredale species through the series described. The possibility of facies control of the genus during Carboniferous times is also discussed. The Yoredale Series consists of repeated alternations of shallow-water sediments, which, in the type-area of Wensleydale, NW. Yorkshire, extend upwards from the Upper Visean (Di-Da junction) into the Namurian (Ei-E2) and thus span the Lower/Upper Carboniferous boundary. According to Dunham (1948) each unit or cyclothem can be stated to consist in general terms of: (1) marine limestone; (2) marine shale; (3) unfossili- ferous (?non-marine) ferruginous shale; (4) sandy shale, shaley sandstone or ‘grey-beds’ (interbedded shales, siltstones, and sandstones); (5) sandstone; (6) ganister or underclay; (7) coal; variations of the succession for individual cyclothems may be considerable. This type of sedimentary succession occurs over practically the whole of the stable Askrigg and Alston Block areas in the north of England and also extends northwards into the Northumberland Trough and Scottish Borderland. Identification of beds, recognition of their age and subsequent correlation from one area to another within the distribution of the Yoredale Series is important, since the series occupies a critical stratigraphic horizon spanning the Visean-Namurian junction. So far most palaeontologic evidence has concerned only the macrofossils and it is unfortunate that on this evidence accurate identification of age and stratigraphic cor- relation have proved difficult. Thus the coral/brachiopod zones are somewhat insensi- tive for such a relatively short period of time and under the prevailing environmental conditions. Goniatites, although extremely sensitive (Rayner 1953; Johnson, Hodge, and Fairbairn 1962) are of rare occurrence and thus of limited application. There has, therefore, existed a pressing need for a study of all aspects of the microfaunal and micro- floral content of the Yoredale Series, in the hope of providing an effective means of identification and correlation. Of the microfauna, conodonts appear to offer considerable possibilities. These fossils, which are of world-wide occurrence, show a large amount of variation in form and rapid evolutionary changes during their long stratigraphic history. In addi- tion they have the added advantage over goniatites that their distribution often occurs over a wider lithologic range. Their remains have been obtained in fairly large numbers from all the major Yoredale limestones digested and from some of the associated shales. The present paper presents the first account of some aspects of these conodont faunas [Palaeontology, Vol. 10, Part 1, 1967, pp. 124-141, pis. 17, 18.] W. J. VARKER: THE GENUS APATOGNATHUS BRANSON AND MEHL 125 and their application in studies of the Yoredale Succession. The study is concerned with the succession within the limits of the Hawes Limestone (basal D,) and the Mirk Fell Beds (E2) (see text-fig. 1). The complete conodont faunas of the Yoredale Series have been examined with a view to producing a zonal scheme for the succession. The present paper, however, is restricted to a single genus, assigned to Apatognathus Branson and Mehl 1934, since it is considered necessary to attempt an elucidation of the various problems concerning this genus before such a zonal scheme may be erected. Apatognathus represents over 10% of the total conodont fauna in many of the samples treated and its appearance in the Yore- dale Series in relatively large numbers and displaying a wide degree of variation is of considerable interest. The genus is relatively uncommon and until recently (Lindstrom 1964, see also p. 1 26) was considered to range from Upper Devonian to Triassic or Creta- ceous strata. The sporadic stratigraphic and geographic distribution of this genus have resulted in a number of problems, some of which are considered in the light of informa- tion resulting from the Yoredale occurrence. Another problem to be considered is the great amount of confusion concerning the orientation of the Apatognathus units. Six species are described, five of which are new. History of Yoredale Studies. Although it is over 130 years since the classic work of Sedgwick (1835) and Phillips (1836), the amount of literature concerning the series in the type-area of Wensleydale, is small. The only accounts published between 1836 and 1958 were those of Hudson in 1924, when he discovered faunal rhythms within the larger scale sedimentary rhythms and 1933, when he revised his earlier work. The account by Moore (1958), ‘The Yoredale Series of Upper Wensleydale and adjacent parts of north- west Yorkshire’, dealt primarily with lateral variations in lithology and the palaeo- geography governing deposition of the series. There are, however, numerous accounts of the Yoredale succession in regions outside the type-area and a detailed historical survey up to 1953 is given by Rayner (1953). Since 1958 interest in these sediments has intensified, particularly with reference to their conditions of deposition. Methods of Study. Samples were collected of Yoredale limestones and some of the asso- ciated shales from various localities of the Askrigg and Alston Blocks (shown in text- fig. 1). There was an intentional degree of stratigraphic overlap or duplication in the collection of material from one collecting area to another. The sampling interval varied, the Gayle and Middle Limestones being sampled at 1-ft. intervals and in no case did the interval exceed 5 ft. Each sample weighed up to 3 kg. of which If kg. were chosen as a standard weight for digestion in 10-15% acetic acid. Shale samples, the most impor- tant of which were the Mirk Fell shales, were broken down by methods which variously included the use of sodium hypochlorite, hydrogen peroxide, and white spirit, the method chosen depending largely upon the characteristics of the shale. Some calcareous shales were treated with acetic acid in the normal manner. All residues were washed and sieved, the required size fraction passing a 20-mesh sieve and being retained by a 100-mesh sieve. These wet fractions were finally dried and the conodonts extracted by hand-picking. 126 PALAEONTOLOGY, VOLUME 10 PREVIOUSLY RECORDED OCCURRENCES OF THE GENUS APATOGNA THUS For many years the genus Apatognathus was considered to be an index fossil of the Upper Devonian (Branson and Mehl 1934; Ellison 1946; Weller et a/. 1948; Mehl 1960). Specimens referred to this genus were, however, found at higher horizons during recent OUERLY BUOY AND WHITFIELD GILL WENSLEYDALE N W. YORKS GUNNER SIDE GILL MIRK FELL GILL BORROW CALF. BECK M/DDLEHOPE BURN SWALEDALE TAN HILL STAINMORE WEAROALE N w YORKS. N W. YORKS. CO. DURHAM 2 3 4 5 Middle Limestone Simonstone Limestone Hordraw Scar Limestone Gayle Limestone Hawes Limestone Mirk Fell Ironstones and Shales Moin Limestone Underset Limestone Three Yard Limestone Crow Limestone Little Limestone Great Limestone Iron Post Limestone Four Fathom Limestone Three Yard Limestone Five Yard Limestone Scar Limestone text-fig. 1. Chart illustrating the Yoredale Succession studied and the location of sampling areas. years (see below) and the genus was thought to occur in Upper Devonian, Middle Tournaisian, Upper Visean-Lower Namurian or Middle Mississippian, Permian, Middle Triassic, and possibly Upper Cretaceous strata. Both the stratigraphic and geographic distribution of these occurrences are important considerations in various sections of this report and a summary is therefore outlined below. Three species of Apatognathus have been recorded from the Upper Devonian of Europe, the U.S.A., and Africa. Themost restricted in range is the type-species, A. varians Branson and Mehl 1934, recorded in America from the Grassy Creek Formation and also from similar horizons by Klapper (1958) and Klapper and Furnish (1962). In Europe the species is recorded in zone toV from Germany by Bischoff and Ziegler (1956) and Freyer (1961). The two remaining species, A. Upper ti Bischoff 1956 and A. inversus Sannemann 1955, differ considerably from the type-species. Lindstrom (1964, p. 153) commented that: W. J. VARKER: THE GENUS APATOGNATHUS BRANSON AND MEHL 127 ‘Several species with the same plan (as Ziegler’s genus Gncimptognathus ) but without the accessory process have been brought to Apatognathus e.g. A. lipperti Bischoff 1956. These species, which do not resemble the type-species of Apatognathus are herein brought to Gnamptognathus. ’ Lindstrom, in addition, considered that some species of Falcodus (Bischoff and Ziegler 1957; Ziegler 1958) seem to belong to Apatognathus. The Upper Devonian thus contains the type-species of Apatognathus plus possibly some represen- tatives at present identified as Falcodus. In spite of the very extensive study given to the Lower Carboniferous of Europe and the Mississippian of America by conodont workers, there is only one record, from Bel- gium, of Apatognathus occurring between the base of the system and the Upper Visean (Europe) or the upper part of the Valmeyeran Series (U.S.A.). This anomalous situation has been noted by several authors. Scott and Collinson (1961) remarked that in spite of the occurrence of the genus in the St. Louis Formation, equivalent to the base of the Goniatites stage of Germany, they have not found it in the Hannibal, Chouteau, or any of the other Lower Mississippian Formations of Western Illinois. They therefore concluded that the Middle Mississippian occurrence might represent a case of homeomorphy similar to that discussed by Rexroad (1958) for the conodont genera Taphrognathus and Streptognathodus. The first record of the genus in the Carboniferous System was that of Bischoff (1957), when he recorded A. various in the Goniatites striatus zone (cu III /?) of Germany. In view of the restricted range of this species in the Upper Devonian and the fact that this record was of a single unfigured specimen, little emphasis could be placed upon this Carboniferous occurrence. However, Conil (1959) has since recorded this species and a form which he compared with this species, both undescribed and unfigured, from the Tn2 Zone of Belgium, which is at about the middle of the Belgian Tournaisian succession and is equivalent to the Z2 zone in England. Hinde (1900) described a conodont fauna from the Scottish Carboniferous Limestone Series of the Midland Valley. This included several new species of conodonts, including Prioniodus geminus and Prioniodus porcatus each of which have since been redescribed by Clarke (1960) and transferred to the genus Apatognathus. Specimens of this genus have also appeared, in large numbers in the St. Louis Formation (Valmeyeran Series) of America (Rexroad and Collinson 1963). This formation is equated with the Goniatites crenistria zone (cu III a) of Europe by Collinson, Scott, and Rexroad (1962). These authors record the lowest Mississippian occurrence of the genus in the Warsaw For- mation (Valmeyean Series), which they equate with the cu II 8 goniatite zone (Visean) of Europe. The genus Apatognathus is no longer considered to occur in strata younger than Carboniferous age, although three species referred to this genus have in the past been described from beds as young as Cretaceous in age. Diebel (1956) described a conodont fauna, which included A. ziegleri sp. nov., from the Upper Chalk, Cretaceous, of the Cameroons but since there have been no reports of any conodonts from the whole of the Jurassic period, a certain amount of uncertainty is cast upon this Cretaceous fauna. Lindstrdm (1964), however, considers this fauna to be too well preserved to have been derived by mechanical re-working of older sediments. Clark and Ethington (1962) equated the middle Triassic species A. longidentatus Tatge 1956 with A. ziegieri and the latter species has since been transferred to the genus 128 PALAEONTOLOGY, VOLUME 10 Gnamptognathus, Ziegler, by Lindstrom (1964). A. tribulosus Clark and Ethington 1962 has been similarly transferred (Lindstrom 1964). Thus, of the eight named species of Apotognathus previously described, only the type- species plus the two Carboniferous species, i.e. A. gemina (Hinde) and A. porcata (Hinde) remained before the present paper. An examination of the genus Apatognathus illustrates the apparently disconnected nature of its various appearances and this resulted in many workers considering most of the forms of Apatognathus to be homeomorphic. Clark and Ethington (1962, p. 107), for instance, expressed an opinion common among recent workers that: ‘. . . of the various species which have been referred to Apatognathus only the type seems to be properly classified. All the others probably should be placed in a different genus.’ The foregoing paragraphs indicate that a majority of the species have recently been transferred to Gnamptognathus but even the remaining Carboniferous representatives of Apatognathus present some problems. As already stated, Scott and Collinson (1961) considered that in view of the absence of this genus in Lower Mississippian formations the Middle Missis- sippian occurrence might represent a case of homeomorphy. Unfortunately, however, the sporadic occurrence of the genus also results in a lack of knowledge of the ancestry of any of these forms. Collinson, Scott, and Rexroad (1962, p.3) presumed the‘homeo- morphs’ to have arisen from Synprioniodina but in view of the deficiency of definite evidence perhaps a more suitable term, with no ancestral implications, would be ‘morphic equivalents’ rather than ‘homeomorphs’. The above authors expressed this doubt in the origin of the various species of Apatognathus by referring to them as Apatognathus ? spp. and the practice is continued by the present author, until such times that the complete ranges and origins of the different species are known. SYSTEMATIC PALAEONTOLOGY The new material which is described in the following section represents over 10% of the whole conodont faunas from the Yoredale limestones. The faunas were well- preserved, easily extracted, and were abundant at certain horizons. All the type speci- mens and other figured specimens occurring in this paper are now deposited in the collection of the Micropalaeontology Laboratory, Department of Geology, University of Sheffield. The reference numbers of the type specimens are included in the descrip- tions. Genus apatognathus Branson and Mehl 1934 Type Species. Apatognathus various Branson and Mehl 1934. Original Generic Description of Branson and Mehl. ‘Units consisting of a sharply-arched base, the limbs of which are denticulate, bar-like, and parallel or slightly divergent. The limbs are joined at the apex on one side of the arch by a thin lamella of variable length. An apical denticle of large size is curved toward one limb of the arch and toward the face of the arch opposite the apical lamella. The limb-teeth are small, discrete and directed toward the face of the arch toward which the apical denticle bends. The symmetry of the arch is broken by the trend of the apical denticle and in some forms by the asymmetrical development of limb denticles.’ Orientation of Units. The variable and yet basically simple form of this genus has W. J. VARKER: THE GENUS APATOGNATHUS BRANSON AND MEHL 129 resulted in much confusion in orientation. Difficulties have arisen over the following factors: 1 . The highly arched character of the unit. 2. The extreme asymmetry of some forms of the genus and the virtual symmetry of others. 3. The variable amount of thickening and twisting which may affect one or both bars. 4. The bars are invariably in different planes. 5. The very variable denticulation. The result is that no two authors have adopted the same method of orientation in their descriptions. The original description and orientation by Branson and Mehl was based upon the assumption that the unit functioned as a sheath about the anterior end of the mandible of the conodontifer, with the limbs or bars roughly horizontal. They therefore suggested the following descriptive terms: the face of the arch without the connecting lamella was designated upper or oral, the side with the lamella aboral, and the limb towards which the apical denticle bends the outer limb or oral bar. However, the conodont is no longer considered to be a jaw-supporting mechanism and in addition the orientation suggested by Branson and Mehl causes confusion since it does not follow the accepted pattern for the orientation of conodonts in general. The orientations used by all the authors who have previously described the genus, in- cluding those species recently transferred to Gnamptognathus are indicated on the hypo- thetical specimen in text-fig. 2a, b. The orientation and nomenclature used in this paper are indicated in text-fig. 2c, d, are outlined below, and can be seen to follow the con- ventional pattern of orientation for the majority of conodonts. The convex side of the unit is the outer lateral side and the concave side of the inner lateral side. The denticles are borne on the oral surfaces of the bars irrespective of the inclination or twisting of the bars. The aboral surface is that which bears the aboral groove whilst the basal pit is at the apex of the unit beneath the base of the apical cusp. In asymmetric forms the apical cusp curves away from the anterior bar and towards the posterior bar, whether the specimen be sinistral or dextral. Directions along the bars are known as apical, towards the apical cusp and adapical, away from the apical cusp. The posterior bar may be recognized by the use of several factors, including: (1) the apical cusp curves towards the posterior bar in asymmetric forms; (2) if the bars are unequally thickened the posterior bar always has the greatest amount of thickening; (3) the posterior bar is inwardly directed, in varying degrees, relative to the anterior bar. Specimen index numbers are compiled as follows, e.g. 26(5)GG202. 26(5) is the film reference, GG the locality of the sample (Gunnerside Gill, Swaledale) and 202 the sample number. Each description includes a statement of the number of well-preserved speci- mens studied, together with (in brackets), the total for that species including identifiable fragments. Apatognathus? chaulioda sp. nov. Plate 17, figs. 1, 2, 3, 5 Diagnosis. An Apatognathus? on each bar of which is a bar cusp approximately the size of the apical cusp and separated from the latter by a few, small, compressed denticles. Description. An asymmetric unit with two bars diverging at 26-35 degrees. From the inner lateral view the two bars are of equal dimensions, with inner lateral sides C 4466 K ANTERIOR (Son.) Ck. ) POSTERIOR (Fay, R.t C.) LATERAL PROCESS OR APICAL LAMELLA (Foy) OUTER OR ORAL BAR (B.& M.) OUTER LIMB OR ANTERIOR PROCESS (Foy) OUTER LATERAL BAR (B.t Z.) INNER LIMB (GE) POSTERIOR LIMBt/?. SC.) POSTERIOR PROCESS (Lm) ANTERIOR (Foy, R.& C.) INNER UMB (Foy) OUTER LIMB (Ck) ANTERIOR LIMB (R. & C.) ANTERIOR PROCESS ( Lm.) ( Son. ,B. & Z.\) (Ck.-,R. S C.) ORAL SIDE ( B. & M.-, Kr. ) OUTER SIDE (Foy) INNER SIDE (D/.-.Lm) INNER LATERAL SIDE (R. SC.) ABORAL SIDE ( B. 6 M.-. Kr. )' INNER SIDE (/try)' OUTER SIDE ( 01 ■, Lm) OUTER LATERAL SIDE (R.S C.) POSTERIOR ( Son.,Ck .) B & M'. — BRANSON AND MEHL 1934, Foy-- FAY 1952, Son. : — SANNEMANN 1955, ZIEGLER 1956, D!-— DIEBEL 1956, Kr — KLAPPER 1958, O.^-CLARKE I960, COLLINSON 1963, Lm. : — LINDSTROM 1964. B. & Z : — BISCHOFF AND R. S C.\ — REXROAD AND DENTICLES APICALLY INCLINED OUTER LATERAL SIDE INNER LATERAL VIEW A? CUSPIDATA SP NOV ANTERIOR VIEW D_ CUSPIDATA SP NOV. text-fig. 2. Diagram illustrating the nomenclature and orientation applied to the genus Apato- gncithus? by previous authors (2a, b) compared with that used by the present author (2c, d). W. J. VARKER: THE GENUS APATOGNATHUS BRANSON AND MEHL 131 inclined to each other particularly at the apex. Each bar is divided into an apical and a longer adapical part by a prominent bar cusp. Thickening in mature specimens is con- centrated at the apex of the unit and extends equally along each bar as a smooth, wide, and sometimes diminishing ridge. The usually strong apical cusp is of variable length, as wide and thick as a bar at its base, sharply pointed, posteriorly curved and inclined, and may be laterally flanged. The bar cusps are similar in size and shape, may be even wider at their bases than the apical cusp, and are apically inclined. The denticles between the apical and bar cusps are shorter than the height of the bar and although fused, maybe discrete in juvenile forms. There is a maximum of about five denticles in this position on each bar but never more on the posterior bar than on the anterior bar. The remaining denticles are discrete, usually longer than the height of the bar, and similar in shape to the apical set. From the outer lateral view, a prominent, wide ridge curves round the apex of the unit and is gradually reduced along the bars. The aboral margin of the bars is sharp and the apical lamella variable in size. From the anterior view, the base of the bar is straight but the height of the bar increases apically and culminates in the inwardly directed apical cusp. Inward inclination of the denticles is slight. From the aboral view, the aboral groove is prominent, deep, and wide and the basal pit is deep and circular. Comparisons. This species is distinctive in its possession of a large bar cusp on each bar. A? scalena sp. nov. has a bar cusp only on the posterior bar. Discussion. The major variations in this species concern the number of denticles between the apical and bar cusps and also the extent of the thickening of the bars. If thickening extends from the apex beyond the base of the bar cusps, the whole length of the bar is usually thickened. Occurrence. The Yoredale Series of the north of England. Range. Hawes Fimestone to the Four Fathom or Underset Limestone. Absent from the Hardraw Scar and Simonstone Limestones. Type Specimen. 26(5)GG202, Plate 17, Figs. 1, 2. Number of specimens. 23(68). Type Locality. Four Fathom Limestone of Gunnerside Gill, Swaledale. G.R. 937007. Apatognathus? cuspidata sp. nov. Plate 17, figs. 4, 6, 7, 8, 9, 10 Diagnosis. An Apalognathusl with small denticles on the anterior bar and larger denticles on the posterior bar, the latter being less steeply inclined than the anterior bar on the inner lateral side, and an apical cusp which is more than half the bar length. Description. An asymmetric species with bars diverging at about 25 degrees. From the inner lateral view the anterior bar is straight and high with a prominent narrow ridge, which in mature specimens extends the whole length of the bar on the 132 PALAEONTOLOGY, VOLUME 10 inner side of the denticles. The inner lateral surface is steeply and uniformly inclined inwards. The denticles are triangular, sharply pointed, apically inclined, strongly inclined inwards, with a small decrease in size adapically and number from 8 to 10 but always one in excess of the posterior bar. The apical cusp is at least half as long as the bars, sharply pointed, as stout as a bar at its base where it is laterally flanged, and inwardly and posterially directed. The posterior bar is straight and highest two-thirds the distance from the apex. Aprominent ridge extends along the bar on the inner side ofthe denticles. The inclination of the inner lateral side is less than that of the anterior bar and also decreases adapically. Apical and inward inclination of the denticles is also less than on the anterior bar, though they may be larger and more discrete. From the outer lateral view, the base of the apical cusp is smooth, convex, and continuous with a strong ridge which extends along each bar. That of the anterior bar curves upwards to the oral margin and accentuates the steep inclination of the outer lateral side. That of the posterior bar is straight. The aboral margins of the bars are sharp. Apical lamella small. From the anterior view, the prominent ridge on the outer lateral side forms the base of the bar in this view. Base slightly convex and the height of the bar decreases adapically. The denticles are fused for one-third of their length. From the aboral view, the aboral groove is narrow, deep, and bounded by two prominent ridges. The basal pit is circular. Comparisons. This species differs from the other species in its combination of a very large apical cusp, strong, regular denticulation, and the difference in inclination of the anterior and posterior bars. It does, however, bear some similarities to the juvenile forms of the species figured by Rexroad and Collinson (1963) as A? porcata (Hinde). Occurrence. The Yoredale Series of the North of England. Range. Simonstone Limestone to the Main Limestone. Type Specimen. 28(6)BB205, Plate 17, fig. 7. Number of specimens. 20(85). Type Locality. Great Limestone, Borrowdale Beck, Stainmore, Westmorland. G.R. 834160. EXPLANATION OF PLATE 17 All figures x41. Figs. 1-3, 5. Apatognathus? chaulioda sp. nov. 1, Inner lateral view of type-specimen 26(5)GG202. 2, Outer lateral view of type-specimen. 3, Inner lateral view of specimen 23(1)MG285. 5, Outer lateral view of specimen 34(3)GB8A. Figs. 4, 6-8, 10. A? cuspidata sp. nov. 4, Inner lateral view of specimen 25(4)SW182, with broken denticles and cusp but with bars complete. 6, Inner lateral view of specimen 3 1 (3 )BB 1 59. 7, Inner lateral view of type-specimen 28(6)BB205. 8, Inner lateral view of specimen 29(2)BB205. 10, Outer lateral view of large specimen 31(2)BB159. Figs. 9, 12, 13. A? gemina (Hinde). 9, Inner lateral view of specimen 81(1)GB110A. 12, Oral view of specimen 80(5)GB110J, posterior bar only, showing extensive lateral thickening. 13, Aboral view of same specimen showing position of aboral groove. Fig. 11. A? petila sp. nov. Outer lateral view of type-specimen 16(6)MG39, with complete anterior bar. Palaeontology, Vol. 10 PLATE 17 VARKER, Carboniferous Apatognatlms ? from England W. J. VARKER: THE GENUS APATOGNATHUS BRANSON AND MEHL 133 Apatognathus? gemma (Hinde) Plate 17, figs. 9, 12, 13 1900 Prioniodus geminus Hinde, pi. 10, fig. 25. 1928 Prioniodina? gemina (Hinde); Holmes, p. 19, pi. 5, fig. 10. 1960 Apatognathus geminus (Hinde); Clarke, p. 4, pi. 1, figs. 1, 2. Description. An asymmetric unit with bars diverging at about 20 degrees. From the inner lateral view, the unit is strong, highly thickened, and twisted at its apex. The bars are straight, with the thickening evident as a prominent ridge extending along each bar. The ridge of the posterior bar, where the thickening is most strongly developed, is higher and sharper than that of the anterior bar. The posterior bar is strongly inclined inwards adapically. The apical twisting of the unit results in the bars being in different planes and the aboral side of the anterior bar may be visible in this view. The apically inclined denticles of the anterior bar are irregular but at least equal in length to the height of the bar and with little inward inclination. Inward inclination of the cusp is strong. The latter is inclined slightly posteriorly and is often flanged asymmetrically, the posterior flange being the larger. The cusp is as broad and thick as a bar at its base. The posterior bar denticles are smaller and more numerous than those of the anterior bar, apically and inwardly inclined, roughly triangular in outline and may be fused at their bases. The outer lateral side of the anterior bar is continuous with the base of the denticles and has a low ridge running near the base of the bar. The cusp is smooth, broad, flat, and continuous with the bars. The posterior bar has an exaggerated, sharp, narrow ridge extending its whole length. The apical lamella is very small and may not be visible. From the posterior view, lateral thickening of the posterior bar is very strong with the result that its oral surface is wider than the height of the bar, convex and with slightly irregular lateral margins. The apical cusp is thick at its base and curves strongly inwards in a smooth curve. From the aboral view, the aboral groove is wide, deep, and bounded by two promi- nent lips. The basal pit is deep and circular. Comparisons: The above description of specimens from the Yoredale Series shows this species to differ from others in its large amount of lateral thickening, particularly of the posterior bar, and the apical twisting of the unit. It is distinguished from A? cuspidata also in its less regular denticulation, the presence of larger denticles adjacent to the apical cusp and a wider aboral groove. Discussion. The denticulation of this species is variable but the number of denticles on the posterior bar exceeds those of the anterior bar. Those adjacent to the apical cusp may be somewhat larger than the remaining denticles. Occurrence. Type locality: Upper Limestone Glencart, Dairy. Upper Limestone, Linn Spout, Dairy, Skateraw. Middle Limestone, Dunbar. Yoredale Series of the North of England. Range in the Yoredale Series. Hawes Limestone to the Middle Limestone. Number of specimens. 22(68). 134 PALAEONTOLOGY, VOLUME 10 Apatognathus? librata sp. nov. Plate 18, figs. 3, 6, 8, 9, 12, 13 Diagnosis. A robust, wide-angled, almost symmetric Apatognathus? with large, subequal denticles on both limbs. Description. Mature specimens are large, strong, approximately symmetric in lateral view, and with bars diverging at 45-50 degrees. From the inner lateral view, both bars are thick, strong, high at the apex, gradually decreasing in height adapically and with flat oral surfaces on which are borne strongly inwardly inclined denticles. The inner lateral surfaces of the bars are steeply inclined towards each other, particularly at the apex, and are almost flat. Denticles of each bar are subequal, longer than the height of the bar, sharply pointed, in contact for over half their length, and with a slight regular decrease in size adapically. In mature specimens a large denticle may be developed on one or both bars and separated from the apical cusp by a denticle of normal size. The apical cusp is central, little larger than the denticles and of similar shape, strongly inclined inwards, and with no posterior inclination. From the outer lateral view, the outer lateral surface is convex and continuous with the outer surfaces of the denticles, the growth lamellae of which are seen to extend into the bars. The small apical lamella is continuous with a prominent ridge which passes down the outer side of each bar becoming more orally placed adapically. From the anterior view, the aboral margin of the bar is slightly convex. The denticles are inclined very strongly inwards and decrease in length adapically. The apical cusp is inwardly inclined at 45-50 degrees and leaves the apex of the unit at an abrupt angle. From the aboral view, the aboral groove is narrow, shallow, and borne on the sharp aboral margin. In mature specimens the basal pit is small and circular. Comparisons. This species is probably the most distinctive of the six species described since no other has such uniform denticulation combined with so high a degree of sym- metry. Discussion. In young specimens the bars are delicate, blade-like, and equal in thickness EXPLANATION OF PLATE 18 All figures x41. Figs. 1 , 2, 4, 5. Apatognathus? scalena sp. nov. 1 and 2, Outer and inner lateral views of type-specimen 32(4)BB213, showing the greater length of the anterior bar and pronounced posterior bar cusp. 4 and 5, Outer and inner lateral views of specimen 33(3)GG217, with short posterior bar and broken anterior bar. Figs. 3, 6, 8, 9, 12, 13. A? librata sp. nov. 3, Inner lateral view of specimen 3 1 (6)BB 1 59, showing large denticle near apical cusp. 6 and 8, Inner and outer lateral views of immature specimen 30(2)BB212. 9, Inner lateral view of specimen 28(4)BB205. 12, Inner lateral view of an almost complete, small, immature specimen exhibiting a marked degree of symmetry 29(5)BB159. 13, Inner lateral view of the type-specimen 18(2)MG132. Figs. 7, 10, 11. A? petila sp. nov. 7, Inner lateral view of large, thickened specimen 20(5)MG259, showing contortion of the apical denticles and a bulbous thickening of the posterior bar. 10, Inner lateral view of specimen 34(5)GB110. 11, Outer lateral view of an immature specimen 24(4)SW182. Palaeontology, Vol. 10 PLATE 18 * l: 4 u .f C f ■|/: •y >7 YARKER, Carboniferous Apatognathus ? from England W. J. VARKER: THE GENUS APATOGNATHUS BRANSON AND MEHL 135 to the denticles, whilst the basal pit is spindle-shaped and relatively larger. The onset of maturity is marked by an extensive thickening of the inner lateral sides of the bars, particularly at the apex. Thus the oral surfaces of the bars become flattened, the inner lateral sides steepened, and the basal pit constricted. Thickening also affects the apical cusp and denticles. Occurrence. The Yoredale Series of the North of England. Range. Gayle Limestone to the Little Limestone. Type Specimen. 18(2)MG132, Plate 18, fig. 13. Number of specimens. 47(157). Type Locality. Simonstone Limestone, Whitfield Gill, Askrigg, Wensleydale. G.R. 935918. Apatognathus petila sp. nov. Plate 17, fig. 11, Plate 18, figs. 7, 10, 11 Diagnosis. An Apatognathus? with a small apical cusp, a strongly inwardly inclined anterior bar on which the denticles increase in size apically, and a posterior bar with uniform denticulation and no inward inclination. Description. An asymmetric unit with limbs diverging at 38-45 degrees. Lrom the inner lateral view, the anterior bar is blade-like and curved mainly at the adapical end. The inner lateral side is steeply inclined inwards particularly at the apex. Thickening is slight. The denticles near the apex of the unit are large, sharply pointed, sharp edged, apically directed, fused for two-thirds their length, and highly inclined inwards. In addition, those denticles adjacent to the cusp may be posteriorly curved and inclined. Adapically the denticles are shorter and develop an adapical inclination, with the last denticle terminating the bar. The apical cusp is only slightly larger than the adjacent denticles of the anterior bar, is of similar shape, highly inclined inwards, and posteriorly inclined and curved. The posterior bar is of uniform height, slightly thickened, and is in a plane almost at right angles to that of the anterior bar. It has no inward inclination on its inner lateral side or denticles. The latter are of uniform length, shorter than the height of the bar, fused for two-thirds their length, apically directed and narrower and more sharply pointed than those of the anterior bar. Lrom the outer lateral view, the outer lateral surface of the unit is smooth, convex, and continuous with the base of the denticles. A low ridge extends down the anterior bar a uniform short distance above the aboral margin and disappears at two-thirds the length of the bar. On the posterior bar, however, the ridge crosses the outer lateral surface from an aboral to an oral position and then runs along the base of the denticles. The denticles of both bars may be of irregular shape or contorted in the region of the apical cusp. Lrom the anterior view, the aboral margin of the bar is convex. The adapical decrease in the height of the bar and length of the denticles is pronounced. The apical cusp and adjacent denticles are directed very strongly inwards. Lrom the aboral view, the aboral groove is wide and deep and bounded by two sharp ridges. The basal pit is large and spindle-shaped. Comparisons. This species differs from others of the genus in its combined lack of a 136 PALAEONTOLOGY, VOLUME 10 distinct apical cusp and the contrast in inclination of the bars. The latter feature, which is more marked than in A? scalena sp. nov. increases towards the apex, where the denticles and anterior bar may be directed inwards at 90 degrees. The contortion of the denticles in the region of the apical cusp has not been seen in other species. Discussion. Only a small amount of thickening takes place but denticles may become fused. Posterior bar denticles appear to be most prone to fusion, occasionally becoming completely fused in groups of three. This species bears some similarities with some of the specimens figured by Rexroad and Collinson (1963) as A? porcata (Hinde), particularly their large, mature forms, but the ontogeny of A? petila sp. nov. shows less variation in form as well as other differences and in view of the fact that the type specimen of A? porcata (Hinde) is a broken specimen consisting of a single bar, the Yoredale Specimens are described as a new species. Occurrence. The Yoredale Series of the North of England. Range. Gayle Limestone to the Main Limestone. Type Specimen. 16(6)MG39, Plate 17, fig. 11. Number of specimens. 38(130). Type Locality. Hardraw Scar Limestone, Whitfield Gill, Askrigg, Wensleydale, G.R. 939915. Apatognathus? scalena sp. nov. Plate 18, figs. 1, 2, 4, 5 1963 Apatognathus? gemina (Hinde); Rexroad and Collinson, p. 7, pi. 1, figs. 12-17. Diagnosis. An Apatognathus? with subequal denticles on the anterior bar but variable denticles and a single large bar cusp on the posterior bar. Description. A highly asymmetric species with bars diverging at about 20°. Lrom the inner lateral view, the anterior bar is straight, twisted on its own axis, its inner lateral side steeply inclined at the apex, and less steeply adapically. The apical part of the bar is thickened with its flat oral surface slightly wider than the denticles it bears. Adapically the bar is blade-like and of equal thickness to the denticles. The latter decrease in size adapically and are of uniform shape. The inward inclination of the denticles increases apically and the denticles adjacent to the apical cusp are, in addition, posteriorly inclined. In young forms the apical cusp appears as a posteriorly directed extension of the anterior bar but in mature forms it is similar in shape and only slightly larger than the adjacent denticles of the anterior bar. The posterior bar is slightly shorter than the anterior bar and straight, with its inner lateral surface uniformly and less steeply inclined. Occurring at its mid-length is a large, compressed bar cusp, which is wider than the height of the bar. Between the apical and bar cusps are a few denticles which in mature forms are small and regular. Also in mature forms the denticle on each side of the bar cusp is commonly larger than the others and may rival the bar cusp in size. Adapically from the latter the denticles decrease in size. Lrom the outer lateral view, a prominent, sharp ridge extends along each bar from the apex. That of the anterior bar maintains a uniform distance from the aboral margin but that of the posterior bar curves up to the base of the bar cusp. The anterior bar is of W. J. VARKER: THE GENUS APATOGNATHUS BRANSON AND MEHL 137 uniform height whereas the posterior bar increases in height from the apex to the bar cusp and then decreases adapically. Apical lamella small. From the anterior view, the aboral margin of the bar is sharp and strongly convex. The anterior bar denticles, up to 16 in number, are of uniform width and shape and in contact for most of their length. The bar curves into the inwardly inclined apical cusp in a single smooth curve. From the aboral view, the aboral groove is wide, deep, and bounded by strong ridges. Basal pit deep and spindle-shaped. Comparisons. This species differs from other species of Apatognathus ? in its large posterior bar cusp which is similar to that found on both bars of A? ehaulioda sp. nov. The anterior bar, however, bears certain similarities with that of A? petila sp. nov. in its uniform denticulation, twisting, and high angle of inclination. Discussion. The bar cusp of young forms is relatively larger than that of mature forms. Occurrence. St. Louis Formation of the Yalmeyeran Series, Mississippian, U.S.A. The Yoredale Series of the North of England. Range in the Yoredale Series. Simonstone Limestone to the Main Limestone. Type Specimen. 32(4)BB213. Plate 18, figs. 1, 2. Number of specimens. 13(51). Type Locality. Great Limestone. Borrowdale Beck, Stainmore, Westmorland. G.R. 834160. DISTRIBUTION OF THE GENUS APATOGNATHUS? IN THE YOREDALE SERIES The distribution through the Yoredale Series of the six species of Apatognathus? described in the present paper is shown in text-fig. 3. This figure shows the genus to be present in every major limestone except the Crow, which was too siliceous to yield any conodonts. The Hawes Limestone contained moderately small faunas of conodonts, up to thirty- five specimens per kilogram of rock, in which A? ehaulioda sp. nov. and A? gemina (Hinde) were the only species of this genus to be present. The lowest occurrences in the Yoredale Series of A? petila sp. nov. and A? librata sp. nov. were in the Gayle Lime- stone, in which they were combined with the above species and occurred in complete faunas of over 1 00 specimens per kilogram. The Hardraw Scar Limestone, however, yielded only three specimens of Apatognathus?, i.e. single specimens ofA?gemina( Hinde), A? petila sp. nov., and A? librata sp. nov. A? ehaulioda sp. nov. was not found but this is not surprising in view of the small size of the faunas which appears to be characteristic of the Hardraw Scar Limestone in the Whitfield Gill locality. The Simonstone and Middle Limestones yielded large numbers of specimens of this genus. The Middle Limestone was in fact the only limestone to contain all six species but, as will be seen from text-fig. 3, A? ehaulioda sp. nov. has a projected range through the Simonstone Lime- stone since it is found as far up the succession as the Underset Limestone. The Five Yard Limestone yielded relatively small numbers of conodonts but these included five species of Apatognathus?. A? gemina (Hinde), which was absent, did not occur in the Three Yard Limestone above, in spite of the fact that the latter yielded the largest faunas in 138 PALAEONTOLOGY, VOLUME 10 the whole of the study, with concentrations exceeding 500 specimens per kilogram in the Gunnerside Gill locality and 350 per kilogram in Weardale. The Underset or Four Fathom Limestone contained A? librata sp. nov., A? scalena sp. nov., A? cuspidata sp. nov., and A? petila sp. nov., plus the highest occurrence of A? chaulioda sp. nov. The large faunas of the Main Limestone included the highest occurrences of A? petila sp. nov., A? scalena sp. nov., and A? cuspidata sp. nov., plus A? librata sp. nov., which was the only species to continue through into the Little Limestone. The Mirk Fell Beds text-fig. 3. Range chart of Apatognathus? species occurring in the Yoredale Series. yielded large conodont faunas but they included no species of Apatognathus?. The genus must therefore disappear between the Little Limestone and the Mirk Fell Beds after having first suffered a drastic decline in numbers above the Main Limestone. POSSIBLE FACIES CONTROL OF THE GENUS APATOGNATHUS? IN VISEAN-MIDDLE MISSISSIPPI AN TIMES Some characteristics of conodont distribution. Conodonts are of world-wide distribution and one of their great advantages in use for zonation purposes is that they are essentially free of facies control. This is evident in both small-scale facies variations from lithology to lithology and also in large-scale variations from, for instance, a basin type of sedimen- tation to a shelf environment. An illustration of this was given by Rexroad (1958) who described the conodonts from the Glen Dean Formation (Chester Series), and who found that out of 27 species, 21 were common to both limestone and shale. Of the other W. J. VARKER: THE GENUS APATOGNATHUS BRANSON AND MEHL 139 species two, which were found only in the shale, were represented by only four specimens, and four found only in the limestone he considered to reflect the method of sampling rather than environmental factors. Facies control of the Visean-Middle Mississippian representatives of the genus Apato- gnathus? During the Visean or Middle Mississippian times Apatognathus? appears to have favoured certain conditions to the exclusion of others. After a long period of absence the genus suddenly appeared in relative abundance in three separate regions and at approximately similar horizons. These three regions, the Illinois Basin of the U.S. A., the Midland Valley of Scotland, and the Askrigg and Alston Blocks of the North of England, although not identical lithologically, are each represented by shallow-water cyclic sediments in which goniatites are rare and the fauna is mainly benthonic. The contrast, rather than being from lithology to lithology, is therefore between a coral/ brachiopod facies where Apatognathus ? is present and a cephalopod facies, where the genus is absent. This is particularly well shown in Britain, where Apatognathus? is absent from the P and E! zones of the Midlands and Lancashire (Dr. A. C. Higgins — personal communication), but is present at equivalent horizons in the coral /brachiopod facies of the Askrigg and Alston Blocks. The facies control of the genus is further illus- trated by the fact that even within the Yoredale Series there are no representatives of Apatognathus? in the Mirk Fell Beds, which consist of a shale and ironstone sequence containing goniatites of E2 age but they do occur at this horizon in the Upper Limestone Group of the Midland Valley of Scotland (Clarke 1960). CONCLUSIONS A number of facts have therefore accumulated as a result of the present study of the Yoredale Series. Most important of these is that well-preserved conodonts are present in abundance, at least in the limestones, from which they are easily extracted. A common constituent of these faunas is the otherwise relatively uncommon genus Apatognathus? Branson and Mehl 1934 which exhibits what is apparently the greatest amount of variation in form which has so far been found in this genus in any one locality. Six species have been described, five of which are new and they have shown themselves to be of value in the stratigraphic succession of the Yoredale Series. When combined with the remainder of the fauna an accurate zonal scheme, based upon conodonts, is possible. All the forms described have been included in the genus Apatognathus? although it is inevitable that further reorganization will be necessary when the ranges and origins of the group are more fully known. At present the term ‘morphic equivalent’ is thus pro- posed as preferable to ‘homeomorph’ which implies a knowledge of the ancestry of the form under consideration. The present study has indicated the type of situation under which the genus might be found in the future, since it does appear to be at least to some extent controlled by the presence of a shallow-water coral/brachiopod facies in which goniatites are uncommon. Acknowledgements. This paper represents part of the work carried out on an investigation of the cono- donts of the Yoredale Series under the tenure of a Department of Scientific and Industrial Research Studentship at the University of Sheffield. The author is indebted to Professor L. R. Moore for his guidance and encouragement, to Dr. A. C. Higgins for his continuous help, to Mr. G. S. Bryant and Mr. B. Piggot for their help with the plates, and to Dr. J. W. Scatterday for correspondence. 140 PALAEONTOLOGY, VOLUME 10 REFERENCES ash, s. r. 1961. Bibliography and index of conodonts 1949-1958. Micropaleontology 7, 213-44. bischoff, g. 1956. Oberdevonische Conodonten (to Id) aus dem Rheinischen Scheifergebirge. Notizbl. Hess. Landesamt. Bodenforsch. 84, 115-37, pi. 8-10. 1957. Die Conodonten-stratigraphie des rhenoherzynischen Unterkarbons mit Beriicksichtigung der Wocklumeria-Siufe und der Devon-Karbon-Grenze. Abh. Iwss. Landesamt. Bodenforsch. 19, 1-64, pi. 1-6. and ziegler, w. 1957. Die Conodontenchronologie des Mitteldevons und des tiefsten Ober- devons. Ibid. 22, 1-136, pi. 1-21. branson, e. b. and mehl, M. G. 1934. Conodonts from the Grassy Creek shale of Missouri. Univ. Mo. Stud. 8, 171-259, pi. 13-21. ching, y. k. 1960. Conodonts from the Kufeng Suite (formation) of Lungtan, Nanking. Acta palaeont. sin. 8, no. 3, 242-8, pi. 1-2. clark, d. l. and ethington, r. l. 1962. Survey of Permian Conodonts of Western North America. Brigham Young Univ. Geol. Stud. 9, pt. 2, 102-14. clarke, w. J. 1960. Scottish Carboniferous conodonts. Trans. Edinb. geol. Soc. 18, 1-31, pi. 1-5. collinson, c. w., scott, a. j., and rexroad, c. b. 1962. Six charts showing biostratigraphic zones, and correlations based on conodonts from the Devonian and Mississippian rocks of the Upper Mississippi Valley. Illinois Geol. Survey Circ. 328, 1-32. conil, r. 1959. Recherches stratigraphiques sur les terrains Dinantiens dans le bord Nord du Bassin de Namur ( Region s'etandant de la Dendre a rOrneau).^4cu^/. Roy. Belg. Mem. de Classe des sciences. 2nd ser., 40, 14. diebel, k. 1956. Conodonten in der Oberkreide von Kameron. Geologie, Jahrg. 5, 424-50, pi. 1-4. dunham, k. c. 1948. Geology of the Northern Pennine Orefield, Vol. 1 Tyne to Stainmore. Mem. geol. Surv. U.K. ellison, s. p. 1946. Conodonts as Palaeozoic guide fossils. Bull. Am. Ass. Petrol. Geol. 30, 93-1 10. • 1962. Annotated Bibliography and Index of Conodonts. Bureau of Economic Geology, Univ. Texas, Austin. ethington, r. l. and furnish, w. m. 1962. Silurian and Devonian Conodonts from Spanish Sahara. J. Paleont. 36, 1253-90. fay, r. o. 1952. Catalogue of Conodonts. Paleont. Contr. Univ. Kans. Vertebrata, art. 3, 1-206. flugel, h. and ziegler, w. 1957. Die Gliederung des Oberdevons und Unterkarbons am Steinberg westlich Graz mit Conodonten. Mitt, naturw. Ver. Steierm. 87, 25-60, pi. 1-5. freyer, g. 1961. Zur Taxionomie und Biostratigraphie der Conodonten aus dem Oberdevon des Vogtlandes unter besonderer Beriicksichtigung des To V/VI. Freiberger Forschungschr. 95, 1-96. hicks, p. f. 1959. The Yoredale Rocks of ingleborough, Yorkshire, Proc. Yorks, geol. Soc. 32, 31—43. higgins, a. c. 1961. Some Namurian conodonts from North Staffordshire. Geol. Mag. 98, 210-24. hinde, g. j. 1900. Notes and descriptions of new species of Scotch Carboniferous conodonts. Trans . Nat. Hist. Soc. Glasgow , 5, 338-46, pi. 9-10. holmes, G. b. 1928. A bibliography of the conodonts with descriptions of early Mississippian species. Proc. U.S. Natl. Mus. 72, art 5, 1-38, pi. 1-11. Hudson, r. G. s. 1924. On the rhythmic succession of the Yoredale Series in Wensleydale. Proc. Yorks, geol. Soc. 20, 125-35. 1933. The Scenery and Geology of north-west Yorkshire. Proc. Geol. Ass. 44, 228-55. Johnson, g. a. l. 1959. The Carboniferous Stratigraphy of the Roman Wall district in western Northumberland. Proc. Yorks. Geol. Soc. 32, 83-130. 1960 Palaeography of the Northern Pennines and part of north-eastern England during the deposition of Carboniferous cyclothemic deposits. Kept. 21st Int. Geol. Congr. Pt. 12, 118-28. 1962. Lateral variation of marine and deltaic sediments in cyclothemic deposits with particular reference to the Visean and Namurian of northern England. C.r. IV Congr. Avanc. Etud. Stratigr. curb., Heerlen, 1958, 2, 323-30. hodge, b. l., and fairbairn, r. a. 1962. The Base of the Namurian and of the Millstone Grit in north-eastern England. Proc. Yorks, geol. Soc. 33, 341-59. W. J. VARKER: THE GENUS APATOGNATHUS BRANSON AND MEHL 141 klapper, G. 1958. An Upper Devonian conodont fauna from the Darby formation of the Wind River Mountains, Wyoming. J. Paleont. 32, 1082-93, pi. 141-2. and furnish, w. m. 1962. Devonian-Mississippian Englewood formation in Black Hill, South Dakota. Bull. Am. Ass. Petrol. Geol. 46, 2071-8. lindstrom, m. 1964. Conodonts. Elsevier Pub. Co. 196 pp. mehl, m. g. 1960. The relationships of the base of the Mississippian system in Missouri. J. Scient. Labs. Denison Univ. 45, 58-107. moore, d. 1958. The Yoredale Series of Upper Wensleydale and adjacent parts of north-west Yorkshire. Proc. Yorks, geol. Soc. 31, 91-148. moore, r. c., lalicker, w., and fischer, a. l. 1952. Invertebrate Fossils. McGraw-Hill, New York. muller, K. J. 1956. Taxonomy, nomenclature, orientation and stratigraphic evaluation of conodonts. /. Paleont. 30, 1324-40, pi. 145. Phillips, J. 1836. Illustrations of the Geology of Yorkshire. Part II, The Mountain Limestone District. London. rayner, d. H. 1953. The Lower Carboniferous rocks in the north of England: a review. Proc. Yorks, geol. Soc. 28, 231-315. remack-petitot, m. l. 1960. Contribution a l’etude des Conodontes du Sahara (bassins de Fort- Polignac, d’Adrar Reganne et du Jebel Bechar) et comparaison avec les Pyrenees et la Montagne Noire. Bull. Soc. geol. Fr. 7th ser. 2, 240-62. rexroad, c. b. 1957. Conodonts from the Chester Series in the type area of south-western Illinois. Rep. Inv. III. St. geol. Surv. 199, 1-43, pi. 1-4. 1958. Conodonts from the Glen Dean formation (Chester) of the Illinois Basin. Ibid. 209, 1-27, pi. 1-6. 1958. The conodont homeomorphs Taphrognathus and Streptognathodus. J. Paleont. 32, 1 158-9. and collinson, c. w. 1961. Preliminary range chart of conodonts from the Chester Series (Mississippian) in the Illinois Basin. Illinois Geol. Survey Circ. 319, 1-11. 1963. Conodonts from the St. Louis Formation (Valmeyeran Series) of Illinois, Indiana, and Missouri. Ibid. 355, 1-28. sannemann, d. 1955. Oberdevonische Conodonten. Senckenbergiana Leth. 36, 123-56. scott, a. j. and collinson, c. w. 1961. Conodont faunas from the Louisiana and McCraney Forma- tions of Illinois, Iowa and Missouri. Kansas Geol. Soc., 26th Ann. Field Conf. Guide Book, 110-42. Sedgwick, a. 1835. Descriptions of a series of longitudinal and transverse sections through a portion of the Carboniferous chain between Penigent and Kirkby Stephen. Trans. Geol. Soc. Lond. ser. 2, 4, 69-101. swan, s. h. 1963. Classification of Genevievian and Chesterian (Late Mississippian) rocks of Illinois. Rep. Inv. III. St. geol. Surv. 216, 7-91. tatge, u. 1956. Conodonten aus dem Germanischen Muschelkalk. Palaont. Z. 30, 108-27, 129-47, pi. 5-5. van den boogaard, m. 1963. Conodonts of Upper Devonian and Lower Carboniferous age from Southern Portugal. Geol. Mijnb. 42, 248-59. weller, J. m. et al. 1948. Correlation of the Mississippian formations of North America. Bull. geol. Soc. Am. 59, 91-126. wilson, a. a. 1960. The Carboniferous rocks of Coverdale and adjacent valleys in the Yorkshire Pennines. Proc. Yorks, geol. Soc. 32, 285-316. ziegler, w. 1958. Conodontenfeinstratigraphische Untersuchungen an der Grenze Mitteldevon/ Oberdevon und in der Adorfstufe. Notizbl. Hess. Landesamt. Bodenforsch. 87, 7-77 , pi. 1-12. w. J. VARKER Department of Geology, Mappin Street, St. George’s Square, Sheffield 1 Manuscript received 11 November 1965 CORTEZORTHINAE, A NEW SUBFAMILY OF SILURO-DEVONIAN DALMANELLID BRACHIOPODS by j. g. Johnson and john a. talent Abstract. Cortezorthinae is proposed for the Siegenian-Eifelian septate dalmanellid Cortezorthis gen. nov., its Silurian to Lower Devonian aseptate precursor Protocortezorthis gen. nov., and their derivatives, Reeftonia Allan and Cariniferella Schuchert and Cooper. New species are Protocortezorthis mndmillensis and Cortezor- this cortezensis from Nevada and Cortezorthis maclareni and C. bathurstensis from the Canadian Arctic. Cor- tezorthis maclareni is type species of Cortezorthis', ‘ Dalmanella ’ fornicatimcurvata is designated type species of Protocortezorthis. Protocortezorthis windmillensis is a temporal and morphologic intermediate between fully differentiated members of Protocortezorthis and of Cortezorthis. Its incipient median septum is recapitulated in early growth stages of Cortezorthis, and its dorsal adductor field is variable between patterns typical of both older and younger forms. The new subfamily Cortezorthinae arose from an as yet undesignated Silurian species of Isorthis. The Silurian members of Protocortezorthis developed distinctive ventral musculature, in part reminiscent of the rhipidomellids. The Devonian members of the Cortezorthinae ( Cortezorthis , Reeftonia, and Cariniferella) evolved away from standard isorthoid muscle patterns and also showed some convergence toward rhipidomellid internal mor- phology. Recent attempts to cast dalmanellid taxonomy in a phylogenetic scheme (Boucot, Johnson, and Walmsley 1965; Boucot, Gauri, and Johnson 1966) and efforts made here bring into focus some broad generalities regarding Devonian dalmanellids. The broad compass of the Dalmanellidae of Williams and Wright (1963) and of Wright (1965) includes several distinctive subfamilies in the Silurian and the Early and Middle Devonian, but members of the subfamily Dalmanellinae are unknown in Devonian beds. Devonian representatives of the family are limited to the isorthids and resserellids. The latter group and the Dicaelosiidae died out during the Emsian or Eifelian. Thus most of the Devonian genera fall into three major groups, Rhipidomellidae (emend. Boucot, Gauri, and Johnson 1966), Schizophoriidae, and Dalmanellidae. Walmsley, Boucot, and Harper show, in a manuscript in preparation, that Isorthis may have been derived from Dalmanella. The family assignment of the cortezorthinids hinges on the derivation of Schizophoria and we believe the evidence still favours its having arisen from Hinantia or Salopina rather than from Isorthis. This is supported by the nature of the internal morphology of the earliest Schizophoria species of early Gedinnian age, discussed later in this paper, which have unfaceted ventral diductor impressions and a narrow ventral myophragm, plus dorsal cardinalia that are charac- terized by strong brachiophore supporting plates that are not associated with prominent adductor muscle bounding ridges. These are features typical of Salopina , but not of Isorthis. Therefore Isorthinae, once regarded as belonging to the Schizophoriidae (Schu- chert and Cooper 1932), must be transferred to the Dalmanellidae and the Cortezorthinae, which had its origin in Isorthis, is similarly placed. If the isorthoids are to be dissociated from the schizophoriids, the major split of [Palaeontology Vol. 10, Part 1, 1967, pp. 142-170, pis. 19-22.] JOHNSON AND TALENT: CORTEZORTHINAE, A NEW SUBFAMILY 143- the punctate orthoids at the superfamily level recognized by Alikhova (1960) probably has real significance and is adopted here. SYSTEMATIC PALAEONTOLOGY Suborder dalmanelloidea Superfamily dalmanellacea Schuchert 1913 [= Rhipidomellacea Alikhova 1960] Family dalmanellidae Schuchert 1913 Subfamily cortezorthinae nov. Diagnosis. Aseptate or septate Dalmanellidae with fixed ventral adductor and un- faceted ventral diductor scars (see appendix of definitions) and progressively divergent brachiophores in Devonian member genera. Discussion. The new subfamily Cortezorthinae is erected primarily to include the new genera Cortezorthis and Protocortezorthis defined below, but includes the previously named genera Reeftonia and Cariniferella as well. Protocortezorthis is thought to have been derived out of one of the Silurian species of Isorthis, but since an understanding of Cortezorthis morphology, ontogeny, and direct ancestry is necessary for elucidation of the subfamily, further discussion is deferred until later in this paper. Genus cortezorthis gen. nov. Plates 19-20 Type species. Cortezorthis maclareni Johnson and Talent sp. nov. Diagnosis. Ventral muscle-field lacking broad myophragm. Brachial valve with rhom- boidal adductor muscle-field and discrete postero-lateral bounding ridges; fulcral plates lacking; median septum long and triangular. Both valves may bear peripheral radial septa. Discussion. Cortezorthis is an unusual dalmanellid even amongst dalmanellids with a dorsal median septum, which themselves are uncommon and at present still relatively poorly known. Most of the septate dalmanellids are small shells and the only genus previously brought to light that attains a size comparable to that of other Palaeozoic dalmanellids is Phragmophora Cooper 1955. The known representatives of Phragmophora are not particularly large for dalmanellids and are considerably smaller than the largest specimens of Cortezorthis as represented by C. maclareni, C. bathurstensis, and C. cor- tezensis described below. The median septum of Cortezorthis is distinctive in being very long and relatively low triangular through its entire length, distinguishing it from the median septum of other known septate dalmanellids, except Muriferella , since they all bear a relatively high triangular structure (text-fig. 1). The second distinctive morphologic element of Cortezorthis is its peripheral radial septa (see appendix of definitions). These appear first in the antero-medial regions, and in the brachial valve they closely adjoin the median septum. The smallest specimens that bear radial septa have a single pair next to the median septum. In larger specimens the 144 PALAEONTOLOGY, VOLUME 10 radial septa become better developed around the antero-lateral periphery with generally decreasing strength away from the mid-line. Since the peripheral radial septa are so extravagantly developed in some forms it is surprising to find that they are wholly absent in others; the evidence at hand suggests that their presence or absence within the genus is merely of specific value since forms that lack them come from different localities and different stratigraphic positions and have fairly clear-cut minor external peculiarities of form that distinguish them from species bearing radial septa. Hypsomyonia Kay sere! la M ystr ophora Vallomyonia Prokopia Phragmophora Monelasmina Muriferel la Cortezorthis text-fig. 1 . Schematic longitudinal sections at the mid-line of the Devonian septate dalmanellid genera showing brachial valve, outline of median septum, and outline of exterior of pedicle valve. Among forms with radial septa and those that lack them, there seems to be little difference in the thickness of the median septum, the shell in general, and the strength of development of the muscle bounding ridges or the anterior elevated edge of the adductor platform in the brachial valve. On the other hand, the unnamed species from Novaya Zemlya (PI. 20, figs. 21—27) has a very faintly impressed dorsal musculature. Its median septum is relatively thinner than in either C. cortezensis or C. maclareni and so are the radial septa; so the possession or absence of a well-developed anterior elevated edge for the dorsal adductor scars appears to be a feature of no more than specific value. In the pedicle valve most species lack a myophragm dividing the ventral diductors, although in a few specimens the adductor tracks are well defined. The largest specimen of C. cortezensis, however, has a fairly prominent ventral myophragm and is uncommon in that regard. Judging from the variation amongst the named and unnamed species of Cortezorthis, the internal feature of consistent taxonomic value in the pedicle valve appears to be short dental lamellae in combination with discontinuous, anteriorly JOHNSON AND TALENT: CORTEZORTHINAE, A NEW SUBFAMILY 145 convergent muscle bounding ridges. In the brachial valve all medium and large-size speci- mens bear a long, low median septum and all that attain a relatively moderate size bear a rhomboidal adductor muscle-field with the postero-lateral bounding ridges of the posterior adductors discontinuous with the brachiophore bases and set within them (PI. 19, figs. 21-23; PI. 20, figs. 18, 28). COMPARISON Relation to Muriferella. There are similarities in the median septa of Cortezorthis and Muriferella Johnson and Talent (in press), but the latter genus has well-defined fulcral plates and an elongate dorsal adductor muscle-field, both of which are lacking in Cortezorthis. The two genera occur together in Nevada and in the Canadian Arctic and in collections bearing small Cortezorthis (e.g. PI. 20, figs. 3-7) the broad muscle scars and divergent brachiophores of Cortezorthis at once distinguish it from Muriferella (cf. Johnson and Talent, in press, pi. 9, figs. 6-10). Relation to Phragmophora. Cortezorthis gen. nov. somewhat resembles Phragmophora in the configuration of the pedicle muscle impressions and in the possession of a dorsal median septum. In the pedicle valve Phragmophora (Cooper 1955, pi. 12, fig. 19) bears a short, transverse muscle-field laid out on the same plan as that of Cortezorthis. The antero-lateral bounding ridges are shorter and converge much more sharply than in Cortezorthis. In the ventral valve of Phragmophora there is a notodeltidium (Cooper 1955, pp. 51, 52, pi. 14a; Biernat 1959, pi. 5). The structure is not present in Cortezorthis although some of the shells examined are exceptionally well preserved. Instead, the apex of the pedicle valve may be filled internally with a deposit of shell material that partially closes the apex of the delthyrium. In the brachial valve, Cortezorthis structures are dissimilar in general layout to those of Phragmophora. The brachiophores and cardinal process are difficult to compare. Basically, the cardinal process of Phragmophora is bilobate (Cooper 1955, pi. 12, fig. 24; Biernat 1959, p. 44, fig. 16) and the myophore of the best-preserved specimen of Cortez- orthis (pi. 19, fig. 2) is relatively similar to the quadrilobate one of Phragmophora schnuri illustrated by Biernat (1959, p. 44, fig. 16c). However, the shaft of the cardinal process of Cortezorthis is not cleft as is the shaft in Phragmophora. The median septum of Phragmophora schnuri is much higher and decidedly more precipitous in the slope of its posterior edge (text-fig. 1). Moreover, the septum does not extend to the anterior margin. In Cortezorthis, small shells bear a median septum that is no more than a ridge. Larger specimens of Cortezorthis bear a median septum that is long, low, and triangular and which does extend to the anterior margin of the valve (text-fig. 1). In addition, the brachiophores of Phragmophora appear to be somewhat more slender and more strongly ventrally directed than they are in Cortezorthis. The well-formed triangular notothyrial platform of Cortezorthis is not developed in Phragmophora as illustrated by Cooper (1955, pi. 12b) nor in the specimens illustrated by Biernat (1959, pi. 6, figs. 9-11). Biernat (1959, p. 52) noted that fulcral plates are lacking in small specimens (ephebic stage) of Phragmophora , but are present in gerontic shells. The latter suggestion is undoubtedly based on a misinterpretation of fulcral plates which, when present, are best seen in small specimens. The gerontic build-up of shell material in and around the sockets to form an anterior overhanging lip should not be confused with true fulcral plates. L C 4466 146 PALAEONTOLOGY, VOLUME 10 Taken together, the configuration of the cardinalia and median septum of Phragmo- phora suggest that the genus was derived from Prokopia (Havlicek 1953) rather than Cortezorthis and its allies. Prokopia is a very small, thick-shelled form that lacks fulcral plates but bears a high triangular median septum that descends precipitously ventrally along its posterior edge. Wright (1965, pp. H338-9) proposed a subfamily Prokopiinae to include Prokopia, Phragmophora, and Monelasmina. However, as shown by Cooper (1955, pp. 53-54) Monelasmina is a schizophoriid genus and is therefore not closely related to Prokopia. Relation to Monelasmina. Cortezorthis differs from Monelasmina (Cooper 1955, pi. 11; Pedder 1959) by attaining a much greater size, but more importantly in a comparison of Monelasmina with small specimens of Cortezorthis that are in the same size range, Cortezorthis differs most markedly by the lack of a high triangular median septum. In addition, Monelasmina bears long bilobate ventral diductor scars even at an early growth stage. Monelasmina is a schizophoriid genus, and it appears possibly to have been derived directly from a late species of Salopina or from Sphenophragmus Imbrie (1959) rather than Cortezorthis. Relation to Hypsomyonia. Hypsomyonia Cooper is a septate Devonian dalmanellid whose phylogenetic relations are still uncertain, thus necessitating comparison with Cortezorthis. Hypsomyonia (Cooper 1955, p. 52, pi. 11, figs. 1-11) even though minute, bears a relatively high triangular median septum and an anteriorly elevated muscle platform. Large specimens of Cortezorthis bear an anteriorly elevated adductor platform and this is probably the source of their assignment to Hypsomyonia (McLaren in Fortier et al. 1963, p. 320); however, as is the case with Monelasmina and Prokopia, small speci- mens of Cortezorthis, the same size as Cooper’s illustrated specimens of Hypsomyonia , differ very markedly by the lack of a high, triangular median septum or an elevated adductor platform in Cortezorthis. Relation to Dalmanellopsis. The genus Dalmanellopsis Khalfin (1948) was thought possibly to be a septate dalmanellid. Khalfin (1948, pp. 208, 209) described a long ridge or septum in the brachial valve of the type species D. septiger. Examination of a specimen of D. septiger sent by Dr. R. T. Gratsianova revealed that the structure in question is only a low medial ridge and not a true median septum. Dalmanellopsis appears to be a valid genus most closely related to Salopina (Boucot, Gauri, and Johnson 1966) and not a synonym of Levenea as it was regarded by Alikhova (in Sarycheva 1960, p. 191) and Wright (1965, p. H334). Cortezorthis maclareni sp. nov. Plate 19, figs. 1-20, Plate 20, figs. 28, 29 1963 Hypsomyonia? sp. A, McLaren in Fortier et al., p. 320. Diagnosis. Cortezorthis with a strong narrow fold (carina) on the pedicle valve and a deep, subangular, narrow sulcus on the brachial valve. Internal margins of both valves bear radially arranged septa. Exterior. Brachial valves are transversely suboval to sub-semicircular while pedicle valves may be transversely shield-shaped or subpentagonal in outline. The valves are JOHNSON AND TALENT: CORTEZORTHINAE, A NEW SUBFAMILY 147 unequally biconvex in lateral profile with the pedicle valve slightly more convex than the brachial valve. The over-all aspect is relatively lenticular. The beak of the pedicle valve is short, pointed, and only slightly incurved over a low, triangular, nearly flat interarea. The ventral interarea is low apsacline to orthocline and is equal to approximately two- thirds of the maximum width of the valves. It is cleft medially by a triangular open delthyrium, enclosing an angle of about 60°. The interarea commonly shows fairly well- developed horizontal growth lines that start a short distance lateral to the edges of the delthyrium which are unstriated. The beak of the brachial valve is small, inconspicuous, and moderately incurved. The dorsal interarea is relatively long, equalling the width of the ventral interarea, and is flat and anacline. The cardinal angles are obtuse and relatively smoothly and strongly rounded. Maximum width is commonly near midlength or slightly posterior to it. Small shells and the posterior portions of larger ones bear a relatively strong narrow fold on the pedicle valve and a well-marked narrow sulcus on the brachial valve. However, toward the anterior of larger specimens the fold on the pedicle valve begins to broaden and become less elevated and the anterior commissure becomes slightly flattened or deflected toward the brachial valve, forming a broad, indistinct, curved margin that is slightly dorsally deflected, in effect, a reversal of the sulcation pattern, but the fold and sulcus developed posteriorly are of an entirely different order of magnitude considering the relative height : width ratio of the features. The ornament consists of numerous, fine, subangular costellae that increase in number anteriorly by intercalation, principally along the sides of shallow interspaces. On some specimens, particularly in the proximity of the fold and sulcus, the angular costellae break down into numerous very fine costellae of about equal size. Fairly well-developed concentric growth lines are present at a few irregular intervals across the shell. There are commonly 10-15 costellae in a space of 5 mm., 10 mm. anterior to the beak of the brachial valve in the mid-region. Interior of pedicle valve. Beneath the level of the delthyrium, in its apex, there is a some- what variable but more or less well-developed pad of secondary shell material that fills the apex of the valve and closes off the apical one-quarter to as much as one-third of the delthyrium. Commonly the external face of the pad of shell material visible within the apex of the delthyrium is seen to bear several lamellae or growth lines that have a con- cave edge facing the hinge line, in effect rounding the apex of the delthyrium. The hinge teeth are relatively ponderous and triangular in cross-section, in the plane of the commis- sure. Their inner edges bear crural fossettes and are directed somewhat more strongly laterally than the edges of the delthyrium. The lateral edges are almost parallel to the median plane. Short dental lamellae are present in small specimens, but are made com- pletely obsolescent by deposition of shell material beneath the hinge teeth and in the umbonal cavities so that the hinge teeth appear to connect directly with the inner sur- face of the valve. A pair of relatively thin, subangular, muscle bounding ridges originate at the base of the hinge teeth and curve slightly inward toward the mid-line to partially enclose the diductor muscle impressions antero-laterally. In plan view the ventral muscle impression is roughly elongate-oval. The adductor scars are located centrally and are relatively broad, low, and very faintly impressed. The diductors are more or less triangular with their long sides lying subparallel to the mid- line. Some specimens have the submedian and lateral diductor lobes differentiated (pi. 20, 148 PALAEONTOLOGY, VOLUME 10 fig. 29) and the vascula media extend anteriorly in a radial fashion from the submedian lobes. In a few specimens the submedian lobes are separated by a very narrow myo- phragm, but in most there is an elongate trapezoidal track medially that is only faintly elevated. There may be a rounded median groove that runs from nearly the anterior edge of the diductor muscle field to the peripheral crenulations. Peripherally the interior bears two sets of crenulations which are most strongly developed anteriorly and which become slightly less pronounced laterally. There is an inner group of relatively widely spaced, short, high, radially aligned, septa, but these do not reach to the edge of the valve. Outside of these and right at the margin of the valve there is a finer set of more numerous crenulations. The crenulate peripheral portion of the interior may be very finely papillose, evidently mirroring the development of the endopunctae. Interior of brachial valve. The sockets are relatively deep, expanding antero-laterally. They are bounded posteriorly by the inner edges of the interarea and medially by the lateral edges of the brachiophores. Basally they are impressed into thick shell material between the brachiophores and the hinge line. On some specimens the anterior edge of the base of the socket is free of the base of the valve overhanging a small cavity sug- gesting that the socket base could be classified as a fulcral plate. However, the brachio- phore base at this point is not in contact with the base of the valve, but is also free. The angle between the long axis of the brachiophore and the plane of the base of the socket at the distal end is about 90°. The brachiophores diverge widely and are relatively ponderous plates of subrectangular cross-section. They project toward the antero- lateral extremities of the pedicle valve rather than being inclined strongly ventrally. The bases of the brachiophores neither converge toward the midline nor diverge from it, but EXPLANATION OF PLATE 19 Figs. 1-20. Cortezorthis maclareni gen. et sp. nov. All specimens are from a single collection, GSC loc. 26513, lower part of lower member of Blue Fiord Formation, south-western Ellesmere Island. Col- lected by D. J. McLaren, 1955. 1, Interior of brachial valve X 3, GSC no. 19106. Note the anteriorly raised adductor muscle platform, the stout median septum, and peripheral septa. 2, Interior of in- complete brachial valve X 3, GSC no. 19107. Note the distinctly quadrilobate cardinal process, the stout median septum, and the peripheral septa. 3, Internal margin of part of brachial valve X 5, GSC no. 19108. Note the peripheral septa and the smaller intercalated marginal crenulations. 4, 5, Interior of pedicle valve X 3 and X 2, GSC no. 19109. Note deeply incised crural fossettes on the inner edges of the hinge teeth. 6, 7, Rubber internal mould and interior of pedicle valve X 1-5. GSC no. 19110. Note the low, angular, anteriorly convergent, muscle bounding ridges and the strong peri- pheral septa. 8-10, Ventral, posterior, and anterior views x 1-25, GSC no. 191 11. Note loss of narrow fold and sulcus near the anterior commissure. 11, Interior of pedicle valve X 1, GSC no. 19112. 12, 13, Rubber internal mould and interior of pedicle valve X 1 -5, GSC no. 19113. Note the bluntly rounded posterior end of the mould of the muscle impression owing to shell material deposited in the apex of the valve. 14, 15, Dorsal and ventral views x 2, GSC no. 19114. Note the angular appearance of the costellae. 16-20, Posterior, anterior, dorsal, ventral, and side views of the holo- type X 1-5, GSC no. 191 15. Note the reversal of the fold and sulcus at the anterior commissure. Figs. 21-23, Cortezorthis aff. bathurstensis Blue Fiord Formation, 100 ft. above base, south bank of Sutherland River, lat. 76° 19', long. 92° 5F, Prince Alfred Bay area, Devon Island, collected by A. R. Ormiston, Aug. 1961. 21, Interior ofbrachial valve X 2, GSC no. 19593. Note the stout median septum and the absence of peripheral septa. 22, 23, Two aspects of brachial valve interior X 3, GSC no. 19594. Palaeontology, Vol. 10 PLATE 19 JOHNSON and TALENT, Siluro-Devonian Cortezorthinae JOHNSON AND TALENT: CORTEZORTHINAE, A NEW SUBFAMILY 149 maintain a fairly consistent angle from their ventral edges to their bases. Medially be- tween the posterior ends of the brachiophores the notothyrial cavity is almost com- pletely filled by a ponderous triangular pad of shell material bearing the cardinal process. The cardinal process is composed of a very short, broad, rounded shaft andaquadrilobate myophore that faces approximately the same direction as does the dorsal interarea. Both medial and lateral lobes are crenulated or are lamellose, but the median pair is commonly grooved further anteriorly. A thick, long, triangular median septum extends from the base of the anterior edge of the notothyrial platform to the anterior commissure of the valve. The median septum may be relatively narrow at its base and be thicker mid- way toward its ventral edge where it again becomes relatively thin and blade-like. The adductor muscle-field is suboval and commonly slightly transversely so, or from this configuration there may be a slight tendency toward a rhombohedral outline and in most specimens the anterior edge of the adductor scars converges toward the median septum at a high angle. The postero-lateral edges of the adductor muscle-field are limited by a pair of relatively strong, straight bounding ridges that lie well within the inner edges of the bases of the brachiophores. The anterior edges of the adductor muscle scars are commonly strongly elevated above the base of the valve. The anterior and posterior adductor pairs are separated by faint, low, rounded ridges that extend anteriorly sub- tending an angle of about 70-75° between them and the median plane. The anterior ad- ductor impressions are commonly radially grooved with the grooves becoming stronger toward the overhanging edge of the platform where the grooves may become very deep and are separated by elongate lobes or rods of shell material. Similar elongate rods or pustules develop fairly strongly on some specimens at the anterior end of the postero- lateral bounding ridges as well as lateral to them beneath the sockets and brachiophores. The area beneath the anterior edges of the adductor platform may be relatively smooth, but grooves deepen again anteriorly toward the periphery where a double set of septa and crenulations is developed similar to those already described for the pedicle valve. The anterior end of the median septum and the strongest radial septa, which commonly are the next adjacent pair, are irregular and deeply pitted, mirroring at least in part the development of longitudinal grooves on the septa that parallel their ventral edges. Shell structure. The shell is thick and is endopunctate. Occurrence. The type lot and the only specimens certainly assignable to C. maclarcni are from Geological Survey of Canada locality 26513 from the south side of Bids Fiord, south-western Ellesmere Island and were collected by Dr. D. J. McLaren in 1955. According to McLaren (in Fortier et al., 1963, p. 320) the collection horizon is about 600 ft. above the base of the lower member of the Blue Fiord Formation. Figured specimens. GSC numbers 19106-16. Cortezorthis maclareni loc. 265 1 3 Figured Specimens Measurements in mm. Length Width Thickness Holotype GSC 19115 Paratype GSC 19114 Paratype GSC 19111 Paratype GSC 19116 180 19 9 8-5 11-0 14-8 50 191 21-5 91 9-6 11-5 5-3 150 PALAEONTOLOGY, VOLUME 10 Unfigured Specimens Length Width Thickness Length Width Thickness 11-4 140 6-0 18-8 20-3 100 12-7 15-3 6-3 18 6 21-0 10-5 13-7 16-6 6-6 18-0 22-0 8-0 14-2 17-5 7-0 19-0 22-7 8-5 lo-4 19 5 7-7 20-6 23-6 9-2 17-7 19-7 9-2 23-4 25-4 11-4 18-3 200 10 3 21-2 25-5 6-4 Cortezorthis bathurstensis sp. nov. Plate 20, figs. 1-13 Diagnosis. Cortezorthis lacking radial septa. Exterior. The valves are transversely shield-shaped to suboval in outline. They are biconvex in lateral profile, with the pedicle valve having the greater convexity. There is a short, pointed, incurved ventral beak and a low, subcarinate, transverse profile; however, no median carina is developed. The brachial valve bears a well-defined median sulcus that is relatively sharp at the umbo and broadens out to something of a medial flattening anteriorly. The ventral interarea is low, triangular, and apsacline, and equal to about half the maximum width of the valves which is attained a little posterior to midlength anterior to obtuse, rounded cardinal angles. The delthyrium is open and triangular, enclosing an angle of about 60°. The dorsal interarea is low, triangular, and well developed. It is flat and anacline on smaller specimens to nearly orthocline on large ones. The ornament consists of fine, rounded costellae that increase in number anteriorly by bifurcation and by implantation. The costellae on the postero-lateral flanks are some- what finer than those on the median half of the valve. A few costellae that originate at the posterior become enlarged anteriorly and give a faint indication of parvicostellation on some specimens. Concentric growth lines are not developed. Interior of pedicle valve. The hinge teeth are prominent and of triangular cross-section on small specimens, but become blunted and directed dorso-laterally on large ones. Crural fossettes are present. The ventral diductor scars are short and cordate on small- to moderate-sized specimens with a very faint low myophragm dividing the scars; poorly developed short muscle bounding ridges that converge slightly toward the midline enclose them laterally. The largest specimen has a long, well-developed myophragm that may be anteriorly split. Adductors are not discernible, but the diductor scars become strikingly elongate and are bounded by long, well-defined, sharp, anteriorly convergent muscle bounding ridges. The interiors are crenulate over half or more of the smallest specimens, but only peripherally on the largest ones. The crenulations on the best preserved, moderate-sized specimens are rounded to very slightly flattened, simple, rod-like structures. Peripheral radial septa are not developed. Interior of brachial valve. The presence of some very small specimens, the smallest being 4 mm. in maximum dimension, allows for the discussion of small- and large-stage brachial valves. The small specimens are very strongly convex, having something of the appearance of a small brachial valve of Schizophoria, but the median sulcus is a point of external distinction. The brachiophores are triangular and plate-like, diverging antero-laterally JOHNSON AND TALENT: CORTEZORTHINAE, A NEW SUBFAMILY 151 at roughly 60° and diverging slightly toward the base of the valve. The sockets are formed between the plate-like brachiophores and the inner posterior margin of the valve, and the slightly overhanging interarea. There appears to be a slight thickening on the lateral sides of the brachiophores to form the base of the socket, but fulcral plates are not developed. The cardinal process is a small rhomboidal callosity at the apex of the notothyrium supported by a very short, thin ridge in the notothyrial cavity. The adductor impressions are broadly pyriform with short, discrete, blade-like, muscle bounding ridges set close to the bases of the brachiophores and diverging parallel to them in a radial fashion. The anterior adductors are rounded and blend imperceptibly with the interior of the valve. There is a small ridge-like median septum that begins approximately at the anterior margin of the dorsal adductor impressions and extends to the anterior commissure with almost no perceptible increase in height. In the smallest specimen the septum has a height approximately one and a half times its width and is considerably less than 1 mm. in height. In a moderate-sized specimen the brachiophores, although still plate-like, develop anterior extensions that project beyond their bases which are joined with the valve interior, and they diverge a little more strongly antero-laterally. The cardinal process is a serrated, chevron-shaped, undivided shaft with its base in the notothyrial cavity and not extended anteriorly as a myophragm. At this stage no ancillary struts are developed forming a notothyrial platform. This is a specimen about 1 cm. across. The largest available brachial valve, approximately 25 mm. across, has fully developed brachiophores that are bent a little, so that they diverge strongly laterally. There is a fully developed notothyrial platform against which the posterior adductors are well defined. The notothyrial platform continues as a well-defined, broad, rounded myo- phragm to about the middle of the adductor impressions where it becomes elevated as a median septum. The septum is relatively thin and rises in height anteriorly, but does not reach the anterior commissure. The posterior adductors are slightly longitudinally grooved in a manner similar to that of Cariniferella, and the blade-like bounding ridges are well defined lateral to the posterior adductors. The anterior adductors are bounded by straight to slightly curved elevated ridges that converge sharply towards the mid-line. No peripheral radial septa are developed. Comparison. Cortezorthis bathurstensis differs from C. maclareni by the absence of radial septa internally, by a thinner shell, and by the absence of a median carina on the pedicle valve. Occurrence. This species is present at GSC localities 67145 and 59036 in the upper part of the Stuart Bay Formation on Bathurst Island. Their age is probably Emsian. Material. There are 22 specimens in the paratype collection of which five are illustrated that include GSC numbers 19595-9. Cortezorthis cortezensis sp. nov. Plate 20, figs. 14-20 Diagnosis. Large, flatly biconvex Cortezorthis with peripheral radial septa and lacking a median ventral carina. 152 PALAEONTOLOGY, VOLUME 10 Exterior. The valves attain medium to large size and are transversely suboval in out- line and unequally biconvex in lateral profile, with the pedicle valve a little more convex; lateral flanks of the pedicle valve are relatively flat. Cardinal angles are obtuse and rounded behind the maximum width which is attained near midlength. The brachial valve has a shallow, poorly defined sulcus. The ventral beak is short and only faintly incurved so that the narrow triangular interarea is relatively low, flat, and apsacline. The delthyrium is open, and relatively broad, enclosing an angle of nearly 90°. The dorsal interarea is flat and anacline. The exterior ornament consists of numerous rounded costellae that increase in number anteriorly by intercalation and bifurcation and which tend to bow slightly with their convex sides toward the mid-line. Interior of pedicle valve. The hinge teeth are short, stubby, triangular extensions of the interarea and are widely divergent, directed somewhat anteriorly and laterally. They are joined to the base of the valve by parallel thickenings of shell material, but dental plates are absent except for the most rudimentary sort of short, faintly differentiated, ridge-like extensions that support the base of the teeth distally. Even on very small speci- mens it is almost always impossible to detect any separate plate-like structure. Crural fossettes are not present. In the smallest specimens the ventral diductor impressions are trigonal and rounded posteriorly with a slightly elevated anterior margin. Poorly defined divergent vascular tracks extend antero-laterally. In the larger specimens strong muscle bounding ridges develop and converge rather abruptly toward the midline coincident with the development of a relatively prominent rounded myophragm between the diductor scars. Interior of brachial valve. The brachiophores are plate-like and broadly divergent, defining sockets at the base of the valve without fulcral plates. The cardinal process is too poorly preserved to characterize accurately on the available specimens, but the noto- thyrial platform is fully developed into a ponderous structure that continues anteriorly as a myophragm to the middle of the dorsal adductors where it joins with a relatively thick, low, median septum that increases in height anteriorly and reaches to the an- terior margin of the valve. The posterior adductors are subtriangular and relatively broad with some longitudinal striation and well-developed discrete bounding ridges. In one specimen a pair of myophragms subnormal to the mid-line delimit the posterior and anterior adductors. The anterior adductors are larger than the posterior ones and are situated on a slightly elevated platform whose anterior edges are nearly straight and which converge sharply toward the mid-line, but become less pronounced just before joining the median septum. The interior is crenulated peripherally and bears radial septa that are most prominently developed near the midline anteriorly. Comparison. Cortezorthis cortezensis differs from C. bathurstensis by the presence of peripheral septa internally, although on the exterior the outline and profile are very similar. Internally the structural features are a little better developed in C. cortezensis and probably this is due to the development of a thicker shell. The ventral beak is a little less strongly incurved in C. cortezensis with the interarea tending to be more flat and the delthyrium broader. C. cortezensis differs from C. maclareni in lacking a median carina on the pedicle valve externally and in the relatively shorter and broader ventral diductor impressions. The two species are very similar in the brachial valve interior although JOHNSON AND TALENT: CORTEZORTHINAE, A NEW SUBFAMILY 153 C. cortezensis does not develop the internal pustules and radial ridges that are especially prominent in C. maclareni. Occurrence. All of the specimens of Cortezorthis cortezensis are from the Eureka- Spirifer pinvonensis zone of Emsian age. Material. There are 38 specimens from the west side of the Cortez Range (USNM loc. 10754), four from the east side of the Cortez Range (USNM loc. 10752), and one from the northern Simpson Park Range of central Nevada. Four specimens are illustrated under USNM nos. 141450-3. 10752 — Wenban Limestone, east slope of Cortez Range, elev. 7950 ft., 1000' N., 700' W. of SE. cor. of sec. 4, T. 26 N., R. 48 E., Cortez quad.. Eureka Co., Nevada. Collectors: A. J. Boucot and E. F. Lawrence, 1963; A. J. Boucot, H. K. Erben, and K. L. Gauri, 1965. 10754 — Wenban Limestone, west slope of Cortez Range, elev. 6875 ft., 800' N., 2900' E. of SW. cor. of sec. 21, T. 26 N., R. 48 E., Cortez quad., Eureka Co., Nevada. Collectors: A. J. Boucot and H. Masursky, 1963. 10762 — McColley Canyon Formation, elev. 6800 ft., 2450' W., 650' N. of SE. cor. of sec. 16, T. 25 N., R. 49 E., Horse Creek Valley quad., northern Simpson Park Range, Eureka Co., Nevada. Collector: J. G. Johnson, 1957. OCCURRENCE OF CORTEZORTHIS Cortezorthis cortezensis is present at two localities in the Cortez Range (USNM locali- ties 10752, 10754) and in the northern Simpson Park Range (USNM locality 10762), all in Eureka County, central Nevada. These occurrences are from the Eurekaspirifer pinvonensis zone that Johnson (1962, p. 166) and House (1962, p. 253) have concluded is of Early Devonian and probable Emsian age. Johnson’s study of the Lower Devonian brachiopods in central Nevada (in preparation) presents additional evidence from the brachiopods and from the conodonts (Walliser in Johnson in prep.) pointing to an Emsian age. An unnamed species of Cortezorthis is present in the lower part (late Siegenian) of the Monogrciptus yukonensis zone in collections of Dr. A. C. Lenz from Yukon Terri- tory, Arctic Canada (Boucot, Gill, Johnson, Lenz, and Talent 1966). These have a fully developed median septum and peripheral septa, but a primitive dorsal adductor scar as in some specimens of Protocortezorthis windmillensis (PI. 21, figs. 3, 9) and are thus intermediate in development between P. windmillensis and C. cortezensis of the Nevada Lower Devonian. Cortezorthis bathurstensis is present at two localities near the top of the Stuart Bay Formation on Bathurst Island (G.S.C. localities 59036 and 67145). Cortezorthis sp., bearing radial septa, is present in the Disappointment Bay Formation of Bathurst Island (G.S.C. locality 59037). All three collections from Bathurst Island appear to be within the interval Emsian-Eifelian and the former two are tentatively assigned to the Lower Emsian. Cortezorthis aff. bathurstensis is present 100 feet above the base of the Blue Fiord Formation on Sutherland River, Devon Island, in collections made by Dr. Allen Ormiston (PI. 19, figs. 21-23). These beds also are of Emsian age according to G. Klapper who has studied the conodonts. Cortezorthis maclareni occurs in the lower part of the Blue Fiord Formation on Ellesmere Island. The collection horizon is of Emsian or Eifelian age (G.S.C. locality 154 PALAEONTOLOGY, VOLUME 10 265 1 3). An unnamed species lacking radial septa occurs in the mid-Blue Fiord Formation on Ellesmere Island (G.S.C. locality 26522). A single specimen from south-eastern Novaya Zemlya (PI. 20, figs. 21-27) comes from beds reported to be of early Eifelian age (Cherkesova, written communication March 1965). Genus protocortezorthis gen. nov. Plate 21, figs. 1-22 Type species. Orthis fornicatimcurvata Fuchs 1919. Diagnosis. Ventral muscle field narrow, with thin bounding ridges that converge toward the midline anteriorly. Diductor impressions separated by a narrow, well-defined, rounded myophragm. Dorsal cardinalia with fulcral plates present or absent. Noto- thyrial platform present. Median septum absent. Discussion. The detailed morphology of one species, Protocortezorthis windmillensis, is described below. The ventral adductor scars are not discernible in P. windmillensis, due probably to poor preservation in the few available specimens. P. orbicularis and P. fornicatimcurvata, on well-preserved specimens, exhibit well-marked, shield-shaped or cordate adductor impressions of a rather distinctive configuration (see Walmsley 1965, pi. 63, figs. 1-8). The same type of ventral adductor impression is repeated in Reeftonia marwicki (figs. 4, 6, 7 of Plate 22 in the present paper) and the close comparison is evi- dent in sketches reproduced in text-fig. 2. Protocortezorthis windmillensis closely re- sembles some species of Cortezorthis , but differs in having more deeply impressed ventral diductors and a well-defined ventral myophragm. Brachial valves are the same except for the absence of a median septum in P. windmillensis, but an incipient median septum and peripheral radial septa are present medially in some specimens. In the brachial valve EXPLANATION OF PLATE 20 Figs. 1-13. Cortezorthis bathurstensis gen. et sp. nov. All specimens from GSC loc. 67145, 85 ft. below top of Stuart Bay Formation, Bathurst Island. Collected by J. W. Kerr, 1964. 1, interior of pedicle valve (xl), GSC 19595. 2, Interior of brachial valve (xl-25), holotype, GSC 19596. 3-5, Two interior views and one exterior view of brachial valve (x 5), GSC 19597. 6-8, Two interior and one exterior view of brachial valve ( X 10), GSC 19598. 9-13, Interior, side, anterior, posterior, and exterior views of pedicle valve (x 1-5), GSC 19599. Figs. 14-16. Cortezorthis cortezensis gen. et. sp. nov. Specimens from Eurekaspirifer pinyonensis zone, Cortez Range, central Nevada. 14, Rubber impression of interior of small pedicle valve (x4), USNM loc. 10754, USNM 141451. 15, Interior of pedicle valve f x 1-5), USNM loc. 10754, USNM 141452. 16, Interior of brachial valve (x2), USNM loc. 10752, USNM 141450. Figs. 17-20. Cortezorthis cortezensis gen. et. sp. nov. Specimen from Eurekaspirifer pinyonensis zone, northern Simpson Park Range, USNM loc. 10762. 17, 18, Ventral and dorsal views of internal mould (x 1), holotype, USNM 141453. 19, Rubber replica of dorsal interior (x 1-25), of specimen in fig. 18. 20, Side view of rubber replica of median septum (x 2), of specimen in fig. 18. Figs. 21-27. Cortezorthis sp. From beds of early Eifelian age, south-eastern Novaya Zemlya, collected by S. V. Cherkesova. 21, 22 Ventral and dorsal views of internal mould (x 2) of specimen in figs. 23-27, GSC 19117. 23-27, Dorsal, side, anterior, posterior, and ventral views (x 1-5), GSC 19117. Figs. 28, 29. Cortezorthis maclareni gen. et. sp. nov. Lower Blue Fiord Formation, Emsian or Eifelian, south-western Ellesmere Island, GSC loc. 26513. Collected by D. J. McLaren, 1955. Dorsal and ven- tral views of internal mould (x 3), GSC 19116. Palaeontology, Vol. 10 PLATE 20 JOHNSON and TALENT, Siluro-Devonian Cortezorthinae JOHNSON AND TALENT: CORTEZORTHINAE, A NEW SUBFAMILY 155 of P. fornicatimcurvata brachiophore supporting plates are present and continue antero-laterally as ridges bounding the posterior adductors. No peripheral radial septa are known in P. fornicatimcurvata. Comparison. Protocortezorthis differs from Reeftonia in only a few minor modifications. Reeftonia has flatter and somewhat wider ventral diductors and commonly lacks a well- defined narrow ridge-like myophragm present in Protocortezorthis. In the brachial valve Reeftonia is almost identical with specimens of P. windmillensis that lack peripheral radial septa (see discussion of variation in Reeftonia below). Reeftonia completely lacks fulcral plates in all known representatives. Protocortezorthis differs from Cariniferella in the form of the valves and in the ventral interior. In Cariniferella the ventral diductor scars diverge antero-laterally and lack B- Protocortezorthis orbicularis text-fig. 2. Sketch drawings of ventral adductor and diductor scars in two cortezorthinid genera. a narrow myophragm. The arrangement of the cardinalia of Cariniferella is close to that of the youngest forms of Protocortezorthis, i.e. P. windmillensis, and that of Reeftonia. The dorsal scar pattern appears to be comparable to that of Cortezorthis and Reeftonia, but the proportions of the several elements and the scar as a whole, relative to the size of the brachial valve, are different. Species assigned to Protocortezorthis: Protocortezorthis windmillensis sp. nov. Isorthis slitensis Walmsley 1965, p. 467, pi. 62, figs. 23-35. Or this fornicatimcurvata Fuchs 1919. Or this orbicularis Sowerby in Murchison (1839, p. 61 1, pi. 5, fig. 16). This species has been redescribed and well illustrated by Walmsley (1965) leaving no doubt as to its relation to P. fornicatimcurvata. Specimens from the Sutherland River Formation illustrated and described by Boucot {in Boucot et al. 1960, p. 5, pi. 1, figs, 13-20, pi. 2, figs. 1-7) as Isorthis orbicularis were examined by Johnson who regards them as belonging to Schizophoria and close to the species Schizoplioria fragilis Kozlowksi (1929). Large specimens of Schizophoria are usually easily distinguished from Isorthis because of the larger brachial valve than pedicle valve in Schizophoria and because there commonly is a broad ventral sulcus in Schizophoria. Internally the brachial valve of Schizophoria has the posterior and anterior adductor muscle impressions separated from one another by ridges that diverge antero-laterally in contrast to ridges that are normal to the mid- line in Isorthis. However, in small specimens, Schizophoria is commonly subequally 156 PALAEONTOLOGY, VOLUME 10 biconvex without a sulcus as is Isorthis szajnochai. Moreover, in small specimens, ridges, dividing the posterior and anterior adductor muscles are not discernible; thus small specimens must be distinguished on a different basis. In the case of the specimens- illustrated by Boucot (1960), the shells are not congeneric with I. szajnochai because the muscle-field is long, but not anteriorly elevated and thus unlike the anteriorly elevated scar of I. szajnochai. Differences in the brachial valve are discussed further below. Specimens illustrated by Boucot also cannot be closely related to Protocortezorthis orbicularis because that form has a much less convex, but sulcate brachial valve (Walm- sley 1965, pi. 63, figs. 9-15). In the writers’ opinion the ventral muscle impressions of the form illustrated by Boucot almost exactly duplicates that of Schizophoria bisinuata Weller (1903, p. 278, pi. 31, figs. 12-13). After examining several score specimens in Boucot ’s collection, from which the Devon Island forms come, the writers found that the median groove on the ventral myophragm is an inconsistent feature and that most specimens do not have it. The type of ventral musculature developed in the Devon Island form and in Schizophoria bisinuata has also been seen in several collections of Schizophoria from limestone of Helderberg age in the Klamath Mountains of California and from the McMonnigal Limestone of early Siegenian age in central Nevada (Johnson 1965). On all of the shells mentioned above it is not uncommon to find that the narrow ridge-like ventral myophragm extends anteriorly beyond the diductor muscle bounding: ridges. In the case of small brachial valves where the ridges dividing the posterior and anterior adductor impressions are not developed, Schizophoria and Isorthis of the szajnochai type are easily distinguished by the nature of the muscle bounding ridges. In Schizophoria the brachiophores are supported by high triangular brachiophore sup- porting plates, but muscle bounding ridges that would outline the anterior adductors are not developed. On the other hand, in Isorthis szajnochai and its relatives, relatively long muscle bounding ridges are present even in early growth stages and bound the anterior adductors with almost equal strength as they bound the posterior adductors. The Devon Island specimens have strong, divergent brachiophore supporting plates as is- typical of Schizophoria , but there is no continuation as ridges lateral to the anterior adductors as in Isorthis. EXPLANATION OF PLATE 21 Figs. 1-13. Protocortezorthis windmillensis gen. et sp. nov. Windmill Limestone ( Quadrithyris zone, of early Siegenian age) Coal Canyon, northern Simpson Park Range, central Nevada. 1,2, Dorsal and anterior views of interior of brachial valve X3. USNM 147338, loc. 10758. 3, Interior of brachial valve x 1-5, USNM 147339, loc. 10758. 4, Interior of brachial valve X 1-5, USNM 147340, loc. 10758. 5, Interior of brachial valve x2, USNM 147341, loc. 10758. 6, 7, Rubber impression and interior of pedicle valve X 1-5, USNM 147342, loc. 10758. 8, 9, Exterior and interior of brachial valve Xl-5, USNM 147343, loc. 10758. 10-12, Exterior, interior, and anterior views of pedicle valve X 2, USNM 147344, loc. 10758. 13, Interior of pedicle valve X 1-5, USNM 147345, loc. 10757. Figs. 14-22. Protocortezorthis fornicatimcurvata (Fuchs 1919). Flaserschiefer of Hiiinghauser Schichten railroad cut, 85 paces NE. of Hiiinghauser railroad station. USNM loc. 10596. Collected by A. J. Boucot, 1957. 14, 15, Rubber impression and internal mould of pedicle valve X2, USNM 147346. 16, 17, Internal mould of brachial valve and rubber impression X 2, USNM 147347. 18, 19, Rubber impression and internal mould of brachial valve X 2, USNM 147348. 20, 21, Internal mould x2and rubber impression x 3 of brachial valve, USNM 147349. 22, Rubber impression of internal mould of brachial valve X 3, impression of USNM 147350. Palaeontology, Vol. 10 PLATE 21 JOHNSON and TALENT, Siluro-Devonian Cortezorthinae JOHNSON AND TALENT: CORTEZORTHIN AE, A NEW SUBFAMILY 157 DISTRIBUTION OF PROTOCO RTEZO RTHIS Protocortezortliis siitensis occurs in the Wenlock age Slite Marl of Gotland (Walmsley 1965, p. 469). Protocortezortliis orbicularis is present in the Ludlovian of the Welsh borderland (Walmsley 1965, p. 467). Protocortezortliis sp. is present in probable Ludlow age beds of the Caparo Formation of the Merida Andes, Venezuela in a collection of R. Shagam, IJSNM loc. 12204. Protocortezortliis fornicatimcurvata is present in the Gedinnian of Germany (Fuchs 1919), France (Barrois, Pruvost, and Dubois 1922, p. 77), and Belgium (Boucot 1960, p. 296). It is also present in the Gedinnian Stonehouse For- mation of the Arisaig area of Nova Scotia (Walmsley, Boucot, and Harper, manuscript in preparation). An unnamed species with closest affinity to P. fornicatimcurvata is present in the lower Monograptus yukonensis zone of late Siegenian age from Yukon Territory, Arctic Canada, in collections made by Dr. A. C. Lenz and examined by Johnson (see Boucot, Gill, Johnson, Lenz, and Talent 1966). The youngest reported occurrence is from the upper Pendikschichten in the Bosporus region (Paeckelmann and Sieverts 1932, pi. 2, fig. 24). The occurrences cited above appear to be a part of the P. fornicatimcurvata lineage. P. windmillensis, a divergent species initiating the lineage resulting in Cortezorthis, is present in the early Siegenian Quadrithyris zone of central Nevada (Johnson 1965). Protocortezortliis fornicatimcurvata (Fuchs 1919) Plate 21, figs. 14-22 1919 Orthis fornicatimcurvata Fuchs, p. 58, pi. 5, figs. 1-6. 1922 Orthis (Dalmanella) lunata Barrois, Pruvost, and Dubois, p. 77, pi. 11, figs. 4-12; non Sowerby. 1942 Dalmanella orbicularis Dahmer, p. 125, figs. 14, 15, 16 a, b\ non Sowerby. 1951 Dalmanella orbicularis Dahmer, p. 91, pi. 7, fig. 1; pi. 9, figs. 20, 21; pi. 10, fig. 6; non Sowerby. 1960 Isorthis fornicatimcurvata (Fuchs); Boucot, p. 296, pi. 10, figs. 6, 7. Discussion. Protocortezortliis fornicatimcurvata compares closely to P. windmillensis described below in the form of the valves with a relatively strongly convex, subcarinate pedicle valve and a gently convex, sulcate brachial valve. In the interior P. fornicatim- curvata has ventral diductor scars closely comparable to those developed in P. wind- millensis, but those on the latter appear for the most part to be slightly broader. In the brachial valve P . fornicatimcurvata has brachiophores less widely divergent than does P. windmillensis and they are connected with brachiophore supporting plates that continue as muscle bounding ridges around the posterior adductors. Because the brachiophore supporting plates are relatively well developed the sockets are defined by fulcral plates. Medially the posterior adductors are divided by a broad myophragm that merges with the brachiophore bases forming a poorly defined notothyrial platform. The anterior adductors are bounded by discrete muscle bounding ridges that converge antero- medially. The internal crenulations of P . fornicatimcurvata (PI. 21, fig. 21) fairly closely resemble those of P. windmillensis and consist of somewhat swollen appearing lobes with minor lobes intercalated. Figured specimens. USNM 147346-50. 158 PALAEONTOLOGY, VOLUME 10 Protocortezorthis windmillensis sp. nov. Plate 21, figs. 1-13 1965 ‘ Isorthis ’ cf. ‘/.’ forncatimcurvata Johnson; p. 371, non Fuchs. Diagnosis. Brachial valve interior with evanescent development of an antero-medial mound of radial septa. Brachiophore supporting plates not developed. Exterior. The shells are of approximately equal width and length and are rounded- trapezoidal in outline. The valves are unequally biconvex in lateral profile with the pedicle valve the larger. The interarea of the pedicle valve is low, apsacline, and nearly flat. It is relatively narrow, generally slightly less than half the maximum width of the valves. The delthyrium is relatively narrow at its apex with gently curved sides enclosing a broader angle toward the hinge line. The interarea of the brachial valve is narrow, band- like, and anacline. The cardinal angles are obtuse and strongly rounded. Maximum width of the valves is generally attained near midlength or anterior to it. The pedicle valves are subcarinate in transverse section and the brachial valves bear a corresponding median sulcus. Large shells are slightly emarginate at the anterior commissure. The ornament consists of fine radial costellae that increase in number anteriorly by bifurcation and by intercalation. There are approximately 12-15 costellae in a space of 5 mm., 10 mm. anterior to the beak. Interior of pedicle valve. The teeth are stout and triangular and diverge antero-laterally. They are supported by short, stout, divergent dental lamellae that nearly join anteriorly with sharply raised, narrow muscle bounding ridges that may be bowed gently laterally at their posterior, but which are gently convergent medially along most of their length. The muscle-field bears a very narrow, sharp, well-defined myophragm dividing the muscle- field throughout most of its length. Adductor scars are not differentiated. The interior is crenulated peripherally by the impress of the costellae. EXPLANATION OF PLATE 22 Figs. 1-7. Reeftonia marwicki Allan 1947. 1-6, Reefton beds, argillite boulder from argillites up- stream from the main limestone in Lankeys Creek above junction with Stony Creek, New Zealand. USNM loc. 11731. Collected by David Ives, 1956. 7, Reefton beds, loose block about £ mile north of Highway 7, Lankeys Creek, New Zealand. USNM loc. 11002. Collected by A. J. Boucot, 1965. 1-3, Dorsal view of rubber impression, internal mould, and anterior view of rubber impression of brachial valve internal mould xl-5, USNM 147351. 4, Internal mould of pedicle valve Xl-5, USNM 147352. 5, Internal mould of brachial valve x 1 -5, USNM 147353. 6, Internal mould of pedicle valve x2, USNM 147354. 7, Internal mould of pedicle valve x 1-5, USNM 147355. Figs. 8-9. Reeftonia alpha (Gill 1949). Kilgower Member of Tabberabbera Formation, locality 22 of Talent (1963), Victoria, Australia. 8, Internal mould of pedicle valve X 1-5, Geol. Surv. Victoria 50700F. 9, Internal mould of brachial valve x2-5, Geol. Surv. Victoria 50700C. Figs. 10-19. Carinferella carinata (Hall 1843). 11-14, Chemung Gp., Bath, New York. Collected by F. Braun; Schuchert Collection. 15-19, Chemung Gp., Arkport, New York, collection of J. M. Clarke. 10-12, Replica of brachial valve cardinalia and muscle impressions x 3, internal mould of brachial valve X 2, and impression of internal mould of brachial valve x 2, YPM S-1087. 13, Internal mould of pedicle valve x2, YPM 24856. 14, Internal mould of brachial valve x 2, YPM 24857. 15-19, Dorsal, anterior, posterior, ventral, and side views X 1-25, YPM S-1088. Figs. 20, 21. Cariniferella tioga (Hall 1867). Chemung, l£ miles N. of Post Creek, Elmira quad.. New York, collection of H. S. Williams. 20, 21, Internal mould of pedicle valve x l,and rubber impression of internal mould x 1-25, USNM 145582. Palaeontology, Vol. 10 PLATE 22 JOHNSON and TALENT, Siluro-Devonian Cortezorthinae JOHNSON AND TALENT: CORTEZORTHINAE, A NEW SUBFAMILY 159 Interior of brachial valve. The sockets are widely divergent and on large shells their posterior edges are partially covered by the inner edges of the interarea. They are defined by gently curved brachiophore bases that overhang the floor of the valve. The brachiophores are widely divergent and are elongate elliptical, nearly plate-like, in cross- section. They are made slightly more convex medially by the addition of a thin pad of shell material. Brachiophore supporting plates are lacking. The notothyrial cavity is partially filled with shell material continuous with a stout, rounded to rectangular myophragm that divides the posterior half of the adductor muscle-field. The cardinal process is elongate and narrows posteriorly. The posterior adductor scars are roughly triangular and are bounded postero-laterally by more or less well-developed muscle bounding ridges that originate medial to the unsupported brachiophores. The anterior adductor scars are bounded by smoothly rounded muscle bounding ridges that curve and join medially. Anteriorly and well beyond the muscle impressions, large specimens may develop a low rod-like median septum or a mound-like group of peri- pheral septa medially that extend to the anterior commissure (PI. 21, figs. 1-3). The group of septa is low and triangular in cross-section with the middle septum the highest. This medial enlargement of the internal edge of the valves fills the gap produced by non-elongation along the carinate antero-medial part of the pedicle valve. Shell structure. The shell substance is finely punctate (endopunctate). Occurrence. The species is known from two localities in the Windmill Limestone at Coal Canyon: 10757— West flank of Coal Canyon, elev. 6320 ft., 1600' N„ 1800' W. of SE. cor. of sec. 17, T. 25 N., R. 49 E., Horses Creek Valley 15' quad., Eureka Co., Nevada. Collectors: J. G. Johnson, M. A. Murphy, and E. L. Winterer 1957; N. G. Lane and E. L. Winterer 1962; H. Masursky 1959, 1961 ; A. J. Boucot 1963. 10758 — East flank of Coal Canyon, big ledge, elev. 6320 ft., 1500' N., 1100' W. of SE. cor. of sec. 17, T. 25 N., R. 49 E., Horses Creek Valley 15' quad., Eureka Co., Nevada. Collectors: J. G. Johnson 1957, 1958; M. A. Murphy and E. L. Winterer 1957; H. Masursky 1959; N. G. Lane and E. L. Winterer 1962; A. J. Boucot 1963. Figured specimens. USNM numbers 147338-45. Comparative morphology. Protocortezorthis windmillensis and Cortezorthis maclareni are distinct, but are closely comparable in so many internal features that a structure-by- structure comparison is worth while. In the pedicle valve of both the beak is short and the interarea narrow with strong triangular teeth to which are connected thin, blade-like, anteriorly convergent, muscle bounding ridges. In this respect the species of the two genera are exceptionally close. The muscle-field of P. windmillensis is relatively slightly longer and bears a strong narrow myophragm separating the diductor tracks anteriorly. In the brachial valve both bear brachiophores of the same general outline and shape that diverge at about the same angle and define sockets that are structurally the same. In addition, both species bear a triangular notothyrial platform of about the same outline. The general layout of the adductor muscle field is very similar in the two species and the similarity is accentuated by development of straight postero-lateral bounding ridges that lie inside the bases of the brachiophores. However, the muscle-field of P. windmillensis is not elevated anteriorly and its brachial valve differs most markedly by the absence of a 160 PALAEONTOLOGY, VOLUME 10 long median septum. Protocortezorthis windmillensis is noteworthy in its possession of an incipient median septum anteriorly as well as short coplanar peripheral septa in the medial region, closely adjacent to the midline. The structure of these anterior septa appears to be fully homologous with structures in Cortezorthis. In summary, Cortezorthis maclareni exhibits close similarity in the general layout of all its internal structures, but some of these structures, such as the median septum, the peripheral septa, and the elevated dorsal adductor platform, are in contrast with the more conservatively built structures of Protocortezorthis windmillensis. The similarity, taken in conjunction with the stratigraphic and geographic positions of the two species, is taken as evidence in support of P. windmillensis as the ancestor of Cortezorthis. The discussion of comparative morphology outlined above might easily have been made between them and the genus Reeftonia (Allan 1947). All of the features found similar between P. windmillensis and C. maclareni, except the development of peripheral septa, are also present in Reeftonia. Genus reeftonia Allan 1947 Plate 22, figs. 1-9 Type species. Reeftonia marwicki Allan 1947, p. 437, pi. 63, figs. 6-9. Discussion. When erecting his new genus Allan (1947, p. 437) pointed to the absence of fulcral plates in the brachial valve and the fact that in the pedicle valve the diductor scars completely enclose the adductor impressions anteriorly as a basis for assignment of Reeftonia to the family Rhipidomellidae. Both features are indeed particularly impor- tant in a number of rhipidomellid genera, particularly members of the Rhipidomellinae, but similarity between Reeftonia marwicki and any of the more typical rhipidomellid genera finds more substance in word comparisons than in comparisons of the fossils themselves. The unequally biconvex shell, the sulcate brachial valve, and somewhat carinate pedicle valve (Allan 1947, pi. 63, figs. 6, 7) are not at all rhipidomelloid in appearance. The pedicle valve diductor impressions illustrated herein are not flabellate and resemble rhipidomellid muscle scars essentially only in the outline of the adductors (text-fig. 2). It is in the brachial valve, however, that the rhipidomellid associations are most obviously distant. The sockets, though lacking fulcral plates, are constructed very differently from those typical of rhipidomellids; and the brachiophores, cardinal process, and posterior myophragm are all different. The adductor muscle scars on the rubber impression illustrated by Allan (1947, pi. 63, fig. 9) are not at all clear. The muscle scars on specimens illustrated in the present paper, however, show an adductor field similar to Cortezorthis and particularly to Protocortezorthis as exemplified by P. windmillensis, but unlike adductor patterns developed in any of the known rhipidomellids. Specimens of Reeftonia illustrated in this paper (PI. 22, figs. 1-9) were selected to show typical Reeftonia muscle scar patterns and to demonstrate the assignment of R. alpha (Gill) to the genus by close comparison with the type, R. marwicki. These illustra- tions do not show the variation of Reeftonia which is known to exist and which has been illustrated by more than 60 figures of specimens of Reeftonia alpha by Talent (1963, pis. 24-28). The variation is striking and is particularly pertinent to the thesis of the present paper that Reeftonia was derived from Protocortezorthis. Several of the speci- mens illustrated by Talent show particularly strong resemblance to Protocortezorthis JOHNSON AND TALENT: CORTEZORTHINAE, A NEW SUBFAMILY 161 fornicatimcurvata while others, and among them those that are reproduced in the present paper as figs. 8 and 9 of Plate 22, show ‘typical’ Reeftonia musculature. A configura- tion like that of P. fornicatimcurvata is particularly well shown by specimens in figs. 14, 15, and 22 of plate 27 of Talent (1963) while the specimen in fig. 25 of the same plate is recognizable as a Reeftonia very close to the ‘typical’ pattern (text-fig. 3b). The essential difference between Protocortezorthis of the fornicatimcurvata type and Reeftonia alpha is a tendency away from elongation of the ventral muscle scar and pre- A - R. alpha D- P. fornicatimcurvata E- P wi n d mitt e nsi s F- P windmillensis text-fig. 3. Sketch drawings of some dorsal internal moulds showing style of muscle impressions and bounding ridges and their variation. sence in some specimens of Reeftonia alpha of a nearly obsolescent ventral myophragm. Tn the brachial valve, specimens of P. fornicatimcurvata do not show variation in the dorsal adductor muscle pattern to a Reeftonia type. Furthermore, in P. fornicatim- curvata, the posterior adductor muscle bounding ridges are smoothly continuous with the bases of the brachiophore supporting plates rather than disjunct as in R. alpha. Variation within the cortezorthinid pattern of dorsal cardinalia and muscle impressions is shown in text-fig. 3. From the discussion of Protocortezorthis windmillensis , earlier in this paper, it should be recalled that both points made above that distinguish Reeftonia from Protocorte- zorthis fornicatimcurvata (i.e. variability toward a Reeftonia dorsal adductor plan with discrete posterior adductor bounding ridges) also distinguish P. windmillensis from P. fornicatimcurvata. Species assigned to Reeftonia : Two species are known, Reeftonia marwicki Allan and Cariniferella alpha Gill (1949, C 44GG M 162 PALAEONTOLOGY, VOLUME 10 p. 95, pi. 3, figs. 1, 6, 7). Gill named a second species Cariniferella beta (1949, p. 96, pi. 3, figs. 2, 3, 4, 9), but Talent (1963, p. 58) has shown these to belong to a single species and has published numerous figures illustrating them under the name Isorthis alpha (1963, pis. 24-27). Talent (1963, pp. 58-60) erred in reporting ful- cral plates in Reeftonia alpha. The grooves that cross the antero-lateral edges of the moulds of the sockets shown in Talent’s figure 19, page 58 (1963), correspond to the edge of slightly elevated sockets constructed on the floor of the valve, but are not fulcral plates. The same mistake in concept (cf. Boucot, Johnson, and Walmsley 1965, p. 335) led Talent to remark that fulcral plates are shown in Allan’s figures of Reeftonia marwicki. Occurrence and Age. Reeftonia is known from the Reefton beds of New Zealand (Allan 1947) and from the Dead Bull and Kilgower Members of the Tabberabbera Formation of Victoria, Australia (Talent 1963, table 3). We consider both occurrences to be of Emsian age. Figured specimens. USNM numbers 147351-5; Geol. Surv. Victoria 50700C, 50700F. Genus cariniferella Schuchert and Cooper 1931 Plate 22, figs. 10-21 Type species. Orthis carinata Hall 1843, p. 267, text-fig. 121, nos. 1-1A. Exterior. Cariniferella is characterized by reverse convexity in the manner of Schizo- plioria , with the brachial valve more strongly convex than the pedicle valve. However, in small shells the distinction is not great. In large specimens the pedicle valve may be nearly flat. The outline is commonly broadly transverse oval, nearly subquadrate. The pedicle valve bears a well-developed narrow median carina and the brachial valve bears a corresponding narrow sulcus that is commonly deep and well marked. The flatness of the pedicle valve combined with the considerable strength of the dorsal sulcus may com- bine to make the anterior margin re-entrant medially. The exterior bears a radial ornament of fine costellae that increase in number by bifurcation and by intercalation. The inter- area of the pedicle valve is low, narrow, triangular, and catacline or may be slightly incurved at the beak. The delthyrium is broadly triangular and on larger specimens may be rounded rather than angular at its apex. The interarea of the brachial valve is ortho- cline. Interior of pedicle valve. The hinge teeth are small, broadly divergent, and triangular in cross-section. They are situated on a thickening of shell material adjoining the palin- trope and are not supported by dental lamellae. Because the teeth are so broadly diver- gent and because there are no dental lamellae the ventral muscle field lies entirely on the floor of the valve and the adjustor scars become well marked on larger specimens. The ventral musculature is short, broad, and cordate. The adductor tracks are com- monly well defined medially and may be accompanied by a moderate development of a low rectangular myophragm that divides the diductor lobes anteriorly. The diductor impressions are fairly well marked laterally where they are slightly divergent and anteriorly where they are bounded by ridges that curve all the way around toward the mid-line. In most specimens the anterior margin of the muscle scars is raised a little above the trough corresponding to the external carina. JOHNSON AND TALENT: CORTEZORTHINAE, A NEW SUBFAMILY 163 Interior of brachial valve. The brachiophores are widely divergent and blade-like and are connected directly to the floor of the valve, defining the inner sides of the sockets. The bases of the sockets lie at the floor of the valve and their posterior portions are bounded by the interarea. There is a well-developed notothyrial platform connecting with a stout myophragm that divides the posterior adductor impressions. A small, elongate, trilobed cardinal process is situated at the apex of the notothyrial platform. In small specimens the muscle scars are only faintly impressed, but in large ones the posterior adductors are broad and subtriangular and may be faintly longitudinally striate. The anterior adductors are smaller and subpyriform so that the whole muscle impression narrows anteriorly. For the most part the musculature is outlined by being impressed into the shell, but short bounding ridges define the anterior adductor scars antero-laterally and the bounding ridges converge toward the mid-line. A faint pair of muscle bounding ridges adjoins the posterior adductor scars laterally. The interior of small specimens is strongly crenulated by the costellae, but in large ones only the area anterior to the muscle impressions shows their impression. Species assigned to Cariniferella: Orthis carinata Flail 1843, p. 267. Orthis tioga Hall 1867, p. 59, pi. 8, figs. 20-29. Dalmanella elmira Williams 1908, p. 56, pi. 3, figs. 6, 8, 11, 13-17. Dalmanella Virginia Williams 1908, p. 58, pi. 4, figs. 10-16. Williams (1908, p. 59) erected a variety beta , believing it to represent the young of Dalmanella Virginia. This is probably true and is reason for revocation of beta as a separate taxon. The specimens are here included within Cariniferella Virginia. Cariniferella iowensis Stainbrook 1945, p. 16, pi. 1, figs. 29-37. Orthis dumontiana Verneuil 1850, p. 181, pi. 4, figs, la, b, c. Schuchert and Cooper (1932, p. 122, pi. 1 8, fig. 1 1) figured a Belgian specimen under the name Cariniferella dumonti, evidently a nomen nullum for C. dumontiana. The figured specimen and a number of others accompanying it in the collection were examined on loan from the Museum of Comparative Zoology, Harvard. They are labelled Orthis dumonti, Koninck collection. Occurrence and age. Cariniferella is fairly common in the Appalachians (Hall 1843; Williams 1908; Stainbrook 1942). It is present in the Independence Shale of Iowa (Stainbrook 1945) and in the Sly Gap beds in New Mexico (Stainbrook 1948). It is represented in the south of Belgium by C. dumontiana (Schuchert and Cooper 1932) and in Spain (Verneuil 1850; Comte 1938). It is probably present in Kazakhstan, Asiatic U.S.S.R., where it has been reported as Cariniferella tioga (Sarycheva 1960, pi. 14, fig. 9). All of these occurrences are of Frasnian age. Figured specimens. Y.P.M. 24856, 24857; S-1087, 1088; USNM no. 145582. COMMENTS ON CORTEZORTHINID MORPHOLOGY Strictly held definitions of brachiopod groups may prove inconsistent because of exceptions, but a summary of observed variability of the characteristic structures can be particularly apt to the definition of a group. The three Silurian to Eifelian genera of the 164 PALAEONTOLOGY, VOLUME 10 Cortezorthinae compose a particularly tight-knit group characterized by ventral diductor and dorsal adductor muscle patterns that show considerable stability across generic lines (text-fig. 4), but that are not presently known to the writers to occur outside the subfamily. In the pedicle valve of Protocortezorthis, Cortezorthis, and Reeftonia the diductor impressions are smoothly rounded in transverse section. They narrow anteriorly between thin but well-defined muscle bounding ridges that commonly can be seen to be discrete posteriorly and not continuous with the adjacent dental lamellae (text-fig. 4a, c). Of the three, Protocortezorthis differs essentially in the presence of a prominent narrow myophragm. Cortezorthis and Reeftonia have the diductors relatively a little wider but less deeply impressed, and Reeftonia commonly has the ventral adductor scars prominently marked. In the brachial valve these genera and Cariniferella have blade-like brachiophores that diverge relatively widely, but with a relatively slight ventral inclination. Between them there is a prominent myophragm, commonly rectangular in cross-section, that joins with a well-defined notothyrial platform bearing the cardinal process. In Protocortez- orthis fornicatimeurvat a the sockets are most elevated; brachiophore supporting plates support the brachiophores at the inner edges of the sockets and connect with the floor of the valve. The resultant structure is one that defines the sockets by fulcral plates. In P. windmillensis the sockets have similar structure, but the brachiophore supporting plates are absent and the sockets thus somewhat overhang the base of the valve. In the younger genera Cortezorthis, Reeftonia , and Cariniferella, the blade-like brachiophores are strongly divergent and are attached directly to the floor of the valve, defining the sockets between them and the margin of the valve. The dorsal adductor pattern is a rhomboidal one in which the posterior adductors are bounded by ridges that do not continue anteriorly around the anterior adductors. In Protocortezorthis fornicatimcur- vata these continue from the brachiophore supporting plates, but in P. windmillensis, which lacks supporting plates, the bounding ridges are separate structures and this is especially true in the younger genera — Cortezorthis, Reeftonia, and Cariniferella. Cortezorthis and Reeftonia exhibit variation in the dorsal adductor impressions, vary- ing between only partially differentiated and fully differentiated posterior adductor bounding ridges. It is notable that discrete, fully differentiated bounding ridges occur (apparently rarely) in Protocortezorthis orbicularis (Holland, Lawson, and Walmsley 1963, pi. 6, fig. 9), but understandable that they occur in that species rather than in P. fornicatimcurvata because the specimens of P. orbicularis illustrated by Walmsley (1965, see pi. 63, fig. 9; pi. 64, fig. 11) show weaker development of brachiophore supporting plates than does P. fornicatimcurvata (see PI. 21, figs. 16, 19). The subfamily Cortezorthinae differs from Isorthinae by its fixed adductors and un- faceted diductors in the pedicle valve and by the development of a distinctive pattern of dorsal adductor impressions unknown in any isorthid. COMPARISON WITH RHIPIDOMELLID AE Two genera, Reeftonia and Cariniferella, that the writers include in the subfamily Cortezorthinae exhibit features of internal morphology that invite comparison with the Rhipidomellidae. The pedicle valve of Reeftonia bears adductor scars like those developed in the subfamily Rhipidomellinae, but since the same type of scar is developed JOHNSON AND TALENT: CORTEZORTHINAE, A NEW SUBFAMILY 165 in Protocortezorthis (text-fig. 2) the feature must cross phylogenetic lines. In Cariniferella the ventral muscle pattern mimics the heterorthinid rhipidomellid genus Heterorthina (Havlicek 1950, text-fig. 10), but the stratigraphic gap is very great and to the writers’ knowledge no Devonian rhipidomellid (that might serve as an ancestor) bears a ventral muscle pattern like that of Cariniferella. text-fig. 4. Sketch drawings of some ventral internal moulds showing style of muscle impressions and bounding ridges and their variation. The brachial valves of Reeftonia and Cariniferella bear similar cardinalia with brachio- phores that define sockets without fulcral plates, and absence of fulcral plates is typical of the Rhipidomellidae. However, the evidence from the cortezorthinid lineage Proto- cortezorthis-Cortezorthis illustrates that fulcral plates are lost during the evolution of Protocortezorthis. The brachiophore and socket arrangement of Reeftonia and Carini- ferella closely duplicates that developed in Cortezorthis (PI. 19, figs. 22, 23). The brachio- phores and sockets of rhipidomellids, though similar in gross aspect, differ consistently in detail from those of Reeftonia and Cariniferella. Rhipidomellid brachiophores typically are more tusk-like or rod-like than plate-like (Boucot, Johnson, and Walmsley 1965, pi. 46, figs. 6, 7) and in most cases bear ridge-like flanges along their length (Hall and Clarke 1892, pi. 6a, fig. 10). Commonly their extremities protrude free (Boucot, Johnson, and Walmsley 1965, pi. 46, figs. 9, 10) although when connected in part to the base of the valve by brachiophore supporting plates, the two-fold nature of the structure is usually distinguishable. Moreover, it is typical of rhipidomellids that the brachiophores are closely set medially and crowd against the cardinal process which is A - P. windmill ensis C- Cortezorthis sp. E - C. cortezensis B - P fornicatimcurvata D - C ma c /are ni F - R. marwicki 166 PALAEONTOLOGY, VOLUME 10 swollen distally (Hall and Clarke 1892, pi. 6a, figs. 3, 7, 10, 15, 16, 21). This is decidedly not the pattern of cardinalia developed in Reeftonia or CarinifereJla or in any other cortezorthinid (cf. pi. 19, figs. 2, 22, 23; pi. 21, figs. 1-5, pi. 22, figs. 1, 3, 10, 12). The adductor impressions in the brachial valve of rhipidomellids are almost without exception so poorly impressed that the lateral and anterior outline of the adductors is- indiscernible on small specimens. Even on large ones, the scars typically are impressed rather than being outlined by muscle bounding ridges. The characteristic rhipidomellid adductor pattern is one in which the posterior adductors are small and triangular with the long sides of the triangles extending from the bases of the brachiophores along the postero-lateral sides of the muscle scars (Hall and Clarke 1892, pi. 6a, figs. 7, 15, 21). The posterior adductors in many forms developed in such cramped quarters that they were reduced even more by thickenings of the brachiophore supports (cf. Boucot,. Johnson, and Walmsley 1965, pi. 45, fig. 26). The anterior adductors in rhipidomellids show a little more variation in outline from subrectangular or transversely suboval to trapezoidal, but commonly are larger than the posterior adductors and are very faintly impressed. The adductor muscle pattern described above is not developed in Reeftonia or Cariniferella. Instead they bear the cortezorthinid pattern (text-fig. 3) with discrete postero-lateral adductor muscle bounding ridges and over-all rhomboidal outline. In addition to specimens of Reeftonia and Cariniferella illustrated herein (PI. 22) the reader may refer to a specimen of Cariniferella illustrated by Cooper (1944, pi. 138, fig. 36) which compares very closely with Reeftonia in all internal features. COMPARISON WITH 1SORTHIS Since Protocortezorthis fornicatimcurvata was assigned to Isorthis by Boucot ( 1 960, p. 296) and Reeftonia alpha to Isorthis by Talent (1963, p. 57) it is appropriate to examine the basis for these assignments in the light of those made in this paper. Isorthis szajnochai bears strong, anteriorly divergent dental lamellae in the pedicle valve, bounding relatively strongly impressed, faceted diductor scars which in turn are divided by an anteriorly prominent adductor platform (text-fig. 5). In Reeftonia, Cortezorthis, and Protocortezorthis the dental lamellae appear to be short, but are joined with, or are closely adjacent to, long, thin muscle bounding ridges that converge anteriorly. The diductor impressions are unfaceted and the myophragm is a narrow rounded ridge rather than an anteriorly prominent platform. The muscle bounding ridges of Protocortezorthis fornicatimcurvata appear to be continuous with the dental lamellae so it is not surprising that a broad view of Isorthis should have included them. Nevertheless, in the light of the present work, the muscle bounding ridges of Protocortezorthis , especially P. windmillensis, and of Reeftonia and Cortezorthis appear to be different structures from the dental lamel- lae of Isorthis szajnochai. The elongation of the diductor scars remains as the principal similarity in the pedicle valve between Isorthis and the cortezorthinids. In the brachial valve more similarity is evident since at least one species of Proto- cortezorthis, P. fornicatimcurvata, has fairly well-developed fulcral plates and a relatively simple quadripartite adductor muscle field defined by more or less prominent muscle bounding ridges. All of the Lower Devonian cortezorthinids have well-developed myo- phragms posteriorly that join a more or less prominent notothyrial platform. In Isorthis szajnochai this type of myophragm is not developed nor is there a prominent notothyrial JOHNSON AND TALENT: CORTEZORTHINAE, A NEW SUBFAMILY 167 platform (text-fig. 5). Instead, the postero-medial portions of the brachiophore bases of I. szajnochcii are relatively widely set apart defining a broad, deep, notothyrial cavity. The morphologic differences in the brachial valve interior appear to be minor but consistent and although some variation between the isorthid pattern and the cortez- orthinid pattern will make difficult the interpretation of some isolated specimens, the morphologic features of both valves taken together should be sufficient to avoid future re-combination of most members of the two groups. /sorfh/s szajnochai text-fig. 5. Sketch drawings of internal moulds of the type species of Isorthis. ORIGIN OF CORTEZORTHINAE Three cortezorthinid genera, Cortezorthis, Reeftonia, and Cariniferella are so distinct morphologically that association with any of the previously known dalmanellid groups on SILURIAN TO GEDINNIAN SIEGENI AN EMSI AN EIFELI AN TO GIVETI AN FR ASNIAN . PROT „ CL 1RTEZORTHH 'iRINIFERE LLA windmil tensis 1 PRO TOC OR TEZOR THIS 1 fornicatimcurvata et at REEFTONIA H — - — — 56 C/ text-fig. 6. Stratigraphic range and inferred phylogeny of the genera composing the subfamily Cortezorthinae. the basis of direct morphologic comparison is less than obvious. Nevertheless, demon- stration that Cortezorthis ancestry includes an intermediate aseptate form exemplified 168 PALAEONTOLOGY, VOLUME 10 by Protocortezorthis windmillensis and that it in turn was derived from the P . fornicatim- curvata group of the Silurian and Gedinnian allows some reasonable conclusions to be drawn regarding the origin of the new subfamily. As pointed out earlier, P. fornicatim- curvata and its relatives differ from typical Isorthis principally by the development of a distinct ventral musculature, but there are so many points of similarity between some early species such as P. orbicularis and P. slitensis shown by Walmsley that there is little reason to doubt that these early species of Protocortezorthis were derived from some Silurian species of Isorthis in the strict sense. Acknowledgements. We are very much indebted to a number of people who have donated or loaned dalmanellid specimens. Dr. A. J. Boucot of the California Institute of Technology made collections of silicified specimens of C. cortezensis and of P. windmillensis. In addition, access to Boucot ’s dalmanellid collections, including ‘ Orthis ’ fornicatimcurvata and Reeftonia marwicki proved invaluable. Dr. G. A. Cooper of the U.S. National Museum loaned specimens of Cariniferella. Dr. S. V. Cherkesova, Scien- tific Research Institute for the Geology of the Arctic, Leningrad, kindly provided the specimen from Novaya Zemlya, and Dr. R. T. Gratsianova, Institute of Geology and Geophysics, Siberian Branch Academy of Sciences, Novosibirsk, loaned specimens of Dalmanellopsis septiger from the Altai Mountains. Dr. j. W. Kerr of the Geological Survey of Canada collected Cortezorthis specimens from Bathurst Island. Dr. A. C. Lenz of the University of Western Ontario loaned specimens from the Monograptus yukonensis zone of Yukon Territory, Canada. Dr. D. J. McLaren of the Geological Survey of Canada most graciously put at our disposal his collection of excellently preserved specimens from Ellesmere Island which form the basis for the type species of Cortezorthis. Dr. Copeland MacClintock of the Peabody Museum of Natural History loaned specimens of Cariniferella carinata from the Schuchert collection. Dr. Allen Ormiston of Pan American Petroleum Corporation provided specimens of Cortezorthis from Devon Island. Professor H. B. Whittington, Harvard University, loaned specimens of Cariniferella doumontiana from the Museum of Comparative Zoology. Johnson’s work was done as a part of a project at Pasadena supported by a grant from the National Science Foundation, number GP-3743. For critical reading of the manuscript at various times we thank Dr. A. J. Boucot, Dr. A. C. Lenz, Dr. A. W. Norris, and Dr. V. G. Walmsley. APPENDIX OF DEFINITIONS Faceted and Unfaceted. Among the Siluro-Devonian dalmanellids, Isorthis, Levenea, and some species of Schizophoria bear ventral muscle scars in which the various components, particularly the submedian and lateral diductor lobes and the adductor track, lie at prominent angles to one another. In some, the separate elements are flat or nearly flat surfaces (as in many orthoids), but flatness alone is not critical to the term as used here. Unfaceted refers to ventral muscle scars in which the various components lie in the same cross-sectional arc (or pair of arcs if a median ridge-like myophragm is present). The cortezorthinids characteristically are unfaceted and this is particularly well displayed by Proto- cortezorthis and Reeftonia (pi. 21, figs. 6, 15; pi. 22, figs. 4, 6, 7, 8). Fixed Ventral Adductors. This term refers to small cordate impressions developed in some cortezor- thinids (text-fig. 2) and typical of Devonian rhipidomellids as distinguished from the track-like ventral adductor site of Isorthis (text-fig. 5) and typical of the Dalmanellidae (Williams and Wright 1963, text- figs. 5-7). Similar distinctions can be made in a number of other brachiopod groups. Peripheral radial septa. Except for incipient development in Protocortezorthis windmillensis the struc- tures are known to the writers only in Cortezorthis and consist of relatively short, plate-like lobes situated radially around the internal periphery of both valves. The distal ends of the septa terminate slightly inside the valve margin where the marginal crenulations are prominent (PI. 19, fig. 3). The height of the septa varies up to four or five times as high as thick and they generally appear first and attain greatest height in the mid-regions (PI. 19, fig. 2). JOHNSON AND TALENT: CORTEZORTHINAE, A NEW SUBFAMILY 169 REFERENCES barrois, ch., pruvost, p., and dubois, g. 1922. Description de la faune Siluro-Devonienne de Lievin (Brachiopodes). Mem. Soc. geol. du Non/ 6 (2), 71-225, pis. 10-17. biernat, g. 1959. Middle Devonian Orthoidea of the Holy Cross Mountains and their ontogeny. Palaeont. Pol. 10, 1-78, 12 pis. boucot, a. j. 1960. Lower Gedinnian brachiopods of Belgium. Louvain Inst. geol. Mem. 21 , 283-324, 3 tables, pis. 9-18. gauri, k. l., and Johnson, j. g. 1966. New subfamily Proschizophoriinae of dalmanellid brachio- pods. Palaont. Zt. 40, 155-72, pis. 12-15. gill, e. d., Johnson, J. g., lenz, a. c., and talent, J. a. 1966. Skeniclioides and Leptaenisca in the Lower Devonian of Australia (Victoria, Tasmania) and New Zealand, with notes on other Devonian occurrences of Skenidioides. Proe. Roy. Soc. Victoria, 79, 363-9, pi. 40. Johnson, J. g., and walmsley, v. g. 1965. Revision of the Rhipidomellidae ( Brachiopoda) and the affinities of Mendacella and Dalejina. J. Paleont. 39, 331-40, pis. 45, 46. MARTINSSON, ANDERS, THORSTEINSSON, R., WALLISER, O. H., WHITTINGTON, H. B., and YOCHELSON, E. 1960. A late Silurian fauna from the Sutherland River Formation, Devon Island, Canadian Arctic Archipelago. Bull. geol. Surv. Can. 65, 1-51, pis. 1-10. comte, p. 1938. Brachiopodes devoniens des gisements de Ferrones (Asturies) et de Sabero (Leon). Ann. Paleont. 27, 39-88, pis. 5-8. cooper, g. a. 1944. Phylum Brachiopoda, in shimer, h. w. and shrock, r. r., Index fossils of North America. 277-365, pis. 105-43, John Wiley and Sons, Inc., New York. 1955. New Genera of Middle Paleozoic Brachiopods. J. Paleont. 29, 45-63, pis. 11-14. dahmer, G. 1942. Die Fauna der ‘Gedinne’-Schichten von Weismes in der Nordwest-Eifel (mit AusschluB der Anthozoen und Trilobiten). Senckenbergiana, 25 (1/3), 111-56. 1951. Die Fauna der nach-Ordovizischen Glieder der Verse-Schichten mit AusschluB der Trilo- biten, Crinoiden, und Anthozoen. Palaeontographica, Abt. A 101, 1-152, 12 pis. FORTIER, Y. O., BLACKADAR, R. G., GLENISTER, B. F., GREINER, H. R., MCLAREN, D. J., MCMILLAN, N. J., NORRIS, A. W., ROOTS, E. F., SOUTHER, J. G., THORSTEINSSON, R., and TOZER, E. T. 1963. Geology of the north-central part of the Arctic Archipelago, Northwest Territories (Operation Franklin). Mem. geol. Surv. Canada, 320, 1-671, illus. fuchs, a. 1919. Beitrag zur Kenntnis der Devonfauna der Verse- und der Hobracker Schichten des sauerlandischen Faciesgebietes. Preufi. Geol. Landesanst. 31 (1), 58-95, pis. 5-9. gill, e. d. 1949. Devonian fossils from Sandy’s Creek, Gippsland, Victoria. Mem. Victoria Nat. Mus. 16, 91-115, pis. 2, 3. gilluly, J., and masursky, h. 1965. Geology of the Cortez quadrangle, Nevada. Bull. U.S. Geol. Surv. 1175, 1-117, 3 pis. hall, j., 1843. Geology of New York. Part IV. Comprising the survey of the 4th geological district. Natural History of New York, 1-683, pis. 1-19. 1867. Natural History of New York, containing descriptions and figures of the fossil Brachio- poda of the Upper Helderberg, Hamilton, Portage and Chemung groups. Palaeontology of New York 4(1), 1-428, pis. 1-63. and clarke, J. m. 1892. An introduction to the study of the genera of Palaeozoic Brachiopoda. Ibid. 8(1), 1-367, pis. 1-20. havlicek, v. 1950. Ramenonozci ceskeho Ordoviku. Rozpravy TJstred. TJstavu geol. 13, 1-135, 13 pis. 1953. O nekolika novych ramenonozcich ceskeho a moravskeho stredniho devonu. Czecho- slovakia, TJstred. TJstavu geol., Vestnlk, 28, 4-9, pis. 1, 2. Holland, c. h., lawson, J. d., and walmsley, v. g. 1963. The Silurian rocks of the Ludlow district, Shropshire. Bull. Brit. Mus. (Nat. Hist.), Geol. 8, 93-171, 7 pis. house, m. r. 1962. Observations on the ammonoid succession of the North American Devonian. J. Paleont. 36, 247-84, pis. 43-48. imbrie, j. 1959. Brachiopods of the Traverse Group (Devonian) of Michigan: Part 1. Bull. Am. Mus. Nat. Hist. 116, 345-410, pis. 48-67. Johnson, j. g. 1962. Brachiopod faunas of the Nevada Formation (Devonian) in central Nevada. J. Paleont. 36, 165-9. 170 PALAEONTOLOGY, VOLUME 10 Johnson, j. g. 1965. Lower Devonian stratigraphy and correlation, northern Simpson Park Range, Nevada. Bull. Canadian Petrol, geol. 13, 365-81. 1966. Middle Devonian brachiopods from the Roberts Mountains, central Nevada. Palaeonto- logy, 9, 152-81, pis. 23-27. and talent, J. A. Muriferella, a new genus of Lower Devonian septate dalmanellid. Proc. Roy. Soc. Victoria (in press). khalfin, L. l. 1948. Fauna i stratigrafiya devonskikh otlozhenii Gornogo Altaya. Izvestiya Tom- skogo ordena Trudovogo Krasnogo Znameni Politek. Inst, imeni S. M. Kirova 65, (1), 1-464, 36 pis. kozlowski, r. 1929. Brachiopodes gothlandiens de la Podolie polonaise. Palaeont. Polonica, 1, 1-254, 12 pis. paeckelmann, w. and sieverts, h. 1932. Neue Beitrage zur Kenntnis der Geologie, Palaeontologie und Petrographie der Umgegend von Konstantinopel; 1. Obersilurische und devonische Faunen der Prinzeninseln, Bithyniens und Thraziens. Abh. Preufi. Geol. Landes, n.f. 142, 1-79, pis. 1-4. pedder, a. e. h. 1959. Monelasmina besti, a new schizophoriid brachiopod from the Upper Devonian of western Canada. Geol. Mag. 96, 470-2, pi. 16. sarycheva,t.g., ed. 1960. Osnovi paleontologii, mshanki, brakhiopodi, Moscow 1-343, pis. 1-7, 1-75. schuchert, c. 1913. Class Brachiopoda in Zittel’s Textbook of Paleontology, 1, 355-420. and cooper, g. a. 1931. Synopsis of the brachiopod genera of the suborders Orthoidea and Pentameroidea with notes on the Telotremata. Am. Jour. Sci., 5th ser. 22, 241-51. 1932. Brachiopod genera of the suborders Orthoidea and Pentameroidea. Mem. Peabody Mus. 4, 1-270, 29 pis. and levene, c. m. 1929. Fossilium Catalogus 1: Animalia, Pars 42: Brachiopoda. 1-140. sowerby, j. de c. 1839. On the fossil shells of the Silurian Rocks, in murchison, r. i.. The Silurian System, 2, 608-722, pis. 1-27, London. stainbrook, M. A. 1942. The Brachiopoda of the High Point Sandstone of New York. Am.J. Sci. 240, 879-90, pis. 1, 2. 1945. Brachiopoda of the Independence Shale of Iowa. Mem. geol. Soc. Am. 14, 1-74, pis. 1-6. • 1948. Age and correlation of the Devonian Sly Gap beds near Alamogordo, New Mexico. Am. J. Sci. 246, 765-90, pis. 1, 2. talent, J. a. 1963. The Devonian of the Mitchell and Wentworth Rivers. Mem. Victoria geol. Surv. 24, 1-118, 78 pis. tscherkessowa, s. w. 1960. Stratigraphie des Obersilurs und Devons des westlichen Sektors der Sow- jetischen Arktis. Prager Arbeitstagung iiber die Stratigraphie des Silurs und des Devons, 175-85. verneuil, m. de. 1850. Note sur les fossiles devoniens du district de Sabero (Leon). Bull. Soc. geol. France (2^me ser.), 7, 155-86, pis. 3, 4. walmsley, v. G. 1965. Isorthis and Salopina (Brachiopoda) in the Ludlovian of the Welsh Borderland. Palaeontology 8, 454-77, pis. 61-65. weller, s. 1903. The Paleozoic faunas. New Jersey Geol. Surv. Kept, on Paleontology, 3, 1-462, 53 pis. williams, A. and wright, a. d. 1963. The classification of the ‘ Orthis testudinaria Dalman’ group of brachiopods. J. Paleont. 37, 1-32, pis. 1, 2. williams, h. s. 1908. The dalmanellas of the Chemung Formation, and a closely related new brachio- pod genus Thiemella. Proc. U.S. Nat. Mus. 34 (1596), 36-64, pis. 2-4. wright, a. d. 1965. Superfamily Enteletacea Waagen, 1884, in moore, r. c., ed., Treatise on Inverte- brate Paleontology, Part H, Brachiopoda. H328-346, Lawrence, Kansas. J. G. JOHNSON Division of Geological Sciences, California Institute of Technology, Pasadena, California, U.S.A. JOHN A. TALENT Geological Survey of Victoria, Melbourne, Victoria, Australia Manuscript received 23 December 1965 THE PALAEONTOLOGICAL ASSOCIATION COUNCIL 1967-8 President Professor T. S. Westoll, The University, Newcastle upon Tyne Vice-Presidents Dr. W. S. McKerrow, University Museum, Oxford Professor F. H. T. Rhodes, University College, Swansea Professor C. H. Holland, Trinity College, Dublin Treasurer Dr. C. Downie, Department of Geology, The University, Mappin Street, Sheffield, 1 Secretary Dr. J. M. Hancock, Department of Geology, King’s College, Strand, London, W.C. 2 Editors Mr. N. F. Hughes, Sedgwick Museum, Cambridge Dr. Gwyn Thomas, Department of Geology, Imperial College of Science, London, S.W. 7 Dr. I. Strachan, Department of Geology, The University, Birmingham, 15 Professor M. R. House, The University, Kingston upon Hull, Yorkshire Dr. R. Goldring, Department of Geology, The University, Reading Other members of Council Mr. M. A. Calver, Geological Survey Office, Leeds Dr. C. B. Cox, King’s College, London Mr. D. Curry, Northwood, Middlesex Miss Grace Dunlop, Bedford College, London Mr. G. F. Elliott, Barnet, Herts. Dr. T. D. Ford, The University, Leicester Dr. A. Hallam, Grant Institute of Geology, Edinburgh Dr. R. P. S. Jefferies, British Museum (Natural History), London Dr. G. A. L. Johnson, The University, Durham City Dr. W. D. I. Rolfe, Hunterian Museum, Glasgow Dr. A. H. Smout, British Petroleum Company, Sunbury-on-Thames Dr. L. B. H. Tarlo, The University, Reading Professor H. B. Whittington, Sedgwick Museum, Cambridge Overseas Representatives Australia: Professor Dorothy Hill, Department of Geology, University of Queensland, Brisbane Canada : Dr. D. J. McLaren, Geological Survey of Canada, Department of Mines and Technical Surveys, Ottawa India: Professor M. R. Sahni, 98 The Mall, Lucknow (U.P.), India New Zealand: Dr. C. A. Fleming, New Zealand Geological Survey, P.O. Box 368, Lower Hutt West Indies and Central America: Mr. John B. Saunders, Geological Laboratory, Texaco Trinidad, Inc., Pointe-i-Pierre, Trinidad, West Indies Western U.S.A. : Professor J. Wyatt Durham, Department of Paleontology, University of California , Berkeley 4, Calif. PALAEONTOLOGY VOLUME 10 * PART 1 CONTENTS Lower Carboniferous spores from North-west England. By m. a. butter- worth and e. spinner 1 The interpretation of size-frequency distributions in molluscan death assem- blages. By A. HALLAM 25 On the structure and phylogenetic relationships of the fern Radstockia Kidston. By t. N. TAYLOR 43 New trilobites from the Tremadoc Series of Shopshire. By r. Hutchison and J. K. INGHAM 47 Variation and ontogeny of some Oxford Clay ammonites: Distichoceras bicostatum (Stahl) and Horioceras baugieri (d’Orbigny), from England. By D. F. B. PALFRAMAN 60 Fossil microplankton in deep-sea cores from the Caribbean Sea. By d. wall 95 Conodonts of the genus Apatognathus Branson and Mehl from the Yoredale Series of the North of England. By w. j. varker 124 Cortezorthinae, a new subfamily of Siluro-Devonian dalmanellid brachiopods. By j. G. Johnson and j. a. talent 142 PRINTED IN GREAT BRITAIN AT THE UNIVERSITY PRESS, OXFORD BY VIVIAN RIDLER, PRINTER TO THE UNIVERSITY VOLUME 10 • PART 2 Palaeontology JUNE 1967 PUBLISHED BY THE PALAEONTOLOGICAL ASSOCIATION LONDON Price £3 THE PALAEONTOLOGICAL ASSOCIATION The Association was founded in 1957 to further the study of palaeontology. It holds meetings and demonstrations, and publishes the quarterly journal Palaeontology. 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SPECIAL PAPER NUMBER ONE FOR I967 and SPECIAL PAPER NUMBER TWO for 1968 are announced overleaf. Other titles will be advertised as soon as they are available. Members of the Palaeontological Association may order the new series singly or by subscription through the Treasurer at the rates given below. Order forms are overleaf. Ordinary and Student Members may subscribe to the series by payment in advance at £3 (U.S. $9.00) per annum or order one copy of Special Paper Number One (for 1967) at £3 (U.S. $9.00). Institutional Members may subscribe to the series by payment in advance at the rate of £6 (U.S. $18.00) per annum or order copies of Special Paper Number One (for 1967) at £6 (U.S. $18.00) per copy. Price to Non-Members. Special Paper Number One is priced at £8 (U.S. $24.00) through B. H. Blackwell Ltd., Broad Street, Oxford, England. The price of later parts will be announced before publication. SPECIAL PAPER NUMBER 1 FOR THE YEAR 1967 Miospores in the coal seams of the Carboniferous of Great Britain A. H. V. SMITH and M. A. BUTTERWORTH National Coal Board, United Kingdom Publication in April 1967 A comprehensive account of the miospore content of all British Carboniferous coal- seams in all the coalfields from Scotland to Kent and South Wales. Eleven successive strati- graphically distinct miospore assemblages are defined and used throughout. The taxonomic information is based on comparisons with material from all relevant areas of Europe and North America, and on the very extensive collecting done for the National Coal Board. The data are presented on 72 clear diagrams and sections, and the spores are illustrated fully on 27 collotype plates. The authors also give full account of their sampling, preparation, and counting procedures. The monograph, by two internationally known British palynologists, is a well-organized critical work which will be most valuable to all Carboniferous stratigraphers, and to all palynologists as the most thorough account of any important area yet published. Price to non-members £8 (U.S. 24 dollars). SPECIAL PAPER NUMBER 2 FOR THE YEAR 1968 Evolution of shell structure in articulate brachiopods ALWYN WILLIAMS University of Belfast, Northern Ireland Publication early in 1968 Electron microscope studies of the skeletal fabric of representative living and extinct articulate brachiopods show that the triple-layering into proteinous periostracum and calcareous primary and secondary shell developed in living rhynchopellides and terebra- talides has always been the characteristic of the articulate shell and may be regarded as the ancestral arrangement. Deviation from this pattern occurred in some groups including the suppression of the secondary calcareous shell layer in the thecideidines and dictyonellidines, the growth of a third calcareous layer among certain spiriferides, and the substitution of a laminar fabric for the orthodox calcareous layers in certain orthides and strophomenides. This work will also be well illustrated with many text-figures and 24 collotype plates. SUBSCRIPTION AND ORDER FORM Institutional Members of the Palaeontological Association Only tick as appropriate A I I Please register this Institution as a subscriber to Special Papers in Palaeonto- — logy at an annual subscription of £6 (U.S. $18.00). Subscriptions should be paid in advance. B I I Please send copies of Special Paper Number One. Price £6 ' ' (U.S. $18.00) per copy. Please send to and invoice to This form should be returned to the Treasurer of the Palaeontological Association Dr. C. Downie Geology Department University of Sheffield Mappin Street Sheffield 1 England. Note. Non-members should order through B. H. Blackwell Ltd., Broad Street, Oxford, England. Special Paper Number One is available to non-members from Blackwells at £8 (U.S. $24.00) per copy. SUBSCRIPTION AND ORDER FORM Ordinary and Student Members of the Palaeontological Association Only tick as appropriate A [ I Please register me as a subscribing member for the Special Paper Series at £3 ' ' (U.S. $9.00) per annum. I enclose £3 (U.S. $9.00) for Number One for 1967. Subscriptions should be paid in advance. B I | Please send me one copy of Special Paper Number One. I enclose £3 (U.S. 1 — 1 $9.00). Name Address Members should return this form together with their remittance directly to the Treasurer of the Palaeontological Association Dr. C. Downie Geology Department University of Sheffield Mappin Street Sheffield 1 England. Cheques, money orders, etc. should be made payable to ‘The Palaeontological Association’. Orders received without remittance cannot be considered. Orders should be placed through the Treasurer but the Special Paper will be distributed directly to members from Oxford University Press. NEW EVIDENCE FOR THE AGE OF THE PRIMITI VE ECHINOI D MYR1ASTICHES GIGAS by t. r. lister and c. downie Abstract. An examination has been made of the acritarchs, chitinozoa, and spores recovered from the matrix of the primitive echinoid Myriastiches gigas. The results strongly support a Silurian age for the fossd and indicate a Lower Ludlovian horizon. The holotype (and only known specimen) of Myriastiches gigas Sollas 1899 is preserved as an internal mould flattened on a slab of indurated grey calcareous mudstone. This was said by Sollas to have a Lower Ludlow age. However, no evidence for this age was given by him and unfortunately the locality of the specimen was not stated and is un- known. Lake was said (in Durham and Melville 1957) to have considered the raphio- phorid trilobites associated with the echinoid to be Middle Ordovician (Llandeilian) and Mortenson (1935, p. 56, 1940, p. 349), accepting this age, regarded Myriastiches as the earliest known echinoid, preceding both Bothriocidaris (Upper Ordovician, approxi- mately Caradocian) and Aulechinus (Ashgillian). Nevertheless, in the opinions of both Stubblefield and Whittington (quoted in Durham and Melville 1957), the raphiophorids compare most closely with Silurian members of the family. Whittington considered that the resemblance to Raphiophorus raoulti (Barrande) from the Bohemian Wenlock, and to two British Wenlock forms, was striking and concluded that ‘the probability of the raphiphorid associated with Myriastriches being of Silurian age is strong’. A fragment of graptoloid stipe, also associated with the echinoid, was considered by Bulman (in Durham and Melville 1957) to be indeterminable, but possibly a mono- graptid or a dichograptid. If the latter, then it most closely resembled a rare species from the Llanvirnian, which, as Durham and Melville pointed out, would conflict with the trilobite evidence even if this indicated an Ordovician age. Melville suggested that it might be possible to settle the question of the age of Myriastiches using microfossils and consequently the specimen was sent to the authors for treatment. Preparation. A small piece weighing approximately 10 gm., was sawn off the base of the slab bearing the holotype. This was cleaned, then dissolved in HC1 and HF respectively. The resulting residue was treated with heavy liquid (ZnBr2) to float oft' the organic microfossils and the final concentrate was mounted in Canada Balsam on glass slides. All the slides are deposited in the Micropalaeontology Laboratory, Department of Geology, University of Sheffield. NATURE OF ASSEMBLAGE The method of concentration proved extremely effective and a rich assemblage of microfossils was obtained, consisting dominantly of acritarchs with associated chitinozoa, [Palaeontology, Vol. 10, Part 2, 1967, pp. 171-4, pi. 23.] C 4471 N 172 PALAEONTOLOGY, VOLUME 10 scolecodonts and spores, and some graptolite fragments. The 10 gm. of original sample yielded approximately 70,000 acritarchs and 100 chitinozoa, a figure similar to that found by Downie (1963) in a sample of Wenlock Shale. Preservation of the material in general, was only fairly good. Both the acritarchs and chitinozoa were to a considerable degree carbonized. The chitinozoa were usually com- pressed, somewhat corroded, and frequently split by rock cleavage. Spines were usually broken, particularly those of the longer-spined acritarchs and the basal appendices of certain chitinozoa genera. Such imperfections hampered specific diagnosis of many specimens but enough complete individuals were recovered to surmount this difficulty. The fossils identified are listed together with their known ranges in Table 1. Comparison. In the assemblage there are 26 species of acritarchs belonging to ten genera. These vary in importance, the principal component of the assemblage being Micrhystri- dium, particularly forms close to M. parinconspicuum, which forms approximately 35 per cent, of the assemblage. Forms belonging to the Baltisphaeridium wenlockensis-B. echino- dermum form group are common, as is B. granulatispinosum. Other species and the genera Veryhachium, Leiofusa, Pterospennopsis, Polyedrixium , Helios, and Lophosphaeridium are present in minor amount. Sphaeromorph acritarchs form about 60 per cent, of the assemblage. The assemblage has little in common with those described from the Llandovery Series. Only seven of the 26 species encountered are present in the Formigosa Formation (Llandovery), described by Cramer (1964) from North Spain, and all of these seven forms, in fact, range up into the San Pedro Formation (Ludlovian). Stockmans and Williere (1963) have described the acritarchs from the Upper Llandovery of Belgium, but only seven of the 38 species they record were present in the Myriastiches assemblage, and all of these are long-ranging forms. None of the species described from the Llandovery of Gotland by Eisenack (1954) were seen. When compared with the Wenlock assemblages closer similarities are apparent. Of the three successive Assemblage Types described by Downie (1963), the highest. Assemblage Type 3 from the Tickwood Beds, shows the closest resemblance to the Myriastiches assemblage, particularly in the high proportion of Micrhystridium and Baltisphaeridium granulatispinosum. Twelve species were common to both assemblages, EXPLANATION OF PLATE 23 Fig. 1. Conochitina cf. claviformis, 1278/C/l, x200. Fig. 2. Ancyrochitina ancyrea (polar view), 1278/D/l, X 1000. Fig. 3. Baltisphaeridiinn wenlockensis (Downie) Stockmans and Williere, 1278/T/5, X 1000. Fig. 4. Sphaerochitina sphaerocephala Eisenack, 1278/0/1, x200. Fig. 5. Ancyrochitina primitiva Eisenack, 1278/L/l, X200. Fig. 6. Leiofusa filifera Downie, 1278/T/8, X 1000. Fig. 7. Baltisphaeridium ramusculosum Deflandre, 1278/E/2, x 1000. Fig. 8. Rhabdochitina magna Eisenack, 1278/D/l, X 200. Fig. 9. Leiosphaeridia wenlockia Downie, 1278/J/2, X 1000. Fig. 10. Veryhachium wenlockium Downie, 1278/Q/2, X 1000. Fig. 11. Pterospennopsis cf. onondagaensis Deunff, 1278/S/4, X 1000. Fig. 12. Baltisphaeridiinn granulatispinosum Downie, 1278/S/2, X750. Fig. 13. Punctatisporites ? dilutus Hoffmeister, 1278/P/l, X 1000. Fig. 14. Scolecouont, 1278/K/l, X 1000. Palaeontology, Vol. 10 PLATE 23 LISTER and DOWNIE, Silurian microfossils LISTER AND DOWNIE: NEW EVIDENCE FOR MYRIASTICHES GIGAS 173 table 1. Range chart showing the known stratigraphic distribution of acritarch and chitinozoa species identified from the Myriastiches assemblage: where necessary ranges have been extended to include unpublished work of one of the authors (T. R. L.). Silurian Wentock £ .§ 3: 5 -§ £ £ 5 s J3 S 6 "-I •~4 Q Michrystridium stellatum X X X X X M. parinconspicuum X X X X X M. nannacanthum X X X X M. imitation X X X M. shinetonense X X X X Baltisphaeridium wenlockensis X X X X B. granulatispinosum X X X X X B. cariniosum X B. ramuscutosum X X X X B. microcladum X X X B. nanum X X X X B. arbusculiferum X X X B. longispinosum var. parvum X X X B. robustispinosum X X X Veryhachium formosum X X X V. rhomboideum X X X X V. rabiosum X X V. trispinosum X X X X X V. wenlockium X X X X X Leiofusa filifera X X X X Leiosphaeridia wentockia X X X X Helios aranaides X X Lophosphaeridium granulosum X X X X Pterospermopsis cf. onondagaensis X X Cymatiosphaera wentockia X X X Polyedrixium cf. pharaonis X Conochitina filifera X X C. lagenomorpha X X X X X X C. tuba X X X C. intermedia X X X X C. cf. claviformis X X X X X X Ancyrochitina ancyrea X X X X X A. primitiva X X X X Sphaerochitina sphaerocephala X X X X X S. pistilliformis Rhabdochitina magna X X X Punctatisporites ?dilutus X X X X Total (species) 3 15 26 30 35 22 including the species Baltisphaeridium arbusculiferum and the genus Polyedrixium neither of which were recorded from lower horizons. Of the many forms described by Cramer (1964) from the San Pedro Formation (Ludlovian), only nine species are present in the Myriastiches assemblage. Flowever, two of these species, Helios aranaides and Baltisphaeridium cariniosum make their first 174 PALAEONTOLOGY, VOLUME 10 appearance at this horizon, whilst Veryhachium rabiosum was recorded only from the Devonian. Moreover, both Helios aranaides and Veryhachium rabiosum first appear in the Lower Ludlow (Eltonian) of Shropshire, currently being investigated by one of the authors (T. R. L.), and in fact it is with these Eltonian assemblages that the closest comparison with the Myriastiches assemblage is to be found. Indeed, all twenty-six species present in the Myriastiches assemblage are found in the Lower Elton Beds, including not only the two species mentioned above, but also a form, here called Polyedrixium cf. pharaonis, which so far has only been recorded from the Lower Elton Beds of Shropshire. The spores all belong to Punctatisporites ? dilutus Hoffmeister, known from the Llandovery, Wenlock, and Ludlow. None of the distinctive spores characteristic of the Upper Ludlow Whitcliffe Beds (Lister, unpublished), nor any Devonian species were seen, so that a Lower, rather than an Upper Ludlow age is indicated. Of the ten species of chitinozoa identified, seven were long-ranging forms, but one species, Sphaerochitina pistil/iformis , has only been recorded from the Ludlow Series (Eisenack 1955), and Conochitina tuba and C. filifera make their first appearance in the Upper Silurian. Without doubt, therefore, Myriastiches is of Silurian age and very likely Lower Ludlow as originally stated by Sollas. Acknowledgement. The authors thank Dr. H. P. Powell (Assistant Curator, University Museum, Oxford) for making available the specimen of Myriastiches. REFERENCES cramer, f. h. 1964. Microplankton from three Palaeozoic formations in the Province of Leon (N.W. Spain). Thesis, Leiden, 255-361. downie, c. 1963. ‘Hystrichospheres’ (acritarchs) and spores of the Wenlock Shales (Silurian), of Wenlock, England. Palaeontology, 6, 625-52. Durham, J. w. and melville, r. v. 1957. Classification of Echinoids. J. Paleont. 31, 242-72. eisenack, a. 1954. Hystrichospharen aus dem baltischen Gotlandium. Senckenbergiana, 34, 205-11. 1955. Chitinozoen, Hystrichospharen und andere Mikrofossilien aus dem Beyrichia-Kalk. Ibid. 36, 157-88. mortenson, T., 1935. A monograph of the Echinoidea: Vol. 2, Bothriocidaroida, Melonechinoida, Lepidocentroida and Stirodonta, pp. 1-647. Reitzel, Copenhagen and Milford, Oxford, New York. ■ 1940. A monograph of the Echinoidea. Vol. 3, 1 Aulodonta with additions to Vol. 2 ( Lepidocentroida and Stirodonta), pp. 1-370. Ibid. sollas, w. j. 1899. Fossils in the University Museum, Oxford: I. On Silurian Echinoida and Ophiur- oidea. Q. J! geoL Soc. Load. 55, 692-715. stockmans, f. and williere, y. 1963. Les Hystrichospheres ou rnieux les Acritarches du Silurien beige. Sondage de la Brasserie Lust a Courtrai ( ICortrijk). Bull. Soc. beige Geol. Paleont. Hydro/. 71 , 450-8 1 . T. R. LISTER C. DOWNIE Department of Geology The University, Sheffield 1 Manuscript received 7 April 1966 A REVISION OF ACASTELLA SPINOSA (SALTER 1864) WITH NOTES ON RELATED TRILO BITES by J. H. SHERGOLD Abstract. Acaslella spinosa (Salter 1864) and Acastella? minor (M'Coy 1851) are redescribed and figured. The synonymy of A. spinosa and A. macrocentrus (Reed 1925) is established. A. spinosa is closely compared to other species attributed to the genus. A. prima Tomczykowa 1962 is recorded for the first time from the late Silurian of the British Isles. Although known for over a hundred years, no complete description from undistorted material of Acastella spinosa (Salter 1864), the type-species, has yet been published. The genus, which ranges across the Siluro-Devonian boundary, has recently become the subject of a good deal of attention from overseas workers who have, in the past eleven years, described or redescribed seven species and five subspecies. The present paper is an attempt to clarify the characteristics of the type-species, thus allowing its relationships with the newer species to be established, a study which has been accomplished with reference both to existing types and to material recently collected. Specimens collected in the 1870s by the Geological Survey while mapping the area around Kendal, Westmorland, and recorded by Aveline et al. (1872, p. 14) as Phacops downingiae (Murchison) are redetermined as Acastella prima Tomczykowa, this being the first record of the species from the British Isles. Acastella? minor (M'Coy 1851) has not been further described since the time of M'Coy. The species has not previously been figured. The material used is located largely in the Geological Survey Museum, GSM. Other repositories are the British Museum (Natural History), BM(NH); the Sedgwick Museum, Cambridge, SM; and the Liverpool City Museum, LCM. The symbols used in the quoted proportions throughout the text are those of Struve (1958, pp. 167-8) and are defined as follows: A, eye length (exsag.); H, the distance from the back of the eye to the posterior border furrow of the cephalon; G, glabellar length (sag.); Gn, glabellar length (sag.) plus the sagittal dimension of the occipital ring; A/G, the large eye index; A/Gn, the small eye index. In the notation used here for reference to the glabellar lobes and furrows, IL, 2L, and 3L are equivalent to the preoccipital, median lateral, and anterior lateral glabellar lobes; IS, 2S, and 3S are the corresponding furrows. Acknowledgements. I am indebted to Dr. J. Shirley for his interest in this work and for his critical reading of the manuscript; Professor T. S. Westoll for providing facilities and D.S.I.R. for the finance which enabled this study to be completed ; Dr. W. T. Dean (British Museum), Mr. D. E. White (Geological Survey Museum), Mr. A. G. Brighton (Sedgwick Museum), and Mr. G. R. Tresise (Liverpool City Museum) for their help and for allowing me to borrow specimens under their care; and Dr. Jerzy Winnicki-Radziewicz for translating the Polish description. Acastella spinosa was originally described as Phacops ( Acaste ) downingiae, var. S, spinosus by Salter (1864, p. 27, text-fig. 7). The variety was based on internal moulds of a distorted cephalon (GSM 19412) and an incomplete pygidium (GSM 19414) which [Palaeontology, Vol. 10, Part 2, 1967, pp. 175-188, pis. 24-25.] 176 PALAEONTOLOGY, VOLUME 10 Salter considered may have been associated with the cephalon. The description was illustrated by a woodcut restoration of the cephalon. Barrois, Pruvost, and Dubois (1922) elevated Salter’s variety to specific status, refer- ring specimens previously identified as Dalmanites heberti Gossellet 1888 to Acaste spinosa (Salter). In 1925 Reed introduced Acastella as a subgenus of Phacops and described a new species, A . macrocentrus, based on an incomplete pygidium from the Upper Ludlovian of Prior’s Frome, Herefordshire. He nominated (1925, p. 75) ‘ Acaste ’ spinosa Salter as the type-species and gave a sub-generic diagnosis compounded from this species and from Acastella macrocentrus. In 1927 Reed contradicted his earlier (1925) statements, quoting as the type-species Phacops ( Acastella ) macrocentrus and giving the horizon as Wenlock Limestone (1927, p. 319). A. macrocentrus (Reed 1925) is shown below to be synonymous with A. spinosa (Salter 1864). Acastella was subsequently classified as a genus by Delo (1935), no type-species being quoted, and as a subgenus of Acaste Goldfuss by R. and E. Richter (1952 and 1954). In their earlier paper (1952, p. 89) the Richters formally selected the species spinosa (Salter 1864) as the type-species of the subgenus and indicated the confusion caused by Reed (1927). In their later paper (1954, pp. 27-28) R. and E. Richter discussed and refigured (pi. 4, figs. 57—58) the holotype cephalon and the pygidium known to Salter. They also described and figured (p. 27, pi. 4, fig. 59) a second cephalon (GSM 19413) from the type locality, while a third, an incomplete cephalon (BM(NH) I 1397) from the Usk Inlier, Monmouthshire, was referred to Acaste ( Acastella ?) sp. (op. cit., p. 28, pi. 4, fig. 60). The latter specimen was mistakenly recorded (p. 70) as from the collections of the Geo- logical Survey Museum. The Richters clarified the synonymy of the species listing the many mistaken references to Acaste spinosa which had become incorporated into the European literature since 1864. Their observations were confined to the poorly preserved material at their disposal so that a complete diagnosis and description of the species was not undertaken. Accordingly, Billet ( 1959), in redescribing Acastella rouaulti (de Tromelin and Lebesconte 1875), Tomczykowa (1962u), in describing A. prima , and Hollard (1963) in describing A. patula , A. granulosa , and A. jacquemonti were not able to make adequate comparisons with the type-species. At the present time, full generic status is again attributed to Acastella by Struve (in Moore 1959), who includes the genus in the subfamily Acastavinae Struve 1958 (Dalmanitidae). A. prima was described by Tomczykowa in 1962. Specimens collected and identified by Aveline et al. (1872) are shown to belong to this species. Acastella? minor was originally described by M‘Coy (1851, p. 161) as Odontocliile caudata ( Brongniart), var. minor. The generic classification of the species remains doubt- ful and is discussed under the section dealing with this trilobite below. SYSTEMATIC DESCRIPTIONS Family dalmanitidae Vogdes 1890 Subfamily acastavinae Struve 1958 Genus acastella Reed 1925 Acastella spinosa (Salter 1864) Plate 24, figs. 1-8, Plate 25, figs. 6-12 J. H. SHERGOLD: A REVISION OF ACASTELLA SP1NOSA (SALTER 1864) 177 1864 Phacops ( Acaste ) Downingiae Murch., var. 8, spinosus Salter, p. 27, text-fig. 7 (woodcut), (GSM 19412). 1925 Phacops ( Acastella ) macrocentrus Reed, pp. 73-75, pi. 11, figs. 4, 4a, (SM A 16539). 1954 Acaste ( Acastella ) spinosa (Salter 1864); R. and E. Richter, pp. 27-28, pi. 4, figs. 57 (GSM 19412), 58 (GSM 19414), 59 (GSM 19413). 1954 Acaste ( Acastella ?) sp. ; R. and E. Richter, p. 28, pi. 4, fig. 60 (BM(NH) I 1397). 1963 Acastella cf. spinosa (Salter); Holland, Lawson, and Walmsley, p. 123, pi. 6, fig. 5 (BM (NH) In 57172). For citations of Acaste spinosa Salter nonsynonymous with Acastella spinosa (Salter 1864) see R. and E. Richter 1954, pp. 23, 24, 26. Holotype. Salter 1864, p. 27, text-fig. 7, woodcut (GSM 19412). Whitclifte Chase, The Whitcliflfe, Ludlow, Shropshire. Topmost Upper Whitcliffe Beds, uppermost Ludlovian, as defined by Holland, Lawson, and Walmsley (1963). Diagnosis. A species of Acastella with the following characteristics: cephalic outline sub- pentangular; frontal lobe moderately convex (sag.), anteriorly rounded or very slightly angled; 3L a little larger than 2L; 1L half as wide as 2L; 2S and 3S impressed to similar depth; 2S reaching but not joining the axial furrows abaxially; occipital ring raised above glabellar side lobes; axial furrows diverging at angles between 22 and 30 degrees; preocular section of facial suture distinctly angled in front of glabella, enclosing a narrow triangular area of fixigena immediately anterior to the glabella; genal spines slender, curved; pygidium subtriangular in outline; 7 (8) axial segments; 5 pleural segments; deep furrows; border bearing 4 or 5 pairs of faint, low swellings on the internal mould; margin entire; slender caudal mucronation lying in near horizontal plane or inclined dorsally at angles of up to 60 degrees. Description (based on specimens preserved as internal moulds). Cephalic outline sub- pentangular; in anterior view gently arched. Fixigenae postero-laterally produced into slender, curved spines. Glabella defined by deep axial furrows diverging at angles varying between 22 and 30 degrees according to preservation, flattened specimens having a larger angle of diver- gence than undistorted material. Lateral profile flat across side lobes, moderately convex (sag.) across frontal lobe. Frontal lobe, in dorsal view, anteriorly gently arched, laterally rounded. In lateral profile there is a marked change in slope at the extreme anterior edge of the glabella which is seen in dorsal view to be formed by a narrow deltoid area described by the preocular section of the facial suture. Axial furrows curve gently around 2L and 3L, the glabellar width decreasing thence evenly to the posterior. The frontal lobe does not extend laterally across the course of the axial furrows. Lobe 3L is typically a little larger than 2L. 1L is about one half as wide (exsag.) as 2L. Adaxially 2L and 3L rise above the level of the median longitudinal field, a characteristic well shown on flattened material such as the holotype, while 1L tends to merge adaxially with it. 3S narrow (exsag.), moderately deep, sigmoidal, with a prominent posterior median deflec- tion. 2S impressed to a similar depth but typically wider (exsag.), abaxially transverse, adaxially with, usually, a strong median deflection to the posterior. 2S reaches abaxially as far as the axial furrow but does not join with it. IS deep and wide (exsag.), curving both abaxially and adaxially to the anterior. All furrows adaxially equidistant from the sagittal line. There is a tendency towards the convergence of the median extremities of 178 PALAEONTOLOGY, VOLUME ]0 3S and IS. A short, faint, longitudinal furrow lies on the sagittal line between the adaxial ends of 3S. Occipital furrow abaxially deeper than IS, less deep but remaining pronounced axially. Occipital ring fairly narrow (sag.), less wide, and with slightly greater convexity (tr.) than 1L; in lateral profile, when preserved, rising above the level of the glabellar side lobes. Genae laterally extensive with marked border flattening. Posterior border furrow wide (exsag.) and deep, joining laterally with the border flattening. Antero-laterally the librigena passes into the doublure but reappears on the dorsal surface immediately anterior to the glabella where it forms a narrow (sag.) triangular area. The preocular section of the facial suture is dorsal intramarginal, becoming marginal at the antero- lateral edges of the glabella. Anterior to the glabella it is markedly angled, having a similar disposition to, but not as pronounced as, that of Acastella tiro (see R. and E. Richter 1954, pi. 5, fig. 13d). The postocular section of the facial suture cuts the lateral cephalic margin opposite 2S. Fixigenae postero-laterally produced into rather long, slender, curved spines, deflected outwards from their bases at an angle of some 1 5 degrees from the continuation of the cephalic margin projected posteriorly parallel to the sagittal line. In their appearance these spines are narrower and more elegant than those produced in Acastella heberti heberti (Gossellet 1888) and A. herberti elsana (R. and E. Richter 1954). They are, however, similar to those of A. jacquemonti jacquemonti Hollard 1963. The genal spines of the holotype, measured from the spine bases, are up to 2-5 mm. in length. Eyes moderately large, subcrescentic in plan situated closer to the glabella than to the cephalic margin, extending from the middle of 1L to the confluence of 3S with the axial furrows ; high ocular platform. The area, H, between the back of the eye and the posterior border furrow is moderately large: A/G, 44-51 per cent.; A/Gn, 35-44 per cent.; H/A, 20-27 per cent. In anterior profile the eye fails to reach the level of the upper surface of the glabella. Palpebral furrows well defined; palpebral lobes raised high above the adjacent palpebral areas; palpebral areas narrow (tr.), abaxially rather flat, adaxially falling steeply towards the axial furrows. Visual surface narrow (vert.), gently convex outwards; very slightly overhanging the ocular platform; sloping outward-forwards a little less steeply than outward-backwards. EXPLANATION OF PLATE 24 Figs. 1-8. Acastella spinosa (Salter 1864). 1. GSM 19412, Holotype cephalon, shell partially removed. Upper Whitcliffe Beds, The Whitcliffe, Ludlow, Shropshire, x4. 2. GSM 102588, Cephalon, internal mould. Upper Whitcliffe Beds, quarry, 385 yd. SE. Patton Grange, SO 5908, 9530, near Much Wenlock, Shropshire, x 4. 3. GSM 102590, Cephalon, internal mould. Upper Whitcliffe Beds, locality as for fig. 2, x4. 4. GSM 84722, Cephalon, internal mould, Perton Bone Bed, quarry near Yew Tree Inn, Prior’s Frome, 3 miles ESE. Hereford, SO 5760, 3915, x4. 5, 6. GSM 102589, Cephalon, internal mould. Upper Whitcliffe Beds, exposure on Row Lane, 504 yd. SSW. Hungerford Farm, SO 5387, 8880, Hungerford, Shropshire. 5, Dorsal view, x 4. 6, Lateral view, x 4. 7. BM(NH) I 1397, Cephalon, internal mould, Lower Llangibby Beds, quarry in wood, Llandegfydd Hill, Usk, Monmouthshire, x4. 8. GSM 102594, Eye, internal mould. Upper Whitcliffe Beds, exposure by Diddlebury-Middlehope road, SO 5032, 8581, Diddlebury, Shropshire, X 16. Figs. 9-1 1. Acastella? cf. minor (M'Coy 1851). 9-11, GSM 84723, Cephalon, internal mould, Down- tonian, quarry near Yew Tree Inn, Prior's Frome, Herefordshire, 3 miles ESE. Hereford. 9, Dorsal view, x4. 10, Lateral view, x4. 11, Anterior view, x4. ■■ Aiv'fc Palaeontology , Vol. 10 PLATE 24 SHERGOLD, Acastella J. H. SHERGOLD: A REVISION OF ACASTELLA SPINOSA (SALTER 1864) 179 Up to about 90 closely packed lenses; dorso-ventral files carrying an approximate maxi- mum of 6 lenses. Hypostome and thorax unknown. Pygidium subtriangular in outline; in posterior profile gently arched; in lateral profile, with the upper surface of the axis in the horizontal plane, the postero-lateral margins curve strongly addorsally culminating in a relatively short, slender caudal termination. This mucronation is frequently strongly curved addorsally, being typically orientated at angles varying between 30 and 60 degrees to the horizontal plane. When inclined at high angles it may rise to the level of the upper surface of the axis. It may, however, occasion- ally lie in a nearly horizontal plane. When viewed dorsally the spine appears to rise imperceptibly from the postero-lateral borders of the pygidium. In cross-section it has an elliptical shape. Axis strongly convex (tr.), rising above both axial furrows and pleurae; composed of seven or eight segments together with a rounded terminal piece. Axial furrows defining the first three segments diverge at a greater angle than those defining the re- mainder of the axis. Strong, deep, transverse furrows separate the first six segments. In lateral view the segments rise to an even height; the terminal piece is low and ends abruptly. A well-defined postaxial ridge extends from the axial termination to the spine base. Five pleurae; in posterior view moderately to strongly convex (tr.) according to preservation, sloping from a marked geniculation both to the axial furrows and border. Laterally the pleurae merge into the unfurrowed border without a marked change of slope. There is, therefore, no border furrow or flattening and the pygidium exhibits a similar condition to that of juvenile holaspides of Acaste downingiae (Murchison) (Shergold 1966). Pleural furrows very strong, wide (exsag.), and deep. Interpleural furrows indistinct but can generally be discerned separating the first three pleurae. Border narrow laterally, widening a little posteriorly; bearing four or five pairs of low, scarcely visible, swellings (segmental traces), set opposite the lateral end of the posterior band of each pleural segment. Such swellings characterize Acastella granulosa Hollard 1963, A. patula Hollard 1963, and A. jacquemonti Hollard 1963, species found in the upper part of the zone of Monograptus uniformis and the lower part of the M. her- cynicus zone to the south of the Anti-Atlas Range in southern Morocco. The margin is entire, without the denticulations characterizing A. heberti e/sana (R. and E. Richter 1954), A. tiro (R. and E. Richter 1954), and A. rouaulti (de Tromelin and Lebesconte 1875). Remarks. The type material of Acastella spinosa (Salter) has been described by R. and E. Richter (1954; pp. 27-28) and further comment is unnecessary. However, it is now possible to reinterpret the specimen discussed and figured by these authors (1954; p. 28, pi. 4, fig. 6), BM(NH) I 1397, as Acaste ( Acastella ?) sp ., from Llandegfydd Hill, Usk, which appears to be comparable with material from other localities in the Welsh Borderlands now assigned to A. spinosa (Salter). The Richters noted that the side furrows 2S slope into the axial furrows, an observation not entirely correct as they do not open into the axial furrows. There seems, in general, to be a considerable variation in the exact position of the abaxial termination of 2S in A. spinosa (Salter). On specimens GSM 19412 and 102590 these furrows obviously terminate before reaching the axial furrows and in these cases it may be noted that the specimens have to some degree been flattened. On GSM 102588 and 102589 the furrows end a little nearer, while on GSM 102585 and 180 PALAEONTOLOGY, VOLUME 10 BM(NH) I 1397 they reach, but do not join with, the axial furrows. It may be possible therefore to relate this variation to preservation. Acastella macrocentrus (Reed 1925) was described from an incomplete, exfoliated pygidium preserved in a limestone matrix, SM A 16539. The right pleura and antero- lateral portion of the axis are missing. On the left pleura five pleural furrows may be dis- cerned and on the axis eight segments together with a rounded terminal piece. In lateral profile the axis, as in Acastella spinosa (Salter), slopes gently after segment 3 to the posterior and terminates, not markedly abruptly, before a narrow postaxial ridge. The border is narrow and there is no marked break of slope at the junction with the furrowed pleurae. Posteriorly the sides of the pygidium rise addorsally to culminate in an up- turned mucronation, the end of which is broken off. The margin appears to be entire. In all these characters A. macrocentrus (Reed 1925) is identical with A. spinosa (Salter 1864) and the two species must be regarded as synonymous. The specimen cited by Squirrell and Tucker (1960, p. 151) GSM 84722, though poorly preserved, is of some interest. It is recorded from the basal Rushall Beds of Prior’s Frome, Herefordshire, the lowest member of the Downtonian in the Woolhope Inlier. Of further interest is the nature of the adhering matrix which is composed of broken shell fragments and abundant thelodont and acanthodian denticles indicating that the specimen has been derived from a bone bed. The bone bed exposed at Prior’s Frome at the base of the Downtonian is equated with the Ludlow Bone Bed of South Shropshire. It is not impossible, therefore, that GSM 84722, has been derived from the uppermost bed of the Ludlovian. The specimen has been damaged, the anterior portion of the cephalon and frontal lobe, glabellar lobe 1L, the occipital ring, and the genal spines are missing, though the impressions cast by these spines can be discerned. The specimen shows the axial furrows diverging at a very similar angle to those of A. spinosa ; the glabellar side furrows conform to a similar pattern, there being a tendency for 3S and IS to converge adaxially; the eyes are of comparable size and are similarly positioned; the surface of the mould is without granulations. In view of the incomplete nature of this specimen (the relationship of the frontal lobe to the preocular section of the facial suture and the anterior cephalic margin is important specifically) and the similarity of the exist- ing characteristics to A. spinosa (Salter) the author is of the opinion that it should be determined as A. cf. spinosa (Salter) until the discovery of further material can make a precise identification possible. The bulk of the material of A. spinosa (Salter) studied is preserved as internal moulds. Material collected by the author and donated to the Geological Survey Museum has been largely prepared out so that external moulds have been lost. Fragmentary external moulds of pygidia are present in this collection but have been considered too poor to figure here. External moulds showing the complete margin of the pygidium, from which it would be desirable to obtain casts, have not been observed. An external mould of a cranidium, BM(NH) In 57172, was figured by Holland, Lawson, and Walmsley (1963, pi. 6, fig. 5) and has not been refigured here. Generally, casts from ex- ternal moulds in this particular species, show little which cannot be gained from internal moulds. The furrows of both cephalon and pygidium are always wider but less deep, though they remain well incised. Range. Upper Leintwardine Beds (terminology after Holland, Lawson, and Walmsley 1963) to the Perton Bone Bed (see below). J. H. SHERGOLD: A REVISION OF ACASTELLA SP1NOSA (SALTER 1864) 181 Distribution. Widespread in the Welsh Borderland Province (both basinal and shelf facies). Usk: BM(NH) I 1397 is recorded from a ‘Quarry in Wood, Llandegfydd Hill, Monmouthshire’. The Acaste downingiae (Murchison) recorded by Walmsley (1959, p. 514) may be this species. The horizon of Walmsley ’s specimen, and possibly also I 1397, is given as Lower Llangibby Beds (Upper Leintwardine Beds). Woolhope: Squirrell and Tucker (1960, pp. 148, 177) record Acostella spinosa (Salter) from the basal Lower Perton Beds (= Lower Whitcliffe Beds) and from the basal Rushall Beds (p. 151), GSM 84722. The same authors (1960, pp. 150, 177) record A. macrocentrus Reed from the topmost Upper Perton Beds (= Upper Whitcliffe Beds). Ludlow: GSM 19412-14, and BM(NH) In 57172 are recorded from the Upper Whitcliffe Beds of Whitcliffe Chase, Ludlow, the type locality. Elies and Slater (1906, p. 220) record Phacops sp. from the Spirifera elevata Beds (= Uppermost Whitcliffe Beds). The locality is not specified. Corvedale: The species has been collected both by Dr. J. Shirley and the author from a number of localities between Norton Camp (Craven Arms) and Bourton (Much Wenlock) (GSM 102585-94), in the topmost 30 or 40 ft. of the Whitcliffe Beds. It is associated with the same fauna as that occurring in the Spirifera elevata Beds of Elies and Slater (1906) at Ludlow. Bishops Castle: The author has, in his possession, a pygidium, BM (NH) It 2036, from a quarry at Cwm Colebatch Farm, Cefn Einion. This locality is some 40 ft. below the horizon of the Ludlow Bone Bed, the exposed strata being equivalent to the upper part of the Llan-Wen Hill Beds (Holland 1959) at Knighton ( = Upper Whitcliffe Beds). Kerry: Earp (1938, p. 156) records Phacops sp. from the Dalmanella lunata Beds (= Upper Whitcliffe Beds). The locality is not given. From the above survey it would appear that Acastella spinosa occurs earliest in the southern and south-eastern inliers in the Ludlovian shelf facies. During Upper Whitcliffian times the species migrates further to the north, spreading over a considerable area with the shallowing of the Ludlovian sea. Relationships. In the following passage Acastella spinosa (Salter) is compared and con- trasted with all those species which have been adequately described and placed with certainty in the genus Acastella. The relationship of A. spinosa (Salter) to A.prima Tomczykowa 1962a. In both species the geometry of outline of the cephalon is similar, as are the courses of glabellar furrows IS and 3S and the segmentation of the pygidium. A. prima differs from A. spinosa in the following characters: anteriorly the glabella is rounded rather than angled; the axial furrows diverge at a slightly lesser angle (20 degrees); 2S reaches and apparently joins the axial furrows laterally; true genal spines are lacking, there being instead, in the adult, short mucronate points, similar to those observed in young holaspides of Acaste down- ingiae (Murchison) (Shergold 1966); similarly the pygidium, though posteriorly distinctly angled, does not possess a caudal spine. No mention is made by Tomczykowa of the condition of the border or margin of the pygidium in respect to indications of segmenta- tion either in the form of swellings or denticulations. Acastella heberti heberti (Gossellet 1888) and A. spinosa (Salter) appear to be closely related. The dorso-ventral files of the visual surface of the former contain a maximum of six lenses, in close agreement with the maximum observed in the latter. Although R. and E. Richter (1954, p. 22) in their diagnosis of A. heberti give the number of pleurae in the pygidium as four, the specimen (pi. 2, fig. 28), ascribed by them to A. h. heberti shows distinctly five pleural furrows. It seems, therefore, that the pygidial segmentation, also, is similar to that of A. spinosa. There is a caudal spine in both species and likewise the pygidial margin is entire, without lateral denticulations either on shell or internal mould. The cephalon of A. h. heberti is, however, more distinctly pentangular in outline; the glabella is more parallel-sided, the axial furrows diverging at only 10 degrees; the frontal lobe is more strongly convex (sag.); 2S just fails to reach the axial furrows abaxially; the 182 PALAEONTOLOGY, VOLUME 10 pygidial border is broad and apparently smooth, no mention being made of the swellings observed in A. spinosa (Salter). Acastella patula Hollard 1963 and A. spinosa (Salter) are similar in the following respects: the axial furrows diverge at an angle of 28 degrees in the former, 22-30 degrees in the latter; the gently angled anterior outline of the frontal lobe; the courses of the glabellar furrows; the angled nature (sag.) of the preocular section of the facial suture; the number of pleural segments in the pygidium and the possession of border swellings. The pygidium, however, of A. patula has a short, inflected point in place of the slender mucronation of A. spinosa ; there is one extra segment in the axis of the pygidium and a slight flattening between the furrowed pleurae and the border; the border swellings of A. patula are stronger and are observed both on the shell and internal mould. Acastella granulosa Hollard 1963 and A. spinosa (Salter) are quite distinct. The former possesses axial furrows diverging at 20 degrees; the glabella is less convex (sag.); 2S abaxially fails to reach the axial furrows; the occipital ring bears a median tubercle; the eye is smaller, extending (exsag.) approximately from IS to the anterior edge of 3L; the pygidium has 6 pleural segments and 9(10) axial segments; the test is highly granulose. Both species possess a caudal spine and have a narrow pygidial border which bears swellings, which in A. granulosa may be seen both on the shell and the internal mould. A. spinosa (Salter) is equally distinct from the three subspecies of A. jacquemonti Hollard 1963. In these the angle of divergence of the axial furrows (20-22 degrees) is slightly less than that of A . spinosa ; the glabella is anteriorly rounded rather than angled ; the eye, where known, is smaller, in A. j. jacquemonti Hollard 1963 extending (exsag.) from IS to the anterior margin of 3L; the occipital ring in A. j. tanzidensis Hollard 1963 bears a median tubercle; in A. j. jacquemonti and A. j. levis Hollard 1963 2S reaches abaxially as far as the axial furrows, but in A.j. tanzidensis fails to do so; in the pygidium each subspecies has 5 (6) pleurae and 8-10 axial segments; the border is wide and markedly flattened in A.j. tanzidensis and A.j. levis but narrow and poorly separated from the pleurae in A. j . jacquemonti, a condition approaching that of A. spinosa. In each case swellings are present on the border but to varying degrees, those of A.j. jacquemonti being strong and present both on the shell and internal mould, those of A.j. tanzidensis and A. j. levis being present only in the internal mould and in the latter being poorly developed. Posteriorly A.j. jacquemonti possesses a short, triangular, caudal point, while the mucronations of A.j. tanzidensis and A.j. levis are long spines, curving upwards in the former, straight in the latter, both of these conditions being exhibited by A. spinosa. A. spinosa (Salter) can be readily distinguished from A. heberti elsana (R. and E. Richter 1954), A. tiro (R. and E. Richter 1954), and A. rouaulti (de Tromelin and Lebesconte 1875), as these species possess on the internal mould of the pygidium marginal denticulations, which are lateral continuations of weak swellings situated on the border. The corresponding external shell may be smooth (A. rouaulti) or with scarcely visible swellings, generally confined to the border. Each species also possesses a rather stout caudal mucronation and genal spines which tend to be more massive than those of A. spinosa. The cephalic outline of A. h. elsana is more markedly pentangular; the glabella is much more parallel-sided, the axial furrows diverging at 10 degrees; the frontal lobe has a somewhat lower convexity (sag.) and the anterior outline is rounded-truncate in plan; abaxially 2S does not reach the axial furrows; the occipital ring is low (vert.); the J. H. SHERGOLD: A REVISION OF ACASTELLA SPINOSA (SALTER 1864) 183 dorso-ventral files of the visual surface contain a maximum of 7 lenses; in the pygidium there are 4 (5) pleural segments, 7 (8) axial segments. A. tiro has a more subtriangular cephalic outline than that of A. spinosa ; the axial furrows diverge at about 20 degrees; abaxially 2S almost reaches the axial furrows; the occipital ring is low (vert.); the dorso-ventral files bear up to 8 lenses; the preocular section of the facial suture is quite distinctly angled (sag.) in front of the glabella; in the pygidium there are 5 pleural and 8 (9) axial segments; the border is wide and separated from the furrowed pleurae by a marked flattening. The cephalic outline of A. rouaulti is similar to that of A. spinosa; the glabella de- creases in width (tr.) less rapidly to the posterior so that the axial furrows diverge at the lesser angle of 15 degrees; the occipital ring is high (vert.), as in A. spinosa , and the courses of the glabellar side furrows are also closely comparable; in front of the glabella the preocular section of the facial suture is more distinctly angled; the border is wide and separated by a flattening from the furrowed pleurae; as in A. spinosa the caudal mucronation is inflected, at up to 30 degrees. Acastella prima Tomczykowa 1962 Plate 25, figs. 4-5, 13-14 1872 Phacops Downingiae , Murch.; Aveline, Hughes and Tiddeman, p. 14. 1962 Acastella prima Tomczykowa, pp. 260-6, pi. 1, figs. 2-5, text-fig. lc. Material. With the exception of one specimen from the Liverpool City Museum, all the available material is from the T. McK. Hughes Collection, Geological Survey Museum. It has been obtained from the Upper Ludlovian of the Kendal and Kirkby Lonsdale regions and consists of two cranidia, TMcKH 1350, 1366; three good pygidia, LCM 60.64 ME, TMcKH 1032, 1336, and several incomplete pygidia, TMcKH 6 (two specimens), 989, 1073, 1350, 1363. Localities. LCM 60.64 ME, Kirkby Moor Flags, Endmoor. TMcKH 6, 1336, 1350, 1363, 1366, Holme Scales, Hutton Bridgend, SE. of Kendal. TMcKH 989, Killington, N. of Kirkby Lonsdale. TMcKH 1032, Gatebeck, N. of Kirkby Lonsdale. Remarks. The following translation from Tomczykowa (1962u, pp. 261-2) gives slightly more information on the species than the short English summary (p. 266) accompanying the paper. Cephalon semicircular, glabella anteriorly broad and rounded. Axial furrows deep and narrow, diverging at 20 degrees. Frontal lobe large. Side-furrows SI and S2 narrow and almost parallel to the occipital furrow and are the same depth as S3 which curves posteriorly and intersects the axial furrows anteriorly near the front end of the eye. Side-lobes LI are half as wide as L2 and the latter half as wide as L3. Occipital ring narrow, medianly wider. Palpebral areas slightly inclined towards the axial furrows. The front margin of the fixigena is linear. The posterior margin is slightly convex and is sigmoidal towards the genal angle where it bears a very distinct, posteriorly directed tubercle. Thorax composed of 1 1 segments. Axis nearly one-quarter of the maximum width. Axial furrows deep and narrow. Pleurae are ended in distinct tubercles. Pygidium small and triangular. Axis narrow and conical, composed of 7 segments and does not reach the posterior margin. Axial furrows deep and narrow. Pleurae composed of 5 ribs which do not reach the edge of the pygidium, rapidly narrowing to the back. Posterior edge pointed. Surface of carapace covered with very fine and dense granulations. 184 PALAEONTOLOGY, VOLUME 10 AcasteUa prima occurs in Poland in the upper part of the Siedlce Beds, at the top of the zone of Monograptus formosus. It is found only in material from the Lebork bore- hole, in northern Poland, and is not recorded from the Holy Cross Mountains. AcasteUa spinosa is reported (Tomczykowa, op. cit., p. 260) from the same borehole at a slightly higher stratigraphical level. All the material from the Kendal area supports the observations of Tomczykowa. TMcKH 1350 shows the immature genal projections and TMcKH 1336 the short, inflected, node-like pygidial termination. The margin of the pygidium of this species is entire and the border smooth. There appears to be no development of border swellings as are found in A. spinosa. The salient differences between A. prima and A. spinosa are to be found in the nature of the mucronations. In the former these are in effect rudimentary projections rather than well-developed spines. Tomczykowa considers (op. cit., p. 266) that this species ‘is a form standing at the boundary of two genera, i.e. Acaste and AcasteUa'. This statement is supported by work on Acaste downingiae (Murchison), where young holaspides of A. downingiae have genal mucronations similar in nature to those of the adult AcasteUa prima (Shergold 1966). AcasteUa? minor (M‘Coy 1851) Plate 25, figs. 1-3 1851 Phacops (Oclontochile) caudata (Brong. Sp.), var. minor M‘Coy, p. 161. 1873 Phacops Downingiae Murchison; Salter, p. 177. Material. Two exfoliated and incomplete cranidia, SM A 37195, 37142. Lectotype (here chosen). The cranidium, SM A 37142. Kirkby Moor Flags, Benson Knot, near Kendal, Westmorland. Extended Diagnosis. Cephalon ogival to subpentangular in outline; in anterior view gently arched. Axial furrows diverging anteriorly at 25 degrees. Frontal lobe moderately EXPLANATION OF PLATE 25 Figs. 1-3. AcasteUa? minor (M'Coy 1851). 1, 2. SM A 37195, Cranidium, exfoliated, Kirkby Moor Flags, Benson Knot, U miles ENE. Kendal, Westmorland. 1, Dorsal view, x4. 2, Lateral view, x4. 3. SM A 37142, Lectotype cranidium, exfoliated, locality as for figs. 1, 2, dorsal view, x4. Figs. 4-5. AcasteUa prima Tomczykowa 1962. 4, 5. GSM TMcKH 1350, Internal mould, cranidium, Kirkby Moor Flags, Home Scales, Hutton Bridgend, 4J miles SE. Kendal. 4, Dorsal view, x 6. 5, Lateral view, x 6. Figs. 6-12. AcasteUa spinosa (Salter 1864). 6. GSM 19414, Pygidium, internal mould. Upper Whitcliffe Beds, The Whitcliffe, Whitcliffe Chase, Ludlow, Shropshire, x4. 7, 8. SM A 16539, Holotype of A. macrocentrus ( Reed 1925), pygidium, exfoliated. Upper Ludlow, Prior’s Frome, Herefordshire. 7, Dorsal view, x4. 8, Lateral view, x4. 9-11. GSM 102592, Pygidium, internal mould, Upper Whitcliffe Beds, exposure on Diddlebury-Middlehope road, SO 5032, 8581, 60 yd. from junction with B 4368, Diddlebury, Shropshire. 9, Dorsal view, x4. 10, Lateral view, x4. 11, Posterior view, x4. 12. GSM 102591, Pygidium, internal mould, Upper Whitcliffe Beds, locality as figs. 9-11, lateral view, x 4. Figs. 13-14. AcasteUa prima Tomczykowa 1962. 13, 14. GSMTMcKH 1336, pygidium, internal mould, Kirkby Moor Flags, Holme Scales, Hutton Bridgend, 4f miles SE. Kendal, Westmorland. 13, Dorsal view, x4. 14, Oblique posterior view, x4. Palaeontology, Vol. 10 PLATE 25 SHERGOLD, Acastella J. H. SHERGOLD: A REVISION OF ACASTELLA SPINOSA (SALTER 1864) 185 convex (sag.), anteriorly obtusely angled; without preglabellar furrow, the anterior glabellar contour being defined by the course of the preocular section of the facial suture;, four rows of tubercles converge on the narrow area between the adaxial extremities of 3S, running from this point radially across the slope of the frontal lobe towards the preocular section of the facial suture. Three pairs of glabellar side furrows readily distinguished; 3S wide (exsag.), shallow, sigmoidal, with median deflection to the posterior; 2S wide (exsag.), a little deeper than 3S, abaxially transverse, adaxially with deflection to posterior, nearly reaching but failing to join abaxially with the axial furrows; IS very wide (exsag.) and deep, curving both adaxially and abaxially to the anterior. The tendency for IS and 3S to converge adaxially is not nearly so apparent as in AcasteUa spinosa. There is no longitudinal furrow on the saggittal line between the adaxial extremities of 3S. 1L less than half as wide as 2L. Occipital ring less wide (tr.) and slightly more convex (tr.) than 1L. Remarks. Under the heading Phacops ( Odontochile ) caudata ( Brongniart ), M'Coy (1851,, p. 161) mentioned specimens from Underbarrow and Benson Knot, near Kendal, West- morland, characterized by a ‘coarsely granulated surface’. These he called Odontochile caudata var. minor. Of the three specimens concerned, SM A 37142 and 37195, from Benson Knot, show the characteristics attributed to them by M'Coy (p. 161). The third, SM A 37143, a poorly preserved and incomplete cephalo-thorax from Underbarrow does not show the diagnostic ornament. Its condition prohibits even an accurate generic determination. Salter, in preparing figures of these specimens for M'Coy, referred them to Phacops downingiae. These plates were, however, subsequently cancelled, and since that time they have remained unfigured. Salter (1873) made further reference to these specimens in his catalogue of fossils in the Sedgwick Museum. All three were listed as Phacops downingiae Murchison. In this work the specimens from Benson Knot were stated (p. 1 77) to be derived from the Upper Ludlow (= Kirkby Moor Flags) and that from Underbarrow was stated (p. 166) to be from the Lower Ludlow (= Bannisdale Slates). The Kendal material apart, there is one other specimen, the internal mould of a cephalon, in the Geological Survey Museum, GSM 84723 (PI. 24, figs. 9-1 1 ). It is labelled as having been derived from the Downtonian of Prior’s Frome, Herefordshire. The matrix also contains an external mould of an enteletacean brachiopod. If the specimen is correctly documented its horizon must be within the basal 10 in. of the Rushall Beds which in this area also contain Camarotoechia nucula, Protochonetes ludloviensis , and Salopian lunata (Squirrell and Tucker 1960, pp. 150-1). The specimen shows the diagnostic characteristics of the type-material from Kendal. It has in common with SM A 37142 and 37195 coarse granulations on the frontal lobe and genae; the anteriorly angled frontal lobe, immediately defined by the preocular section of the facial suture; glabellar lobes of similar size and convexity and side furrows of similar depth, length, and attitude. In addition, the specimen shows the characteristics of the eye and its relationships to the glabella and posterior border furrow. The eye is subcrescentic in plan view, situated more or less centrally on the cheek between the glabella and the cephalic margin; extending from IS to the anterior edge of 3L; A/G, 41 per cent.; A/Gn, 34 per cent.; H/A, 30 per cent. In anterior profile the eye fails to reach the level of the top of the glabella; in lateral profile the top of the visual 186 PALAEONTOLOGY, VOLUME 10 surface slopes very gently to the anterior. Palpebral furrow well defined; palpebral lobe rather low; palpebral area sloping with low inclination to the axial furrows. Visual surface gently convex outwards, overhanging slightly the high ocular platform; narrow (vertically); bearing less than 100 lenses; 19 dorso-ventral files carrying (right eye, GSM 84723) 6 or 7 lenses at the maximum height of the surface. GSM 84723 differs, however, from the Kendal material in the proportions of the glabella, which is markedly subpentangular. In view of this difference and the dearth of comparably preserved material from Kendal the specimen has been classified as Aeastella? cf. minor (M‘Coy 1851). Comments on the classification of A ? minor. M‘ Coy’s species has been placed questionably in the genus Aeastella Reed. It has characteristics typical of both Aeastella and Scotiella Delo 1935. The pygidium, which might settle the issue, remains, unfortunately, unknown. The genus Aeastella is typified by well-developed glabellar furrows, both on the shell and when preserved as internal moulds. There is a well-defined preglabellar furrow in all species. The pygidial margins of the earlier species are generally entire, apart from the caudal mucronations though, as in the case of A. spinosa, there may be low swellings faintly indicated on the border. In the later species of Aeastella the margins of the pygidium are often denticulate. In the genus Scotiella , however, the anterior and median lateral glabellar furrows are ‘faint to obsolete’ (Delo 1935, p. 409; 1940, p. 33). The pygidial margins, as in the early species of Aeastella , are entire. Two distinct types of cephalon have previously been classified as Scotiella. The type- species, S. logani (Hall 1860), is characterized by an anteriorly rounded glabella on which the furrows are but faintly impressed. Also attributed to the genus (Delo 1940, pi. 2, figs. 18-20) is S. logani (Hall) var. conservatrix McLearn in which the glabella is anteriorly obtusely angled, as in Aeastella? minor , and which shows quite clearly three well-incised pairs of glabellar furrows. In addition, the holotype of this species, Peabody Museum, Yale University, YPM 472, shows the same arrangement of tubercles on the frontal lobe as are present in A? minor. Similarly, two types of trilobites have been described as Scotiella by Tomczykowa (19626), S. samsonowiezi Tomczykowa, with anteriorly angled frontal lobe, and S. opatowiensis Tomczykowa with an anteriorly rounded glabella. Although Tomczykowa (19626, p. 201) states that the Polish species ‘are characterized bv the presence of one lateral furrow (SI) only’, on the accompanying plates two anterior pairs, though faint, are visible on both species. An exfoliated speci- men of S. samsonowiezi (pi. 34, fig. 4) shows that the furrows are wider and stronger on the internal mould. It also shows the presence of radially dispersed tubercles on the frontal lobe. Two species-groups may be thus discerned among species currently classified within the genus Scotiella. The one, typified by the type-species, having faint glabellar furrows and anteriorly rounded frontal lobe, includes S. logani , S. obsoleta Ulrich and Delo 1940 and 5. opatowiensis Tomczykowa 1962. The second, having well-defined glabellar furrows and obtusely angled glabella in front, embraces S. logani (Hall) var. conservatrix McLearn and S. samsonowiezi Tomczykowa 1962. The species referred here to Aeastella? minor (M‘Coy 1851) has strong affinity to the latter group. Of the two species-groups only the first can certainly be classified as Scotiella under J. H. SHERGOLD: A REVISION OF ACASTELLA SPINOSA (SALTER 1864) 187 the conditions originally proposed by Delo (1935). The latter group, by virtue of their well-defined glabellar furrows, are considerably closer to Acastella. They may be differentiated, however, from species of that genus by the absence of a preglabellar furrow and by the characteristic presence of tubercles, well seen on the internal mould, on the frontal lobe of the glabella. Accordingly it is proposed that these species should be temporarily classified as Acastella ?, pending further revision of Scotiella. STRATIGRAPHICAL CONCLUSIONS Acastella spinosa occurs commonly in the Upper Whitcliffe Beds, highest Ludlovian, in the Welsh Borderlands. It is also reported from boreholes in the north of Poland, Podlasie Beds, and from the Holy Cross Mountains, Poland, Rzepin Beds. Acastella prima occurs in the Kirkby Moor Flags, high Ludlovian, of Westmorland and in beds lying across the junction of the Siedlce and Podlasie Beds in northern Poland. It is not reported from the Holy Cross Mountains. Acastella? minor s.s. is confined to the Kirkby Moor Flags of Westmorland, although a similar species, A? cf. minor, is known from the ?Downtonian of the Welsh Borderlands. Close relatives, Scotiella logani var. con- servatrix and S. samsonowiczi, occur in the Stonehouse Formation of Arisaig, Nova Scotia, and in the lower part of the Rzepin Beds of the Holy Cross Mountains, Poland, respectively. The latter occurs between the graptolite zones of Monograptus formosus and M. angustidens (Tomczykowa 1962c, pp. 96-97). It may be possible, therefore, to offer a correlation based on these trilobites between the Kirkby Moor Flags of the British Isles and the higher Siedlce (= higher Wydryszow) Beds and lower Podlasie (= lower Rzepin) Beds of Poland. REFERENCES aveline, w. t., hughes, t. mck., and tiddeman, r. h. 1872. The Geology of the Neighbourhood of Kirkby Lonsdale and Kendal. Mem. geol. Surv. Engl. & Wales. barrois, c., pruvost, p., and dubois, G. 1922. Description de la faune siluro-devonienne de Lievin. Mem. Soc. geol. N. 6, Mem. 2, Fasc. 2 (1920), 1-225, pi. 10-17. delo, d. m. 1935. A Revision of the Phacopid Trilobites. J. Paleont. 9, 402-20. 1940. Phacopid Trilobites of North America. Spec. Pap. geol. Soc. Am. 29, 1-135, 13 pi. earp, j. r. 1938. The higher Silurian rocks of the Kerry District, Montgomeryshire. Q. Jl Geol. Soc. Load. 94, 125-60, pi. 12, 13. elles, g. l. and slater, i. l. 1906. The highest Silurian rocks of the Ludlow District. Ibid. 61, 195— 222, pi. 22. hall, j. 1 860. Description of New Species of Fossils from the Silurian Rocks of Nova Scotia. Can. Nat. Geol. 5, 144-69. Holland, c. h. 1959. The Ludlovian and Downtonian rocks of the Knighton District, Radnorshire. Q. Jl. Geol. Soc. Lond. 114, 449-82, pi. 21. lawson, j. d., and walmsley, v. g. 1963. The Silurian rocks of the Ludlow District, Shropshire. Bull. Br. Mus. nat. Hist., Geol. 8, 93-171, 7 pi. hollard, h. 1963. Les Acastella et quelques autres Dalmanitacea du Maroc presaharien, leur distri- bution verticale et ses consequences pour l’etude de la limite Silurien-Devonien. Notes Serv. geol. Maroc, 176, 1-66, 4 pi. m'coy, f. 1851. A Synopsis of the Classification of the British Palaeozoic Rocks, with a Systematic Description of the British Palaeozoic Fossils in the Geological Museum of the University of Cambridge. Fasc. 1, 1-184. fillet, j. 1959. Revision de Acastella rouaulti (de tromelin et lebesconte) 1875. Bull. Soc. geol. Fr. 7ime ser., 1, 939-43, pi. 1. C 4471 o 188 PALAEONTOLOGY, VOLUME 10 reed, f. r. c. 1925. Some New Silurian Trilobites. Geol. Mag. 62, 67-76, pi. II. 1927. Recent work on the Phacopidae. Ibid. 64, 308-21, 337-53. richter, r. and richter, E. 1952. Phacopacea von der Grenze Emsium/Eiflium (Tril.). Senckenberg. leth. 33, 79-108, pi. 1-4. 1954. Die Trilobiten des Ebbe-Sattels und zu vergleichende Arten (Ordovizium, Got- landium/Devon). Abh. senckenb. naturforsch. Ges. 488, 1-76, pi. 1-6. salter, J. w. 1864. Monograph of the British Fossil Trilobites from the Cambrian, Silurian and Devonian Formations. Palaeontogr. Soc. ( Monogr .), 1-80, pi. I-VI (issued Aug. 1864). 1873. A Catalogue of the Collection of Cambrian and Silurian Fossils in the Geological Museum of the University of Cambridge, ix-xlviii, 1-204. Cambridge. shergold, j. h. 1966. A revision of Acaste downingiae (Murchison) and related trilobites. Palaeontology 9, 183-207, pis. 28-32. squirrell, h. c. and tucker, e. v. 1960. The geology of the Woolhope Inlier, Herefordshire. Q. J( Geol Soc. Lond. 116, 139-85, pi. 15. struve, w. 1958. Beitrage zur Kenntnis der Phacopacea (Trilobita). 1. Die Zeliszkellinae. Senckenberg. leth. 39, 165-220, pi. 4. 1959. In Moore, R. C. Treatise on Invertebrate Paleontology. Pt. O, Arthropoda 1. tomczykowa, E. 1962a. O trylobicie Acastella prima n. sp. Instytut Geologiczny. Kwart. Geol. 6, 260-6, pi. 1 (Polish, English summary). 19626. Orodzaju Scotiella Delo z warstw rzepiriskich Gor Swietokrzyskich(On the genus Scotiella Delo (Trilobita) from the Rzepin Beds of the Holy Cross Mts.). Acta geol. pol ., Ksiega Pam. J. Samsonowicza, 187-205, 2 pi. (Polish, English summary). 1962c. Zespoly fauny w sylurze Polski. (Faunal assemblages in the Silurian of Poland.) Biitl. Inst. geol. 174 (for 1962), 93-105 (Polish), 110-13 (English). walmsley, v. g. 1959. The Geology of the Usk Inlier (Monmouthshire). Q. Jl Geol. Soc. Lond. 114, 483-521, pi. 22. J. H. SHERGOLD, Department of Geology, The University, Newcastle upon Tyne I. Manuscript received 22 December 1965 DEVONIAN MEGASPORES FROM THE W YBOSTON BOREHOLE, BEDFORDSHIRE, ENGLAND by m. g. mortimer and W. G. chaloner Abstract. Nine species of megaspores are described from the Geological Survey Wyboston Borehole, Bedford- shire, England. Of these, five species are new, one forming the basis of a new genus, Heliosporites. Two single occurrences of large megaspores referable to Carboniferous genera are recorded, together with a new occurrence of the species Cystosporites devonicus Chaloner and Pettitt. The mean maximum size of all the species represented is 8 10 p. While this is a higher figure than that for most Devonian megaspores described hitherto, it is still smaller than the corresponding figure for Carboniferous megaspores. The diversity of megaspores now known from the Devonian suggests that heterosporous plants were more abundant at that time than their representation in the macrofossil record would indicate. Some aspects of the classification of the Palaeozic dispersed spores are dis- cussed. The assemblage is regarded as probably of Frasnian age. In the course of preparation of spore assemblages from a Geological Survey boring at Wyboston, Bedfordshire, 18 miles west of Cambridge (Pugh 1956, Edmunds 1956, Edmonds and Dinham 1965), megaspores were found in samples Bt 4284, depth 700 ft. 7 in., Bt 4350, depth 720 ft. 3-4 in., Bt 4354, depth 721 ft., Bt 4356, depth 721 ft. 5 in., and Bt 4358, depth 722 ft. 1 in. In samples of Bt 3710 and Bt 3711 (counterparts of each other), at depth 560 ft. 3 in., fish fragments occur which have been compared to the genus Bothriolepis. Spore assem- blages have been obtained from samples at all levels from 611 ft. down to 722 ft. depth. The lowest spore-bearing sample (Bt 4358) directly overlies a basal conglomerate of Old Red Sandstone facies, 14 ft. thick, and this in turn rests on rocks of Cambrian age. The present study offers no basis for separating the spore assemblages from the different horizons between 700 ft. and 723 ft., and these are here treated as a single group for general age considerations, which are discussed below. Acknowledgements. We express our thanks to the Director of the Geological Survey of Great Britain, Sir James Stubblefield, F.R.S., for allowing us access to the cores from Wyboston, and to Mr. M. Mitchell, of the Palaeontological Department, for his help and for the interest he has taken in the palynological investigation. PREPARATION TECHNIQUES Preparations were commenced either by soaking fragments of rock in a hot 50 per cent, solution of non-ionic detergent, or in a cold 20 vol. H202 solution. Either treatment disaggregated even the more indurated samples, and was followed by treatment with cold 10 per cent. HC1 (1 hour), cold 70 per cent. HF until no further reduction in bulk occurred, warm 50 per cent. HC1 (ten minutes) and cold concentrated HN03 (treatment between 1 and 12 hours, according to the degree of coalification). No alkali treatment was used. Separation of the organic fraction of the residue from the remaining minerals was achieved either by flotation in zinc bromide solution (of specific gravity 2-0), when the [Palaeontology, Vol. 10, Part 2, 1967, pp. 189-213, pis. 26-29.] 190 PALAEONTOLOGY, VOLUME 10 residue was large, or by the use of a vibraflute (Tschudy 1960), when the residue was small. A particularly clean preparation was obtained from Bt 4284, which was treated with ultrasound in a tank at 40 kc/s for 2\ minutes, after the warm HC1 stage. When a persistent fluo-silicate gel occurred, this was adequately dispersed by the use of ultrasound and the zinc bromide flotation was applied subsequently. Test slides were made before ultrasonic treatment and every 30 seconds during treatment, to check on any selective loss of spores. The megaspores were picked out of the aqueous residues and further macerated individually, in Schulze solution, if necessary. The larger spores were mounted singly in Canada Balsam and the smaller in glycerin jelly. Sections of the specimens of Heliosporites variabilis gen. et sp. nov. and of Hystrico- sporites obscurus sp. nov. were obtained by embedding the spores singly in an Araldite- Epon resin, prepared as described by Mollenhauer (1964). Each spore was embedded in a pre-hardened capsule of resin, orientated so that the equatorial plane of the spore was parallel to the axis of the capsule. Serial sections were then cut parallel to the polar axis of the spore at 1 or 2 ^ intervals, with a glass knife, on a Reichert rotary microtome. All the slides are deposited in the Palaeontology collection of the Geological Survey and Museum (numbers prefixed PF). SYSTEMATIC TREATMENT The classification adopted here is that of Potonie and Kremp (1954), as subsequently modified by those authors (1955, 1956) and Potonie (1956, 1958, 1960). One of the problems innate in a morphographic classification is the degree of impor- tance to be attached to the various criteria available for separating the higher taxa. One feature which has received widely different rating by different authors is the separation of the two layers of the exine to leave a gap (variously referred to as the formation of an air sac, saccus, bladder, cavity, or mesospore). Potonie and Kremp recognized two con- trasting situations involving such separation of exine layers. Where a thin, smooth, and crumpled body is sometimes present within a larger thick-walled spore the former was referred to as a mesospore. This term was coined by Fitting (1900) for an apparently comparable structure seen in the megaspore of some living species of Se/aginel/a. Other workers (Zerndt 1934, Schopf 1938) had pointed out that spores identical in other re- spects might differ in the presence or absence of such a mesospore. The presence of this thin-walled inner body was accordingly not rated as of great significance within the morphographic classification, and spores with and without a mesospore were in some cases included within the same genus. This practice has been widely followed by sub- sequent authors (Dettmann 1961 in Banksisporites , McGregor 1960 and Richardson 1965 in Bihar isporites). The second possibility distinguished by Potonie and Kremp (1945) was the formation of a saccus; in this case an air-filled cavity (or cavities) are formed within the exine, the sacci of Pinus being a typical example. Potonie and Kremp treated this as a feature of much greater taxonomic consequence than the presence of a mesospore and used the possession of sacci as a criterion for including spores (or pollen) bearing them in their Anteturma Pollenites. Some of the spores included in Pollenites on the basis of their air sacs had proximal germination (with triradiate sutures) while others had distal germi- nation. These authors were aware that such a grouping (Pollenites) included not merely MORTIMER AND CHALONER: DEVONIAN MEGASPORES 191 true pollen (such as bisaccate conifer pollen) but also the microspores of some hetero- sporous plants (e.g. Endosporites) but evidently accepted this as an unavoidable feature of any such empirical classification. Dettmann (1963) has since attempted to remove from the Anteturma Pollenites those triradiate spores with an air sac (which she terms cavate) leaving in Pollenites only true pollen grains with distal germination (for which she would reserve the term saccate). In the former category (cavate spores) Dettmann includes megaspores with what earlier workers have called a mesospore, together with those triradiate small spores previously called saccate. All these triradiate ‘cavate’ spores (her suprasubturma Perinotrilites) she separates from triradiate spores without such a cavity in the exine (her suprasub- turma Acavatitriletes). In the present work a mesospore is noted as a variable character of the species Hystricosporites multifur catus, H. obscurus , and Biharisporites simplex. In these last three species the specimens with a mesospore comprise less than half the population of the species, so that specimens lacking it are in no sense exceptional. Thus the application of Dettmann’s proposed revision of the Anteturma Sporites to Palaeozoic spores encounters the practical difficulty that spores which would otherwise be placed in the same genus or even species may be separated at the level of a suprasubturma. Richardson (1965) has proposed a new subturma Pseudosaccititriletes as a subdivision within Anteturma Sporites, Turma Triletes. The definition of pseudosaccate, however, corresponds closely with Erdtman’s (1952) description of a saccus, so that the term pseudosaccate seems unnecessary. Richardson adds to the diagnosis that the ‘exine may have . . . infrastructure’ (in the same way as Erdtman adds ‘baculoid elements usually sticking to the undersurface of the exine’) but in discussing the subturma Richardson removes some genera from Potonie and Kremp's Anteturma Pollenites, Turma Saccites, because they do not show saccus infrastructure. Apart from this difficulty over the definition of terms, the use of the subturma Pseudosaccititriletes would cause the same difficulty in placing spores with a mesospore as the use of Dettmann’s suprasubturma Perinotrilites. It would be very desirable to separate pollen from spores sensu stricto in a classification of fossil spores, if this were possible. But at the present time there is no morphological criterion discernible in the fossil spores themselves which will form a basis for separating all pollen from all spores sensu stricto. It is implied by both Dettmann and Richardson that the presence of infrastructure in the saccus is such a criterion, but this is not yet certain. Nor is it always easy to determine, in a saccus with small-scale ornament, whether the ornament is on the inner or outer surface, as, for instance, in Endosporites. We therefore prefer to adopt Potonie and Kremp’s practice of classifying all saccate spores sensu lato together, and of keeping together spores which are otherwise similar, whether they possess a mesospore or not. Anteturma sporites H. Potonie 1893 Turma triletes Reinsch 1891 Subturma azonotriletes Luber 1935 Infraturma laevigati (Bennie and Kidston) R. Potonie 1956 Genus trileites (Erdtman) ex Potonie 1956 Type species. T. spur ins (Dijkstra) Potonie. 192 PALAEONTOLOGY, VOLUME 10 Trileites lcmgi Richardson 1965 Plate 26, fig. 1 Description. Two specimens have been found. They have oval ambs, diameters 252 p and 328 p and walls 8 p thick. There are several large arcuate secondary folds near the equator. The triradiate markings are 105 p long on both (f-f of the radius), but these are clearly visible only for about half their length. There is a small concavely triangular area at the apex where the exine is thinner than elsewhere; the corners of this triangle coincide with the ends of the readily visible triradiate mark. The triradiate mark is continued by faint lines on the exine (not sutures) and at their extremities these are continued by faint curvaturae. The exine is scabrate and one specimen is marked all over with depressions caused by pyrite crystals (as described by Neves and Sullivan 1964). Occurrence. Wyboston Borehole, depths 722 ft. and 700 ft. Remarks. These spores are considered to fall within the circumscription of T. langi. When discussing this species, Richardson remarks on the lack of curvaturae, although he refers to the thin apical triangle as a contact area. The sides of this triangle are seen to be concave, both in Richardson’s plate 88, fig. 10 and in the Wyboston specimens, so that they cannot be curvaturae according to the definition of Potonie and Kremp (1955). Consequently the thin apical triangle cannot correspond to the contact area, which is defined both by Potonie and Kremp and by Couper and Grebe (1961) as being bounded by the curvaturae. The observation of the true curvaturae running convexly between the extremities of the triradiate mark confirms this argument and also shows that the contact faces in fact occupy a large part of the proximal face of the spore. This also supports Richardson’s placing of the species in the genus Trileites, typical members of which have curvaturae. A thin apical area within the contact area has now been noted in several Devonian spore species. Retusotriletes distinctus Richardson 1965 (also from the Middle Old Red Sandstone), Cyclogranisporites sp. and Calamospora witney ana Chaloner (1963) from the Witney Borehole, Trileites wybostonensis sp. nov., and the megaspore of Barinophyton richardsoni (Dawson) Pettitt (1965) all show an analogous thin apical triangle. All are associated with triradiate marks without lips and in which sutures may be lacking (e.g. Cyclogranisporites) or only partly developed (e.g. T. langi). Possibly at EXPLANATION OF PLATE 26 The slides referred to are in the Geological Survey and Museum Palaeontological Collection. All magnifications x 200, unless otherwise stated. Fig. 1. Trileites langi Richardson. Proximal face of specimen showing faint curvaturae, scattered globules of exinous material around apical area, and polygonal depressions caused by pyrite crystals ; Slide PF 3948. Fig. 2. Trileites fulgens (Zerndt) comb. nov. Proximal face of specimen showing triradiate lips, wedge- shaped arcuate ridges, scabrate exine, and mesospore; PF 3949. Figs. 3, 4. Trileites wybostonensis sp. nov. 3, Holotype, proximal face, X 100; PF 3950. 4, Detail of haptotypic features, X 1000. Figs. 5-9. Hvstricosporites multifurcatus (Winslow) comb. nov. 5, 6, Two types of spine ending, both found on one specimen, x 1000. 7, Proximal view of specimen with parallel sided spines; PF 3952. 8, Lateral view showing membranous lips; PF 3953. 9, Proximal face of specimen with tapering spines, X 100; PF 3951. Palaeontology, Vol. 10 PLATE 26 ■‘■'s'.'' MORTIMER and CHALONER, Devonian megaspores •Oh! MORTIMER AND CHALONER: DEVONIAN MEGASPORES 193 dehiscence the whole of the thin area was used as an exitus instead of splits occurring along the sutures as in most living triradiate spores. Previous records. Trileites langi was found by Richardson in most of the beds examined in the Orcadian basin, Eifelian and Givetian in age. He also records the similarity of T. langi to Archaeozonotriletes incrust atus Archangelskaya from the lower Frasnian of the Russian platform. The three specimens recorded by Winslow(1962,pl. 17, figs. 10-12) as Triletes sp. from the Bedford shale of Ohio (basal Mississippian) are also very similar to T. langi in size and appearance, and she has remarked on the unobtrusive continua- tions of the triradiate mark. An interesting comparison may also be made with the specimens of Triletes sellingi Sen (1958) from the Upper Devonian of Bear Island. These resemble Trileites in being smooth with a short triradiate mark ‘possibly extending up to often indistinguishable arcuate ridges’. The minute tubercular outgrowths, which sometimes occur, could be comparable to the scattered globules of exinous material noted by Chaloner 1963 in T. oxfordiensis. Sen’s reference of Nathorst’s specimens to Bentzisporites Potonie and Kremp, remains problematical, as there is no evidence of their possessing a cingulum. Trileites fulgens (Zerndt) comb. nov. Plate 26, fig. 2 1937 Triletes fulgens Zerndt, Type 8, Zerndt, p. 5, pi. 1, figs. 1-9. 1955 Laevigatisporites fulgens (Zerndt) Potonie and Kremp, p. 53. Description. Only one complete specimen has been found in the present material. It has a subcircular amb, with diameters 403 p and 428 p. The triradiate mark is 150 p long, i.e. § radius or more, with labra 30 p high at the apex and 25 p broad. The triradiate mark terminates at arcuate ridges, wedge-shaped in profile, 10 p broad and 15 p high, which delimit the contact faces. The wall is 10 p thick. By reflected light the exine appears smooth and shiny, but by transmitted light it is seen to be scabrate. With the aid of an oil immersion objective a thin, folded, laevigate mesospore can be seen. Occurrence. Wyboston Borehole, depth 720 ft. Remarks. This spore is excluded from Biharisporites because it lacks ornament. The orientation of this spore is slightly oblique, which indicates that it was spheroidal or sub- spheroidal in life, and therefore it does not belong to the genus Laevigatisporites (see Chaloner 1953, 1963). The Wyboston specimen is similar to the type species of Trileites, T. spurius Dijkstra, in the possession of long, high triradiate lips, strongly developed arcuate ridges, and lack of ornament. Dijkstra measured three specimens, the smallest of which is about double the size of the Wyboston specimen. The other Mesozoic species of Trileites all differ from the Wyboston specimen in lacking either high lips or arcuate ridges, or both. The Devonian species T. langi Richardson has barely discernible arcuate ridges and T. oxfordiensis Chaloner has reduced arcuate ridges. The Wyboston spore falls at the lower limit of the described size range of Trileites fulgens and its measurements are proportionately small. In appearance it closely resembles Zerndt’s figures of T. fulgens. Zerndt lays emphasis on the ‘greasy lustre’ of T. fulgens. MORTIMER AND CHALONER: DEVONIAN MEGASPORES 193 dehiscence the whole of the thin area was used as an exitus instead of splits occurring along the sutures as in most living triradiate spores. Previous records. Trileites langi was found by Richardson in most of the beds examined in the Orcadian basin, Eifelian and Givetian in age. He also records the similarity of T. langi to Archaeozonotriletes incrustatus Archangelskaya from the lower Frasnian of the Russian platform. The three specimens recorded by Winslow (1962, pi. 17, figs. 10-12) as Triletes sp. from the Bedford shale of Ohio (basal Mississippian) are also very similar to T. langi in size and appearance, and she has remarked on the unobtrusive continua- tions of the triradiate mark. An interesting comparison may also be made with the specimens of Triletes sellingi Sen (1958) from the Upper Devonian of Bear Island. These resemble Trileites in being smooth with a short triradiate mark ‘possibly extending up to often indistinguishable arcuate ridges’. The minute tubercular outgrowths, which sometimes occur, could be comparable to the scattered globules of exinous material noted by Chaloner 1963 in T. oxfordiensis. Sen’s reference of Nathorst’s specimens to Bentzisporites Potonie and Kremp, remains problematical, as there is no evidence of their possessing a cingulum. Trileites fulgens (Zerndt) comb. nov. Plate 26, fig. 2 1937 Triletes fulgens Zerndt, Type 8, Zerndt, p. 5, pi. 1, figs. 1-9. 1955 Laevigatisporites fulgens (Zerndt) Potonie and Kremp, p. 53. Description. Only one complete specimen has been found in the present material. It has a subcircular amb, with diameters 403 p and 428 p. The triradiate mark is 150^ long, i.e. | radius or more, with labra 30 p high at the apex and 25 p broad. The triradiate mark terminates at arcuate ridges, wedge-shaped in profile, 10 p broad and 15 p high, which delimit the contact faces. The wall is 10 p thick. By reflected light the exine appears smooth and shiny, but by transmitted light it is seen to be scabrate. With the aid of an oil immersion objective a thin, folded, laevigate mesospore can be seen. Occurrence. Wyboston Borehole, depth 720 ft. Remarks. This spore is excluded from Biharisporites because it lacks ornament. The orientation of this spore is slightly oblique, which indicates that it was spheroidal or sub- spheroidal in life, and therefore it does not belong to the genus Laevigatisporites (see Chaloner 1953, 1963). The Wyboston specimen is similar to the type species of Trileites , T. spurius Dijkstra, in the possession of long, high triradiate lips, strongly developed arcuate ridges, and lack of ornament. Dijkstra measured three specimens, the smallest of which is about double the size of the Wyboston specimen. The other Mesozoic species of Trileites all differ from the Wyboston specimen in lacking either high lips or arcuate ridges, or both. The Devonian species T. langi Richardson has barely discernible arcuate ridges and T. oxfordiensis Chaloner has reduced arcuate ridges. The Wyboston spore falls at the lower limit of the described size range of Trileites fulgens and its measurements are proportionately small. In appearance it closely resembles Zerndt's figures of T. fulgens. Zerndt lays emphasis on the ‘greasy lustre’ of T. fulgens. 194 PALAEONTOLOGY, VOLUME 10 which he only examined dry, by reflected light. He does not mention the presence of the mesospore, which would, of course, be invisible in a dry specimen. However, the meso- spore is sufficiently variable in its presence or absence in other megaspores (see discus- sion of Systematic Treatment) for this not to be considered an important character. Zerndt’s figures of T. fulgens show oblique as well as proximo-distal compressions, indicating that it was spheroidal or subspheroidal in life. Arnold (1950) comments that T. fulgens is easily recognized by its (subspheroidal) shape. It is noted that the only difference between the descriptions of Trileites spurius and Trileites fulgens is in their size. Previous records. Namurian A and B, Polish Coal Basin. Pennsylvanian, Michigan Coal Basin. Trileites wybostonensis sp. nov. Plate 26, figs. 3, 4 Diagnosis. Triradiate megaspores with circular amb, maximum diameter 250-880 p (mean 613 p; 17 specimens). Complete specimens with large arcuate secondary folds. Triradiate mark very short, 15-30 p long, averaging of spore radius, simple, straight, and without lips. Outermost exine layer continuous over thin, circular, apical area, with radius § to f of length of sutures. Inner exine layer forming darkened ring around thin area. Ring 10-20 p broad, proximally with steep edge (measured depth 10 p), but distally grading into normal exine thickness and colour; distal margin of dark ring some- times scalloped. Wall thickness at equator 9-12 p, surface scabrate. Holotype. Slide PF 3950, Plate 26, fig. 3. Occurrence. Wyboston Borehole, depths 721 ft., 722 ft. Dimensions. Maximum diameter range 250 -880 p (mean of 17 spores 613 p)\ wall thickness 9-12 p; triradiate mark of spore radius. Remarks. Spores with a short triradiate mark are usually placed in the genus Calamo- spora Schopf, Wilson, and Bentall, but this genus is characterized by its thin, laevigate, much folded wall, and relatively small size (under 350 p), so that to place the large thick- walled scabrate spores of T. wybostonensis here would be inappropriate. Large, relatively thick-walled, smooth megaspores, both with and without curvaturae, have previously been included in Trileites. In its very short triradiate mark, the present species differs from all others in the genus. In this respect its inclusion represents an extension of Potonie’s circumscription of the genus. T. wybostonensis particularly resembles T. langi in shape, wall thickness, ornament, and in having a thin apical area. It differs in the extreme shortness of the triradiate mark, the shape of the apical area, and greater size range. Infraturma apiculati (Bennie and Kidston) R. Potonie 1956 Genus hystricosporites McGregor 1960 Type species. H. delectabilis McGregor. Remarks. Two evidently similar genera have been erected to include megaspores with grapnel-shaped appendages and no prominent equatorial feature; Dierospora Winslow 1962 and Hystricosporites McGregor 1960. Despite the two-year interval between these MORTIMER AND CHALONER: DEVONIAN MEGASPORES 195 two works, the description of the genus Dicrospora was evidently drawn up before the publication of McGregor’s genus. Comparison of the type species of the two genera shows that they are in various respects closely similar. D. porcata is characterized by broad radiating ribs on the contact faces, but inspection of McGregor’s plate 1 1, fig. 13, shows that H. delectabilis also has this distinctive feature. In addition, both species have a wide size range ( D . porcata 70-550 p, H. delectabilis 145-340 n, both without the spines); the bifurcate tipped spines may have expanded or bulbous bases. An apparent point of difference between these authors’ descriptions is that D. porcata has the contact faces free of spines, whereas H. delectabilis has spines on both proximal and distal faces. Evidently McGregor does not mean that the proximal faces are covered with spines, since his plate 11, fig. 13, shows that the contact faces, which occupy about half the proximal face, are free of spines. Winslow’s plate 11, fig. 4, shows the same arrangement of spines extending on to the proximal face outside the contact areas. It is thus only difference of wording which at first glance makes the descriptions appear different. Another apparent difference in the descriptions of the two species is that Winslow refers to a ‘zonarial ridge’ in D. porcata, bearing 15-30 spines, whereas McGregor emphasizes that Hystricosporites lacks any equatorial flange or concentration of spines in the equatorial region. Winslow’s plate 11, fig. 4, shows that the ridge is not equatorial in position, and may better be regarded as representing arcuate ridges. On this interpretation there is no equatorial feature, as McGregor says. There is, however, in both D. porcata and H. delectabilis a concentration of spines on the arcuate ridges. An estimate of the number of spines on the ridges in McGregor’s plate 11, fig. 13, gives 20, which is within Winslow’s counts of 15-30. Another apparent difference is attributable to a difference of view. Winslow figures D. porcata in both proximo-distal and lateral orientations, and describes it as having prominent thin lips to the triradiate mark. These are not visible in her plate 11, fig. 4 (promixo-distal compression), but are seen in her plate 22, fig. 15 (lateral compression). McGregor only figures a proximo-distal compression and describes H. delectabilis as lacking ‘greatly elevated triradiate lips’. However, he does also speak of the lips being ‘sometimes raised and convoluted’; which is just the appearance that collapsed high thin lips give in proximo-distal compression. There are thus no significant points of difference and many striking points of simi- larity between D. porcata and H. delectabilis, as described and figured by their authors. Generally the measurements of the former encompass those of the latter, probably because Winslow measured 17 specimens and McGregor about 10. A puzzling feature is that Winslow estimates proximo-distally and laterally compressed specimens to be equally abundant in her population, whereas McGregor apparently only observed proximo-distal compressions. However, this does not affect the material similarity of the two species, which are concluded to be conspecific. The name Hystricosporites delectabilis McGregor has priority and Dicrospora porcata Winslow becomes its junior synonym. The other species of the genus Dicrospora described by Winslow including Dicrospora multifurcata should accordingly be referred to Hystricosporites. Hystricosporites multifurcatus (Winslow) comb. nov. Plate 26, figs. 5-9 1962 Dicrospora multifurcata Winslow, p. 52, pi. 11, figs. 4, 5, pi. 12, fig. 5, pi. 22, fig. 15. 196 PALAEONTOLOGY, VOLUME 10 Description. Triradiate megaspores with rounded triangular amb, body diameter 1 14 — 233 p (mean of 1 1 spores 173 p) plus long spines 70 p to 120 /x (mean 86 p). The tri- radiate mark is long, reaching the equator, and has thin membranous lips. In lateral compression the lips may be up to 60 p high at the apex. In proximo-distal compressions the curvaturae are seen as a membranous structure 15-20^ broad. The proximal face is scabrate. The remainder of the exine is covered with long, parallel-sided or, occasionally, tapering appendages, slightly expanded at the bases, and sometimes joined to an adjacent spine for part of their length. The spines do not taper at the tips, but are baculate, with 2-5 small spines, 1-5 p long, arising from the flat tops. The main spines are usually longitudinally grooved or fluted, but sometimes cylindrical, and the minute apical spines are always homogeneous in texture. Wall thickness 6-10 p distally, less proxim- ally. A mesospore is seen in five spores, i.e. in about half the observed specimens. Occurrence. Wyboston Borehole, depths 700 ft., 721 ft., 722 ft. Remarks. These spores are very close to the description and figures of Dicrospora malti- furcata. Winslow only describes spores with striate spines and suggests that this appear- ance may be due to collapse of a hollow structure. Our observation of homogeneous spines on some well-preserved specimens suggests that the striation may be an effect of corrosion. Winslow does not mention a mesospore, but since specimens with and without it, but comparable in all other respects, are about equally abundant in the Wyboston material, this is not considered a specific difference. Previous records. D. multifurcata is recorded by Winslow from the uppermost Middle Devonian to basal Mississippian of Ohio. Hvstricosporites obscurus sp. nov. Plate 27, figs. 1-5 Diagnosis. Triradiate megaspores 177-440 p in equatorial diameter (mean of 31 spores 303 p), plus spines 18-60 p high; body characteristically dark and difficult to clear by maceration. Amb in proximo-distal compressions circular or rounded subtriangular. Lateral and oblique compressions frequently encountered. In lateral compression with subdued apical prominence formed by contact faces and high triradiate lips. Angle at apex approximately a right angle, maximum distance from apex to curvatura about | polar axis. Lips 60-150 p high at apex, thin. Contact faces about 10 p thick, remainder of wall 15-30 p thick. Curvaturae emphasized by close-set palisade of bifurcate spines. Bifurcate spines also scattered over remainder of exine, from 10-25 being seen at the margin of the spore. Spines 1 8-60 p high, i.e. \ to ^ of body diameter. In some spores spines EXPLANATION OF PLATE 27 All magnifications x 200, unless otherwise stated. Figs. 1-5. Hvstricosporites obscurus sp. nov. 1, Holotype, oblique view; Slide PF 3954. 2, Lateral view of characteristically dark specimen; PF 3955. 3, Proximal view of specimen sectioned, photographed in open glycerin jelly mount. 4, Section, showing shrunken mesospore; PF 3957. 5, Lateral view of specimen showing membranous lips and mesospore; PF 3956. Figs. 6-8. Bi/iarisporites simplex sp. nov. 6, Ornament of small rods and coni, X 1000. 7, Proximal view of specimen showing scabrate contact areas and characteristic secondary folds ; PF 3959. 8, Holotype, slightly oblique view showing triradiate mark and mesospore; PF 3958. Palaeontology, Vol. 10 PLATE 27 MORTIMER and CEIALONER, Devonian megaspores MORTIMER AND CHALONER: DEVONIAN MEGASPORES 197 arising directly from the exine and tapering from 12 g. wide at their bases to 3 /x, then bifurcating to form pitchfork or anchor-shaped ends, each prong tapering from 2 or 3 ft to zero over a length of 7-10 g. In other spores spines arising from either conical or bulbous bases, 25-30 g wide at base and 6-9 g high, and tapering sharply to 12 fx wide at base of main spine. Contact faces free of spines, scabrate. Remainder of exine between spines scabrate. Spines homogeneous in texture. Mesospore observed as a thin, folded inner membrane in eight spores, i.e. a quarter of the specimens. Holotype. Slide PF 3954. Body diameter 315 [x, spines 45 g. Plate 27, fig. 1. Occurrence. Wyboston Borehole, depths 720 ft., 721 ft., 722 ft. Dimensions. Body diameter 177-440 g (mean of 31 spores 303 /x); wall thickness 15-30 ft; spines 18-60 p high; triradiate lips 60-1 50 /x high. Remarks. The section parallel to the polar axis (PI. 27, fig. 4) shows that the main wall thickness is spongy in texture and envelops a thin, homogeneous layer (the mesospore), which is free from it. Dettmann and Playford (1963) illustrate a free homogeneous inner wall layer in Spinozonotriletes uncatus Hacquebard. They argue that this is intexine and refer to the ‘granular’ main wall as exoexine. H. obscurus differs in structure from 5. uncatus in a homogeneous zone at the inner margin of the exoexine. The spores of H. obscurus agree well with the generic diagnoses of McGregor ( Hystrico - sporites) and Winslow ( Dicrospora ) (see discussion of the genus Hystricosporites). H. obscurus differs from H. (al. Dicrospora) amherstensis in its relatively much shorter spines (| to ^ body diameter compared with 4) and generally smaller size, and from H. (al. D .) bedfordi in lacking a pseudoflange. H. obscurus lacks radiating ribs on the contact faces and thus differs from H. delectabilis McGregor, H. corystus Richardson, H. porrectus (Balme and Hassell) Allen, and H. costatus Vigran, all of which can be seen from their authors’ plates to possess this feature. It also lacks the distal extension of the exoexine (‘crumina’ of Allen) of H. coronatus Vigran. The five specimens assigned to ‘ Dicrospora sp. B’ by Winslow (body diameter 1 30— 50 g), however, have shorter spines (y to ^ body diameter) and may be small specimens of H. obscurus. The figure (Winslow, pi. 12, fig. 2) shows them to have a dark body. ‘£>. sp. B’ is from the Bedford shale in Ohio, i.e. basal Mississippian in age. Genus biharisporites Potonie 1956 Type species. B. spinosus (Singh) Potonie. Biharisporites simplex sp. nov. Plate 27, figs. 6-8 Diagnosis. Triradiate megaspores, originally more or less spheroidal, 200-630 /x in diameter (mean of 43 specimens, 309 /x), characteristically with large secondary folds. Triradiate mark J-§ of spore radius, simple, straight, and without labra. No arcuate ridges. Curvaturae not present as structures, but represented by a sharp or gradual change in surface ornament. Curvaturae emphasized, in about 10 per cent, of specimens, by secondary arcuate folding, but more often obscured by the large secondary folds 198 PALAEONTOLOGY, VOLUME 10 referred to above. Contact faces scabrate. Remainder of exine ornamented with small,, close-set coni, standing 1-1 J p high, and tapering evenly from bases \ p in diameter. Coni homogeneous in texture and remarkably constant in size, shape, and dense distri- bution. Coni usually entire, and often with axis of each cone curved. In a region 5-15 p wide, bordering the contact faces, sculptural elements reduced in size, but not coalesced.. Wall thickness 3-6 p. A thin walled, laevigate, folded mesospore observed in 19 spores,, i.e. under half of specimens. Holotype. Slide PF 3958; specimen with mesospore; Plate 27, figs. 6, 8. Occurrence. Wyboston Borehole, depths 700 ft., 720 ft., 722 ft.; most commonly found at 700 ft. Dimensions. Diameter range 200-630 p, mean of 43 spores, 309 p; wall thickness 3-5 p; triradiate- mark § of spore radius; coni 1-lip high, 1 p diameter at base. Remarks. Chaloner, in 1959, when describing B. ellesmerensis, has discussed whether Devonian spores should be placed in a genus based on Gondwanan (i.e. Carbo-Permian) material. B. submamillarius McGregor 1960 and B. parviornatus Richardson 1965, both based on Devonian material, have since been included in the genus. The tubercles of B. submamillarius bear tiny spines and the varied sculptural elements of B. parviornatus are terminated by short cones, so that both are as nearly ‘approximate to coni in Potonie’s sense’ (Chaloner 1959, p. 323) as B. ellesmerensis. B. simplex has coni less than twice as high as broad, which is clearly within Potonie’s sense. The mesospore reported in the type species, B. spinosus (Singh) Potonie, and also in B. myrmecodes ( Harris) Potonie and B. datmensis (Srivastava) Potonie, is not mentioned in the case of B. echinatus (Miner). Potonie (1956, p. 31) appears to regard it as a specific character of the types pecies. This has allowed freedom for the inclusion in the genus of B. ellesmerensis and B. ocksensis neither of which shows the mesospore, and B. submamillarius and B. parviornatus in which it is sometimes developed. A greater or lesser separation of the intexine to form a mesospore has also been noted in several other Palaeozoic megaspores, e.g. in Triletes globosus by Winslow (1959). Potonie describes the exine of Biharisporites as ‘thick, with small coni’. Particularly thick walls have been recorded in the cases of B. datmensis (15-20 p) and B. ocksensis (up to 40 p), but a thick wall has not been noted as a feature of other species, including the type species B. spinosus. In B. simplex the wall is not thick compared with the spore diameter, but from the figures it appears to be about the same relative thickness as in B. spinosus. It thus involves no morphographic extension of Potonie’s circumscription to include B. simplex in Biharisporites. Comparison. B. simplex differs from all other species of the genus in the absence of labra bordering the triradiate sutures. B. parviornatus most closely resembles B. simplex in general aspect and both have very small sculptural elements. B. simplex is different, however, in having regular ornament all of one type. Pettitt (1965) has recently described megaspores from Archaeopteris cf. jacksoni some of which show an evenly developed ornament of tiny coni, similar to that of B. simplex. In spite of a strong similarity in this and other aspects, these spores differ from B. simplex in having labra 5 p thick and in their smaller size. MORTIMER AND CHALONER: DEVONIAN MEGASPORES 199 Subturma lagenotriletes Potonie and Kremp 1954 Genus lagenoisporites Potonie and Kremp 1955 Type species. L. rugosus (Loose) Potonie and Kremp. Lagenoisporites sp. Plate 28, fig. 1 Description. Only two specimens have been found in the present material. The most complete and better preserved is a flask-shaped triradiate megaspore 378 p in maximum diameter including apical prominence. The prominence is equal in height to half the polar axis. The better-preserved specimen is split into three valves, the splits following the triradiate sutures and extending nearly to the distal pole. The contact faces thus lie free and flat. Each shows two darkened lines connecting the ends of an arcuate ridge and meeting at an angle of 120°. These lines represent the junction of lips and contact faces. The upper part of the contact face (about § of the median length) formed the elevated lips. The contact faces are delimited by low, gently curving arcuate ridges 6-9 p high. The ridges are about 15 p broad, fading distally into the exine surface. The spore wall is 20 p thick. The contact faces are 5 p thick. The exine is scabrate. Occurrence. Wyboston Borehole, depth 721 ft. Remarks. The apical prominence in this species differs from that of Lagenicula pauli- .spinosa sp. nov. in showing a clear demarcation between what may be regarded as con- tact areas and the elevated lips. Potonie and Kremp (1955) give the lack of any distinct ornament and a more or less smooth exine, coupled with possession of a gula, as the essential characters of the genus Lagenoisporites. They include in the genus both forms in which the gula (apical promi- nence) is formed by expansion of the whole contact faces (e.g. L. rugosus ), and those in which it is formed only by parts of the contact faces near the apex (e.g. L. simplex). Spinner (1965) has recently discussed the name Lagenoisporites and emphasized the importance of restricting this genus to megaspores with a completely smooth exine. The specimens from the Wyboston boring are not laevigate, but scabrate. They lack any measurable ornament, however, and so fall within Potonie and Kremp’ s slightly wider circumscription ‘more or less smooth’. Consequently, these specimens are placed in Lagenoisporites sensu Potonie and Kremp. The Carboniferous type species L. rugosus has a more or less smooth exine, and the apical prominence shows some variety of form. It has a wide size range, but the smallest specimens are larger than the Wyboston spores and have a relatively smaller apical prominence and punctate exine. Lagenoisporites nudus (Nowak and Zerndt) Potonie and Kremp has a smooth smaller apical prominence and the exine may be rugose. There thus seems to be no suitable species to which to assign these spores, but the material is so far insufficient for the erection of a new species. Genus lagenicula (Bennie and Kidston) Potonie and Kremp 1954 Type species. L. horrida Zerndt. 200 PALAEONTOLOGY, VOLUME 10 Lagenicula paulispinosa sp. nov. Plate 28, figs. 4-5; text fig. 1 Diagnosis. Flask-shaped triradiate megaspores 390-565 g in maximum dimension (mean of 5 spores 473 g), including apical prominence. Conical prominence formed by the whole of the contact faces and at its maximum extent equal in height to half the polar axis. Contact faces delimited by low gently curving arcuate ridges about 15 g broad and 10 g high. Spore wall 15 g thick. Body with scattered relatively short spines 9-12 g high standing on conical bases approximately 5 g at base and 5 g high, and then tapering gradually to the apex. Spines homogeneous, remainder of exine finely granular. Orna- ment continued on to the contact faces as cones and verrucae diminishing in height towards spore apex. text-fig. 1. Ornament on two typical areas of exine of Lagenicula paulispinosa. Drawn on photographic prints, which were afterwards bleached out; x 500. Holotype. Slide PF 3961 ; Plate 28, fig. 4. Occurrence. Wyboston Borehole, depth 721 ft. Remarks. The spines are commonly broken off leaving the conical bases only as orna- ment. L. paulispinosa is distinguished from L. subpilosus forma major (Dijkstra) ex Chaloner by its shorter, sparser, and stouter spines, and by its much smaller size EXPLANATION OF PLATE 28 All magnifications x200, unless otherwise stated. Fig. 1 . Lagenoisporites sp., lateral view of specimen flattened into three segments, x 100; Slide PF 3960. Figs. 4, 5. Lagenicula paulispinosa sp. nov. 4. Holotype, lateral view showing well-developed apical prominence; PF 3961. 5, Free segment showing reduced ornament on raised lip, X 100; PF 3962. Figs. 2, 3, 6-10. Heliosporites variabilis gen. et sp. nov. 2, Proximal face of specimen with spines on cingulum, x 100; PF 3963. 3, Holotype, proximal face, showing short triradiate ridges on exoexine and cingulum of bizonate appearance with radial striae, x 100; PF 3964. 6, Specimen with relatively short triradiate ridges and thin outer part to cingulum, x 100; PF 3967. 7, Proximal view of separation between intexine and exoexine, X500; PF 3966. 8, Specimen sectioned, photographed in open plastic mount. 9, Section, showing separation of intexine and exoexine, high lips and wedge-shaped cingulum; PF 3965. 10, Proximal view of spore lumen, showing folded intexine, X500; PF 3968. Palaeontology, Vol. 10 PLATE 28 f. ' j '-r KSfc*1 10 MORTIMER and CHALONER, Devonian megaspores MORTIMER AND CHALONER: DEVONIAN MEGASPORES 201 (about half). L. devonica Chaloner, which is of comparable size, has a lower apical prominence and lacks spines, being ornamented with rugulae and muri, and indeed L. devonica differs from all other species of the genus in its very subdued apical feature. The ornament of L. paidispinosa is of such small dimensions that it is not evident when a specimen is observed dry, by reflected light. When viewed under these conditions, the exine then comes within the description ‘more or less smooth’ which is Potonie’s criterion for Lagenoisporites. These two megaspore genera were originally founded on species described from observation of dry specimens, so that it is possible that spores belonging to Lagenicu/a paidispinosa , if only observed dry, might be placed in Lagenoi- sporites. However, megaspores should ideally be observed by transmitted as well as reflected light, which may provide extra information, as in this case. Since L. paidi- spinosa has a small-scale ornament of discrete sculptural elements, it is assigned to Lagenicula rather than Lagenoisporites. Turma zonales (Bennie and Kidston) Potonie 1956 Subturma zonotriletes Waltz 1935 Infraturma cingulati Potonie and Klaus 1954 Genus heliosporites gen. nov. Heliosporites variabilis sp. nov. Plate 28, figs. 2, 3, 6-10 Diagnosis. Triradiate megaspores with rounded sub-triangular amb, maximum dia- meter 190-535 p (mean of 35 specimens 318 p). Exine two-layered. The outer layer, or exoexine, spongy in texture and entirely enclosing the intexine. The two layers attached over the entire distal face of the spore lumen, but with a cavity between them in the region of the proximal face, deepest at the proximal pole and diminishing towards the equator (PI. 28, fig. 9). In optical section a slight gap may be seen around the periphery of the inner body (PI. 28, fig. 7). Exoexine thickened centrifugally to form a massive wedge-shaped cingulum which tapers towards the equator, sometimes evenly, giving the cingulum a homogeneous appearance in plan view, and sometimes unevenly, giving a slightly bizonate appearance with an indistinct thicker inner part near the spore lumen, and an outer membranous part. The cingulum, in either case, may be simple and entire, or show fine radiating striae, or foveae of various sizes, or develop a small number of wide-based spines or baculi. Triradiate lips formed only of exoexine, highest at the proximal pole and extending on to and sometimes across the cingulum. Lips membranous, and in well-preserved specimens showing fine close-set parallel ribs. Surface of exoexine scabrate. Inner layer, or intexine, homogeneous in structure and forming a thin ( 1-3 p) laevigate wall to the central lumen with distinct sutures extending about \ of its own radius. The central lumen occupying about § of the total diameter of the spore, sometimes with the proximal face secondarily folded (PI. 28, fig. 10). Holotype. Slide PF 3964; Plate 28, fig. 3. Occurrence. Wyboston Borehole, depths 700 ft., 720 ft., 721 ft., 722 ft. Dimensions. Maximum diameter 190-535 p (mean of 35 spores 318 p); ratio of spore lumen to total 202 PALAEONTOLOGY, VOLUME 10 diameter, 1:2-5; length of lips from § to length of total radius; height of lips up to 35 ju at apex. Number of spores having spines on cingulum, 4 out of 35 examined. Remarks. These spores are seen in section to have a wedge-shaped cingulum, as defined by Potonie and Kremp (1955), and figured in sections of Densosporites by Hughes, Dettmann, and Playford (1962). Zonalesporites brasserti (Zerndt) Potonie and Kremp has an equatorial feature which, although described by Potonie and Kremp as a ‘cingulum’, differs somewhat from that of Densosporites in being composed of many overlapping and partially fused hair-like elements. This equatorial feature is, moreover, of different texture from the body of the spore and is often found separated from it (e.g. Zerndt 1934, pi. 23, figs. 7, 12). Damaged specimens from the Wyboston boring do not break in this way, but may be broken across both cingulum and central area, or part of the cingulum may be chipped away. This cohesion is due to the continuity of the cingulum with the exoexine over the central area. In addition to this difference in structure, in Zonale- sporites the ratio of the body to the total diameter is much larger (1:1-5 mean value taken from measurements of published figures) than in the Wyboston spores <1 : 2-5). The type species of the genus Triangnlatisporites Potonie and Kremp, T. triangulatus, which appears by transmitted light to have a homogeneous equatorial feature, also differs in structure from H. variabilis. Guennel (1954) has demonstrated that in T. tri- angulatus the central body is free of exoexinous covering over the contact faces. The central body may be entirely freed from this covering either in fossilization or prepara- tion, and either part of the spore may be found separately (Guennel, pi. 1, fig. c; Hoskins and Abbott, fig. 14). The megaspores of Selaginellites suissei Zeiller (Chaloner 1954) and S. crassicinctus Hoskins and Abbott (1956) agree closely with T. triangulatus. Hoskins and Abbott’s sections show the flange to have a dense margin against the central body, and not to thin out progressively towards the outer margin, which is rounded in section. Sections of H. variabilis show all parts of the exoexine to be of equal density, and the outer margin is acute in section. Thus the structure of Heliosporites variabilis is such that it cannot be included within any existing megaspore genus, and we accordingly propose a new genus based on this species. The cingulum and small cavity between the exoexine and the intexine of H. variabilis recall the structure of the microspore genus Densosporites (Berry) Butterworth et al. A small cavity between the exoexine and the intexine was first demonstrated in Denso- sporites by Smith (1960), and later in sections by Hughes, Dettmann, and Playford (1962) Allen (1966) has emphasized that Densosporites is excluded from the category of ‘cavate’ spores, and we accept this. Heliosporites is therefore placed with Densosporites, in the infraturma Cingulati. The sections of Cirratriradites avius figured by Allen show an interesting proximal separation between the spore wall layers, analogous to that seen in H. variabilis. In other respects, of course, the structure of C. avius is very different, since the exine is three layered and the exoexine across the distal face surprisingly thick (as also demonstrated in C. elegans by Hughes, Dettmann, and Playford). Cirratriradites, of course, falls within the usually accepted size limits for assignation to a miospore rather than a megaspore; indeed, certain species are known to represent lycopod microspores (Chaloner 1954; Hoskins and Abbott 1956). MORTIMER AND CHALONER: DEVONIAN MEGASPORES 203 Previous records. No megaspores comparable with H. variabilis have been recorded previously, with the possible exception of Hymenozonotriletes corrugatus Archangelskaya (1963) from the lower Frasnian of the Russian platform. This is a spore of the same general shape and size range as Heliosporites variabilis and with a wide ‘otorochka’. The ‘otorochka’ is described as having a finely or deeply notched margin (similar to the chipped margin of corroded specimens of H. variabilis ). It sometimes shows isolated spines or ramifying small folds and veinlets; the triradiate mark has high lips and may or may not extend across the ‘otorochka’. All these features may be seen in H. variabilis. It is unfortunate that the Russian word ‘ otorochka ’ covers both a solid border (cingulum or zona) and a hollow border (saccus). However, Archangelskaya evidently understands her spore to be saccate, since she says ‘spore coats meet only in polar regions’; and this is borne out by her mention of small folds in the ‘otorochka’. Her figures (PI. 14, figs. 1, 2) throw no further light on this aspect. Fig. 1 shows such small folds, but fig. 2 is very similar to corroded H. variabilis (several of the Wyboston specimens show such a darkened central area, and radial folding in the thinner part of the cingulum). In view of Archangelskaya’s comment, we prefer to treat our spore as specifically distinct for the time being. Infraturma zonati Potonie and Kremp 1954 Genus triangulatisporites Potonie and Kremp 1954 Type species. T. triangulatus (Zerndt) Potonie and Kremp Triangulatisporites sp. Plate 29, figs. 1-3 Description. Triradiate megaspore with rounded triangular amb, 1450 p in maximum diameter (only one complete specimen measured). It has a relatively narrow equatorial flange (zona) from 50 p to 125 p wide, not always widest at radial extremities. The sutures are long, equal to radius of spore cavity. The lips are 125 p high at apex, de- creasing to about J of original height at margin of spore cavity, there diverging and merging with flange. The proximal face in the immediate vicinity of the apex is free of ornament. About J distance towards equator radiating rugulae develop, about 15 p high and wide. These either continue in radiating alignment to margin of the spore or inter- connect to form an irregular reticulum. The flange is either membranous with radiating ribs, or somewhat thicker with verrucae and rugulae on its surface. The ornament is con- tinued on the distal surface as an irregular polygonal reticulum with lumina 60 p to 100 yu. across. Occurrence. Wyboston Borehole, depth 720 ft. Remarks. This species is readily recognizable by its distinctive ornament and equatorial feature. Twelve fragments with a maximum dimension of 800 p or more, have been found, usually representing one-third of a spore, which has split along the triradiate sutures. The specimens are always strongly compressed. The equatorial feature is usually attached. The Mesozoic megaspore genus Horstisporites Potonie 1956, has variable reticulate ornament, but lacks any equatorial feature. Species of the Palaeozic genus Triangulati- sporites have been demonstrated by Guennel 1954 and by Spinner 1965 to consist of a C 4471 P 204 PALAEONTOLOGY, VOLUME 10 simple central body which may be detached from an outer layer forming the lips, equatorial feature, and reticulum, but in our spore there is no sign of this double structure. The equatorial feature in our spore is not a typical zona, but it does in some cases resemble the compound equatorial feature of the Upper Devonian species T. rootsi Chaloner, although always without gaps. The ratio of the spore lumen to the total diameter is 1 : 1 -2, compared with a typical figure for other species of Triangulatisporites of 1 : T3 (taken from measurements of published figures). In other respects our spore agrees well with Triangulatisporites, and in view of the limited material available this seems the most appropriate generic assignment. Genus zonalesporites (Ibrahim) Potonie and Kremp 1954 Type species. Z. brasserti (Stach and Zerndt) Potonie and Kremp. Zonalesporites sp. Plate 29, fig. 4 Description. Only one near-complete specimen has been found. It is a triradiate mega- spore with rounded-triangular amb. The dimension from the apex of the triangle to the midpoint of the opposite side is 1400 p. The triradiate mark has straight raised ridges, 65 p broad at the apex of the spore, and running onto and across the cingulum, 25 p broad at extremities. It has a massive wedge-shaped cingulum 125-225 p broad, broadest opposite the ends of the triradiate sutures. The cingulum has a narrow, darkened inner ring near the spore lumen. The darkened ring is further emphasized by a secondary fold in the distal surface. The cingulum is continuous with the exine over the spore lumen. The exine is apparently of two layers, which peel apart at the broken edges. On the proximal face the exine is relatively thick, without folds, and on the distal face it is thinner. Occurrence. Wyboston Borehole, depth 700 ft. Remarks. This species resembles those of Triangulatisporites in having a homogeneous equatorial structure, but it is not a zona, nor is it detachable from the central body. The species further differs from Triangulatisporites in the thickness of the distal face (in Triangulatisporites this carries the reticulum and is continuous with the zona), in the absence of any trace of a reticulate ornament and in the markedly larger size (about EXPLANATION OF PLATE 29 All magnifications x 50 unless otherwise stated. Figs. 1-3. Triangulatisporites sp.. Proximal view of specimen, photographed by transmitted light to show narrow zona; PF 3969. 2, Distal view of same specimen, photographed dry by reflected light to show reticulum. 3, Part of zona, by transmitted light, x 200. Fig. 4. Zonalesporites sp.. Proximal view of near-complete specimen, showing continuity of cingulum with central area and long triradiate ridges; PF 3970. Figs. 5-7. Cystosporites devonicus Chaloner and Pettitt. 5, Lateral view of large fragment with apex: PF 3971. 6, Miospore appressed to surface of same specimen, x 500. 7, Detail of haptotypic features of same specimen, x 200. Figs. 8-10. Cystosporites sp. 8, Lateral view of fragment, possibly with distal extremity, showing longi- tudinal striae in equatorial region; PF 3973. 9, Miospore appressed to same specimen, x200. 10, Lateral view of fragment broken along triradiate sutures and showing darkened apical area; PF 3972. Palaeontology, Vol. 10 PLATE 29 R :V->« ^ ®bBP IJy'. | ft a..i> 10 MORTIMER and CHALONER, Devonian megaspores MORTIMER AND CHALONER: DEVONIAN MEGASPORES 205 double). The ratio of the spore lumen to the total diameter is 1:1-5, which is less than the mean value for Triangulatisporites but the same as the mean value for Zona/esporites (1 : 1-5). Spinner (1965) has emended the genus Zona/esporites to include megaspores with some range of equatorial features from a corona to a zona. However, Zona/esporites sp. differs from other members of Zona/esporites s.l. in the continuity of the body and cingulum, and in the unusual feature of a distal face thinner than the proximal. It is, however, included in the size range for the genus and lacks any body ornament, in addition to the points of similarity mentioned above, so that this generic assignation is preferred for the time being. Fragments of this species are quite frequently encountered in the Wyboston material, usually representing a sector of the spore, broken apart along the triradiate mark. Turma cystites Potonie and Kremp 1954 Genus cystosporites Schopf 1938 Type species. C. breretonensis Schopf. Cystosporites devonicus Chaloner and Pettitt 1964 Plate 29, figs. 5-7 Description. Two specimens have been found, each representing the large (‘fertile’) member of the tetrad, but neither of them complete. Both are of an elongate shape, oval at one end and broken off at the other, lengths 880 p and 1200 p. The triradiate mark is near the rounded end, 150 p in maximum extent, and on the better-preserved specimen showing lips 3 p wide. The contact areas are weakly developed and the arcuate ridges not discernible. The entire exine is scabrate. The exine is 3-5 p thick in one case and 5-10 p in the other, apparently of a single layer. Arcuate and longitudinal folds follow the shape of the spores. The distal end of the spore is missing in each case. No other abortive spores were found adhering to the contact faces. Occurrence. Wyboston Borehole, depths 720 ft., and 721 ft. Remarks. These spores have the polar axial elongation characteristic of the fertile mem- ber of a Cystosporites tetrad. In the haptotypic features, in the finely granular nature of the whole exine and in the longitudinal folding, they are closely comparable to C. devonicus , which is from the basal Frasnian of Scaumenac Bay, Quebec (Westoll in Richardson 1965). Associated miospores. There are two spores adhering to the exine of one specimen, of 55 p and 60 p diameter respectively. They have long, simple triradiate marks and a narrow equatorial feature (about 5 p). They are very similar to the two miospores found by Chaloner and Pettitt adhering to the surface of C. devonicus and referred by them to cf. Lycospora sp. Chaloner and Pettitt have discussed the significance of the occurrence of their Cysto- sporites at this Upper Devonian horizon. This additional record (and the following one) confirms their report, and demonstrates that this extreme development of heterospory was not an exceptional isolated occurrence in the Scaumenac Beds. 206 PALAEONTOLOGY, VOLUME 10 Cystosporites sp. Plate 29, figs. 8-10 Description. Three elongated fragments of megaspores have been found, 504 p, 1385 p’ and 1575 p in length respectively. Two are split along the triradiate sutures, leaving only one valve in the apical region (PI. 29, fig. 10) and the third has an irregular prolongation of the exine obscuring the intact end. The apices are darkened in a region of 20-25 p radius, which probably represents the contact areas. The exine is scabrate, except in the central (equatorial) regions, where longitudinal striae give a fibrous appearance. The wall is 9-12 p thick, splitting into two layers at the rough edges. There are no secondary folds. Occurrence. Wyboston Borehole, depth 721 ft. Remarks. These spores have the polar axial elongation characteristic of the fertile megaspore Cystosporites. The irregular prolongation of the exine at the end of one specimen may be a distal stalk similar to that of C. devonicus and C. giganteus (Zerndt) Schopf but it is not certain that it is in fact at the distal end of the spore. The spores differ from C. devonicus in the small contact areas and the nature of the exine in the central area. Associated miospore. One thin-walled spore, diameter 60 p, and with a short simple triradiate mark is appressed to one fragment. THE AGE OF THE MEGASPORES The megaspores have been found at depths between 700 and 720 ft. in the Wyboston Borehole. Fish fragments which occur at depth 560 ft. 3 in. have been compared to the genus Bothriolepis, which indicates a Middle or Upper Devonian age, with a probability in favour of the latter (H. A. Toombs pers. comm, to W. G. C. 1965). Only three of the megaspore species have been reported previously. Trileites langi is known from the Eifelian and Givetian of the Orcadian basin (Richardson 1965), and similar forms from the lower Frasnian of the Russian platform (Archangelskaya 1963), the Upper Devonian of Bear Island (Sen 1958), and the basal Mississippian of Ohio (Winslow 1962). Hystricosporites (al. Dicrospora ) nndtifurcatus is only known in Ohio, and there ranges from Upper Middle Devonian to basal Mississippian. Cystosporites devonicus is only known from the basal Frasnian of Quebec (Chaloner and Pettitt 1964). To these may be added the occurrence of Hymenozonotriletes corrugatus (which may be comparable with Heliosporites varicibilis ) in the lower Frasnian of Bashkir (Archangel- skaya 1963). Together these suggest a late Middle Devonian or more probably early Upper Devonian age. The megaspores are accompanied by well-preserved assemblages of miospores, show- ing a wide diversity of morphology. Spores with bifurcate appendages are especially abundant. It is hoped that these will form the subject of a later paper. The occurrences of spores with bifurcate spines, and of other distinctive genera found in the Wyboston Borehole and previously recorded in other places, are summarized in text-fig. 2. In comparing these records it must be noted that the Orcadian Old Red Sand- MORTIMER AND CHALONER: DEVONIAN MEGASPORES 207 stone sequence comes to an end in the Givetian, and the Spitsbergen Devonian succes- sion low in the Frasnian. In Western Australia only Frasnian sediments were sampled in the Caernarvon Basin and Famennian in the Canning Basin. More weight must there- fore be given to the records from the succession of the Russian platform which runs from the Eifelian to the top of the Devonian system and on into the Carboniferous, and SPORE GENUS FAMENN 1 AN FRASNIAN GIVETIAN 1 EIFELIAN EMSI AN SIEGENIAN GEDIN N IAN o text-fig. 2. Chart of the ranges in the Devonian period of some spore genera found in the Wyboston Borehole. has been studied by several workers. These Russian records indicate a Givetian or lower Frasnian age for the Wyboston assemblage. It must be noted, however, that some important papers (e.g. Tchibrikova 1959, 1962 and Archangelskaya 1963) are, like the present paper, based on material from borings which is dated only on palynological evidence. This tentative dating does, however, give some support to that suggested by the megaspores alone, and it is in line with the indication of the fish remains. POPULATION STUDIES OF SPORES WITH BIFURCATE SPINES It is emphasized that the assemblages here studied were not consciously selected in any way. As mentioned above, test slides were made in the various stages of the preparation procedures, to reassure us that there had been no sensible loss of any of the constituents. It is, however, also recognized that any preparation procedure is in its nature a selection of the spores out of all the other constituents of the rock samples, and that the 100 per cent, recovery of the total spore assemblage is an ideal rarely achieved. Different pro- cedures do discriminate to some extent against varying elements of the assemblage. This 208 PALAEONTOLOGY, VOLUME 10 has been quantified for three rock samples of diverse type by Hughes et al. (1964; see especially tables 6-8). Any attempt to compare spore assemblages must take account of this factor, and any difference between them must be of a greater order than that attri- butable to laboratory selection, before it can be significant. Large spores with bifurcate spines were abundant in all the samples discussed in this paper, but especially so in sample Bt 4284, at depth 700 ft., where they comprise over 75 per cent, of the assemblage. Spores with bifurcate spines have been widely reported from sediments of Middle and Upper Devonian age but only Richardson has commented table 1. Relative percentages of species with bifurcate spines at depth 700 ft., Wyboston Borehole. * Species recorded by Richardson from the Orcadian basin. °/ /O * Ancyrospora grandispinosa 9 *A. ancyrea var. brevispinosa 20 * A. ancyrea var. ancyrea 3 A. trocha 19 * A . longispinosa 2 A . langi 1 Other species of Ancyrospora 31 Hystricosporiles delectabilis 14 *Perotrilites bifurcatus 1 100 on an abundance of them. He estimates them often to form as much as 50 per cent, of the assemblage from localities throughout the Orcadian Basin (Richardson 1962). Some comparison has been made with Richardson’s work on the stratigraphic distribution of such spores in the Orcadian basin. Table 1 shows the relative percentages of the various species with bifurcate spines at depth 700 ft. Richardson’s table (1962, fig. 14) shows that in Orcadia Ancyrospora ancyrea is not associated with A. grandispinosa, A. longi- spinosa, and Perotrilites bifurcatus above the Achanarras horizon, which straddles the Eifelian-Givetian boundary. However, only 35 per cent, of the bifurcate-spined spores from Wyboston correspond with the species found in the Orcadian basin. Text-fig. 3 shows a plot of spine length against body to spore-diameter ratio, similar to Richardson’s 1962 table, and shows a scatter distinct from either of the two populations plotted by him (Eifelian-Givetian and M. Givetian respectively). If this were due to a slight evolu- tionary difference between the Wyboston spores and the Orcadian spores, the inference would be that the former are of earlier age than the latter. The available palaeontological evidence indicates the reverse to be the case. A small difference in depositional environ- ment could, however, readily account for such a difference in population. Spores re- covered from clastic sediments must have been subject, in the process of sedimentation, to the normal processes of sorting which are highly sensitive to differences of size and weight in the transported and deposited particles. The representatives of a single species in such a sedimentary environment will have a ‘population structure’ which may be a very modified version of that of the biological population from which it was derived. Apart from spores with bifurcate spines, little comparison with the Orcadian assem- blages is possible, since both spores with biform appendages and spores with pointed spines are infrequent in our material. MORTIMER AND CHALONER: DEVONIAN MEGASPORES 209 THE DISTINCTION BETWEEN MEGASPORES AND MIOSPORES McGregor (1960), Richardson (1962), and Winslow (1962) have remarked on the considerable range in size observed in some Middle and Upper Devonian species, straddling the 200 /x figure which in the Carboniferous is a practical, if arbitrary, dividing line between megaspores and miospores. This feature is illustrated again in two species from the Wyboston material, Heliosporites variabilis (diameter range 190-535 /x), and text-fig. 3. Scatter diagram to show ‘body ’/spore diameter ratio plotted against spine length of Ancyrospora ancyrea ; based on 35 specimens from depth 700 ft., Wyboston Borehole. Hystricosporites obscurus (diameter 1 77-440 /x). Richardson and Winslow have sug- gested that the variable size of these spores may be related to the incomplete establish- ment of heterospory in the parent plants. Winslow mentions the possibility that while larger specimens of D. multifurcata (size range 100 p, to 300 /x without spines) may have functioned as megaspores, the smaller specimens may have functioned as their corre- sponding miospores. DISCUSSION The affinities of the megaspores. In addition to these genera whose sizes range across the 200 p, limit discussed above, several of the species described in this paper are smaller than the average size of Carboniferous megaspores. The upper size limit of Trileites langi is 400 /j. (Richardson 1965), of Hystricosporites obscurus 440 /x, of Lagenicula paulispinosa 565 /x, of Lagenoisporites sp. 420 /x, and of Biharisporites simplex 630 /x. However, others (e.g. Triangulatisporites sp., Zona/esporites sp.) are not much smaller than Carboniferous species of these genera. Such large megaspores have long been known from the Upper Devonian. Sen (1958) redescribed three species from the Upper 210 PALAEONTOLOGY, VOLUME 10 Devonian of Bear Island with size ranges between 1000 p and 2000 p which had been originally described but not named by Nathorst. Chaloner (1959) found specimens of Biharisporites ellesmerensis up to 1610 ft in diameter in the Upper Devonian of Ellesmere Island, and, commenting on the rise in mean size of megaspores from the Devonian into the Upper Carboniferous, sought to correlate this with the rise of the arborescent lycopods during the latter period. The species of megaspores described in this paper have a mean maximum size of 810 ft, considerably below the Upper Carboniferous mean of 1600 ft cited by Chaloner, and to this extent they are consistent with the pattern of pro- gressive size increase suggested by the earlier evidence. Although many of the very large Carboniferous megaspores are now known to be correlated with arborescent lepidodendrids and sigillarians, size of the megaspore alone is no reliable indication of size of the parent plant. Some of the largest lepidostrobi (e.g. Lepidostrobus browni ) were presumably borne on arborescent lepidodendrids and yet bore relatively small megaspores. Perhaps the only aspect of the present megaspore assemblage from which palaeobotanical deductions may safely be made is their con- siderable diversity of form. Only one Devonian lycopod ( Cyclostigma kiltorkense ) has been shown to be heterosporous. Only three other genera of Devonian plants ( Enigmo - phyton , Barinophyton, and Archaeopteris ) are believed to be heterosporous and these have singularly simple azonate megaspores. It is evident from the present study that the heterosporous plants of the Devonian must have far exceeded in number, and perhaps in diversity, their known representation in the megafossils. The rock samples. The samples between 700 ft. and 722 ft. 1 in. depth, in which the megaspores were found, are medium-grey flaggy siltstones or mudstones with silty partings. The horizontally bedded sequence is interrupted at depth 719 ft. 8-11 in. by a thin conglomerate. Plant remains of two kinds occur, and are concentrated on particular bedding planes. The more common are compressions of fragments of naked axes from 1 to 3 mm. broad and up to 5 cm. long. None show any spines, leaves, or other emergences. Many are longitudinally striate, some with one or more stronger central striae. They are probably fragments of spineless psilophytes. The less common are billets of wood up to 4-5 cm. broad and 9-5 cm. long, being limited in length by the size of the hand specimens. They have thickness up to 0-5 cm., are mostly coalified and partly pyritized, with subregular cross-fractures of the type described by Arnold (1934). One end of each piece is preserved on any one core, and is the rounded shape characteristic of water-worn wood. The wood is of the ‘gymnospermous type’, either Progymnospermopsida or possibly, true Gymno- sperms. Although on some fragments individual wood elements could be recognized, the details of pitting could not be discerned. There are fish teeth in the mudstone at 700 ft. depth (Bt 4284). Mica is common in the siltstone, sometimes covering a bedding plane. Pyrite is also common, in places forming groups of crystals in the body of the mudstone and partly replacing plant fragments. There is limonite staining round the larger plant fragments. Small particles of coaly material are common throughout. There is very little calcium carbonate. Other samples, less rich in spores, show fragmentary lamellibranchs and ostracods, also concentrated on particular bedding planes. All the fossils so far mentioned could have been deposited in a freshwater environ- MORTIMER AND CHALONER: DEVONIAN MEGASPORES 211 ment. Some other microfossils have also been found in the spore preparations. These are rare acritarchs and occasional chitinozoans and conodonts. The first two groups belong to simple long-ranging types and it is possible that they have been reworked from older sediments. In the case of the conodonts this seems less likely, since they are well pre- served. Cases of reworked conodonts are known and have been discussed by Lindstrom (1964) and Krebs (1964). Both admit that well-preserved conodonts may be reworked. On the other hand, the occurrence of the conodonts accords with Youngquist’s observa- tion (1951) that these fossils are commonly associated with plant remains in a near-shore environment, and also frequently with fish remains. The oscillation in grain size and fossil content, suggests a shallow-water environment, with occasional downwashes of plant material from nearby land, but the degree of salinity of the environment is not known. REFERENCES allen, k. c. 1966. Lower and Middle Devonian spores of North and Central Vestspitsbergen. Palaeontology , 8, 687-748, pi. 94-108. archangelskaya, A. d. 1962. A new spore assemblage and the problem of the Middle and Upper Devonian boundary in the Volga-Ural region. Dokl. Akad. Nauk, 142 [In Russian; English trans- lation in Dokl. (Proc.) Acad. Sci. USSR , 142, 55-56 publ. by Amer. Geol. Inst., Washington 1964. 1963. New spore finds from Devonian deposits of the Russian platform. Ministerstvo. geol. i ochroni Nedr. SSSR , Moscow, 37, 18-30 [In Russian], Arnold, c. a. 1933. A Lycopodiaceous strobilus from the Pocono Sandstone of Pennsylvania. Amer. J. Bot. 20, 1 14—17. 1934. The so-called branch impressions of Callixylon newberryi (Dn.) Elkins and Wieland and the conditions of their preservation. J. Geol. 42, 71-76. 1950. Megaspores from the Michigan Coal Basin. Contr. Mas. Paleont. Univ. Mich. 8, 59-111. balme, b. e. 1960. Upper Devonian spores from the Caernarvon Basin, Western Australia. Palaeo- botanist, 9, 1-10. and hassell, c. w. 1962. Upper Devonian spores from the Canning Basin, Western Australia. Micropaleontology, 8, 1-28. butterworth, m. a. et al. 1964. Densosporites (Berry) Potonie and Kremp and related genera. Report of C.I.M.P. Working Group No. 2. C.R. 5. Congr. Int. Strat. Geol. Garb. Paris. chaloner, w. g. 1953. On the megaspores of Sigillaria. Ann. Mag. Nat. Hist. 6, 881-97. 1954. Notes on the Spores of two British Carboniferous lycopods. Ann. Mag. not. Hist. 12 (7), 81-91. 1959. Devonian megaspores from Arctic Canada. Palaeontology, 1, 321-32. 1963. Early Devonian spores from a borehole in Southern England. Grana Palvnologica, 4, 100-10. and pettitt, j. m. 1964. A seed megaspore from the Devonian of Canada. Palaeontology, 7, 29-36. couper, r. a. and grebe, h. 1961. A recommended terminology for spores. Unpublished report of C.I.M.P. working group. Krefeld. dettmann, m. e. 1961. Lower Mesozic megaspores from Tasmania and South Australia. Micro- paleontology 7, 71-86. 1963. Upper Mesozoic microfloras from South Eastern Australia. Proc. R. Soc. Victoria, 77, 1-148. dijkstra, s. J. 1946. Eine monographische Bearbeitung der karbonischen Megasporen. Meded. geol. Sticht. Ser. C-III-I, 101 pp. 1951. Wealden Megaspores and their stratigraphical value. Meded. geol. Sticht. n.s. 5, 7-21. edmonds, e. A. and dinham, c. h. 1965. Geology of the country around Huntingdon and Biggleswade. Mem. Geol. Surv. U.K. 212 PALAEONTOLOGY, VOLUME 10 Edmunds, F. H. 1956. In Mem. Geol. Surv. Summ. Prog, for 1955, p. 32. felix, c. J. 1954. Some American arborescent lycopod fructifications. Ann. Mo. Bot. Gdn. 41, 351-94. guennel, g. h. 1954. An interesting Megaspore species found in Indiana Block Coal. Butler Univ. bot. Studies, 11, 169-77. Harris, t. m. 1935. The fossil flora of Scoresby Sound, East Greenland, part 4. Meddr Gronland, 112, 1-176. H0EG, o. a., bose, m. N., and manum, s. 1955. On double walls in fossil Megaspores. Nytt Magasin for Botanikk, 4, 101-7. hoskins, J. h. and abbott, m. l. Selaginellites crassicinctus, a new species from the Desmoinesian series of Kansas. Am. J. Bot. 43, 36^16. hughes, n. f. 1964. Extraction of spores and other organic microfossils from Palaeozoic clastic sedi- ments and coals. Report of C.I.M.P. working groups 10 and 11. C.R. 5. Congr. Int. Strut. Geol. Curb. Paris. dettmann, m. e., and playford, g. 1962. Sections of some Carboniferous dispersed spores. Palaeontology, 5, 247-52. krebs, w. 1964. Zur faziellen Deutung von Conodonten-Mischfaunen. Senckenberg. leth. 45, 245-84. lindstrom, m. 1964. Conodonts. Elsevier. Amsterdam. mcgregor, d. c. 1960. Devonian spores from Melville Island, Canadian Archipelago. Palaeontology, 3, 26-44. mollenhauer, h. h. 1964. Plastic embedding mixtures for use in electron microscopy. Stain Technol. 39, 111-14. naumova, s. n. 1953. Spore and pollen assemblages of the Upper Devonian of the Russian platform. Trudy Inst. Geol. Akad. Nauk SSSR, 143 (Geol. Ser. 60). [In Russian; French trans. B.R.G.M.] neves, r. and sullivan, h. j. 1964. Modification of fossil spore exines associated with the presence of pyrite crystals. Micropaleontology, 10, 443-52. pettitt, J. m. 1965. Two heterosporous plants from the Upper Devonian of North America. Bull. Br. Mus. nat. Hist. Geol. 10, 83-92. pierart, p. 1964. Decouverte de Megaspores et Miospores dans le Givetien de Roncquieres (Brabant, Belgique) Bull. Soc. beige Geol. Paleont. Hydro!. 73, 1, 82-100. playford, g. 1962. Lower Carboniferous microfloras of Spitsbergen, part 1. Palaeontology , 5, 550-618. 1963. Part 2. Ibid. 5, 619-78. potonie, r. 1956. Synopsis der Gattungen der sporae dispersae, Teil 1. Geol. Jb. Beih. 23. 1958. Teil 2. Ibid. 31. and kremp, g. 1955. Die Sporae dispersae des Ruhrkarbons, ihre Morphographie und Stratigraphie, mit Ausblicken auf Arten anderer Gebiete und Zeitabschnitte. Teil. I. Palaeonto- graphica 98 B. 1956. Teil II. Ibid. 99 B. pugh, w. J. 1956. In Mem. Geol. Surv. Summ. Prog, for 1955, p. 15. Richardson, J. b. 1960. Spores from the Middle Old Red Sandstone of Cromarty, Scotland. Palaeontology, 3, 45-63. 1962. Spores with bifurcate processes from the Middle Old Red Sandstone of Scotland. Ibid. 5, 171-94. 1965. Middle Old Red Sandstone spore assemblages from the Orcadian Basin, North-east Scotland. Ibid. 7, 559-605. schopf, j. m., 1938. Spores from the Herrin (No. 6) coal bed in Illinois. III. Geol. Surv. Rept. Inv. 50, 1-73. wilson, L. r., and bentall, r. 1944. An annotated synopsis of Paleozoic fossil spores and the definition of generic groups. Rep. invest. III. St. geol. Surv. 91, 1-72. sen, J. 1958. On the Megaspores described by Nathorst from the Upper Devonian of Bear Island. Geol. For. Stockh. Fork. 80, 2. spinner, e. 1965. Westphalian D Megaspores from the Forest of Dean coalfield, England. Palaeontology , 8, 82-106. surange, k. r., singh, p., and srivastava, p. n. 1953. Megaspores from the West Bokaro Coalfield (Lower Gondwanas) of Bihar. Palaeobotanist, 2, 9-18. MORTIMER AND CHALONER: DEVONIAN MEGASPORES 213 taugourdeau-lantz, j. 1960. Sur la microflore du Frasnien inferieure de Beaulieu (Boulonnais). Revue Micropaleont. 3, 144-54. TCHiBRicKOVA, E. v. 1959. Spores from Devonian and earlier deposits in Bashkir. Izd. Akad. Nauk SSSR , 3-175 [In Russian], 1962. Spores from Devonian terrigenous deposits of the Bashkir region and the southern slopes of the Urals. Akad. Nauk Bashkir, 353-476 [In Russian]. teichert, c. and schopf, J. m. 1958. A Middle or Lower Devonian psilophyte flora from Central Arizona and its palaeogeographic significance. J. Geol. 66, 208-17. tschudy, r. 1960. The vibraflute. Micropaleontology, 6, 325-6. vigran, J. o. 1964. Spores from Devonian deposits, Mimerdalen, Spitsbergen. Skr. norsk Polarinst. 132. winslow, m. r. 1962. Plant spores and other Microfossils from Upper Devonian and Lower Mississip- pian rocks of Ohio. Prof. Pap. U.S. geol. Surv. 364. youngquist, w. L., hawley, r. w., and miller, a. k. 1951. Phosphoria conodonts from south-eastern Idaho. J. Paleont. 25, 356-64. zerndt, J. 1934. Les Megaspores du Bassin Houiller Polonais, partie I. Trav. geol. Com. Pubis, sites. Acad.pol. Sci. Lett. 1, 1-55. 1937. Partie II. Ibid. 3, 1-78. M. G. MORTIMER, Geology Department, University College London, Gower Street, London, W.C.l W. G. CHALONER, Botany Department, University College London, Gower Street, Manuscript received 31 December 1965 London, W.C.l SILURIAN ODONTOPLEURID TRILOBITES FROM SWEDEN, ESTONIA, AND LATVIA by DAVID L. BRUTON Abstract. All of the presently known Silurian odontopleurid material from Sweden has been revised along with recently collected material from Estonia and Latvia. For the first time photographs are given of the holotypes- of Odontopleuva ovata Emmrich and Leonaspis mutica (Emmrich). Examination of the latter shows that it is specifically distinct from the Swedish species L. marklini (Angelin) and the British species L. coronata (Salter). Acidaspis lmghesi Lake is considered to be a synonym of O. ovata. The new genus Anacaenaspis (type species A. gotlandensis gen. et sp. nov.) is established for specimens which differ from Acidaspis Murchison in lacking the stout occipital spine. The holotype of ' Acidaspis ’ emarginata Schmidt is refigured and has been assigned to Anacaenaspis. Newly described are two species of Leonaspis, L. varbolensis from the lowermost Llandovery of Estonia and Latvia, and L. muldensis from the uppermost Wenlock of Gotland. A previous record of the Bohemian species Miraspis mira (Barrande) in the Silurian of Scania has not been confirmed and it appears likely that all the material belongs to M. cardiolarum (Hede). Many of the specimens have been illustrated with the aid of stereoscopic photographs. The Island of Gotland has attracted many palaeontologists to its shores and large collections of Silurian fossils have been made. Angelin (1854) in his ‘Palaeontologia Scandinavica’ illustrated the largest single collection of Silurian odontopleurids from Gotland but, unfortunately, his descriptions were all too brief and the stratigraphic locations are vague. Earlier, Loven (1845) described specimens of Leonaspis crenata (Emmrich) in great detail, and later Lindstrbm (1885) supplemented many of Angelin's descriptions with the aid of newly collected material. From the less abundant collecting areas in Vastergotland, Dalman (1828) described as Calymene? centrina (= Leonaspis centrina ) one of the first odontopleurid trilobites to appear in the literature. More recently Hede (1915) described specimens from the Colonus Shale of Scania. Outside Sweden, principally in Germany, Emmrich (1839; 1844-5), Beyrich (1846), Roemer (1885), and Wigand (1888) illustrated several specimens obtained from erratics of Graptolithengestein. These erratics, derived from the sub-Baltic outcrops of this horizon, were deposited during the penultimate (Saale) glaciation along the Pomeranian, coast and as far east as Silesia. Emmrich’s (1839) classic ‘Dissertatio de Trilobitis’, contains the description and illustration of Odontopleura ovata the type species of the genus Odontopleura. Schmidt (1885) described one odontopleurid species from the Silurian of Estonia. In 1963 it was my good fortune to be able to study the large collection of Silurian odonto- pleurids from Gotland at the Natural History Museum, Stockholm, and a smaller collection at the University of Uppsala. Specimens from Lund and the types of Emmrich and Beyrich from the Humboldt University, East Berlin, were obtained on loan and were examined at Uppsala. A visit to the Soviet Union in April and May 1965, enabled me to examine and photograph material recently obtained from borings which penetrated the Silurian suc- cession in Latvia and on the Estonian Baltic Islands of Saaremaa and this, and other material from Estonia, is described in this paper. [Palaeontology, Vol. 10, Part 2, 1967, pp. 214-44, pis. 30-36) DAVID L. BRUTON: SILURIAN ODONTOPLEURID TRILOBITES 215 The terminology used in this paper is the same as that employed in previous publi- cations (Bruton, 1965; 1966n, b). All specimens were lightly coated with ammonium chloride before photographing and, except where stated, were taken by the author. The isolated specimens obtained from the Mulde Marl were all mounted on pins and these have been blacked out where they showed on the print; otherwise the photographs have not been retouched. The stereoscopic pairs were made in the same manner as outlined in a previous publication (Bruton 1965, p. 344). Acknowledgements. I am most grateful to Professor E. Jarvik, Swedish Museum of Natural History