On Pal˦ozoic arcid˦

385

ORDINARY MEETING. FRIDAY, MAY 4TH, 1888. F. W. R.UDLER, Esq., F.G.S., Hon. Sec. A.I., President, in the Chair. The donations to the Library since the previous meeting were announced, and the thanks of the Association accorded to the various donors. The following were elected Members of the Association:-W. E. Darwin, B.A., F.G.S. j E. Evans; A. S. Foord, F.G.S.; Miss M. 1. Gardiner; F. May; and R. L. Mond. The following papers were then read :-' On Palreozoic Arcidle,' by Mr. J. LOGAN LOBLEY, F.G.S., and' On Pterodactyls,' by Mr. E. T. NEWTON, F.G.S.

ON PALEOZOIC ARCIDE. By J. LOGAN LOBLEY, F.G.S. So great is the number of fossil Lamellibranchs that hitherto there has been no such general and complete examination of British species as that to which the Brachiopods of British rocks were subjected by Dr. Davidson. The folluwing contribution to a general review of British Fossil Lamellibranchiata may therefore not be altogether without interest for this Association. Palreozoic forms of A rcidre possess, however, more than a mere systematic value, since they have a general scientific interest that will be recognized by all our Members. One of the two earliest families of the Lamellibranchiata known, if not quite the earliest, the Arcidre, flourish at the present time in all the seas of the globe, giving thereby a conspicuous proof of the marvellous continuity of bio-morphic types, or general organic form and structure, from early geological times to the' present day. But great as is the generally interesting character of this wonderful fact in itself, its significance or indirect teaching is exceedingly great also, for it VOL.

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clearly indicates th at other commandingly important fact, th e COIItinui ty of general inor gani c condit ions which must have existed to allow of the uninterrupt ed succession of ge nerally similar organisms, all requiring, therefore, a generally similar environment for th eir existence and welfare, as well as for the development of th e typ e. As silent, yet eloquent teachers of these g reat fact s, P alreozoic Arcidre arc sur passed by only one other zoological family, th e Lingul idai, fossil repr esent ativ es of which occur iu still earlier rocks than th ose in which th e remains of th e earliest kn own Arcidre have been found; whi lst this family of Br achiopoda, like th e Arcid re, is still existing , Ev en Li ngu las, however, are perh aps less cogent in their evidence t o th e untrav elled En glish naturalist, since we must go t o distan t seas to find a living L ingula, while highly developed and , so to speak, robust members of th e family Arcidre live in our British seas, and their shells may be picked up by our children on the sands of our English coast. To a Lond on geologist, familiar with th e large P ectunculus Plumeteadiensie, with which portions of the Wo olwich Beds are crowded, with th e sma ll P. decussatus, abounding in one of th e zones of th e London Clay, and with the beauti ful P. glycimel'i8, perhaps th e commonest fossil of the Red Crag of East An glia, Palreozoic species of th e same family to which t hese familiar Tertiary shell s belong, must have a special interest and significance. That members of thi s family ar e found in th e oldest rocks yielding lamellibr anch fossils, is otherwise a noteworthy fact, since th ey are much higher in the scale of zoomorphic development than many other families of th e Class, t hat might, th erefore, bc expected to occur in these rocks. But t his insta nce of high er forms first appearing is by no means uniq ne, for have we not t he largest and most highly ornamented trilobites in th e Menevian rocks, with smaller and simpl er genera in rocks much newer, and g raptolites, both large and complex, in abundance in th e Llandeilo, with mucb more apparently prim itive and smaller forms in th e Ludlow rocks? Such facts, pl'i'lJlcZ facie in dissonance with the evolution 11ypOth esis, may be account ed for, 01' rather, as it were, excused on th e gr ound of the imperfection of th e geological record, and confident predictions may be indulged in th at a more exten sive and complete examination of Cambrian or Pre-Cambrian rocks will reveal earlier

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and simpler forms in older strata, but, nevertheless, the anomaly is worthy of thoughtful consideration and ought not to be hastily set aside. It is not, however, the object of this paper to discuss such a question as this, but rather to give the results of discovery and examination. The great bivalved class of Mollusca, named Lamellibl'anchiata, by De Blainville, from the lamellar or plate-like character of the branchial or gills of the living mollusk, and formerly called Conchifera by Lamarck, has recently been renamed Pelecypoda, or axe-footed, in order that this Class may have a designation in uniformity with those of the other great divisions of the Mollusca. This name, Peleefpoda, has been used by Prof. Tryon, the author of the great American work, the' Manual of Conchology,' now in course of publication, and subsequently by Dr. Paul Fischer, in the splendid 'Manual de Conchyliologie et de Paleontologie Conchyliologique,' published only last year, and it is, moreover, adopted by our distinguished English palseontologist, Mr. Etheridge, in the new edition of Prof. Phillips's' Manual of Geology.' I am, however, sufficiently conservative to adhere to good old familiar names, at least for some little time after the first publication of new designations, and although Pelecypoda is an old name revived, it has not been used for so long a time that it has the effect of a new word. It is based, too, on a less important organ than the name Lamellibranchiata, and an organ, moreover, that is not common to all Mollusca, since the so-called podi of Brachiopoda are not feet or organs of locomotion at all. I may add that although a longer word, Lamellibranchiata, is more euphonious than Pelecypoda, while a little variety is more pleasing and, perhaps, too, more mnemonical than a dull uniformity in classificatory nomenclature. I will, therefore, in this paper speak of Arcidee as lamellibranchs, The Class Lamellibranchiata-to adopt a good classification especially useful to palseontologists, though one not favoured by Tryon or Fischer-has been divided first into Monomyal'ia and Dimyaria, or those having only one adductor muscle, as the oyster and the pecten or scallop, and those having two, as the cockle and the mussel. The order Dimyaria, in which is the family Arcidre, is divisible into the Siphon ida and the Asiphonida, some genera being

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furnished with siphon-like organs for the intaking of food-bearing and oxygen- bearing water, and its subsequent ejection, and other genera being devoid of such organs. Then, again, some genera possess siphons which can be protruded outside the shell, and withdrawn again at will; and, since the retractile siphon is indrawn into a cavity in the body of the mollusk, the pallium, or mantle, is deeply indented by a bay or sinus, and this is clearly indicated by the" pallial impression" or marking on the interior surfaces of the shell, and so the mere shell alone suffices to establish the possession Or non-possession of a retractile siphon by its former occupant. Thus two other divisions are constituted the Inteqro-pallialia and the Sinu-pallialia-s-or those having the pallial impression simple or unindented, and those in which this line on the inner side of the shell is indented by a sinus, and it will be obvious that as this division is founded on an enduring marking on the enduring part of the lamellibranch, it is of very great classificatory value to the palreontologist. The fossils of the Palreozoic rocks, especially those from Lower Silurian and Cambrian strata, are sometimes so imperfect and deficient in distinct characters that an attempt to arrange them with zoological correctness is necessarily attended with difficulty, and the results arrived at are best considered rather as approximations to correctness than as final determinations. For our knowledge of fossil Arcidre we are much indebted to American palreontologists, and the names of Vanuxem, Emmons, Conrad, Billings, and Hall must remain with those of Sowerby, Phillips, McCoy, and Salter associated with this, perhaps the oldest, family of the Lamellibranchiata, and the remarkable discoveries of our associate, Dr. Hicks, in the Tremadoc rocks of Ramsey Island, South Wales, in 1872, while extending the known range of Arcidse, and, indeed, of the Class Lamellibranchiata, gave to science a new and well-marked genus that must be placed in this family. In the year 1873, at the Bradford Meeting of the British Association, I read a paper giving the stratigraphical distribution of the British Paleeozcie species of Arcidre then known. Since that time but few additions have been made to the list, and consequently the statement of their distribution now will not differ much from

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that published in the British Association Report. Neither have I seen reason to alter the determinations of the generic affinities of the species on which the census of the distribution was founded. The possession of the retractile siphon then appeared to me to be so important a zoological and physiological character that I considered that Integro-pallial and Sinu- pallial genera ought not to be included in the same family, and that Arcidee should be restricted to those genera agreeiug with the type genus Area, on which the family is founded, in being integra-pallial, and accordingly it was proposed in the paper above-mentioned to remove the genera Leda, Yoldia, and Solemya, as ainu-pallial genera from Arcidse altogether, and to establish a new and distinct family founded upon the genus Leda, the Ledida, and this view was not opposed by the Section. In the large work by Professor Tryon the lamellibranchs are not yet reached, but that author has completed a smaller work in three volumes, entitled, 'Structural and Systematic Conchology,' based upon the wonderful book of Dr. Samuel Woodward, the well-known and justly-esteemed' Manual of the Mollusca,' a book in which the maximum of sound knowledge and scientific information is compressed into the minimum of space, and I have great satisfaction in finding tbat my proposal of fifteen years ago for the restriction of Arcidse has been adopted in the classification given in this recent general work on the Mollusca, as well as in that of the still more recent work of Dr. Paul Fischer. With the elimination of the sinu-pallial genera the definition of the family Arcidse can be made both simple and distinct, and will run in its briefest form as follows : Arcidm include those integra-pallial dimyarian lamellibranchs, having a serrated hinge or hinge-line, which may be either straight, curved, or beut. The following is the original diagnosis by Carpenter :-Shell regular, equivalve, with strong epidermis; ligament exterior, occupying an area between the beaks; hinge with a long row of similar comb-like teeth; pallial line distinct; muscular impressions sub-equal; structure corrugate, with vertical tubuli in rays between the ribs or striee, Many generic and sub-generic names have been given to species corresponding more or less with this description, and the following,

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excluding Leda, have been used for fossil species from Palreozoic rocks considered to belong to Arcidre : Arcs, by Linnreus, 1758. Byssoarca, by Swainson, 1840. Ctenodonta, by Salter, 1851. Cucullrea, by Lamarck, 1801. Cucullella, by McCoy, 1851. Cyrtodonta, by Billings, 1858. Davidia, by Hicks, 1872. Glyptarca, by Hicks, 1872.

Lyrodesma, by Conrad, 184,1. Macrodon, by Lycett, 1845. Mathe ria, by Billings, 1858. Megambonia, by Billings, 1859. Nucula, by Lamarck, 1799. Palrearca, by Hall, 1859. Tellinomya, by Hall, 1847. Vanuxemia, by Hall, 1858.

Undoubted species of the family Arcidre have also been assigned by various authors to genera of other families, such as Cleidophorus, Cypricardites, Pullastra, Actiuodonta, etc. Of the sixteen designations in the list of genera proposed for Palseozoic Arcidse objection may be taken to the following : Byssoarca, Cyrtodonta, Davidia, Lyrodesma,

Matheria, Megambonia, Tellinomya, Vanuxemia.

The genus Bys8oal'ca was founded by Swainson, on a character which must be admitted to be of very considerable importance, and sufficient in the estimation of most to entitle its possessors, apart from other considerations, to separate generic distinction. The byssal orifice is, however, a character common to species which may otherwise be considered typical Areas and Macrodons. The retention of the genus Byssoarca would not, therefore, tend to that simplification of classification which is so desirable, and its absorption in the genera Area and Macrodon may perhaps on these grounds be assented to. Of Cyrtodonta it is sufficient to say that, as defined by Billings, it is quite equivalent to Palcearca of Hall, aud us the latter name had priority, and is now generally used, the name C!Jrtodonta llIay doubtless without objection be omitted from our lists. The genus Dauidia, which was established by Dr. Hicks on two species from the Tremadoc rocks of the neighbourhood of St. David's, was by the author placed in Arcidse. I dissented from this at the time, and wrote :-" I fear I can scarcely agree with Dr. Hicks in this determination. Through the kindness of that

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gentleman I have had abundant opportunity of carefully examining th e original specimens, and I do not find anything ill either the form or th e hinge line to justify Davidia being given to Arcidee.' This opinion is also suppor ted by Profes sor Tryon and Dr. Fischel', who have not given Davidia a place amongst the Areidee. The several Am erican species described under the names Megambonia and Vanllxemia, by Billings and Hall, do net appear to possess characters sufficiently distinctive from those of Palcearca t o justify th e retention of either of those names. Of Math eria tenera (Billings) it may be urged that not possessing posterior teeth it is ent itled to be considered a separate genus; but no similar species has been yet found in our British rocks. The name Tellinonuja was given by Hall to a group of species which may with gr ea.t pr opriety be placed in the genus Ctenodonta, and, indeed, in the original diagnosis it is difficult to find anything at variance with a description of typical species of Ctenodonta. The name is now, moreover, used for species of Anatinidce, and it may th erefore be eliminated from lists of Arcidce, With respect t o Lyl'odesma, I must venture to disagree with Prof. Tryon, who places thi s genus in A rcidce. The distinctly trigonal form, and especially the radiating teeth of th e hinge line, in my opinion, take it out of relati onship with .Area, and ally it with the Triqonida, in which family it was placed by 'Voodward. Neither does Prof. Tryon's exclusion of the g enus Nucula from the Arcidce appear to me to be justified, and still more must I object to its being allied with Leda, nor can I understand how this can consistently be done, The reason for the exclusion of Leda from the .Arcidre, this genus being sinu-pallial, must be equally potent against its alliance with th e integro-pallial genus Nueula, yet it is sought to est ablish th e family Nu culidce to include Leda and other sinu-pullial genera. This to me appears lik e making a matter right, and th en immediately after makin g it wrong again. It is tru e that th e general form of Nucula differs from the Arcian typ e, but not so much 80 as that of Lurodesma, which by th e same author is placed in Arcidte, or, indeed, as that of Palcearca, and, moreover, th e nuculoid form is that of Ctenotionta, which every author includes in Arcidce, If the existence of the cartilage-pit in th e hinge lin e be deemed a sufficient cause for the exclusion of N ucula from alliance with

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Arca, it will not suffice to ally it with Leda, which has a distinctly different pallial line, but will rather separate it from relationship with both genera. At present, however, I prefer to retain Nucula in Areidm, especially as there is only one species ascribed to the genus in our Palseozoic rocks, and that may possibly be a Ctenodonta. With the eliminations for which reasons have been stated, and the retention of Nueula, the list of genera of Arcida represented in British Palreozoic rocks will be reduced to the following eight, arranged according to their affinities : Oucullella Area Glyptarea Ououtlaa Palaarca Macrodon (Itenodonta Nueula.

(1.)

ARCA,

Linneeus.

Etym., Area, a chest. Shell equivalve or nearly so, thick, subquadrate, ventricose, strongly ribbed or cancellated ; margins smooth or dentated, close or sinuated ventrally; hinge straight, teeth very numerous, transverse; umbones anterior, separated by a flat, lozenge-shaped ligamental area, with numerous cartilage-grooves; pallial line simple j posterior adductor impression double; pedal scars two, the posterior elongated. The genus Area restricted to those species having straight hingelines with both the anterior and the posterior teeth transverse, but including the Byssoarca of Swainson, or those having abyssal opening, is represented by about nine species in our Palreozoic rocks. Though several species from Caradoc strata were named Arca by Portlock, no true A1'ca has yet been found lower than Lndlow rocks, the earliest being the A1'ca primitina from the Ludlow of Freshwater East, figured and described by Prof. Phillips in the third volume of the' Memoirs of the Geological Survey.' The Silurian Areas of Portlock appear on examination to properly belong, some to Palcearca and some to Ctenodonta, to the latter of which genera the Arca Eastnori of Sowerby and the Area subaquali« of McOoy must be given. Area primitiva is the only Silurian species, nor do any appear in

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Devonian rocks, and we do not find the genus well represented until the Carboniferous Limestone is searched, but from this formation eight species have been obtained. The five so-called species of Area from the Permian ascribed to Area striata, A. tumida, A. Loftusiana, and A. Kingiana should all be included in MaerodQn, since the posterior teeth of the hinge-line are horizontal. Thus the genus Area is represented in British rocks by one species in the Ludl ow rocks and by nine species in the Carboniferous Limestone as follows : Distribution, Ludlow. A. primitiua, Phill. Carboniferous Limestone. A. cancellata, Mart, A. clathrata, McCoy. A. costellata, McCoy. A. fimbriate, McCoy. A. Lacordaireana, De Koninck. A . lan ceolata, McCoy. A. reticulata, McCoy. A. semicostata, McCoy. A. obtusa, Phill. (2.) Genus CUCULL.£A, Lamarck. Etym., Cucullue, a cowl. Shell sub-quadrate, ventricose; valves close, striated; hingeteeth few and oblique, parallel with the hinge-line at each end; posterior muscular impression bounded by an elevated ridge. Cucullrea is well characterized by the obliquity of the teeth and the posterior elevated ridge, which latter is an especially valuable feature for the identification of tbe genus, since it is one which casts distinctly indicate, the incision in the cast produced by the interior ridge not, being easily obliterated. This genus has not been found in rocks lower than the Middle Devonian, Cuwllrea amygdalina of Phillips from the Marwood quarries being the earliest British species yet known. Some doubt must remain about this species, and also respecting the C.

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Hardingii of Sowerby from the Upper Devonian in consequence of the interior not having been shown in the figures. Six species from the Upper Devonian have been referred, three doubtfully, to (lucullcea ; and five species from thc Carboniferous Limestone complete the number of British Palreoaoic species of this genus.

Dietribiuion; Middle Devonian. ? C. amygdalina, Phill. (Pal. Foss.). Upper Devonian. ? C. amygdalina, Phill, C. angusta, Sow. (Geol. Trans.). ? C. complanata, Phill. (Pal. Foss. Pullastra sp.}, C. depressa, Phill. (Pal. Foss.). ? C. Hardingii, Sow. (Geol. 'Irans.), C. trapezium, Sow. (Geol. Trans.). Carboniferous Limestone. ? C. amygdalina, Phill. C. arquta, Phill. (A,-ca, sp. De Koniuck). ? C. Hardinqii, Sow. C. tenuistria, McCoy (Carb. Foss.). C. trapezium, Sow. (3.) Genus MACRODON, Lycett. Etym., j1.aKpor;, long, and ooo~$', a tooth. Shell thick, sub-rhomboidal, beaks anterior; hinge with a few oblique anterior teeth, and one or more long, laminar posterior teeth, parallel with tbe hinge-line. These laminar teeth distinctly separate 111 acrodon from Arca and Ouculloa, both' of which genera it resembles in outward form. Though six so-called species referable to Arcidre have been described from Permian rocks, there does not appear to be sufficient differentiation to justify the constitution of more than one species. The oldest of the six names, striatus, may be retained, and thus the Macrodon striatus will include the Mytilites striatus of Schlotheim and Byssoal'ca striatus of King, B. tumida (King), B. Kingiana (Verneuil), B. antiqua of Munster, B. Loftusiana (House), and the Oucullaa sul cata of Sowerby.

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This species, M. striatus, is our only Palseozoic Macrodon, none appearing in rocks lower than the Permian. Distribution,

Permian. M. striatus, SchI. (Byssoarca, sp. King). " ., (Mytilites, sp. SchI.) (Ak. Miinch.) . •, , , ( Cucullcea sulcaia, Sow.). " " (Byssoarca tumida, King). " ,,( " Kingiana, Vern., King). " ." ( " antiqua, Munst., King).

"

"(,,

Loftusitma, House, King).

(4.) Genus CTENODONTA, Salter. Etym., KTd., a comb, and Mov>, a tooth. Shell elongately oval, subequilateral, smooth, or finely concentrically striate; valves moderately convex; hinge represented by two diverging comb-like denticulated margins without a special hinge-area between them and the beak, and below the latter, not interrupted by a pit; ligament apparen tly external, posterior to the beak. This appears to have been the most important genus of Arcidai in Palreozoic times, since 41 species of Ctenodonta have been recorded, while no other genus is represented by more than 14 species. Ctenodonta may be briefly described as Nucula without the cartilage pit in the hinge-line. The teeth are numerous and tramverse, and the nuculoid form exists in all the species here included under (ltenodonta, The numerous species from Palreozoic rocks, originally described as Nuculo: by Phillips, McCoy, and others, have been divided between Ctenodonta, Palcearca, and Leda, with the exception of Nucula Tateana, of King, from the Permian. The two Tremadoc species of Ctenodonia discovered by Dr. Hicks, C. 11'1 enapiensis and C. (lambriensis, extend the stratigraphical range of the genus into the Cambrian rocks. Though the Palcearca socialis of Salter, from Arenig and Llandeilo strata, is not very fully figured or described, I am inclined to place it in Ctenodonta from its general form, reserving those species only, for the genus Palceorca, which have the posterior

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J. L. LOBLEY ON PAL.EOZOIC ARCID.E.

extremity greatly expanded. The removal of Portlock's and McCoy's Nuculas and Areas to Ctenodonta give nine species of this genus to Caradoc or Bala strata, though one, C. obliqua, stated by Mr. Ruddy to occur in rocks of Bala age, near Corwen, is somewhat doubtful. Three appear in Lower Llandovery; seven in Upper Llandovery j two in Wenlock; and five in Ludlow rocks. The Devonian rocks have yielded five species. In the Carboniferous Limestone the maximum development of Ctenodonta is found, 19 species having been described, but these, with one exception, were originally ascribed to Nucula ; and two species are recorded from the Millstone Grit. Sowerby's Nucula aqualis and N. accipiens from the Coal Measures have also been given to (ltenodonta, The large pebbles of the very interesting Budleigh Salterton Pebble Bed have yielded numerous fossils, showing the Palseozoic age of the original rock of which the pebbles are water-worn fragments, the bed itself being of Triassic age. Mr. Wyatt-Edgell described two species of lamellibranchs from these pebbles, which he ascribed to Arcida, and one of the two he named a Otenodonta. The locality of the rock whence the pebbles came is doubtful, but their fossils seem to be Continental rather than British species, and it is considered by many that the pebbles are from the Gres Armoricios: of Brittany, in France, and of probably Arenig age. Mr. Pengelly, however, thinks they are from Cornish rocks, but as this is doubtful the species from the pebbles cannot with certainty be included in lists of British species other than as derived fossils in Triassic rocks. Distribution.

Tremadoc. C. Cambriensis, Hicks (Q. J. G. S., Vol. xxix, p.47, PI. v). C. Menapiensis, Hicks (Q. J. G. s., Vol. xxix, p. 47, P!. v). Llandeilo. C. socialis, Salt. C. val'icosa, Salt. Caradoc. C. ambigua, Port!. (Pectunculus sp., Rep. Lond.). C. lceuis, Sow. (Nucula sp., Siluro Syst.). C. levata, Hall. O. oblique, Portl. (Nucula sp.),

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C. 1'egula1'is, PortI. (Area sp., Rep. Lond.). C. seitula, McCoy (Area sp., Silur. Foss.), C. eubacuta, McCoy (Nueula sp., Siluro Foss.), C. subtruncata, Portl. (AI'ca sp., Rep. Lond.). C. transoersa, Portl. (Area sp., Rep. Lond.). C. »aricoea, Salt. Lower Llandovery. ? C. vW'ieosa, Salt. C. psittacina, Salt., MS. Upper Llandovery. C. Anglica, D'Orb. (Nucula sp., Prod. Pal.). C. deltoidea, Ph ill. (Nucula sp., Mem. Geol. Sur., Vol. ii}, C. Eastnori, Sow. (AI'ca sp., Siluro Syst.). ? C. rhomboidea Ph ill. (Nueula sp., Mem. Geol. Sur., Vol. ii ), C. subequalis, McCoy (Area sp., Pal. Foss.). C. subcylindl'ica, McCoy (Nucula sp., Siluro Foss.). C. sulcata, His. Wenlock. C. Anglica, D'Orb. C. interrupta, Brod. C. sulcata, His. Ludlow. C. Anglica, D'Orb. C. thracioides, Salt. C. subequalis, McCoy. C. 8ulcata, His. C. obesa, Salt. Lower Devonian. C. Krachtce, Roem. Middle Devonian. C. lineata, Phill. t Nucula sp., Pal. Foss.). Upper Devonian. C. antigua, Sow. C. latissima, Phill. (Nucula sp., Pal. Foss.). ? C. lineata, Phill. ? C. plicata, Phill. (Nuc'1lla sp., Pal. Foss.). Cl pullastriformis, McCoy (Nucula sp.) (Pullastra antiqua, Sow.). Carboniferous Limestone. C. antigua, Sow. (Pullastm sp.; Geol. Trans., Vol. r),

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C. cuneaia, PhilI. (Nur:uZa Sp., Geol. York.). C. attenuata, Flem. (Nucula sp., Carbo Foss.). C. carinata, McCoy (Nucula sp., Carbo FORS.). C. cylindl'ica, McCoy (Nucula sp., Carbo Foss.). C. breoirostruni, Phill. (Nucula sp., GeoL York.). C. delta, McCoy (Nucllla sp., Carbo Foss.). C. gibbosa, Flem. (NlIcula sp., B. A.). C. laoiroetrum, PortI. (Nllcula sp., Rep. Lond.). C. lineata, Phill. (Nucula Rp., Pal. Foss.). C. lonqirostris, McCoy (Nucula sp., Carbo Fose.). C. luciniformis, Phill. (Nucula sp., Geo!. York.). C. oblonga, McCoy (Nucula sp., Carbo Foss.). C. palma; Sow. (Nucula sp., Min. Conch.), C. rectanqularis, McCoy (Nucula sp., Carbo Foss.). C. stilla, McCoy (Nucula sp., Carbo Foss.), C. tumida, PhilI. (Nucula sp., Geo!. York.). C. undulata, Phil!. (Nucula sp., Geo!. York.). C. uniliteralis, McCoy (Nucula sp., Carbo Foss.). Millstone Grit. C. gibbosa, Flem. C. undulata, Phill. Coal Measures. C. cequalis, Sow. (Nucula sp., Geo!. Trans., Vol. v). C. accipiens, Sow. (Nucula sp., Geo!. Trans., Vol, v).

(5.) Genus CUCULLELLA (McCoy). Etym., diminutive of Cucullaa, Shell thin, margins not crenulated, ligament external; no cartilage pit; teeth numerous, on a nearly straight cardinal line; anterior muscular scar bounded by a ridge; pallial line simple. What Oucullaa is to Arca, so is Cucullella to Ctenodonta, Cucullelta having a bent hinge-line and an interior ridge bounding one of the adductor muscular scars. In the case of this genus, however, the ridge bounds the anterior, not the posterior, scar as in Cucullaa, The three species of Sowerby called Cucullaa antiqua, C. ouata, and C. Cawdol'imust be placed in Cucullella, and to these are

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L. LOBLEY ON PALJEOZOIC ARCIDJE.

399

now to be added C. angulata of Baily, and C. coarctata of Phillips. Three of these are in Caradoc or Bala strata; two, C. antiqua and C. coarctata, are recorded by Mr. Marl' as occurring in rocks which appear to be of Lower Llandovery age; two are in Upper Llandovery rocks, and three in Ludlow beds. No species of this genus having been described from Devonian, Carboniferous, or Permian rocks, it appears that Cucutlella is confined to Silurian strata. Distribution. Caradoc. C. antiqua, Sow. (Cuculltea sp., Siluro Syst.), C. angulata, Baily. C. coarctata, Phill. (Nucula sp., Mem. Geol. Sur., Vol. ii). Lower Llandovery. C. antiqua, Sow. C. coarctata, Phill. Upper Llandovery. C. antiqua, Sow. C. ovata, Sow. (CucuUrea sp., Siluro Syst.). Wenlock. C. ovata, Sow. Ludlow. C. antiqua, Sow. C. Cauidori, Sow. (CucuUrea sp., Siluro Syst.), C. ovata, Sow.

(6.) Genus GLYPTARCA (Hicks)." Etym., ')'AV7TTO., carved, and Arca•. Inequilateral, strongly ventricose; beak near the anterior end, prominent, overhanging the hinge-line, more or less pointed at the extremity; two diverging ridges extend from the umbo to the margin, and enclose a triangular sulcus, having its base at the margin, which it thereby indents; anterior muscular impression strong, posterior less distinct; hinge-area narrow, plate thick, with three teeth in front of the umbo; surface strongly marked with growth lines. • 'Quart. Journ, Geo1. Soc,' Vol. xxix,!,.

M,.

400

J . L. LOBLEY ON l'AL..EOZOIC AR ClD..E.

The last discovered genus of Palssozoic ArcidlB, Glyptarca, occurring as it does in the pre-Silurian Tr emadoc rocks in great abundance, and in none other so far as we yet know, possesses considerable interest. It is to the important work of Dr. Hicks in South Wales that science is indebt ed for thi s addition to the family Arcida. Glyptarca is characterized by a distinct anterior depression extending from th e umbo to the ventral margin, and has thus a general resemblance to Grammysia, but that genus has two narrow sulci while Glyptarca has one only, which as it approaches the ventral margin considerably widens. Of the two species described by Dr. Hicks, G. primceva is abundant in th e Tr emadoc rocks of Rams ey I sland near St. Da vid's, while t he second species, which its author has done me the honour of naming after myself, is comparativ ely rare. Distribution. Tremadoc. G. Loblepi, Hicks (Q. J. G. S., Vol. xxix, p. 48, PI. v), G. primoma, Hicks (Q. J. G. S., Vol. xxix, p. 4R, PI. v) .

(7.) Genus PALEARCA (Hall). Etym., '7I'(X,Aa{O'i, ancient, and Area. Shell equivalve, inequilateral; umbones near the anterior end or terminal; general form obliquely tumid, transversely subrhomboidal ovate; posterior extremity larger than the anterior, and usually broadly rounded ; two to eight oblique ant erior teeth beneath, or a little in front of the umbones; two to four remote lateral teeth. parallel with the binge-line; pallial line simple; muscular scars two, anterior sometimes deeply excavated; posterior superficial; ligament external. The exclusively Palseozoic genus Paltearca is characterized in its general form by the larg eness of the posterior and t he small. ness of the anterior area, and the consequent obliquely tumid form of the whole. The teeth are not so numerous as in Ctenodonta, and the posterior teeth are oblique or almost parallel with the hinge-line. The known range of Palaarca, like that of Ctenodonta, has been extended by Dr. Hicks, who has described two species, P. Hopkin80ni and P. oboloidea, from the Tremadoc rocks of Ramsey Island . Mr . Salter described three species from Lla ndeilo str ata, but

J. L.

401

LOBLEY ON PAL.lEOZOIC ARCID.IE,

one, the P. socialis, having been removed to Ctenodonta, two species only appear to occur in those rocks, while seven are recorded from the Caradoc. Not only is Palcearca essentially Palseozoic, but, like Cucullella and Glyptw'ca, it is confined to strata below the Devonian, two species in the Upper Llandovery, and one, P. Edmondiijormis, in the Upper Ludlow, being the latest representatives of the genus

Palreal'ca. Distribution. Tremadoc.

P. Hopkinsoni, Hicks (Q. J. G. S., Vol. xxix, p. 48, PI. v). P. oboloidea, Hicks (Q. J. G. S., Vol. xxix, p. 48, PI. v). Arenig.

P. amygdalus, Salt. (Mem. Geo1. Sur., Vol. iii). Llandeilo.

P. amygdalus, Salt. P. Billinqsiana, Salt. (Mem. Geo1. Sur., Vol. iii). Caradoc.

P. Billingsiana, Salt. P. Bulla, Salt. (Mem, Geol. Sur., Vol. iii). P. dissimilis, Portl, (Al'ea sp., Rep. Lond.), P. Edmondiiformis, McCoy (Arca sp., Pal. Foss.). P. modiolaris, Salt. (Mem, Geo!. Sur., VoL iii). P. obiiqua, PortJ. (Arco sp., Rep. Land.). P. obscura, Salt. (Mem. Geo1. Sur., Vo1. iii). P. quadrat«, Salt. (Mem. Geo1. Sur., Vol. iii). Llandovery.

P. lingualis, Phill. (Nucula sp., Mem, Geo1. Sur., Vol. ii). Upper Ludlow. P. Edmondiiformie, McCoy. (8.) Genus

NUCULA,

Lamarck

Etym., diminutive of Nux, a nut. Shell trigonal, with the umbones tnrned towards the short posterior side; smooth 01' sculptured, epidermis olive, interior pearly, margins crenulated ; hinge with prominent internal cartilage-pit, and a series of sharp teeth on each side; pallial line simple. A greater number of Palzeozoic Arcidce have been originally described under the name of Nucula than under any other generic VOL.

X., No.8.

30

402

J. L. LOBLEY ON PAL.EOZOJC ARCJDE.

designation, and yet, with one exception, all have been assigned to other genera. It is true that in several of these species there is not direct evidence for removing them from Nucula, but when it is found that every Palreozoic nuculoid species in which the hingeline has been fully seen is a Ctenodonta, those species the hinge-line of which is not yet known may more fairly be given to (ltenodouta than to Nucula. The majority of the others have been assigned to Leda since they have the peculiar extension of the posterior extremity so characteristic of that genus, while no contradictory internal characters have been noticed. Whether Nucula Tateiana, of King, from the Permian, is or is not a true Nucula it is difficult to ascertain, inasmuch as Prof. King discovered the species after the plates for his monograph were ready, and there is, therefore, no published figure. The diagnosis is very brief and incomplete, leaving untold that which is necessary to be known. The author, however, writes of the species as a true Nucula, and on this testimony from so competent an observer as Prof. King it has been allowed to remain. The genus Nucula is represented, therefore, in British Palseozoic rocks by but one species, the N. Tateiana which Prof. King obtained from the Permian Magnesian Limestone of Humbleton Hill, Durham.

Distribution. Permian. N. Tateiana, King (Perm. Foss.) Thus it appears that the total number of species of the family Arcido: occurring in British Paleeozoic rocks so far as is yet known

is 88, with a stratigraphical distribution as follows : Tremadoc, 6; Arenig, 2; Llandeilo, 4; Caradoc, 21 ; Lower Llandovery, 4 ; Upper Llandovery, 10; Wenlock, 4; Ludlow, 10; Lower Devonian, 1 ; Middle Devonian, 2; Upper Devonian, 11; Carboniferous Limestone, 33; Millstone Grit, 2; Coal Measures, 2; Permian, 2. But it is right to add that some authors recognize as distinct species several forms here regarded as varieties. Upwards of thirty years ago Professor Phillips drew attention to the fact that the earliest families of the Lamellibranchiata were Arcidm and Mytilidm. This still appears to be true, as all the lamellibranchs since discovered in Cambrian rocks are assignable to those two families.

J. L.

TABLE

SHOWING

403

LOBLEY ON PALlEOZOI C AR CIDlE . STRATIGRAPHICAL DISTRIBUTION FOSSIL ARCIDE.

OF

BRITISH

---.-------_._-----------------AReA• .J. canoellata, Mart.

... 1. clathrata, McCoy .. A. costellata, 1I1c Coy .. A.flmbriata, McCoy . A Lacordaireana, De Kon. 1. lanc eolata, McCoy . L obtusa, Phill. . A. primitiva, Phill. . A . reticul ata, McCoy . A . semicost aia, McCoy

... ...... ...... ... ... ...., •••

• ••

• • ,

0 ••

• • •• ,

0

... ... ...... ... ... ..

• • •

,

x

• ••

x

.

,

x

x .,

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•• •

• 0

•

.

x

• ••

x

•

• • • a . a • • • aa

,. ,

x ••• . . . ••. ' "

x x x

CUC ULLlEA.

C. amygdalina, PhilI. .., C. angusta, Sow. C argut a, Phill. C. complanata, Phill, ...

.0

•

0

.

x x

)(

,,, .. , .

r:. dep ressa; Phill,

..

C. Hardingii, Sow. C. tenuistria, McCoy C. trapezium, Sow.

.

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x

x

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x

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,

'" ., . x

x

MACHODON.

.

M. st riates, Sch!.

,. ,

'"

.,.

C l' EN O DONT A .

C accipiens, Sow. C. aqualis, Sow. C. ambigua, Portl. C. Anglica, D'Orb,

C antiqua , Sow. C attenuata, FJem.

... .. , ...

.

...

•

. . C. breoirosirum, Phill .. C. Cambriensis, Hicks .. C. carinata, McCoy .. C. cuneai a, Ph ill, ...

,.

,

. .. . . ... .. . . . .. . .. .. . . . ....... ... . . . . .. .

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... x

)(

404

J. L. LOBLEY

ON PAL1EOZOIC AROIDM. '0 I'l
'" ..,

Ol

~

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CTENODON1'A

(continued).

...

C. cy lindri ca, McCoy C. delt a, McCoy... C. delt oidea, Phil! . , C. Enstnori, Sow. C. gibbosa, F Iero. C. interr upta, Brod. 0. Krachia , Roem, C. lirostrum, PortJ. O. le vis, Sow. C. lati ssima, Ph ill. C. levat a, Hall C. li neat a, PhilJ. C. longirostris, McCoy... C. lllciniformis, Phill . C. M enap iensis, Hicks ... C. obesa , Salt . ... O. obliqua, P ortJ. O. oblonqa , McCoy O. pa lmre, Sow... . C. p li cat a, Phill. C. psittacina, Sa lt. MS. O. pullasiriformis , McCoy C. r ectangular is, McCoy C. regularis, PorlJ. C. r homboidea , Ph ill . C. sci tula , McCoy C. sociali s, Salt.... C. stilla , McCoy C. subaouia , McCoy C. su baqua lis, McCoy C. subc!Jlindr ica, McCoy C. subtruncat a, Portl. C. sulcate; His . C. thracioides, Salt. C. transversa, Portl. ... c. t nnn d a , Phil l. ... C undulata, Phil l. C. uni lite ra lis , McCoy .. . ... C. »aricosa, Salt .

... ... ..

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...

...

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x

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to •

x

x

... ... ... ." ... .. . x ... ... ... ... .. . x ... ... .., ... x ... ... ... ... .. . x

x

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x

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... ... ... ... ... .. ... ... ... ... .,. ... ... ... .... ... ... ... .. ... .., ... ... ... ... .., ... ... ... ... ... ... x x x ...

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<1>

405

J. L. LOBLEY ON PAL.EOZOIC ARClD£. '0 cd '; ee '"

"

...:. & '" '"

p '" ..., . oS ..... 'C

.;

g , "~ ]"' H. e .'" a 'a ' " '8 .s 11 ..oJ o § .8 § '" '" ''"" g > bO~ '"0 _" ~ .£o ~ " ::<1 s .!!: 13'o" 'a - QO ~~~ ~ '5. '" HH " ' 0 . ' " H C) ,...:j " ' " ~ C) Po< Eo<
cd

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-- ---

CUCULLELLA.

c. angulata,

Baily C. ant iquo, Sow. C. Caiodori, Sow. C. eoarctata, Phill . C. ocaia, Sow.

...

... ... ... ... ...

...

.. ... . ..

,

..... . . 0' . 0' ... ... ......

•• 0

.. .

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'0' , . •

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• • •

x

x x

x • 0 0

"

•

• •

•

... 0 ••

x

x

x x . . • ' 0'

x x x

GLYPTARCA.

G. Lobleyi, Hicks G. primava, Hicks

... ."

...

x

...

x

'0 '

'0'

PAL..EARCA.

P. amygdalus, Sal t . ... P . B illiugsiana, Salt. ... P. bull a, Salt. ... P . dissimilis, PortI o P . Edmondiiformis, McCoy P. Hop kinson i, Hicks ... P. lingualis, Phill. P . modiolaris, Salt. P . oblique, Por bl, P. oboloidea, Hicks P. obscura, Salt. ... P. quadrata, Salt.

... ...

...

... ...

...

x x

.....

... x

• 0' . • •

... ...

'0 0

.0' . 0'

x x x

'0' , . , '0' . 0'

x

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,

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... . ,1 . 0. X

...

... ... ... ... ... x ...

' 0 ' ' 0'

x

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• • • • 0'

0 ••

... • 0'

x

x x

x

NUCULA. ?

N. Tateiana, King

...

... ... .. ...... ,

"0

...

.. . ... ... ... ... ...

• .. ' oo

x