( 343 ) X.—On the Structure and Affinities of the Platysomidse. By RAMSAY H. TRAQUAIR, M.D., F.R.S.E., Keeper of the Natural History Collections in the Museum of Science and Art, Edinburgh. (Plates III.-VI.) (Eead 5th May 1879.) INTRODUCTION. The genera, which I at present include under the family term Platysomidce, are the following:— 1. Eurynotus, Agassiz. 2. Benedenius, Traquair. 3. Mesolepis, Young. 4. Eurysomus, Young. 5. Wardichthys, Traquair. 6. Cheirodus, M'Coy. 7. Platysomus, Agassiz. Eurynotus and Platysomus (incl. Eurysomus) were classified by AGASSIZ in his Lepidoid family of Ganoids, the former genus forming in his opinion a transition between the latter and Amblypterus* By GIEBEL, Eurynotus and Platysomus were included in his "Heterocerci Monopterygii," along with the Palseonis- coid genera known at that time, and unfortunately also along with certain other very heterogeneous elements {Eugnathus, Conodus, Megalichthys).^ By QUENSTEDT Platysomus was also placed among the Heterocercal Ganoids, immediately after Palceoniscus, Amblypterus, and Pygopterus.\ But already, before the appearance of QUENSTEDT'S " Handbuch," Sir PHILIP GREY-EGERTON § advocated the removal of the genus Platysomus to the family Pycnodontidse on the following grounds:—The mandible of a specimen of Platysomus macrurus, Agassiz, from Ferry Hill, showed two rows of peculiar teeth with flattened crowns, supported on constricted necks, the dentary element of the jaw on which they were placed being also a " dense triangular bone, very similar to the Pycnodont jaws found at Stonesfield and elsewhere." * Poissons Fossiles, vol. ii. pt. 1, p. 153. f Fauna der Vorwelt, vol. i. pt. 3, Leipzig, 1848. I Handbuch der Petrefactenkunde, Tubingen, 1852. § On the Affinities of the Genus Platysomus, "Qu. Journ. Geol. Soc, London," v. (1849), p. 329-332. VOL. XXIX. PART I. 4 T 344 RAMSAY H. TRAQUAIR ON THE MUNSTEK'S genus Globulodus, founded upon rounded pedunculated teeth from the Kupferschiefer, was cancelled, and merged in Platysomus, AGASSIZ having also previously expressed a suspicion that these teeth appertained to the last named genus. Sir PHILIP also considered his views as to the Pycnodont nature of Platysomus to be completely corroborated by the form and arrangement of the scales. For he had made the important discovery that the so-called " dermal ribs " of the Pycnodonts were in reality nothing more than thickenings of the anterior margins of the scales, obliquely sliced off above and below for articulation with'the adjoining scales of the same dorso-ventral band. Pointing out that a similar conformation was to be found in the high and narrow scales of Platysomus, he maintained that the squamation as well as the dentition justified the incorporation of that genus with the Pycnodont family. In this view AGASSIZ concurred, and in a letter quoted by Sir PHILIP says, that the "teeth are conclusive evidence for placing Platysomus with the Pycnodonts." It must at the same time be remembered that AGASSIZ himself had previously stated that the jaws of Platysomus were armed with " petites dents en brosse tres-pointues," and that in Platysomus gibbosus " on apercoit quelques petites dents au bord du maxillaire superieur.""* And with regard to Globulodus, he had also, besides suspecting its identity with Platysomus, ex- pressed himself as follows with regard to its supposed Pycnodont affinities— " Nous connaissons du moins dans la famille des Lepidoides les genres Tetra- gonolepis et Dapedius, dont les dents e"galement petites sont plus on moins renfle" es au sommet; mats je ne connais point de Pycnodontes qui aient des dents pidiculees comme celles du genre Globulodus."^ As regards Eurynotus, Sir PHILIP GKEY-EGERTON announced in the following year \ that it also had obtuse teeth, having received from HUGH MILLER a letter on the subject, with a cast of a specimen from Fifeshire, showing some rounded palatal teeth in situ. He, however, hesitated to remove Eurynotus to the Pycnodont family, and stated regarding its dentition—" These " (the teeth) " at first sight would seem to indicate a Pycnodont, but a comparison of the dentition of this family with other fishes, having blunt rounded teeth, especially with Lepidotus and Tetragonolepis, shows that there is so great a difference in the arrangement of the teeth in the two families, that even without the test of microscopic examination, the true affinities of the fish can be determined." Accordingly Sir PHILIP retained Eurynotus as a Heterocercal Lepidoid, admit- ting, however, that its dentition, as well as that of Amblypterus macropterus {Rhabdolepis, Troschel), as ascertained by GOLDFUSS, invalidated the definition of that family given by AGASSIZ. * Poissons Fossiles, vol. ii. pt. 1, p. 165. f Ib- P- 203. \ Qu. Journ. Geol. Soc. London, vi. (1850). STRUCTURE AND AFFINITIES OF THE PLATYSOMIDJS. 345 These views as to the position of Platysomus met with very considerable acceptance; accordingly we find, in the systematic works of GEINITZ,* PiCTET,t and M'COY,! this genus included in the family Pycnodontidse. Nevertheless there were some dissentient voices. VOGT, in his classification of the Ganoids, published in 1852,§ continued to associate Platysomus, as well as Eurynotus, with the Palceonisci, placing them together in the subfamily " Palce- onisciden " of the family Monosticha. HECKEL|| and WAGNER,1T both of whom had laboriously studied the Pycnodontidse, also declined to admit into that family either Platysomus or Tetragonolepis {Pleurolepis, Quenstedt), the latter genus having also, on account of its scales, been subsequently brought by Sir PHILIP GREY-EGERTON under the same category. Their objections as regards Platysomus were chiefly founded upon its heterocercal tail, fulcrated fins, and non-possession of the peculiar premandibular bone, or " Vorkiefer " of the Pycnodonts. With regard to the teeth of Platysomus macrurus {Eurysomus, Young), and those of Globulodus, Dr WAGNER recalled attention to the fact that AGASSIZ originally hesitated to recognise the latter as Pycnodont, adding,— " Ich setze hinzu dass die Zahne von Platysomus die grosste Aehnlichkeit mit denen des Lepidotus zeigen, also keinesweges auf die Pycnodonten hinweisen," stating also that we knew nothing of the condition of the upper jaw in Platy- somus. He admitted that the form of the body and of the scales were in favour of Pycnodont affinities; the other characters were, however, either not exclusive, or in contradiction with the peculiarities of the Pycnodonts. Dismembering the old " Lepidoidei" of AGASSIZ, Dr WAGNER now proposed to constitute a new family of " Stylodontes," which should include besides Platysomus, also the genera Pleurolepis, Quenst. ( = Tetragonolepis, Bronn, ILgerton),Homoslepis, Wagner, Heterostrophus, Wagner, Dapedius, De la Beche, and Tetragonolepis, Agassiz (=JEchmodus, Egerton). We shall see in the sequel that the associa- tion by Wagner of Platysomus with those other genera is just as unnatural as the classification which he himself wrote to oppose. In 1866, however, Professor YOUNG,** in awell-known paper, declined to accept the peculiar dentition of Platysomus macrurus as characteristic of all the species which had been referred to that genus, and recalled attention to the " dents en brosse," mentioned by AGASSIZ in his generic definition, which he said " are not Pycnodont, but Lepidoid ( = Lepidosteid)." Minutely describing the structure, of a small Carboniferous fish, which he referred to the Platysomus parvulus of AGASSIZ, he stated that it also had its jaws " armed with slender conical teeth," * Dyas, Leipzig, 1861, p. 8. f Traite de Palseontologie, 2d ed., 1854, vol. ii. p. 208. J British. Paleozoic Fossils, p. 614. § Zoologische Briefe, vol. ii., Frankfurt, 1852. || Beitrage zur Kenntniss der fossilen Fische Oesterreichs, Denkscnr. Ac. Wien. xi. 1856. IT Miinchener gelehrte Anzeigen., Bd. L., 1860, pp. 80-99. ** On the Affinities of Platysormw and Allied Genera, " Qu. Journ. Geol. Soc." 1866. 346 KAMSAY H. TRAQUAIR ON THE and accordingly he separated Platysomus macrurus as the type of a distinct genus Eurysomus. More than this, he described two entirely new though closely allied genera, Amphicentrum and Mesolepis, in the former of which the dentition is entirely peculiar, while in the latter the teeth somewhat resemble those of Eurysomus, consisting of blunted cones with constricted necks. Though not correct in all his osteological details, Professor YOUNG clearly showed that these genera, in spite of the differences in their dentition, are naturally related to each other, and that Eurynotus also cannot be disassociated from them, notwith- standing the more palasoniscoid aspect of its scales. Unable to include these forms in the Pycnodontidee proper, he proposed to class them, along with that family, in a new " suborder," which should be equivalent to the suborders Crossopterygidse and Lepidosteidse, established a few years previously by Professor HUXLEY. TO this suborder he gave the name " Lepidopleuridse," its principal, and indeed only tangible character being the mode of articulation of the scales "by strong ribs traversing their anterior margin internally," a character nevertheless absent in Eurynotus. According to Dr YOUNG, this suborder included five families which he tabulated as below:— I.—VENTRAL FIN WANTING. PLATYSOMID^E.—Teeth uniserial, conical, sharp. Palate bones edentulous. —Platysomus, Agassiz, partim. AMPHICENTRID^E.—Dorsal and ventral margins sharply acuminated. Teeth in the form