﻿platysomattd.t:. 527 



now re-named Styracopterus fulemtus, without definition (11. H. 

 Traquair, Ann. Mag. Nat. Hist. [6] vol. vi. 1890, p. 492). 



Generically indeterminable remains, probably of Palaeoniscidae, 

 are also named thus: — 



Turseodus acutiis, J. Leidy, Proc. Acad. Nat. Sci. Philad. 1857, 

 p. 167. — Triassic (?); Phoenixville, Chester Co., Pa. [Jaw ; 

 Academy of Sciences, Philadelphia.] 



Urosthenes ausindls, J. 1). Dana, Amer. Journ. Sci. [2] vol. v. 

 (1848), p. 433. — Hawkesbury Series; New South Wales. 

 [Tail ; accidentally destroyed by lire, j 



Isodus leptognatlms, F. M'Coy, Ann. Mag. Nat. Hist. [2J 

 vol. ii. (1848), p. 3. — Lower Carboniferous ; Moyheeland, 

 Draperstown, Ireland. [Dentary bone ; Dublin Museum.] 



Family PLATYSOMATIDJE. 



Trunk deeply fusiform or irregularly rhombic ; tail heterocercal ; 

 scales rhombic, ganoid, firmly united with peg-and-socket articula- 

 tions. Head-bones well developed, ganoid ; no median series of 

 cranial roof-bones ; eye far forwards and high in position ; snout 

 prominent; mandibular suspensorium nearly vertical, slightly 

 inclined downwards and forwards in the more specialized genera. 

 A series of broad branchiostegal rays, with a small anterior 

 azygous element at the symphysis of the mandible. Dorsal fin 

 single, much extended. 



As remarked in an elaborate memoir by Traquair l , the osteology 

 of the genera of this family, so far as known, is identical with that 

 of the genera of Paheoniscidas, the only essential difference being 

 that in the present case specialization results in the extreme 

 deepening of the head and trunk, whereas in the last-mentioned 

 family the result is remarkable elongation of the whole body and 

 the widening of the gape of the mouth. The typical Platysomatidae 

 have short, stout jaws, with a chiefly tritoral dentition ; while the 

 Palaeoniscidse are chiefly rapacious fishes, with conical laniaries. 



It is also worthy of note that in the only typical genus in which 

 the endoskeleton of the trunk has been clearly observed (Platy- 

 somus), the double series of robust dorsal fin-supports extends far 

 in advance of the origin of the fin itself. The same arrangement is 

 distinctly exhibited in the problematical Permian fish, Dorypterus, 



1 R. H. Traquair, " On the Structure and Affinities of the PlatysomicUe," 

 Trans. Roy. Soc. Edinb. vol. xxix. (1870), pp. 343-391, pis. iii.-vi. 



