370 RAMSAY H. TRAQUAIR ON THE 
Usual length about 33 inches. Body deep and rounded; back strongly and 
evenly arched from the occiput to the narrow tail pedicle; ventral contour 
more gently curved from the throat to the commencement of the anal fin, from 
which it then slopes rapidly upwards in a manner corresponding to the down- 
ward direction of the dorsal line opposite. Flank scales, exclusive of the 
articular peg, about 23 times as high as broad; all over the body they are 
marked externally with exceedingly close and delicate strize, vertical to the long 
axis of the fish. Dorsal fin commencing rather behind the highest point of the 
rounded back, acuminate in front, and falling away to a narrow fringe-like 
form behind, anal similar in shape, but about one-sixth part shorter. Pectorals 
small with distinctly articulated rays, ventrals not observable. External bones 
of head for the most part minutely striated; some granulation observable 
upon the parietals and frontals ; operculum very high and narrow, interoper- 
culum very small. 
The above description is principally taken from a specimen in the Museum 
of Practical Geology, labelled Platysomus striatus ;* others are in the collections 
of Messrs E. W. Binney, F.R.S. of Manchester, and J. Warp, F.G.S. of Long- 
ton. All are from the “ Dalemoor Rake” ironstone of Stanton-by-Dale, 
Derbyshire. Its specific distinctions are clear and unmistakeable. From the 
large Permian species gibbosus, rhombus, and striatus, it is obviously dis- 
tinguished by the rounded contour of the back, being especially widely 
removed from P. striatus by the greater anterior acumination of the dorsal and 
anal fins, and the sharp turning forwards of the dorso-ventral bands of scales 
so prominent in that species, being here hardly perceptible. From P. gibbosus 
and rhombus it is equally distinct. As regards the Carboniferous species, the 
want of the dorsal peak and the finer sculpture of the scales at once dis- 
tinguishes it from P. parvulus, while from P. rotundus, the shorter dorsal fin, 
the proportionally broader scales, with their closer and more delicate sculpture, 
are diagnostic marks which strike one at the first glance. P. Forsteri is a large 
species which has not yet been found entire; but the character of the scale 
ornament is rather different from that of P. tenwistriatus, the strize being more 
undulating, usually more or less oblique to the anterior margin even in the 
flank scales, and tending to become abruptly intercalated. 
Geological Position.—The genus Platysomus is characteristic of the Permian — 
and Carboniferous formations, and if we except the remains catalogued by Messrs 4 
Younc and Armstrone as “ P. declivus,” from the Carboniferous Limestone of — F 
Braehead,t which I have not seen, no trace of it has been found below the 
* This is probably the same specimen from Derbyshire, “ in the Jermyn Street collection,” to which — 
Professor Youne refers (op. cit. p. 305), in support of his statement that P. striatus is common to the — 
Carboniferous and Permian formations. <A 
+ Carboniferous Fossils of the West of Scotland, Glasgow, 1871, p. 75. Catalogue of the 
Western Scottish Fossils, ‘ British Association Guide Books,” Glasgow, 1876, p. 64. q 
