590 BRITISH PALAZOZOIC FOSSILS. [ Pisczs. 
The Celacanthi can only be distinguished from the Sawroids by the imbrication of the scales. As at first 
defined, the principal characters were, the hollowness of the bones and rays (which were cartilaginous within, 
coated with a thin calcareous shell), the tapering of the spinal column into the middle of the tail, and the rays 
of the caudal fin having interapophysary bones like the dorsal (these are well seen in our figure of Holoptychius 
Sedgwicki) ; the first definitions also include some teeth of the Pyenoid type. 
Genera :—1, Calacanthus; 2, Glyptolepis; 3, Holoptychius; 4, Gyroptychius; 5, Dendrodus; 6, Lam- 
nodus; 7, Asterolepis, &e. 
Genus. GLYPTOLEPIS (Ag.) 
Gen. Char.—Scales thin, subquadrate, rounded; surface nearly smooth, concentrically imbricated round 
a central point; interior shewing a finely radiated, cellular structure; teeth sharp, conical, deeply furrowed 
longitudinally, implanted in imbricating plaited sockets; one detached ventral fin, surrounding a pointed, scaly 
process, directed backwards; two dorsal and two anal fins close to the heterocercal tail, nearly equal and opposite 
each other, the posterior pair largest ; the caudal is broad and truncate. 
These are moderate sized fishes, with blunt, flat, rounded heads, and two large triangular plates covering 
the throat in place of the branchiostegous rays. I much doubt the propriety of separating this genus from 
Dipterus, since I have examined the original types of this latter genus. 
GLYPTOLEPIS LEPTOPTERUS (Ag.) 
Ref —Ag. Old Red Fish, t. 20 and 21. 
Dese.—Body about three inches thick and twelve long, covered with dull, nearly circular, strong, slightly 
convex scales, about five or six lines in diameter, each marked with small, sharp, irregular, concentric wrinkles, 
round a nearly central, prominent point, crossed on the anterior part by a few radiating ridges: when the 
surface is destroyed the scales are seen to have a very minutely-radiated structure, about thirty-five radiating 
lines in the space of one line. Teeth about one line long, nearly uniform, close, conical, coarsely sulcated at 
the basal portion. 
There is but one sort of teeth seen in the jaw externally. 
Position and Locality Old Red sandstone, Lethen Bar. 
Genus. DIPTERUS (Sedg. and Murch.) 
Syn. = Dipterus Ag. = (? Glyptolepis Ag.) + Polyphractus Ag. + Ctenodus Ag. 
Gen. Char.—Small fusiform fishes, with compressed heads, and perfectly heterocercal tails, and two dorsal 
fins precisely opposite two similar anal fins, the second of each largest, placed rather close and far back ; a strongly 
marked lateral line; scales circular, thickest in the middle, variously carved, either with concentric lines round 
a nearly central point, or, more rarely, with fine longitudinal ridges on the exposed part. Lateral line impressed. 
This genus was first described in a joint memoir, “ On the Deposits contained between the Primary Rocks 
and the Oolitic Series in the North of Scotland,” published by the Rey. A. Sedgwick and Mr Murchison, in the 
3rd Vol. 2nd Series of the Transactions of the Geological Society of London (1835), and named by them from 
the double dorsal fins. In the excellent figures by Mr Scharf, which accompany this memoir, we also find the 
character of the double anal fins opposite the dorsals clearly represented; the heterocercal structure of the 
tail is also noticed, and the scales are stated to be round and imbricated. Thus far the characters are generic, 
and in accordance with the views of Baron Cuvier, and of MM. Valenciennes and Pentland, who agreed 
with the authors in their interpretation of the specimens. Three species were figured, and characterized by 
their dimensions, the size of the scales, and the proportions of the fins—namely the D. brachypygopterus, 
D. macropygopterus, and D. Valenciennesi, and certain fragments were provisionally named D. macrolepidotus, 
although with the express caution that they considered the generic reference quite uncertain, from the imper- 
fection of the specimens. 
