[542] It is with peculiar pleasure that I inscribe this new species of Gyrodus to Sir R. I. Murchison, in commemoration of those extended and successful geological researches in the Russian empire, which have conferred additional honour on his distinguished name.
The fishes of the genus Gyrodus have the body large, flat, and elevated; the dorsal and anal fins are very long; and the tail is forked, with equal elongated lobes. The scales are laterally connected by strong processes, as in Lepidotus.
Other genera related to the foregoing occur in the Oolite; as for example, Microdon, thus named from the smallness of its very numerous flat angular teeth, arranged in many rows; Placodus, in which the teeth are few, flat, and of great size;[543] and Platysomus (flat-body), with orbicular, clavate, teeth.
[543] Odontography, pl. xliii. fig. 1, and pl. xxx. fig. 2.
In these fishes, also, the dental organs are well adapted for the comminution of shell-fish, and other hard bodies.
Cephalaspides of the Devonian System.—The remains of the three genera of Ganoid fishes that we have now to notice are of a very remarkable character, and are found exclusively in the Devonian or Old Red system; most frequently in Scotland, but also in other parts of the British Isles, and in Europe and America. These fishes agree in one general character, that of having extensive osseous plates, or scutcheons; their general aspect will be understood by reference to [Lign. 199], 200, 201. There are no vestiges of the bodies of the vertebræ, which, therefore, were probably cartilaginous. These fishes constitute a distinct family with the name Cephalaspides, from the character of the first genus we propose to describe.
