Along with these, and not improbably their enemies, were certain Sharks ([Fig. 104]), known to us only by the spines which were attached to their fins as weapons of defence, and by detached bony tubercles which protected their skin. These remains are chiefly interesting as indications that two of the great leading divisions of the class of fishes originated together.
In the Devonian age the Ganoids and Sharks, thus introduced in the Silurian, may be said to culminate. The former, more especially, are represented by a great variety of species, some of them nearly allied to their Silurian predecessors ([Fig. 106]), others of forms and structure not dissimilar to those of the few surviving representatives of the order, or altogether peculiar to the Devonian ([Fig. 107]). So numerous are these fishes, and of so many genera and species—and this not merely in one region, but in widely separated parts of the world—that the Devonian has not inaptly been called the reign of Ganoids. As an illustration at once of the very peculiar forms of some of these fishes and of their wide distribution, I figure here along with the British species a Cephalaspis ([Fig. 105]) found in the Lower Devonian of Gaspé, in the same beds with some of the antique Devonian plants described in the last chapter.
Fig. 106.—Devonian Placoganoid Fishes (Pterichthys cornutus, Cephalaspis Lyelli), from Scotland.
Fig. 107.—Devonian Lepidoganoid Fishes (Diplacanthus and Osteolepis). After Page and Nicholson.
