Fig. 377: Acrodus nobilis. Fig. 378: Hybodus reticulatus, a. Part of fin, commonly called Ichthyodorylite, b. Tooth. But the remains of fish which have excited more attention than any others are those large bony spines called ichthyodorulites (a, Figure 378), which were once supposed by some naturalists to be jaws, and by others weapons, resembling those of the living Balistes and Silurus; but which M. Agassiz has shown to be neither the one nor the other. The spines, in the genera last mentioned, articulate with the backbone, whereas there are no signs of any such articulation in the ichthyodorulites. Fig. 379: Chimæra monstrosa. Fig. 379: Chimæra monstrosa.[3] These last appear to have been bony spines which formed the anterior part of the dorsal fin, like that of the living genera _ Cestracion_ and _Chimæra_ (see _a,_ Figure 379). In both of these genera, the posterior concave face is armed with small spines, as in that of the fossil _Hybodus_ (Fig. 378), a placoid fish of the shark family found fossil at Lyme Regis. Such spines are simply imbedded in the flesh, and attached to strong muscles. “They serve,” says Dr. Buckland, “as in the _Chimæra_ (Fig. 379), to raise and depress the fin, their action resembling that of a movable mast, raising and lowering backward the sail of a barge.”[4] Reptiles of the Lias.—It is not, however, the fossil fish which form the most striking feature in the organic remains of the Lias; but the _Enaliosaurian_ reptiles, which are extraordinary for their number, size, and structure. Among the most singular of these are several species of _Ichthyosaurus_ and _Plesiosaurus_ (Figs. 380, 381). The genus _ Ichthyosaurus,_ or fish-lizard, is not confined to this formation, but has been found in strata as high as the White Chalk of England, and as low as the Trias of Germany, a formation which immediately succeeds the Lias in the descending order. It is evident from their fish-like vertebræ, their paddles, resembling those of a porpoise or whale, the length of their tail, and other parts of their structure, that the Ichthyosaurs were aquatic. Their jaws and teeth show that they were carnivorous; and the half-digested remains of fishes and reptiles, found within their skeletons, indicate the precise nature of their food.