. Elements of geology, or, The ancient changes of the earth and its inhabitants as illustrated by geological monuments. Geology. 422 SAURIANS OF THE LIAS. [Ch. XXI. rus ; 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. These last appear to have been bony spines which formed the anterior part of the dorsal fin, like that of the living Ces- tracion and Chimcera (see a, fig. 455). In both of these genera, the. CMmcera monstrosa* a
. Elements of geology, or, The ancient changes of the earth and its inhabitants as illustrated by geological monuments. Geology. 422 SAURIANS OF THE LIAS. [Ch. XXI. rus ; 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. These last appear to have been bony spines which formed the anterior part of the dorsal fin, like that of the living Ces- tracion and Chimcera (see a, fig. 455). In both of these genera, the. CMmcera monstrosa* a. Spine forming anterior part of dorsal fin. posterior concave face is armed with small spines, as in that of the fossil Hybodus (fig. 454), 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 Chimcera (fig. 455), to raise and depress the fin, their action resembling that of a movable mast, raising and lowering backwards the sail of a ; f 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. 456, 457). The genus Ich- thyosaurus, 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 fish4ike vertebrae, their paddles, resembling those of a porpoise or whale, the length of their tail, and other parts of their structure, that the habits of the Ichthyosaurs were aquatic. Their jaws and teeth show that they were carnivorous; and the half-digested remains of fishes a
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Keywords: ., bookcentury1800, bookdecade1860, booksubjectgeology, bookyear1868
