

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 barge." 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, 4 57). 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 and 

 reptiles, found within their skeletons, indicate the precise nature of 

 their food.§ 



A specimen of the hinder fin or paddle of Ichthyosaurus communis 

 was discovered in 18^0 at Barrow-on-Soar, by Sir P. Egerton, which 

 distinctly exhibits on its posterior margin the remains of cartila- 



* Agassiz, Poissons Fossiles, vol. iii., tab. C, fig. 1. 



f Bridgewater Treatise, p. 290. 



X Ibid., p. 168. § Ibid., p. 187. 



