FOSSIL REPTILES. 365 



reptiles, without the teeth affording us any indication of the 

 age. 



There are, however, ichthyosauri of much larger size, espe- 

 cially in the species platyodon, being twenty feet and upwards. 

 A cranium in possession of Mr. Johnson, of Bristol, measured 

 in breadth, behind, two feet six, and its longitudinal diameter 

 was fourteen inches. M. Cuvier has vertebrae six inches in 

 diameter, which he refers to individuals of at least one-and- 

 twenty feet in length. One found near Bath, in the oolite, 

 measured nearly seven inches, and many portions of fins from 

 Newcastle announced individuals of very large size. 



On the whole, the ichthyosaurus did not fall far short, in 

 size, of the masasaurus of Maestricht, already described, whose 

 length has been calculated at five-and-twenty feet. 



M. Gotthelf de Fischer has described, under the name of 

 tooth of ichthyosaurus, a conical tooth, found on the banks of 

 the Occa, nineteen inches long, and seven broad at its base, hol- 

 lowed with a conical cavity about seven inches in depth. This, 

 indeed, would indicate a reptile of most enormous dimensions, 

 but M. Cuvier thinks, with great probability, that it is only the 

 tusk of an elephant. 



The Plesiosaurus. 



This genus is also entirely English, and altogether due to the 

 sagacity of Mr. Conybeare. Some vertebrae mixed with those 

 of the crocodile and the ichthyosaurus in the lias of the neigh- 

 bourhood of Bristol, appeared to him to differ from those of 

 both these genera. A considerable portion of a skeleton, in the 

 collection of Colonel Birch, confirmed him in his notions con- 

 cerning the species from which these debris proceeded. He 

 added, to complete them, some bones of the extremities found 

 with these vertebrae, and thus was enabled to publish, in 1821, 

 the characters of the new animal, in a memoir, conjointly with 



