301 



Species I. PI. prisons. The cervical vertebrae in this 

 species are the thickest in the series. All the bones 

 of this genus, figured in the Geological Transactions, 

 belong to this species. It occurs in lias. 



animal approximates, in these respects, more nearly to the crocodile : 

 they therefore describe plesiosaurus as a marine animal, intermediate 

 in its structure between the ichthyosaurus and crocodile. 



" The teeth have not been decidedly ascertained ; a peculiar tooth, 

 however, not belonging to any species of ichthyosaurus, yet evidently 

 of the crocodilean type, occurs in the lias, and may, with great pro- 

 bability, be referred to this animal. " 



I am happy in having been favoured by Mr. Conybeare, since 

 the publication of his paper, with the following account of the head 

 of this animal, which has been lately found : 



" Of the head of this animal only a single specimen approaching 

 to completeness has yet occurred. It was discovered by Mr. Thomas 

 Clarke, in the lias of Street, near Glastonbury : unfortunately, it is 

 much crushed, but is yet sufficiently perfect to exhibit its most es- 

 sential osteological characters. 



" These characters when viewed collectively, present, as might 

 have been expected, an assemblage sui generis; taken separately, 

 they exhibit partial approximations to the ichthyosaurus, the crocodile t 

 and the lacertian family, (more strictly so called, as considered exclu- 

 sively of the crocodilean branch), nor is there any structure which 

 may not be paralleled from one of these three types : on the whole, 

 we should be inclined to pronounce (though not without hesitation) 

 the approximations to the latter class to be most close and important. 



" Its general contour, the character of its temporal fossae, and 

 the position of its ossa quadrata, resemble the lacerta, iguana, &c. ; 

 but the small size of the nostrils, the conformation of the palatal 

 and pterygoidal parts of the roof of the mouth (as far as the speci- 

 men enables us to judge of them), and the dentition, remove it 

 from this type. 



" It agrees with the ichthyosaurus in the position and small size 

 of the nostrils, and in the structure of the palatal and pterygoidal 

 parts (in which both animals approximate to the crocodilean type) ; 

 but it differs in the comparative shortness of its snout, which gives 

 an entirely dissimilar character to its whole contour, in carrying its 

 teeth in distinct alveoli instead of a continuous furrow, and in all 



