29(3 



Division IT. Enalio sauri*, comprising genera dif- 

 fering from the recent, and fitted to live entirely in 

 the sea. 



Ichthyosaurus.^ A marine, oviparous animal; closely 

 agreeing in the whole osteology of the head and sternum 

 with the saurian tribe, except that the bones are usually, 



The fossil remains which have been thus given to their proper 

 animals, are 1st, the supposed crocodile of Spence ; 2d, the sup- 

 posed crocodile of Link ; 3d, the sapajou of Swedenbourg ; 4th, a 

 skeleton in the Royal Museum of Berlin. The supposed skeleton 

 of a crocodile in the Cabinet of Dresden is supposed also to belong 

 to the monitors. 



* Ev#A/0<7, marine, and #U0<7, a lizard. 



f Naturalists are under great obligations to Sir Edward Home 

 and Professor Buckland for their long continued perseverance in the 

 investigations respecting the nature of this fossil animal. 



At the desire of Mr. Conybeare I state, that, in drawing up the 

 following notice, which includes an outline of the pi ogress made in 

 developing the structure and relations of this animal since his com- 

 munication to the Geological Society, he wishes to acknowledge his 

 obligations to the same friend to whom he has alluded in the published 

 memoir, as inclined to refer the ichthyosaurus rather to the lacertian 

 division of the sauri than to the crocodilean type. It has been his 

 own endeavour to expose, as fairly as possible, its relations with both. 



The account above given of its dentition is now confirmed by a 

 suite of decisive specimens of teeth, both in, and detached from, the 

 jaw, containing every stage of the process. It will at once be seen, 

 that it differs most essentially from that of the monitor, &c. in 

 whose teeth a large bony secretion, supplying the place of the root, 

 unites them to the maxilla, with which this osseous mass is organ- 

 ically incorporated : the new teeth, formed in distinct alveoli, pierce 

 laterally, or transversely, across this osseous mass. In the ichthyo- 

 saurus there is no similar osseous union, but the base of the tooth, 

 which lies quite freely in its place, is a simple prolongation of the 

 conical body of the tooth, exactly as in the crocodile. The den- 

 tition is a point so important, that it has been necessary to dwell 

 upon it more at length. The illustration of these points will form 

 the subject of a memoir shortly to be laid before the Geological 

 Society. 



