Iig6 CLASS REPTILIA. 



south of England, and also in those of France and Germany ; some 

 of the species from the latter deposits having been described as 

 Alligator. The genus has also been recorded from the Upper 

 Eocene of North America. The last, and in respect of cranial 

 characters the most specialised, group of Crocodiles is now divided * 

 into the two genera Caiman and Alligator. In these forms both 

 the first and the fourth lower tooth are received into pits in the 

 upper jaw, so as to be concealed when the mouth is closed ; the 

 upper teeth bite on the outer side of the lower ones ; the supratem- 

 poral fossae are very small, and are occasionally obliterated ; and 

 the third lower tooth is smaller than the fourth. Caiman is dis- 

 tinguished by the presence of a ventral armour, and also by the 

 circumstance that the nasals do not extend across the nares ; and 



Fig. 1094. — Oblique left lateral and palatal view of the facial part of the cranium of Diplocynodon 

 hantoniensis ; from the Upper Eocene of Hampshire. Reduced. 



is now confined to Central and South America. In Alligator, "on 

 the other hand, which occurs at the present day in North America 

 and China, the ventral armour is absent or extremely thin, and the 

 nasals extend forwards so as to divide the narial aperture. Remains 

 which are probably referable to Caiman occur in the Pleistocene 

 cave-deposits of Brazil ; but it does not appear that there is any 

 certain evidence of fossil species of Alligator ; the European, and 

 probably some of the North American forms which have been re- 

 ferred to that genus, belonging to Diplocynodon. Finally, the name 

 Isselosaurus has been recently applied to Crocodilian remains from 

 the Middle Eocene of France which may really belong to one of the 

 above-mentioned genera. 



Order X. Ornithosauria. — The Pterodactyles, as the mem- 

 bers of this extinct order are commonly termed, are among the 

 most remarkable and strange Reptilian forms that Palaeontology has 



1 According to the arrangement adopted by Mr Boulenger in his British 

 Museum Catalogue of this order. 



