XVI MAEINE EEPTILES OF THE OXFOED CLAY. 



adapted for a pelagic life, bnt still to a mucti smaller degree than the wliale-like 

 Ophthalviosaunis. 



If these animals, as we suppose, lived near the shore, the conditions of life 

 ■would be much more various than in the case of a truly pelagic animal, and 

 this would probably account for the much greater variety of form found among 

 them than among the Ichthyosaurs. One of the most remarkable circumstances 

 about these Oxford Clay reptiles is the occurrence in a limited area of so large 

 a number of closely related species and genera, in the case both of the Plesiosaurs 

 and of the Crocodiles. This can be reasonably accounted for by supposing that 

 the conditions under which the different forms lived presented considerable 

 variety, some, for instance, living in shallow, some in deeper water, some perhaps 

 in swamps, and some in rivers or river-estuaries. For the same reasons, although the 

 Ichthyosaurs 0])hthalmosaurus and Baptanodon are generically identical, it by no 

 means follows that the American Plesiosaurs contemporary with them will, when 

 better known, be found to be closely similar to the English species. 



Although in the Cretaceous period the Plesiosauria had spread over the whole 

 world, being known not only from Europe and North America but also from 

 Asia, South America, South Africa (a species discovered lately), Australia, and 

 New Zealand, it is not certain how far the Elasmosauridae spread, for in most 

 cases too little is known about the skeleton of these foreign species to make it 

 possible to determine to what family they belong. 



The Plesiosaurs Avere no doubt predaceous, their long sharp teeth being well 

 adapted for the prehension of living prey, which would probably be swallowed 

 whole. Ihe occurrence of numerous stones in the stomach of these animals, first 

 observed by Mr. Thomas Codrington * in a Plesiosaur from the Upper Greensand 

 of Wiltshire, and since noticed in the case of various English and American 

 species, may indicate that the food was broken up in a muscular stomach by 

 the aid of these stones, much as in the gizzard of a bird. No specimen of an 

 Elasmosaur in which the stomach-stones are preserved has been collected from 

 the Oxford Clay, but in the case of a Pliosaur, Peloneustes, Mr. Leeds has obtained 

 a hard mass lying within the ribs, containing many stones of various sizes, from 



* 'Wiltshire Archaeological Magazine,' vol. ix. (1803) p. 170. 



