276 THEORY OF THE EARTH. 



of at least ten species belonging to all the orders, 

 are found there *. 



The crocodiles of the period in question ap- 

 proach our common crocodiles in the form of the 

 head, while, in the deposits of the Jura period, 

 we find only species allied to the gavial. 



A species has been found at Argenton, which 

 is remarkable for its compressed, sharp teeth, ha- 

 ving their edges dentated like those of certain 

 monitors f . Some remains of it also occur in our 

 gypsum quarries {. 



The tortoises of this period are all fresh-water 

 ones: some of them belong to the subgenus 

 Emys ; and there are species, both at Mont- 

 martre , and still more especially in the molasse 

 sandstones of the Dordogne ||, which are larger 

 than any living species known ; the others are 

 Trionyces or soft tortoises IF. This genus, which 

 is easily distinguished by the vermiculate surface 

 of the bones of its shell, and which at present 

 exists only in the rivers of warm countries, such 



* " Researches," vol. iii. p. 304 et seq. 



t Id. vol. v. part ii. p. 166. 



J Id. vol. iii. p. 335 ; vol, v. part ii. p. 166. 



Id. vol. iii. p. 233. 



|| Id. vol. v. p. 232. 



IT Id, vol. iii. p, 329; vol, v. part ii. p, 222, 



