TORTOISES AND TURTLES. 



107 



relations the reptiles, to lose their teeth. Thus as 

 already mentioned, the Fish-Lizards of the Cretaceous 

 rocks of the United States are all characterised by the 

 absence of teeth ; and, as we shall subsequently have 

 occasion to notice, a similar condition obtains in the 

 Pterodactyles, or flying reptiles of the same deposits, 

 by which feature they are widely distinguished from 

 their Old World allies. 



All the fossil tortoises and turtles at present known 



f 



FIG. 31. Left side of the skull of a Land-Tortoise, with the lower jaw displaced. 

 in, pm, upper jaw ; s, cheek-bone ; t, cavity of ear ; /, pf, bones over the eye 

 and nose-cavity ; p, hollow of the temples ; o, posterior spine. 



to us agree with existing types in the absence of teeth, 

 as well as in the general characters of the shell ; and 

 we have at present (on the assumption that some mode 

 of evolution is the true explanation of the mutual 

 relationships of the different groups of animals) no 

 evidence to connect the Chelonians very closely with 

 any other type of reptiles. It is, however, quite 



