CHELONIA 229 



Certain it is that the common box tortoise, of like form and habits, 

 occurs not irarely on the arid plains, far from water. 



The neck and legs became fully retractile within the shell; 

 the digits were shortened up, without a vestige of webbing mem- 

 brane between them; the phalanges were reduced in nimiber to two 

 in each toe, and nearly all the toes have well-formed claws. The 

 feet are placed squarely upon the ground, and the body is elevated 

 in walking. They can swim, when by accident they are thrown 

 into the water, only as any terrestrial mammal can. 



About forty species of land tortoises are known throughout 

 the world at the present time, though North America, the probable 

 original home of the tribe, has but three, all small. The larger 

 species are all now denizens of islands, especially the Galapagos 

 Islands, where the giant tortoises have long been famous. And 

 many of our living forrris have changed but little since Eocene 

 times. In the Oligocene and Miocene they inhabited western 

 North America in enormous numbers. In the Bad Lands of South 

 Dakota one can often see the remains of a dozen or more of these 

 giant tortoises at one time, specimens varying from one to three 

 feet in length of shell. In river deposits, those of the late Miocene 

 or early Pliocene, the writer has seen areas of an acre or more 

 literally strewn with their remains, as though droves of them had 

 been overwhelmed and perished together. About fifty species of 

 these land tortoises are known from the American Tertiary, thirty- 

 two of them belonging to the modern genus TesPudo, which com- 

 prises the giant tortoises of the Galapagos. The largest known 

 species of the group is one of Testudo from the Pliocene of India, 

 which had a shell six feet in length. Why the larger species became 

 extinct in Pliocene times on the mainland to survive only in the 

 islands is not known; possibly their carnivorous enemies became 

 too cunning and too numerous. 



SEA-TURTLES. CHELONIDAE 



The sea-turtles, or Chelonidae comprise fi.ve or six Kving species, 

 inhabitants for the most part of tropical and subtropical oceans, 

 of which the green or edible turtle {Chelone), the hawksbill turtle 



