368 



ZOOLOGY 



Tortoises 

 and turtles 



Photograph by E. R. Sanborn, N. Y. Zo&l. Soc. 



FIG. 145. Giant land tortoise (Testudo vicina) from the Galapagos Islands. Sim- 

 ilar large tortoises formerly inhabited continental areas, but they have died out, 

 leaving only a few species on islands. 



6. The tortoises or turtles (Chelonia) are easily rec- 

 ognized by the bony covering of the body and the tooth- 

 less jaws. The covering or shell consists of a dorsal or 

 upper portion, called the carapace, and a ventral or 

 lower plastron. In very young animals the shell is soft, 

 the plates not being fully ossified. The surface is 

 covered with horny shields, which according to Gadow 

 are phylogenetically older than the underlying bony 

 plates, and do not correspond with them either in num- 

 ber or position. These shields furnish the well-known 

 tortoise shell, which is obtained from the hawksbill 

 turtle (Chelone imbricata) of tropical seas. In certain 

 river turtles the shell is covered with soft, leathery skin 

 instead of hard shields ; the soft-shelled turtle of the 

 United States is an example. In the leathery turtle 

 (Sphargis) the limbs are transformed into paddles, and 



