324 SYSTEMATIC ZOOLOGY 



in the habit of walking or swimming. In all of these the shell 

 is covered with horny scales. One of the best known in the 

 United States is the painted turtle, Chrysemys picta, which is 

 found from the Gulf of Mexico to the Gulf of St. Lawrence. 

 It is dark brown above, with the scales bordered with yellow, 

 and the marginal plates marked with concentric red lines ; the 

 plastron is yellow. Another species of this genus is found in 

 the West. Xorth and east of the Ohio the speckled turtle, 

 Chelopus guttatus, is very abundant ; the carapace is black with 

 small yellow dots, which increase in number with age. To the 

 epicurean the most familiar turtle is the diamond-back terrapin, 

 Malaclemmys palustris. It lives in marshes along the Atlantic 

 coast from New York to Texas and even farther south. The 

 adult male has the carapace about fifteen centimeters long; 

 the female, which is considered the more valuable because of 

 the eggs she contains, may be two or three centimeters longer. 

 They are very abundant about Charleston, and the two sexes 

 are known respectively as bulls and cows in the market. They 

 are rapidly diminishing in numbers owing to the enormous quan- 

 tities captured yearlv and their slow rate of growth. The 

 snapping turtle, Chelydra serpentina, is found in America from 

 Canada to Equador, and may attain a length of about a meter. 

 It lives in the water or on land and is one of the fiercest 

 reptiles found in the United States. The genus Testudo 

 includes turtles which are strictly land animals ; one of the 

 most familiar in the United States is the gopher turtle, whose 

 shell is often about forty-five centimeters in length. A giant 

 fossil tortoise of India is worthy of mention because of its great 

 size ; it was six meters in length, and the carapace was nearly 

 two and a half meters high. 



Order 4. Crocodilia 



The Crocodilia (Gr. tcpo/co&eiXos, crocodile) are represented in 

 all tropical countries of the world, and in their internal structure 

 are the most highly developed of the Reptilia. They have an 

 elongated body with four well-developed legs and often claws 

 on the digits. The tail is laterally compressed so as to serve 

 as an oreran for swimming. The bodv is covered with a thick, 



