PINE-LIZARD AND ITS ALLIES: REPTILIA 359 



a very convex upper shell ; the lower portion is provided 

 with a transverse hinge, which makes it possible for the 

 animal to bring the two parts of the shell closely together, 

 thus forming a box, within which are concealed head, neck, 

 legs, and tail. A remarkable sex-dimorphism occurs ; the 

 eyes of the male are red, those of the female, brown. More 

 flattened species, like the painted tortoise (Chrys'emys) and 

 the spotted tortoise (Nan'emys), are better adapted to an 

 aquatic existence. 



Alligators and Crocodiles. The large reptiles known as alli- 

 gators and crocodiles belong to the Crocodil'ia (Lat. crocodilus, 

 crocodile). The heart in the crocodilians is highly specialized, 

 having four separate chambers by the complete separation of 

 the two ventricles. Alligators (Fig. 184) differ from croco- 

 diles in having the canine teeth of the lower jaw fitting into 

 pits in the upper jaw ; in the crocodiles they fit into notches 

 in the side of the jaw. A species of each kind is found in 



FIG. 184. Photograph of Alligator 



Florida, though both have been sought so eagerly for the 

 teeth and skin that they are now found only in the more 

 inaccessible places. Crocodilians are also found in China, 

 Africa, southern Asia, and South America. They frequent 

 the edge of rivers, ponds, and lakes, lying in wait for their 



