DISTRIBUTION OF ORGANISMS. 169 



them to be often denominated Soft Tortoises. The feet are 

 palmated for swimming, and the toes exhibit three claws. 

 These animals are of fierce and energetic character, living 

 upon fishes and reptiles, and not scrupling to attack the 

 young alligators. They dart out their head at their prey 

 with inconceivable rapidity, and tear it with their sharp- 

 edged beaks and claws, after the manner of the predaceous 

 birds. 



The Emydes, sometimes called Fresh-water Tortoises, 

 sometimes Marsh Tortoises, are of many various species, 

 haunting lakes, marshes, and small rivers in Asia, Africa, 

 Australia, but more particularly America, where the proper 

 habitat is most largely presented. They have shelly cases, 

 which in youth exhibit the imperfect closing peculiar to the 

 turtles, but afterwards become complete. Certain species can, 

 by flexures in the case, close in their head, tails, and feet, so as 

 to set enemies at defiance. The feet are palmated, and pro- 

 vided with five claws before and four behind. A remarkable 

 rapidity of movement distinguishes this family, which devours 

 not only aquatic worms, insects, mollusks, and small reptiles, 

 but carrion. Among the emydes are species, such as Cestudo 

 Carolina and Emys Muhlenburgii, which tend to a land life, 

 and have the feet less palmated than the rest. There are also 

 genera, Pyxis and Kinyxis, the one belonging to the Old 

 World, the other to the New, which are regarded as con- 

 necting links between the emydes and land tortoises. 



Several aquatic genera of remarkable forms are not yet 

 settled in any definite place in our systems. One of these, 

 the Emysaura Serpentina, which has a large head and a 

 crocodilian tail, lives in the North American rivers, feeding 

 on fish and small birds. Another, Chelys Fimbriata, or 

 Matamata, with hardly any tail, has a large neck and snouted 

 head, in which the mouth opens crosswise ; it belongs exclu- 

 sively to the rivers of Guiana. Mr. Swainson makes of these 

 genera a group, to which he gives the name of Chelydrida. 



Last are the Land Tortoises (Testudines), in which, with a 

 perfect osseous case, there are extremities formed entirely for 

 land progression, terminating in rounded callous stumps, with 



