

DISTRIBUTION OF ORGANISMS. 191 



In all the remaining chelonia, the paddle-form of the ex- 

 tremities is exchanged for legs and feet, the latter furnished 

 with claws. 



The River Tortoises (Tryonkes), conspicuous tenants of the 

 Ganges and Euphrates, the Niger and Nile, the Mississippi 

 and Ohio, are next in size to the turtles, some being three feet 

 long. With an imperfect development of the osseous case, they 

 are enveloped in a soft skin, which has caused 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 rep- 

 tiles, 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, some- 

 times 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 after- 

 wards become complete. Certain species can, by flexures in 

 the case, close-in their head, tail, and feet, so as to set enemies 

 at defiance. The feet are palmated, and provided 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 Cistudo 

 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 connect- 

 ing 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 (Fig. 101), 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 

 exclusively to the rivers of Guiana. Mr. Swainson makes of 

 these genera a group, to which he gives the name of Chely- 

 dricla. 



