426 Vertebrata. 



(tortoiseshell) , separated by grooves; their boundaries do not corre- 

 spond with those of the bony plates, although the arrangement is 

 similar. The rest of the body is covered by small scutes ; small bony 

 plates may develop in some scales, as in certain Lacertilia. 



The Chelonians feed partly on plants, partly on animals. They 

 are dull, sluggish creatures, terrestrial, freshwater, or marine. Many 

 are able to withdraw head and limbs within the edge of the shell. 



1. Mud Turtles (J/mi/(i»), mostly flattened animals, with webbed toes ; 

 live in freshwater, but many can also walk about on land. More exclusively 

 aqiiatic is thfe Fresbwater Tortoise {genus Trionyx, etc.), witb large 

 swimming feet (each with three claws), shell without horny plates ; ferocious 

 animals ; Asia, Africa, North America. 



2. Tortoises {Testudinidae), closely alhed to the Mud Turtles ; differing 

 chiefly in the much arched cai-apace, and the very short feet, in wbich the toes 

 have grown together and which possess short claws (club-footed) . The Grecian 

 Tortoise {Testudo Qrxca) inbabits South Europe. 



3. Turtles (Cheloniae) have a flattened carapace and immovably connected 

 toes without claws, or with rudiments only ; tbe fore limbs much larger than the 

 bind, forming a strong fin-Uke steering apparatus. They attain a consider- 

 able size ; hve in the sea, but the eggs are laid on land, buried in the sand. One 

 species in the Mediten-anean. 



Order 4. Crocodilia. {Crocodiles). 



This order differs from other living Eeptiles, and approaches Birds 

 and Mammals in many respects : as in the divided ventricle, the 

 structure of the brain and the cochlea, and also in the thecodont 

 dentition (teeth in sockets) . The Crocodiles have large heads with 

 the nares on the upper side of the snout, webs between the hind 

 toes, and a long compressed swimming tail ; claws present only on 

 the three inner toes of each foot ; five toes on the forefeet, four 

 on the hind. In the skin there are numerous bony plates (especially 

 on the dorsal side). The anus is a longitudinal slit. For the way 

 they breathe with the mouth open in the water, and for other 

 peculiarities, see above. 



Crocodiles, which may attain a length of about ten metres, live in 

 warm countries in fresh water, rarely on the sea-shore, but they also 

 frequent the land ; they are rapacious beasts and carrion feeders. The 

 eggs are laid on land, either buried in earth or among decaying plants, 

 -etc.; the female guards them, and sometimes also the young ones. 



The Crocodilia of the present day may be divided into thi-ee groups ; (1) 

 Alligators {Alligator), with short snout and impei-fectly webbed hind feet ; the 

 fourth tooth of the lower jaw bites into a cavity in the upper jaw ; America 

 (one species in East Asia) : (2) True Crocodiles {Crocodilus), with long snout 

 and complete webbing between the hind toes ; the fourth tooth of the lower jaw 

 bites into a notch on the side of the upper jaw ; in both the Old and the New 

 World: (3) G-avialidse {Bhamphostoma), mth very long, slender snout and 

 complete webs ; the fourth tooth of the lower jaw bites into a notch ; India. 



