392 



ZOOLOGY 



toise-shell are used in the manufacture of bags, ornaments, and 

 the like. 



Probably the chief value of the group to man is in the de- 

 struction of noxious insects by lizards and rodents by snakes. 



425. Classification of Reptiles. 



Order I. Chelonia (Turtles and Tortoises}. The Chelonia are reptiles with 

 short, flattened or dome-shaped bodies enclosed in a case formed by a dorsal shield 

 (carapace) and a ventral (plastron). In some the carapace and plastron make a 

 rather tight-box practically covering the animal. In others they are smaller and 

 the edges are further apart. In these the appendages may protrude more, and 

 the freedom of motion is much greater. The jaws are covered with a horny case 



FIG. 197. 



FIG. 197. 



Common Box Tortoise (Cistudo Carolina). 

 Shufeldt. 



Photographed from life by Dr. R 



and are destitute of teeth. The quadrate bone is firmly fused to the cranium. 

 The sternum is absent. Turtles seem rather more common in the northern hemi- 

 sphere. The largest species are marine and may attain a weight of half a ton. 

 Some live in fresh water and others on land. The flesh of some species is much 

 prized for food. The green- turtle of the Atlantic coast is one of the choicest, its 

 flesh being much used for soups. The large hawkbill-turtle of the tropical seas 

 furnishes "tortoise-shell," used in combs and other ornaments. The shells of 

 the leather-back and other "soft-shelled " turtles are not completely ossified. The 

 "snappers" are ferocious animals, the big snapper of the Southern states being 

 particularly vicious. 



Order II. Lacertilia (Lizards). Reptiles in which the body is usually covered 

 with small scales. Two pairs of limbs are ordinarily present; but either or both 

 may be wanting. The quadrate bone is somewhat movable. The teeth are not 

 in sockets of the jaw. Sternum present. The cloacal opening is transverse. 



