Chapter II 



CHELONIA— TURTLES, TERRAPINS, AND TOR- 

 TOISES 



The members of this order may be entirely aquatic, 

 only partly so, or entirely terrestrial, with paddle-shaped 

 limbs in the case of the first, with club-shaped limbs in 

 the case of the last, and intermediate in structure in the 

 second category. In this book the forms living entirely 

 on land are designated under the name of Tortoises, those 

 living both on land and in water as Terrapins, and the 

 exclusively aquatic forms as Turtles ; the last mentioned 

 are further divisible into fresh-water and marine. 



The body of these animals is protected by a bony shell, 

 usually covered with horny shields, into which the head, 

 neck, limbs, and tail may be retracted. This shell is 

 composed of numerous bones, the principal being expan- 

 sions of the vertebrae and ribs, forming the carapace, or 

 dorsal buckler, the neck and tail being the only movable 

 portions of the spinal column, and clavicles and abdominal 

 bones forming the plastron or ventral buckler. The 

 carapace and plastron are usually connected by a lateral 

 part known as the bridge. Both the bony plates and the 

 horny shields on the shell afford excellent characters for 

 the purpose of classification, but as the shields only are 



