LIZARDS, TORTOISES AND BATRACHIANS 391 



and lighter ; abdomen yellowish ; tail pale bluish or greenish below. 

 Length 5 inches. 



Usually considered a southern form ; but Cope notes a specimen 

 taken in Burlington county, N. J. ; and H. D. Reed informs me that a 

 specimen in the collection of Cornell university w T as captured Ap. 23, 

 1892, on the Caroline hills, southeast of Utica N. Y. by W. J. Terry. 



B. CHELONIA 



Turtles 



The turtles and tortoises, which comprise the order Chelonia, may 

 be defined as reptiles having the skeleton mainly external. The 

 body is inclosed in a shell of bony plates consisting of a dorsal cara- 

 pace (to which the vertebrae and ribs are firmly fused) and a ven- 

 tral plate or plastron. Both of these are covered over with horny 

 plates which are composed of the well known tortoise shell. 1 



The vertebrae of the neck and tail are free and movable. The 

 limbs are well developed and usually terminated by claws. In some 

 forms there is a web between the toes, while in the marine forms 

 (not included in this list) the feet have the form of nippers. Teeth 

 are never developed, the jaws being covered by a layer of horn. 



Their eggs, which have a tough leathery shell, are laid in the dry 

 sand and are hatched by the heat of the sun. Like all reptiles, the 

 young leave the egg in the form of the parent, and thus do not 

 undergo any metamorphosis, as do the batrachians. They breathe 

 by lungs throughout their entire existence. 



The Chelonia are found both on land and in w T ater, many forms 

 being apparently equally at home in either. 



Omitting the marine turtles, our forms represent four families. 



1 Trionychidae, soft-shelled turtles 



2 Chelydridae, snapping turtles 



3 Kinosternidae, box or musk turtles 



4 Emydidae, pond turtles 



Family 1 trionychidae 

 Soft-shelled turtles 

 Body flat, round ; carapace not completely ossified, and with the 



1 The tortoise shell of commerce is derived from one of the marine forms. 



