28, 29.] 



TORTOISES AND TURTLES. 27 



Cheloniidm or true Marine Turtles. Their feet are transformed 

 into long compressed fins, the anterior pair considerably longer 

 than the posterior, the digits being enclosed in a common 

 skin, out of which only one or two claws project; the carapace 

 is broad and much depressed, but large interspaces between 

 the extremities of the ribs remain unossified; it is covered with 

 symmetrical horny plates. These Turtles are thoroughly marine 

 animals, their fin-like feet and their light shell rendering them 

 the best swimmers in the class of Reptiles. They sometimes 

 live hundreds of miles distant from the shore, to which, however, 

 they periodically return in order to deposit from 100 to 250 soft- 

 shelled eggs, which are buried in the sand. The food of some species 

 (Chelone my das) consists exclusively of algae; others (Thalasso- 

 chelys) subsist upon fish and mollusca. They are found in all 

 the intertropical seas, but sometimes they travel far into the tem- 

 perate regions, specimens being occasionally captured on the 

 British coasts. The flesh and eggs of all the species are edible, 

 the Green Turtle (Chelone my das) being the most esteemed. The 

 Hawk's-bill Turtle (Chelone imbricata) furnishes the commercial 

 tortoise-shell; the finest sort comes from Celebes, whence it is 

 exported to China. Specimens of polished shell from the Indian 

 Ocean and Jamaica are exhibited. A common Atlantic species 

 is the Loggerhead Turtle (Thalasso chelys caretta), which forms an 

 exception to all other recent Chelonians in having five instead of 

 four epidermic plates on the side (costals). 



The Trionychida are Freshwater Turtles, with much depressed [Cases 

 shell, which is covered with soft skin, and not with epidermic plates ; 

 the digits are movable, strongly webbed, and each foot has only 

 three sharp claws, belonging to the three inner digits, exactly as in 

 Crocodiles. The jaws are covered with fleshy lips, and the snout 

 is produced in a short tube bearing the nasal orifices, and enabling 

 the animal to breathe while the rest of the head is submerged 

 under water. These animals are thoroughly aquatic and carni- 

 vorous, and inhabit the hotter parts of Asia, Africa, and North 

 America. We may note the Javanese and Gangetic Trionyx 

 (Trionyx javanicus and ganyeticus) , and the Nilotic Trionyx (T. 

 triunguis), as showing the largest size attained by these Turtles. 



20, .30. 



