CHELONIANS. 469 



the plastron, are distinctive marks of this tortoise. In its native 

 regions it reigns as a tyrant, producing great havoc among the 

 finny tribes ; it is very voracious, and eagerly seizes a hook 

 baited with a fish. 



The females visit the shore in May to lay their eggs. These 

 are globular in shape and brittle ; they are hatched in July. It 

 is said that in its fierceness and voracity, this Tortoise will at- 

 tack small quadrupeds, aquatic birds, and young alligators. The 

 Trionyx of the Nile, G. JEgyptiacus, is much valued in Egypt, 

 on account of the services it renders in devouring the eggs and 

 young of the crocodile. 



Tortoises of the genus Cryptopus, or Aspidonectes, have the 

 plastron broad, and capable of closing up in front, so as to shut 

 in the retracted head and limbs ; in the rear they have a cartila- 

 ginous valve on each side, for shutting in the 4iind limbs. 



A. spinifer, (Lat. thorn-bearing or prickly,) is a species com- 

 mon in Lake Champlain, and in most of our western rivers. 

 Length fourteen inches. 



SECOND SUB-ORDER. CHELONID.E, OR CHELONII. SEA TURTLES. 

 PINNATED. 



The entire structure of the Sea Turtles shows an express 

 adaptation to aquatic habits. Not only is the carapace greatly 

 flattened, but the limbs, in which the toes are not externally dis- 

 tinct, are likewise flattened and modified into large oars. On 

 land, these animals shuffle along in the most awkward manner, 

 and make, with toilsome efforts, only a slow progress ; but they 

 plough the waves, dive and ascend with admirable address and 

 dexterity. They swim almost entirely by means of their front 

 limbs; the other pair acting independently and being chiefly 

 useful in aiding to balance the body, and guide the general 

 course. They feed chiefly on marine plants. The gullet of 

 these Turtles is lined with long cartilaginous processes, all tend- 

 ing towards the stomach. These appear designed to prevent the 

 return of the food when the water which is swallowed in con- 

 nection with it is regurgitated. 



The Sea Turtles never resort to the shore, except to deposit 

 their eggs. They lay them at night and in large companies. 

 Those of most of the species are both nutritious, and agreeable 

 to the taste. "American Sea Turtles," says Agassiz, " lay their 

 eggs towards the end of May, or in the beginning of June. They 

 lay a large number of them, about one hundred at a time, or 

 even more, which they deposit on shore, in the dry sand. Their 



UNIVERSITY 



OF 

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