258 NATURAL HISTORY. 



long head and neck forward with great velocity, and often spring upwards, making a loud hiss. 

 The females lay their eggs in dry sand. They inhabit the rivers flowing into the northern borders 

 of the Gulf of Mexico, the Mississippi and its tributaries, to the foot of the Rocky Mountains, the 

 northern lakes, and the Mohawk, but not any other Atlantic stream. 



One genus of these Mud Tortoises (Cryptopus) has the plastron so arranged behind, as to close 

 the opening between it and the carapace completely, by means of a kind of gristly lid on each side, 

 the tail opening having a special one. There is a Southern Indian kind, and it is rather common 

 on the coast of Coromandel, living in fresh water. It forms an article of diet. There is another 

 species in the river Senegal in Africa. 



The Egyptian Trionyx is probably the fyvs of Pliny, and inhabits the Nile and some other 

 African rivers. It is sometimes three feet in length, and is a great enemy to the Crocodiles, devour- 

 ing their eggs and young. 



The Gangetic Trionyx* has the bony carapace rather longer than broad, with a slight swelling 

 in front on the vertebral line. Its surface is coarse and rugged without prominent tubercles. 

 The species is found in the Ganges and its tributaries upwards to Nepal, and at Penang, and in 

 rivers, and on the sea coast. It has a fierce disposition, and defends itself desperately by biting, 

 and it utters a low, hoarse, cackling noise. The largest shell is twenty-three inches in length. Other 

 species are from China, Japan, Camboja, Borneo, and Singapore, and the Philippine Islands. 



The genus Cycloderma is one of this family, and a species is called the Senegal Mud Turtle. 



FAMILY IV. THE CHELONIADES. THE MARINE CHELONIANS. THE TURTLES. 

 There are three genera in this family, two of which have much in common, but the third 

 differs from the others considerably. All have the extremities adapted for swimming, and the 

 carapace and plastron more or less incomplete in the bony parts. The first genus (Chelonia) contains 

 the Edible Turtles, of which there may be more than one specie*, but the type is the Green Turtle 

 of commerce and city feasts (Chelonia midas).\ They are free swimmers in the gi'eat oceans 

 within the tropics, and sometimes they wander beyond this limit. Liking deep water for much 

 of their prey is found in the warm surface water, not near shallows they beach themselves on 

 almost all the islands where there is a sandy shore in which they can dig a hole and deposit 

 their eggs. They are seen very generally about the warmer parts of the ocean within a few 

 miles of land, and also hundreds of miles and farther from it, swimming or floating on the 

 surface, and diving for a long time before reappearing. Although cumbersome on land, the 

 largest of them, which may be seven feet in length, and weighing 800 Ibs. or 900 Ibs., swim easily 

 and rapidly, and the smaller individuals, which may be watched in an aquarium, are most elegant 

 in their natation, feathering their flat and curved arms with great skill when desiring to change 

 the level of their swim. They live on the gelatinous swimming things of the ocean, the Cuttle- 

 fish tribes, the mollusca without much shell, and probably on fish. When near land they devour 

 marine plants, such as the Zostera, and some are stated to wander on shore after green food. 

 At certain times of the year shoals of them arrive at the laying stations, and usually choosing the 

 night, crawl upon the beach, burrowing, as it were, in the sand with their flippers. The females lay 

 a number of spherical eggs, like tennis-balls in shape, which are slightly flexible and membranous 

 externally. Mr. Moseley, in noticing the Turtles of Ascension Island, writes* : " At Ascension Island 

 Turtles are collected, and by the side of the ' pond ' in which they are kept there is an enclosed space 

 of sand. The Turtles dig deep holes in it large enough to bury themselves in, and lay their eggs at 

 the bottom. The eggs are always covered up by the Turtle, and evidently require moisture as well as 

 an equable temperature, of no very great amount, however, for the sand in which hatching takes 

 place does not feel warm to the hand, but rather cool. Evidently the former opinion that these eggs 

 were incubated by the direct heat of the sun is erroneous." The fresh egg is not quite full, so that 

 there is a depression or crumple upon it, but shortly before hatching it becomes tense. When 



* Trionyx ganycticus (Cuvier). 



t The Green or Edible Turtle is said to be restricted to the Atlantic Ocean, but this is not the case. It is found in the 

 Western Pacific, in the Tropics, and probably elsewhere in that great ocean. Moseley found them at the Admiralty Islands. 

 Some naturalists make a new species (Chelonia virgata) of the East Indian kinds. 



J "Notes of a Naturalist on board the Challenger." 



