TURTLE. 575 TURTLE. to eight eggs, clioose the afternoon for egg-laying. The eggs of sn.ipping turtles iire usually splieri- cal and about the size of a walnut. The shell is tough and leathery. Certain other turtles lay oval eggs, and a few eggs having a shell of a fine porcelain texture. The eggs hatch slowly, some kinds only after three or more months. As soon as the young, water-loving turtles hatch they begin to creep aliout and to travel down inclines until they eventually reach water. All the species are extremely tenacious of life: they are capable of extraordinary abstinence, and of living long after having sustained injuries which would have been iniinediatcly destructive to almost any other animal. They are also re- markable for their longevity, examples of which are mentioned under Tortoise. EcoKOMic Value. The ilesli of those which subsist on animal food is musky and unpleasant ; but that of vegetable feeders is much esteemed. The eggs of most species are excellent. Va.st quantities of eggs of the large Amazonian 'arrati' {Podocncmis expansa) are also pressed to obtain oil of large commercial value. The most highly esteemed for food is the green turtle (q.v. ), and its relative the 'edible' turtle of the East Indies. Many smaller kinds are eaten, including the favorite American terrapin (q.v.), the snapping turtle (q.v.), and other freshwater forms. Cla.ssification. The Chelonia were at first divided according to modifications of the feet. Cope, recognizing the separability of Trionychoi- dea, also, in 1870, emphasized a division based upon the mode of carrying the neck, one group (Pleurodira) bending it sidewise in withdrawing the head, and the other (Cryptodira) withdraAV- ing it in an 8-shapeil curve in a vertical plane. A more worthy division is Athecfe for the shell- less Spargidfp, or leatherbacks, and Thecophor.a for all other kinds. Boulenger's classification is as follows: f Athecffi Sphargidie. i PelomedusidEe. - Cbelydidfe. f Carettocbel.rdidffi. Chelydridce, Dermateniydidee. Cinosternidji*. Platjsternidae. Testudinida;. Chelonidje. Trioiiychoidea. ...Trion.vchidffi. The PelomedusidEB are a small family of African and South American turtles including the large and valuable 'arrau.' The family Chelydid.ne in- cludes the curious matamata (q.v.). certain long- necked Australian types (Chelodina), and the South American Hydromedus:i. The Caretto- chclydid.T> are a family in which is set a strange small turtle of New Guinea, whose 'shell' is cov- ered with soft skin instead of horny shields. Of the cryptodirous families, the Chelydridse are rep- resented by the various snapping or 'alligator' turtles (q.v.). and the Dermatemydida' liy a few species of aquatic tortoises of Central .merica. The Cinostcrnidse are the family of the North American 'skunk' or 'stinkpot'" turtles. (See Musk Tortoise.) Platysternidie includes only a single Siamese water-tortoise. The Testudinidte, on the other hand, are the most populous of Chelonian families and nearly cosmopolitan. The Che- LO.NIA Theco- phora I Pleurodira Cryptodira shell in this family is always covered with well- developed horny shields, the plastron has nine bones, and the neck is completely retractile. About twenty genera with more than 1 10 species are now recognized: but the generic distinctions are not easily recognized by external appearances. Here are classilied the North American 'mud- turtles' of the genus Chrysemys, which abound in all still waters, as do the 'pond-tortoises' (Eniys) of Europe, the terrapins (q.v), and the box-tortoises (Cistudo). The last get their name from the fact that the plastron, which is united with the carapace by ligaments, is di- -ided into two movable lobes, connected by a hinge permitting them to be lifted up against" the overhanging carapace, and closing both ends of the shell perfectly after the animal has drawn within its defenses. The common box-tortoise of the United States (Cisftido Carolina) is entirely terrestrial. numerois everywhere and very inter- esting in its habits. In this family, also, 'fall the various land-tortoises (q.v.) of the type-genus Testudo. Most of the foregoing are terrestrial or fresh-water forms, while the remainder are marine and have the limbs modified into swim- ming paddles or 'flippers.' The family Che- lonidie contains many great extinct forms, from the Cretaceous to recent times, and a few existing species, of which the green turtle, hawksbill, and loggerhead (qq.v.) are representatives. The order Trionyelioidea contains only the family Trionychida>. which have no rigid "plates on the flat carapace, but a soft leathery skin, and the plastron imperfect. See SoFT-SiiELLEn Turtle. Fossil Turtles. The origin of the Chelonia is uncertain. Otoca?lus, an armored cotylosaur from the Permian of Texas, has been suggested by Cope as a possible progenitor, but the relationship is extremely doubtful. Certain characters of shoul- der-girdle and ventral abdominal ribs in the plesiosaurs indicate that this order may have genetic afl;inity with the turtles, and the dicy- nodonts and placodonts of Triassie age resemble turtles remarkably in many structures of the skull and limb-bones. ( See Tiieromorpha.) All these groups belong to the synapsid division of Eeptilia. Little evolution is demonstrable within the chelonian order from its first appearance in the European Upper Trias to the present, except in the degeneration of the carapace and elongation of the digits in the marine forms. The oldest turtle known is Proganoelielys, from the Keuper (Upper Trias) of Germany." A probably primi- tive character in this genus is the well-developed row of supra-marginal plates. The Lower .luras- sic strata have, as yet, yielded no chelonian re- mains, but in the Upper .Turassic. Cretaceous, and the Tertiary they are abuiuhiiit. chiefly in the Northern Hemisijhere. The existing suborders Cryptodira and Pleurodira appear to be fully dilferentiated in the Upper Jurassic, the Triony- chia in the Upper Cretaceous of North America, As a rule the known .Jurassic turtles have a solidly roofed skull like that of the recent green turtle, and a well-developed carapace. Professor Baur's opinion is that the earliest turtles were swamp-turtles, and that the .soft-shelled Triony- cliia and the marine families evolved from these along one line, and the land tortoises along an- other. Crvptodir.a is the suborder most widely represented among fossils, as among recent tur-
