With regard to the integument of the carapace and plastron, the number, colour, and shape of the investing plates of horn or shell, as it is termed, vary considerably. The subjoined cuts will convey a better notion than words of their arrangement in a laud and marine species ; but it must be considered that these are mere examples, and that the variety is very great.
Systematic Arrangement and Natural History.
Aristotle has mentioned three principal groups of Tortoises, or at any rate genera, under the names of :Cowin weenie& for the Laud Tortoise ; XekiLys or Oakacrcria for the Sea-Tortoise or Turtle (' Mist. Anim., iL 17); and 'Eniis for the Fresh-Water Tortoise (Ibid., v. 33). Gesner remarks that there are three "summa genera" of Tortoises : the 1st, terrestrial ; the 2nd, living in fresh-waters ; and the 3rd, in the waters of the sea. Messrs. Dumeril and Bibron copy his Corallarium de Testudinibus in Genere,' to show how far it accords with their own arrangement, as follows f terrestris Testudo marina, XeAct,v7) Testudo maH Mas marinas, Miff Oakciv Tam aut eat ant in puriore, ut lacubus, aquft dulei amnibua.
crenosk ut paludibus.
Linnaeus placed the form at the head of his Amphibia Reptilia, under the generic name Testudo.
Cuvier divides them into five sub-genera the Land-Tortoises (Tegudo, Brongn.) ; 2, the Fresh-Water Tortoiaes,(Eurp, Brongn.), including the Box-Tortoises (Terrapene, Merrem ; Einosternon, Spix ; Cistudo, Fleming); 3, the Marine Tortoises ; 4, the Chelydes (Testudo fimbriata); 5, the Soft Tortoises (Trionyx, Geoff.).
Dr. J. E. Gray, in his Catalogue of the Tortoises, Crocodiles, and Amphiabmnians, in the Collection of the British Musemn; 1849, makes the Chelonia, the third order of Reptiles in his arrangement, come under his second section, Cataphracta, the Squamata being the first.
Family 1. Test ud i n idce. • Genera :—Testudo. Chersina. Kinixys. Pyxis.
Family 2. Ernyd Genera :— Geotinyda. Flays. Cyclemys. Malaclemys. Giatudo. Kinosternon. Chelydra. Platysternunt.
Family 3. Chelydidce.
Genera :—Sternotherus. Pelomedusa. Hydraspis. Chelymys. Phryn op& Chelodina. Ilydromedusa. attys. Peltocephalus. Podocnemis.
Family 4. Tr ionycidce. Genera :—Trionyx. Emyda.
Family 5. Cheloniadce.
Genera :—Sphargis. Chdania. Caretta. Caouana.
Messrs. Dumeril and Bibron, in their elaborate and highly valuable• Erpetologie,' divide the Tortoises, or Chelonians, into the following families :—Ist, the Chersites (Chersians, or Land-Tortoises) ; 2nd, the Elea ites( Elodhuis, or Marsh-Tortoises); 3rd, the Potamitos ( Potemkin e, or Itiver-Tortoises) ; 4th, the Thalesaites (Thalaariana, Sea-Tortoises, or Turtles).
Of these groups the authors observe that Chersites is not perfectly limited, for some of the species arranged by them under the succeed ing family (Elodites) seem to form a natural passage between the Land- and Marsh -Tortoises. Such are Cist ado Carolina and Emys MuAlenburgii, which are in reality Paludiues, or Marsh-Tortoises, with distinct toes, though they pomoss only very short membranes and but slightly palmated feet The principal characters which distinguish the Chersitea, or Cher Bien% from the three other divisions of the order Chelonia are thus defined :—Body short, oval, convex, covered with a carapace and a plastron; four feet ; no teeth. But Jleesrs.Dum6ril and Bibron remark that the principal distinction may be enunciated by this simple term drawn from the conformation of the limbs, and which indicates per fectly the manner of life of the group—stumpy feet (des pattes en moignou):—this would recall the condition of those feet, namely, that they are short, =shapely, though nearly of equal length, with toes but little distinct, nearly equal, immoveable, united by a thick akin, and conglomerated into a sort of truncated mass, callous in its periphery, on the outside of which one only distinguishes horny cases, a sort of hoofs which for the most part correspond with the last phalanges they incase, and would consequently show that these animals live only on the land, never in the water. The other three .'groups differ from the Last and from each other in the form of the feet The Thalassites, or Thalassians, have the carapace very muoh depressed, and their two pairs of feet, unequal in length, are flattened into the form of oars or solid fins, because their toes are always con joined and hardly distinct from each other, incased as they are in these paddles.