The LIMBS are typically pentadactyle and complete, and are most primitive in water-tortoises, e.g. _Chelydra_ and _Emys_, in which the carpus consists of the typical ten separate elements, including the pisiform. In _Testudo_ the centrale is fused with the intermedium, and the first three distal carpals are also fused together. In the marine turtles the limbs are transformed into paddles, but all the bones retain their independence; the pisiform {321}and the first metacarpal are enlarged and flattened, thereby giving additional width to the paddle. The tarsus remains less primitive; the centrale and the proximal elements have a tendency to fuse together, most completely in land-tortoises; the fifth distal carpal is enlarged, and stands out hook-like from the rest. The number of the phalanges of the fingers and toes varies slightly. It is noteworthy that none of the Chelonia possess more than three phalanges. The three middle fingers and toes have mostly three phalanges; the pollex and hallux have always two; the number of phalanges of the fifth finger varies from three to one, of the fifth toe from two to none. The greatest reduction occurs in _Testudo_ and its allied genera of typical land-tortoises, _Homopus_, _Pyxis_, and _Cinixys_, the formula for the fingers being 2, 2, 2, 2, 2 or 1, and 2, 2, 2, 2, 0 for the toes. In _Pelomedusa_ all the fingers possess two phalanges only, owing to fusion of the first and second phalanges with each other. [Illustration: FIG. 66.–The bones composing the plastron of _Chelone mydas_. On the right side the position of the covering horny shields[128] is indicated by dotted lines. _a_, Anal horny shield; _ab_, abdominal; _f_, femoral; _g_, gular; _h_, humeral; _ig_, intergular; _im_, infra-marginals; _p_, pectoral.] The SHELL, which is the most characteristic feature of the Chelonia, consists of the dorsal "carapace" and the ventral "plastron." Each is composed of a considerable number of bony plates which arise as ossifications of nearly the whole thickness of the cutis, only a thin layer of subcutaneous connective tissue remaining soft and lining the inside of the shell. We restrict ourselves to a description of the shell of the Thecophora, leaving the discussion of the peculiar shell of _Sphargis_ to p. 336 f. Very young tortoises are still soft, and the plates which are beginning to ossify are not yet suturally united. The plastron (Figs. 66 and 67) consists of the paired epi-, hyo-, hypo-, and xiphi-plastral plates, and the unpaired endo-plastral plate.