Sub-Family L—Cryptodere Medians.
Cryptoderes are not only distinguished from the Pleuroderes by the power of completely concealing their cylindrical neck with its sheath of loose skin under the middle of the carapace; but also by their head, which is nearly equal in width to its height at the oceiput The eyes are always lateral, and their orbits so large that the diameter of the cavity nearly equals a fourth of the total extent of the cranium considered with regard to it.', length. The jaws of the Cryptoderes are stronger than those of the Pleuruderes ; sometimes they are simply trenchant, sometimes more or less dentilated on their edges, which are straight, or sometimes sinuous. In the greater number of species the anterior extremity of the upper beak offers a large notch, on each side of which may be seen pretty constantly a rather strong tooth ; in which case it is rare for the corresponding extremity of the mandible not to curve upwards towards the muzzle in a sharp point. In short, in such cases the upper beak closely resembles that of birds of prey.
Sub-Genus 1.—The Clausilea.
Ciatudo, Fleming, reformed by Gray.—Feet with five toes, the pos terior with four claws only; plastron wide, oval, attached to the buckler by a cartilage, moveable before and behind on the same transversal menial hinge, furnishod with twelve plates; twenty-five marginal horny plates or scales.
C. Carolina ; C. Amboinensis ; C. trifesciata.
Sub-Genus 2.—The Gapers.
C. Europma and C. Dierdii.
Emya, Dum. and Bibr.—Feet with five toes, the posterior with four nails only • plastron wide, immoveable, solidly articulated upon the carapace, furnished with twelve plates ; two axillary and two inguinal shells ; head of ordinary size ; tail long.
1st Group.—European Emydes. E. Caspica ; E. Sigritz.
2nd Gronp.—American Emydea.
E. E marmorea, ptdehella, geographica, E. mean.
Inicat serrata,E Dorbignii, E irrigate, E decussate, Erubrirentris, E. rugasa, E. Floridana, E ornate, E. concinna, reticulate, E. Tata°, E. pieta, E and Aluhlenbergit% 3rd Group.—African Emys.
E. 8petigleri.
4th Group.—Oriental Emydes.
E Tr-(loge, E. liettesii, F. llamiltonii, E. K testa, E Bealei,
E eras:kohl', E. spinosa, E. °cella°, E. tririttata,E. Duraucellii, and E. lineata.
Tetraonyx, Lesson.—Five toes, one of them without a nail on all the feet ; sternum solid, wide, furnished with six pairs of plates; twenty five marginal scales.
1'. Lessonil ; Y. Baska.
Plat ysternon, armed or shielded, and too large to enter under the carapace ; upper jaw hooked ; sternum wide, immoveable, fixed solidly to the carapace, with short alm ; three sterno-costal scales; five nails on the anterior feet ; four only on the posterior feet ; tail very long, scaly, without a crest.
P. megamhalturn.
Emysaura, Dem. and Bibr.—Ilead large, covered with small plates ; muzzle short; two hardies under the chin ; plastron Immoveable, cruciform, covered with twleve plates • three Menlo-costal scales • nails on the fore feet, four on the hind feet ; tail long, by a scaly crest.
E. serpentine. It lives in lakes and rivers, feeding on fish, and, as it would seem, on young birds. This is Test ado serpentine, Linn. ; Chelydra serpentine, Schweigg., and Chelonura serpentine, Say, &c.
Staurotypus, Wagler.—Head sub-quadrangular, pyramidal, covered in front with a single very delicate scale only ; jaws more or less hooked ; barbles under the chin ; twenty-three limber scales ; sternum thick, cruciform, moveable in front, furnished with eight or eleven scales ; axillary and inguinal scales contiguous, placed on the sterno costal sutures; anterior feet with five nails ; posterior feet with four only.
8. triporeatus ; S. odoratus, so called from the musky odour which it is said to exhale.
Kinosternon, Wagler.—Head sub-quadrangular, pyramidal ; a single rhomboidal plate upon the cranium ; jaws slightly hooked ; barbles under the chin ; scales of the shell slightly imbricated; limbar plates to the number of twenty-three; sternum oval, moveable before and behind on a fixed piece, furnished with eleven scales ; alas short, narrow. sub-horizontal ; a very large axillary plate and an inguinal still larger ; tail long (in the males), unguiculate.