K. scorpioides. It lives in marshes and on river-banks. K. Pennsylra nicum liven in muddy waters, feeding on small aquatic animals, and exhaling a strong musky odour. K. hirtipm Sub-Family 2.—Pleurodere Elodians.
The Pleurodcres, as their name indicates, have all of them the neck retractile upon one of the sides of the anterior aperture of the cara pace; but they are never able completely to draw it in between their fore feet and under the middle of the buckler and plastron, like the Cryptoderes.
Peltocephalus, Dam. and Bibr.—Head large, sub-quadrangular, pyramidal, covered with large, thick, slightly imbricated plates ; jaws extremely strong, hooked, without dentilations ; eyes lateral ; plates of the carapace slightly imbricated ; no nuchal plate; feet slightly palmated : two large rounded scales at the heels; nails straight, robust ; tail unguiculate.
P. Traeaxa.
Podoenemis, Wagler.—Head slightly depressed, covered with plates; front hollowed with a large longitudinal furrow ; jaws slightly arched, without dentilations ; two barbles under the chin; no nuchal plate ; sternum wide, immoveable ' • feet largely palmated, the posterior ones carrying at the heels two large but delicate rounded scales ; tail short, not unguiculate.
P. e.rpansa. It lives in streams and rivers. P. Dumeriliana.
Pentony.r, Dum. and Bib.—Head large, depressed, covered with plates; muzzle rounded ; jaws slightly arched, trenchant ; two barbfes under the chin ; no nuchal plate; sternum immoveable ; five claws on all the feet ; tail moderate, not unguiculate.
P. Capenzis ; P. Adansonii.
Sternotherus, Bell—Head depressed, furnished with great plates ; jaws without-dentilations; no nuchal plate ; sternum wide, with very narrow lateral prolongations; free anterior portion of the plastron rounded, moveable : five claws on each foot.
S. Hider; S. nigricans ; S. castaneus.
Platemys, Wagler, as reformed by Messrs. Dumtril and Bibron, com prising part of 11Ydraspis of Gray, Platemys, Rhinenvs, and. Phrynops of Wagler.—Head flattened, covered with a single delicate scale or with a great number of small irregular plates ; jaws simple; two barbles under the chin ; carapace very much depressed ; sternum immoveable ; five claws on the fore feet, four on the hind.
It embraces the following species :—P. Martindla (Brazil and Cayenne) ; P. Spirii (Brazil) • P. radiolata (Brazil, where it lives in the marshes); P. gibba ; P. Geoffreana (young sent from Buenos Ayres by M. d'Orbigny); P. Waglcrii (Brazil); P. Nieuwiedii (Brazil); P. Caudiehaudii (Brazil); P. Ilitarii (Brazil); P. (Cayenne); P. riches (Brazil, banks of the River Solimoens); P. Schweiggerii (South America); P. Macquarie (Macquarie River, Australia).
Chdodina, Fitzinger.—Head very long and very flat, covered with delicate skin ' • muzzle short, gape wide, jaws feeble, without dentin Cone ; no barbles to the chin ; neck very much elongated ; a nuchal plate, plastron immoveable, very wide, rounded in front and solidly fixed on the carapace : sternal aim very short ; intergular scale larger than each of the gulars ; four claws on each foot ; tail excessively short.
Chelys, Dum. and Bibr.—Head much depressed, wide, and triangular; nostrils prolonged into a proboscis ; gape wide, jaws rounded, of but little thickness; neck furnished with long cutaneous appendages, two barbles to the chin; a nuchal plate ; five claws on the fore feet, four on the hind feet.
The gape extends beyond the ears. Messrs. Dumiril and Bibron remark that the jaws are rounded, narrow, and not simply covered with soft skin, as Cuvier, Wagler, and Gray believed, but protected by horny cases, like those of all the other Chelonians; only in Chdys they are extremely delicate.
Matemate. It lives in stagnant waters. A female lived some months at Paris and laid three eggs, one of which was hatched and the young animal preserved in the Paris Museum.
It would seem that individuals of this family attain a large size. Messrs. Dun:Aril and Bibron quote Pennant as mentioning some which weighed 701bs. ; one which he kept three months weighed 201ba., and its buckler was 20 inches in length, not reckoning the neck, which measured 134 inches. Their mode of life and habits seem to have great similarity. They swim with much ease both on the surface and at mid-water. The lower part of their body is generally pale white, rosy, or bluish ; but their upper parts vary in their tints, which are most frequently brown or gray, with irregularly marbled, dotted, or ocellated spots. Straight or sinuous brown, black, or yellow lines are disposed symmetrically on the right and left, principally on the lateral parts of the neck and on the limbs. During the nights, and when they believe themselves to be secure from danger, the Potamians coma to repose on the islets, the rocks, the fallen trunks of trees upon the banks, or floating timber, whence they precipitate themselves in the water at the, sight of man or at the least alarming noise. They are very voracious and agile, and pursue, as they swim, reptiles, especially young crocodiles and fishes. Their flesh being esteemed they are angled for with a hook and line baited with small fish or living animals, or with a dead bait, to which the angler gives motion and apparent life ; for they are said never to approach a dead or immoveable prey. When they would seize their food or defend themselves they dart out their head and long neck with the rapidity of an arrow. They bite sharp with their trenchant beak, and do not let go till they have taken the piece seized out ; so that their bite is much dreaded, and the fishermen generally cut off their heads as soon as they have caught them.