FAMILY III. TRIONYCHIDÆ.

(Soft Tortoises.)

These are large Tortoises which have no horny shell, but the carapace and plastron are covered with a soft skin. The ribs do not reach to the border of the carapace, nor are they united through the whole of their length, the parts analogous to sternal ribs being replaced by a simple cartilage; and the sternal pieces are partly dentelated as in the Turtles, and do not cover the whole inferior surface. The feet, like those of the preceding family, are webbed, but not lengthened; only three toes of each foot are furnished with nails. The horny beak is covered on the outside with fleshy lips, and the muzzle is produced into a short trunk. The tail is short, and the anal orifice of the body is situated near its extremity.

The Soft Tortoises inhabit great rivers and lakes, where they live upon aquatic animals; they are eminently carnivorous and voracious, and pursue with agility in the water, fishes, and especially young crocodiles. Notwithstanding the nature of their food, their flesh is esteemed for the table, and hence they are caught with a hook and line: it is necessary, however, as MM. Duméril and Bibron assert, that the hook should be baited with a living prey, or at least that the motion of apparent life should be communicated to it, if dead, as they are said never to touch a dead or immoveable prey. This does not apply, however, to the eggs of Crocodiles, which the

Soft Tortoises devour greedily in the African and Indian rivers. In seizing their food, or defending themselves, they dart out their long neck with the sudden rapidity of an arrow. The

grasp of their powerful and trenchant beak is sharp and deadly, nor is it relaxed until the piece is taken clean out; and as they are bold and ferocious, they are much dreaded even by those who fish for them.

Like the Emydes, the Soft Tortoises love to repose on the islets and points of rock, on the fallen trees at the rivers' margins, or on floating logs of timber, whence they drop into the water on the slightest alarm. They swim with ease and swiftness, both on and beneath the surface.

No species of this Family is found in any of the rivers of Europe. The Nile, the Niger, and the Senegal, the Euphrates, and the Ganges, the Mississippi, the Ohio, and their tributaries, and the great lakes of the St. Lawrence, are the localities known to be inhabited by various species of Trionychida.

GENUS TRIONYX. (GEOFF.)

The species belonging to this genus, which includes the majority of those known, are distinguished by the following characters. The carapace is surrounded by a cartilaginous circumference, very wide, floating behind, and deprived of bone externally. The hinder part of the plastron is too narrow to hide the posterior limbs completely, when the animal draws them up under the carapace.

The common Soft Tortoise of North America

(Trionyx spiniferus, LESUEUR) inhabits the great lakes, and many of the rivers of that continent. It is a ferocious tyrant of the waters, devouring ducks and other fowl, the young of alligators, and fishes, with great voracity. It attains a large size.

Pennant mentions some which weighed seventy pounds; one which he kept for three months weighed twenty pounds, and the buckler or carapace of this specimen was twenty inches in length, while the neck and head measured thirteen inches and a half more. The upper parts vary in tint, being brown or grey of various shades, irregularly marbled, and frequently studded with dots: the under surface is whitish, or of the same tint as the human nails.

Towards the end of April or May, according to M. Lesueur, the females of this species crawl out of the rivers, for the purpose of seeking out places suitable for the deposition of their eggs. Sandy spots exposed to the sun are chosen, and

to obtain these they will often scale a steep bank that is ten or fifteen feet above the water's edge. The eggs are deposited in hollows, to the number of fifty or sixty, the old Tortoises laying more than young ones. They are spherical in form; the shell is calcareous but in a slight degree, and is therefore more fragile than that of the eggs of the Emydes that inhabit the same waters. M. Lesueur counted in the ovary of a female twenty ready for laying, and an immense number of others, varying in their dimensions, from the size of a pin's head to the full volume attained when they become covered with the calcareous shell. They are caught by persons who angle for them with a hook and line, baited with a small fish; when drawn on shore they are dangerous, darting the head to the right and left with incredible velocity; they often inflict severe bites on their captors, so that the prudent chop off their heads as soon as they draw them out of the water; the flesh is very delicate in flavour.

It is believed that the Soft Tortoises pair, and that the male remains constantly attached to the same female, two individuals of different sexes being commonly seen together in any given locality.

FAMILY IV. SPHARGIDÆ.

(Leathery Turtles.)

In this and the following Family, the carapace is very much depressed, and their two pairs of feet, which are of unequal length, are flattened into the form of oars or solid fins, their toes being

united so as to be scarcely distinguishable, and incased in the common integument. They all inhabit the ocean, which they never leave except for the purpose of depositing their eggs.

The Sphargida, or Leatherbacks, have the bony structure of the carapace and plastron invested with a leathery skin instead of horny plates. In the young animal this is tuberculous, but in adults it is smooth, though marked with several ridges, slightly serrated, which run down through the whole length of the carapace and plastron.

GENUS SPHARGIS. (ILLIG.)

The one or two species which belong to this genus compose the whole Family. Their remaining characters may be thus summed up: the carapace has seven longitudinal ridges, the plastron five; the paddles have no distinct nails; the muzzle is pointed; the jaws are of great power; the upper has a sharp tooth on each side near the tip, behind which is a deep notch, and another triangular notch in front separates the two teeth, which receives the sharp up-turned point of the lower mandible; the opening of the eyelids is almost vertical, and when closed the edge of the posterior (answering to what is ordinarily the lower) overlaps that of the anterior; the fore limbs are much more developed than the hind, and are of great length and breadth.

The species that inhabits the Mediterranean (Sphargis coriacea, LINN.) has occasionally strayed to the shores of our own islands. Some of the specimens taken here have weighed seven hundred