three heads to show the difference in the characters of the jaws. 1, a species of marine Turtle; 2, the Trionyx ferox, (Gymnopus spiniferus, Bibron;) 3, the Matamata.

2

Notwithstanding the horny beak with which the jaws of Tortoises in general are furnished, the sense of taste is decidedly higher in these than in other reptiles. The tongue is thick, fleshy, very moveable, and composed of numerous muscles; nevertheless, it is not capable of being protruded from the mouth, the cavity of which it fills it is provided with salivary glands and nerves of taste. In the terrestrial Tortoises, in which the sense of taste is most perfect, its surface is thickly covered with papillæ; in the marine species, however, it is smooth; in other aquatic groups, its surface is more or less furrowed, and especially in those which inhabit marshes.

The eyes of Tortoises resemble, in many respects, those of birds. There are always three eyelids; two are external, continued from the common skin of the head, and vary in form in different genera: one is internal, and resembles the membrana nictitans of birds; it is moved by muscles destined to that office. With regard to the sense of smell, it appears to be at a low degree; the internal olfactory apparatus occupying but a very limited space. The nostrils open on the most anterior part of the upper mandible, and are close to each other. In the fluviatile, (fluvium, a river,) or river species, and in the Matamata, (see the preceding figure,) the nostrils are prolonged into a sort of flexible proboscis, which the animals can raise for the purpose of respiration, between the large floating leaves of aquatic plants, while they lurk with their bodies concealed below them, and immersed in the water, there

D

lying in wait for small birds, fishes, or frogs, on which they dart, and which constitute their food.

As Tortoises are mute, or utter but an indistinct noise, the sense of hearing cannot be expected to be very acute the internal auditory apparatus, is, in fact, extremely simple, and there is neither an external tympanum, nor any orifice; in the Matamata, however, (see preceding fig. 3,) there is a sort of triangular prolongation, formed by the integument of the skull, and which seems to act as a valve to the orifice of an osseous auditory canal, and which widens outwardly; in the interior of this is a frame, on which the skin is stretched, so as to perform the office of a tympanum.

From the preceding survey of the general characteristics of the Chelonia, we shall now descend to an examination of those structural peculiarities, which lead to a subdivision of the order into natural families; and in so doing, we lay the foundation of a correct knowledge of the strange and interesting group under examination.

In the first place, then, we direct our attention to the limbs, or locomotive organs of the Chelonia; which, in their general form, and in the arrangement and condition of the toes terminating them, furnish, as in other races of vertebrate animals, a clue to habits and modes of life.

At a cursory survey, we at once perceive that a large group presents itself, in which the toes are so enveloped in the skin, that their independent mobility is either impossible, or very limited. The feet, in fact, resemble mere stumps, or rather, perhaps, those of the elephant, with this difference, that the toes are still less distinct and free, and the soles less soft and elastic; while the animals in their slow, laboured, and crawling progress, do not put the whole of the sole to the ground, but only the edge of the sole, furnished with horny lamina, tubercles, or hoof-like nails, and which indicate the situation of the ultimate joint of each of the toes. (See the annexed sketches.)

Such is the structure of the feet in the first family

of the Chelonia, namely, the true land Tortoises; and it is their primary characteristic; to which it may be added, that their carapace is boldly vaulted, its elevation often equalling its breadth. Another group presents itself, distinguished also by an immobility of the toes, or phalanges, as great as in the terrestrial Tortoises. Here, however, we find a very dif

In

ferent modification of the THE ANTERIOR AND POSTERIOR LIMBS OF A
feet; such, indeed, as would
render them almost useless as organs of progression
on the ground, but which, a moment's inspection as-
sures us, must fit them admirably for aquatic progres-
sion, and for contending with the roughest waves.
short, we see them depressed, flattened, enlarged, and
fashioned as oars. Limbs thus modified, are exclu-
sively characteristic of marine Tortoises; animals which
live far out in the wide ocean, and which only approach
the shore for the purpose
of depositing their eggs;
and there, their progres-
sion is slow and awkward
in the extreme. The limbs
are of unequal length, and
so utterly incapable are
they of being applied firm-
ly to the ground, that when
the animals are turned upon
their back on the sand, they B
cannot recover their na-
tural position, or they find
the utmost difficulty in the
effort. In these marine
Tortoises, or Turtles, which

ANTERIOR AND POSTERIOR FLIPPERS OF CORIA
CEOUS TURTLE. A, ANTERIOR. B, POSTERIOR

generally attain to large dimensions, the carapace is very broad, more or less depressed, and of a somewhat heartshaped outline. We give the anterior and posterior flippers of the Leathery Turtle, (Spargis coriacea.)

Thus, then, we have two very distinct groups, one terrestrial, the other marine. But if we look again more narrowly, we shall find a number of Tortoises, which cannot be referred to either of these groups: the toes so far from being completely buried, are apparent externally, and moveable, but are united

to each other by means of an intervening web, of greater or less extent, as in the annexed figures. These feet are adapted either for the land or for water; and, accordingly, Tortoises thus

distinguished are sometimes found on the land, usually in marshy places, or in water, and are more aquatic in proportion to the developement of the webs. Some species, indeed, seldom come to land; but it is fresh water which they inhabit, and not the sea.

ous,

These web-footed, or fresh-water Tortoises, however, do not form one, but two natural families, distinguished from each other both by their general structure and their habits. In one family, and that the least numerthe jaws, the bones of which are almost denuded, are covered by a fold of skin, which fulfils the office of true fleshy lips. The plastron and carapace are not sheathed with horn, but covered with a smooth, naked, coriaceous, or leathery skin. The body is singularly depressed, and the circumference of it is generally soft and flexible. The plastron is joined to the carapace by a cartilage; the feet are greatly flattened, and are furnished with five toes, of which three only are armed with straight and hard nails; from this circumstance, they have derived

the name of Trionyx. All the known species live in the great rivers of the hotter latitudes of the globe, and may be, therefore, designated as fluviatile, or river Tortoises⚫ they are fierce and carnivorous.

The other web-footed family is characterized by the toes being distinct and moveable, and all armed with nails, instead of only three. The jaws are invested with a horny beak, and are destitute of fleshy lips. The feet are well adapted for terrestrial progression; but still more so for swimming, from the existence of intervening webs. All the species live both on the land and in the water, giving preference to humid places, to boggy lands and marshes, or to the margin of small streams; and they dive and swim with great facility. To this family may be given the name of Marsh Tortoises, or Emydes.

But the Emydes, or Marsh Tortoises, subdivide themselves into two minor groups; one distinguished by the conical figure of the head, the elevation of its upper surface, the lateral position of the eyes, and by the cylindrical form of the neck, which is invested in loose skin, constituting a sort of sheath to the head when withdrawn beneath the carapace, of which it then occupies the centre of the anterior portion; the neck being folded like the letter z. This section approaches the nearest to the

terrestrial Tortoises.

The second group is distinguished by the depressed contour of the head, and by the position of the eyes; these, instead of being lateral, are placed on the upper part of the head, and have often a vertrical aspect. The interval between the carapace and plastron has a great lateral extent; and the neck, which is elongated and covered with close skin, destitute of folds, is bent to one side, to enable the animals to conceal the head beneath the carapace. MM. Dumeril and Bibron term the first group Cryptodera, from KρUTтos, (cryptos,) concealed, and deipn, (deiré,) the neck; the second group, Pleurodera, evpov, (pleuron,) the side, and deɩpŋ, (deiré,) the

from

neck.