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conformity with this dispensation, the anterior extremity of the upper bill in the majority of species exhibits a large notch, and on each side of it a sufficiently strong tooth, reminding the observer of the beak of the higher raptorial birds.

In some of this group, Nature, which, in the chelonian forms that we have already noticed, had contented herself with a lid either before or behind, carries out what may be termed the box principle, by making, as in the genus Cistudo, a moveable lid both before and behind. In this subgenus a cartilage attaches the wide oval plastron to the buckler. This cartilage is moveable both before and behind, turning on the same transversal mesial hinge, and, at the will of the animal, presenting nothing but a well-closed box to the prying eyes of the enemy. In Kinosternon, also, the oval sternum is moveable before and behind on a fixed piece; but in Staurotypus, the thick cruciform sternum is moveable in front only. In others, again, Platysternon and Emysaura, for example, the plastron is immovable.

The Potamians, or true river-tortoises, whose species have been confounded under the name of Trionyx, have among them some which grow to a considerable size. To say nothing of one which was kept by Pennant, and weighed twenty pounds, seventy pounds have been stated as the weight attained by certain individuals. Inhabiting the streams and rivers, or great lakes of the warmer regions of the earth, their habits are generally similar. Swimming with much ease either upon or beneath the surface of the water, they pursue young crocodiles, other reptiles, and fishes, which their agility enables them to make their prey. They are also said to be great destroyers of the eggs of the crocodiles, especially in the Nile and the Ganges. The angler baits his hook for them with small fishes or other living bait, unless his skill enables him so to play a dead or artificial one as to

deceive the sharp eyes of these tortoises, whose flesh is considered very good for the table. If he goes out with proper tackle, the sport is satisfactory enough; but one of them took the fly of a justly-celebrated singer and skilful disciple of old Izaak's school, while he was fishing for trout. He thought he had got hold of an old boat; but, unwieldy as his prize was, he would probably have landed it if left to himself. His stupid attendant, however, rushed forward and seized the line, which, thus deprived of the spring of the rod, could not bear the strain, and the potamian got clear off.

Islets, rocks, floating timber, or the trunks of fallen trees on the banks, are the favourite places of resort to which these tortoises come for repose during the night. But they are very wary, and the least noise sends them immediately into the water. They are troublesome customers to those who are not aware of their mode of attack. When they seize their prey, or are on the defensive, they suddenly and most rapidly dart out their retracted head and long neck like lightning, biting most sharply, and rarely relaxing their hold till they have taken the piece, into which they have fixed their cutting and pertinacious bill, out. The fisherman, therefore, either cuts off their heads as soon as he has secured them, or reins them up with a sort of bridle, so as to prevent the dreaded bite; and in this last state, I have been told, they are often exposed alive for sale in the markets.

In the months of April or May, the sandy spots on the banks of the rivers or lakes which have a good exposure to the sun are sought out by the females, as the places of deposit of their eggs, to the amount of some fifty or sixty; and in July the young make their appearance. The patience of a German is proverbial; with the eternal pipe in his mouth, he calmly follows out his subject, and follows it out well; but when we find Monsieur Lesueur

patiently counting the ova in the ovary of a potamian mother, and deliberately giving the results, we pause, and thank the gods, who have disposed the mercurial mind of one of our near neighbours to quietly settle down to ovarian statistics. In the ovary of a pregnant potamian, M. Lesueur counted twenty ripe eggs, ready to come forth at the bidding of Dame Nature. Then he saw a quantity of ova, varying in size from that of a pin's head to the goodly volume of rotundity which they attain, when the calcareous coat, which is necessary for the protection of the egg when it is exposed to the dangers of this world, is superadded: what the tottle of the whole' is, may be ascertained by those who feel disposed to inquire of M. Lesueur; and if they will consult the oracle, they will rise from the consultation wiser men, unless they have sounded all the shallows and depths of testudinate life.

But enough, and, for the reader who is not zoologically disposed, more than enough. He has been led, if he has condescended to follow, from the land to the marsh, from the marsh to the lake, stream, and river, the residences of the various modifications of testudinate life. A short repose should be placed at his disposal before, in the course of our narrative, he follows these great rivers of the old and new world, in which the freshwater-tortoises disport themselves, into that ocean in which all rivers, great and small, are lost. But there, in that boundless waste of waters, we shall find that Nature has modified the Chelonian type into the Thalassian shape, which occupies a distinguished reptilian place in the present world, and in that which is gone for ever.

October, 1850.

265

CHAPTER XI.

HE extremities modified for walking on land in the

THE

*

case of the Chersians, shuffling about in marshes and ponds in the case of the Elodians, and swimming in rivers with a good garnish of claws to enable the Potamians to scramble upon banks and logs, to say nothing of the help of the said claws in enabling them to secure their prey, take, in the Thalassians, an unmistakeable oar-like shape. No half-measures would enable a turtle to row placidly on the mirror-like sea, when

The air is calm, and on the level brine
Sleek Panope with all her sisters plays,

or beat the billows when the ocean is agitated by storms such as burst forth in tropical latitudes. But these paddles have a double office to perform. They are formed to act, not only as organs of swimming, but as instruments of progression on the tide-furrowed shore, when the females travel up to deposit their eggs; and to this end, in most of the species, the paddle is furnished with one or more nails, which greatly assist the animal in its advance on land.

Only five well-defined recent species are known, if Mr. Gray be right in considering Chelone virgata and Chelone maculosa of Dumeril and Bibron as varieties of Chelone mydas; and this existing state of the limitation of the marine form of these reptiles opens a new and

* Marsh tortoises.
† River tortoises.
Sea tortoises, or turtles.

N

most interesting point of view, when compared with the fossil evidences of the development of this sub-family in the ancient seas of our globe. Professor Owen, in his valuable History of British Fossil Reptiles, describes no less than eleven well-defined fossil species of chelone found in Britain, to say nothing of fragments. Such a catalogue, as he justly observes, leads to conclusions of much greater interest than the previous opinions respecting the chelonites of the London clay could have suggested.

Whilst (writes the Professor) these fossils were supposed to have belonged to a freshwater genus, the difference between the present fauna and that of the eocene period, in reference to the chelonian order, was not very great; since the Emys (cistuda) Europæa still abounds on the continent after which it is named, and lives long in our own islands in suitable localities. But the case assumes a very different aspect when we come to the conviction, that the majority of the eocene chelonites belong to the true marine genus chelone; and that the number of species of these extinct turtles already obtained from so limited a space as the Isle of Sheppy, exceeds that of the species of chelone now known to exist throughout the globe.

The Professor comes to no hasty conclusion, when he states that the ancient ocean of the eocene epoch was much less sparingly inhabited by turtles than that which now washes the shores of our globe; and that these extinct turtles presented a greater variety of specific modifications than are known in the seas of the warmer latitudes of the present day. Nor does the inference stop here; for, as he well says in continuation, the indications which the English eocene turtles, in conjunction with other organic remains from the same formation, afford of the warmer climate of the latitude in which they lived, as compared with that which prevails there in the present day, accord. with those which all the organic remains of the oldest tertiary deposits have hitherto yielded in reference to this interesting point.

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