FOSSIL TORTOISES AND TURTLES.

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pose that the small number of fragments collected at Brentford have rather been transported thither from the debris of some deeper mineral bed.

It must nevertheless be admitted that the bones of crocodiles are extremely rare in these diluvial soils.

Cuvier has not seen them either in those immense collections of bones of all sizes that have been made in the Val' d'Arno, or in those of Germany, or in any of the French deposits. "This circumstance," says he, "must appear the more extraordinary, as crocodiles live at the present day in the torrid zone with the elephants, the hippopotami, and all the other genera which have furnished those bones. I am, however, just now informed that some have been recently found in the diluvial beds of the Val' d'Arno." This want or rarity of crocodile remains in diluvial soils should excite no surprise whatever, for the rising flood of waters which killed the land quadrupeds, would not prove fatal to the amphibious crocodile. Hence as these two classes of animals did not die together, they could have no common place of sepulture. The crocodiles would in fact hold by their favourite element at the retiring of the waters, and come thus to be transferred from rivers to the ocean. Many would probably be destroyed in the catastrophe, and a few might die from age, whose remains may have been left on the land when the waters were drawn off into their new reservoirs.

The variety of living tortoises is so considerable, as to make it difficult to decide whether a fossil tortoise belongs to an unknown species or not.

On the left bank of the Aar, a little way north of the town of Soleure, are numerous quarries of Jura limestone, which was certainly formed under the sea, yet in which the remains of tortoises (emydes) and crocodiles occur. A shield was found 24 inches long, and 20 broad. Similar specimens have been dug out of the ferruginous sandstone of the county of Sussex; in the soft sandstones of Dordogne and Switzerland, strata reckoned superior to the chalk formation; and in the clay strata of the Isle of Sheppy.

The above figure represents a fossil tortoise of the trionyx tribe, found in the gypsum quarries of Aix. The shield is seen to have lost a portion of its margin. The vertebral plates form a ridge in the middle of the back, like the trionyx carenata of Geoffroy. The trionyx of Java and the Ganges is the only one possessed of a similar shield, though there are differences sufficient to distinguish this from every living species now known.

Remains of sea turtles are found in the neighbourhood of Maestricht, in those celebrated quarries of a kind of coarse chalk of a sandy appearance, excavated in the mountain of St. Pierre, and they

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are promiscuously mixed with such a variety of marine productions and bones of gigantic saurians (lizards and crocodiles) as have rendered this mountain famous in geology.

It now remains to treat of the most celebrated fossil reptile, one which occasioned most controversy, having been taken at one time for a crocodile, at another for a saurian of some other order, and lastly for a cetaceous animal, or even for a fish.

Its bones have been hitherto found only in one canton of inconsiderable extent, in the hills which border the east or west side of the valley of the Meuse in the environs of Maestricht. The gangue is a very tender calcareous stone. This limestone bed is at least 489 feet thick. In many parts of it, nodules of silex are found, which along with the circumstance of the stone changing by degrees into chalk, a few leagues up the valley of the Meuse, proves the mass to belong to the chalk formation. It contains moreover the same fossils as the chalks of Meudon, and the other portions of the Paris basin; namely, sharks' teeth, gryphites, belemnites, and ammonites. All these shells are found along with the bones, in the lower parts of the mass which are also the most tender. The upper parts are harder, and contain more madrepores, so that none of these are collected unless when some fragments fall down from the top of the mountain. Several of them are converted into silex.

The numerous marine products with which this rock is filled are generally very well preserved, although they are rarely petrified, and the greater part of them have lost only a portion of their animal

So.

substance. The most bulky and remarkable are the bones of an extraordinary animal, whose skull has been found entire. The lower jaw exhibits fourteen teeth on each side, all conformable in construction to the teeth of monitors; but the monitors have only 11 or 12; the crocodiles have 15, which are very unequal; the present teeth are equal or nearly The iguana's teeth are considerably more numerous. In those teeth there are large and pretty regular holes, to the number of 10 or 12. There are 5 or 6 in the iguana's; from 6 to 7 in the monitor's; in the crocodiles there are a great many small and irregular ones; but in a dolphin there are only 2 or 3 towards the end of the jaw. The whole composition of the lower jaw bone, in fact, indicates more numerous relations with the monitor, than with any other of the saurian tribe, and excludes the cetacea, which, like the land mammifera, have each side of the lower jaw in a single piece. The teeth in the palate alone prove that the fossil head did not belong to a crocodile or a cetaceous animal, for neither of these animals has palatal teeth. The coronoid process of the fossil jaw is a distinct bone, corresponding to a supplementary bone along side of it.

Though this fossil remain approaches more to the monitor than to any other animal, yet it has some peculiarities.

The crocodiles, monitors, safe-guards, and dragons of La Cépède, have palates devoid of teeth. The iguanas, the anolis, and the ordinary lizards participate with several serpents, batracians (frog tribe), and fishes, in this singular armour in the palate. Accord

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ing to Cuvier the head of this fossil animal serves to rank it between the monitors and the iguanas. But what an enormous size it has in comparison of

any of the monitors and iguanas known! None of these living animals have probably a head longer than 5 or 6 inches; and that of the fossil in question is nearly 4 feet! In zoology, when the head, and especially the teeth and jaw-bones are given, nearly all the rest may be inferred, at least as far as essentials are concerned: hence there is no difficulty in classing the vertebræ when the head is once ascertained. The fossil seems to have belonged to an aquatic and swimming animal, somewhat like the crocodiles, using its tail as an oar from right to left, but not from above downwards like the cetacea. Several of its vertebræ have been found and described; particularly at Siechem. The spine of the animal was composed of 133 vertebræ, constituting a length of 21 feet. This number is just about double of what the crocodile has, namely 68; but

it

agrees very well with the monitor's, in which there may be counted from 117 to 147.

As the jaw-bone was 4 feet long, the animal must have had a total length of about 26 feet, and its head approached to one-sixth of the whole, a proportion similar to that of the crocodile, but very different from the monitors, whose head forms hardly one-twentieth of their length. The tail is ten feet long, somewhat less than the half of the total length. It is therefore shorter than in the crocodile, in which animal the tail exceeds by one-seventh the length of the rest of the body, and it is much shorter than in the monitors, whose tail is one-half longer than the