place, we would say, that while desirous of giving to the public, works upon scientific subjects, leading the reflective mind to trace the power of God in creation, the great aim of the Society that publishes this volume is to enforce the truths of revelation. Nor should it be deemed out of place to speak of the mercy, in redemption, of that God whom we behold in creation, and which he has provided for man; who above the beasts that perish, is the possessor of an immortal soul, and accountable at that bar where Divine revelation assures us we must all one day stand, Rom. xiv. 10; 2 Cor. v. 10.

ORDER I.-CHELONIA, OR TORTOISES.

THE TORTOISES, which form the first order of Reptiles, are too remarkable in their external character to be confounded with any other. Like the armadilloes and pangolins, among the mammalia, they are clothed with natural armour; but it differs from the armour of the mammalia referred to, inasmuch as it is not a simple horny addition to the skin, but is, in reality, part and parcel of the skeleton itself. The skeleton, in fact, is thrown to the outside of the body, so as to form an external bony envelope, covered with a horny or leathery sheathing, and inclosing, as in a box, the internal organs and other portions of the osseous frame-work, which do not enter immediately into its composition.

If we examine a common Tortoise, we shall find the shell, as it is termed, or more properly, the horn-sheathed osseous box, from which its head, limbs, and tail emerge, to consist of a vaulted portion, or buckler, covering the back; and an abdominal portion joined to the former, along the sides: the back plate, or dorsal buckler, is termed the carapace, (clypeus,) and consists of the vertebræ of the back and loins, and also of the ribs. The dorsal vertebræ, or those of the back, are not only immovable, but are strangely modified. The bodies being but little developed, while the superior spinous processes are converted into a series of broad osseous plates running along the centre of the carapace, and connected together by sutures, like the bones of the human skull; the ribs, again, are changed into flat expanded bones, all united firmly together, and also to the edges of the flattened spinous processes, the whole forming a consolidated plate. To the margin of the plate thus formed, is added

a third set of bones, regarded, and perhaps correctly, as representing the sternal ribs of the crocodile and other lizards: these bones are united to the extremities of the expanded ribs, and form the circumference of the carapace, which they assist in completing. From their character and situation they may be termed the costo-sternal plates, (costa a rib, sternum the breast-bone).

The annexed sketch of the ske

leton, and under

surface, of the

carapace of the European Marsh Tortoise, (Cistu do Europea,) will serve to show the structural peculiarities described The vertebral co lumn, the bones of the pelvis and of the limbs, are very evident, as are also the expanded ribs, a, a, and the sternal ribs, or

costo

sternal plates, b,b.

The abdominal buckler is termed the plastron,

(sternum,) and consists of nine osseous portions, of which eight are in pairs; the ninth is single, and occupies the anterior part of the plastron. The form of the plastron varies remarkably in the different species; generally, however, the single plate is surrounded by the first two pairs of bones, as in the following sketch; a representing this single portion. The distinct plates forming the

plastron are thus denominated by M. Geoffrey: a, the entosternal bone, (bone with in the sternum;) b, b, the episternal bones, (bone upon the sternum ;) c, c, the hyosternal bones, (the middle bones;) d,d, the hyposternal bones, (substernal bones ;) e, e, the xiphisternal bones, (swordbones of sternum,) answering to the xiphoid cartilage of the sternum in mammalia.

The osseous portion of the plastron of a very different

group of Tortoises is here figured; it shows how great is the extent of variation to which the bones composing it are subject. It is, indeed, principally in terrestrial Tortoises, and in the marsh Tortoises, though less completely in the latter, that the plastron forms a solid, compact whole; in the river Tortoises, and those which inhabit the sea, and usually named turtles, the anterior and

posterior bones are slender and narrow, while the lateral bones are broader, and branch out into dentated projections, resembling, in some degree, the antlers of the elk, or fallow deer. In the river Tortoises, the centre, as in the preceding figure, is not ossified.

As it is in the Tortoises of terrestrial habits that the

plastron presents the greatest solidity, so it is in these animals that it presents some of the most remarkable differential characteristics. Its union to the carapace is by an extensive lateral surface; and at this line of union it is sometimes slightly moveable, but mostly fixed by an unyielding suture. Its anterior and posterior margins. are generally indented or notched, for the more free egress of the neck and the tail. Sometimes, however, they are simply truncate, or, on the contrary, prolonged into a point. In one genus, however, the plastron is furnished with a transverse hinge, giving mobility to the anterior portion; so that the animals can retract their head and fore limbs within the carapace, and close the plastron upon it, so as to shut them in. These species constitute the genus Pyxis. There is, however, another genus in which the carapace, instead of being one solid whole, has the posterior portion distinct from the anterior and moveable, so as to close upon the hinder margin of the plastron, and shut in the hinder limbs and tail. This genus is termed Cinixys. The annexed figure represents the shell: A is the moveable portion of the

In the marsh Tortoises, which resemble the terrestrial Tortoises in the general construction and union of the plastron, there are genera which have this abdominal shield also furnished with transverse hinges. In the genus Cinosternon, the plastron has two moveable valves,