The universal prevalence of such delicate hydraulic contrivances in the Siphuncle, and of such undeviating and sys-: tematic union of buoyancy and strength in the air-chambers, throughout the entire family of Ammonites and Nautili, are among the most prominent instances of order and method, that pervade these remains of former races that inhabited the ancient seas; and strange indeed must be the construction of that mind, which can believe that all this order and method can have existed, without the direction and agency of some commanding and controlling Intelligence.

Theory of Von Buch.

Besides the uses we have attributed to the sinuous arrangement of the transverse septa of Ammonites, in giving strength to the shell to resist the pressure of deep water, M. Von Buch has suggested a farther use of the lobes thus

of the dorsal margin of the shell. This Siphuncle, and also the shell and transverse plates, are converted into thin chalcedony, the pipe retaining in these empty chambers the exact form and position it held in the living shell.

The entire substance of the pipe, thus perfectly preserved in a state that rarely occurs, shows no kind of aperture through which any fluid could have passed to the interior of the air-chambers. The same continuity of the Siphuncle appears at Pl. 42, Fig. 3. and in Pl. 36, and in many other specimens. Hence we infer, that nothing could pass from its interior into the air-chambers, and that the office of the Siphuncle was to be more or less distended with a fluid, as in the Nautili, for the purpose of adjusting the specific gravity, so as to cause the animal to float or sink.

Dr. Prout has analyzed a portion of the black material of the Siphuncle, which is so frequently preserved in Ammonites, and finds it to consist of animal membrane penetrated by carbonate of lime. He explains the black colour of these pipes, by supposing that the process of decomposition, in which the oxygen and hydrogen of the animal membrane escaped, was favourable to the evolution of carbon, as happens when vegetables are converted into coal, under the process of mineralization. The lime has taken the place of the oxygen and hydrogen which existed in the pipe before decomposition.

formed around the base of the outer chamber, as affording points of attachment to the mantle of the animal, whereby it was enabled to fix itself more steadily within its shell. The arrangement of these lobes varies in every species of Ammonite, and he has proposed to found on these variations, the specific character of all the shells of this great family.*

*The most decided distinction between Ammonites and Nautili, is founded on the place of the siphon. In the Ammonite, this organ is always on the back of the shell, and never so in the Nautilus. Many other distinctions emanate from this leading difference; the animal of the Nautilus having its pipe usually fixed near the middle, (See Pl. 31, Fig. 1,) or towards the ventral margin (Pl. 32, Fig. 2, and Pl. 42. Fig. 1.) of the transverse plates, is thereby attached to the bottom of the external chamber, which is gene. rally concave, and without any jagged termination, or sinuous flexure, of its margin. As the siphon in Ammonites is comparatively small, and always placed on the dorsal margin (Pl. 36, d. and Pl. 39, d,) it would have less power than the siphuncle of Nautili to keep the mantle in its place at the bottom of the shell; another kind of support was therefore supplied by a number of depressions along the margin of the transverse plate, forming a series of lobes at the junction of this plate with the internal surface of the shell.

The innermost of these, or ventral lobe, is placed on the inner margin of the shell (Pl. 39, V.;) opposite to this, and on the external margin, is placed the dorsal lobe (D,) embracing the siphon and divided by it into two divergent arms. Beneath the dorsal lobe are placed the superior lateral lobes (L,) one on each side of the shell; and still lower, the inferior lateral lobe, (1,) next above the ventral lobe.

The separations between these lobes form seats, or saddles, upon which the mantle of the animal rested, at the bottom of the outer chamber; these saddles are distinguished in the same manner as the lobes-that between the dorsal and superior lateral lobe, forming the dorsal saddle (S. d.,) that between the superior and inferior lateral lobes, forming the lateral saddle (S. L.,) and that between the inferior lateral and ventral lobe, the ventral saddle (S. V.) This general disposition, variously modified, pervades all forms of Ammonites; but when, as in Pl. 39, the turn of the shell increases rapidly in width, so that the last whorl nearly, or entirely, covers the preceding whorls, the additional part is furnished with small auxiliary lobes, varying with the growth of the Ammonite to the number of three, four, or five pairs. (PL. 39, a. 1, a. 2, a. 3, a. 4, a. 5.)

The uses ascribed by Von Buch to the lobes of Ammonites in affording attachment to the base of the mantle around the margin of the transverse plates, would in no way interfere with the service we have assigned to the same lobes, in supporting the external shell against the pressure of deep water. The union of two beneficial results from one and the same mechanical expedient, confirms our opinion of the excellence of the workmanship, and increase our admiration of the Wisdom in which it was contrived.

Conclusion.

On examining the proofs of Contrivance and Design that pervade the testaceous remains of the family of Ammonites, we find, in every species, abundant evidence of minute and peculiar mechanisms, adapting the shell to the double purpose of acting as a float, and of forming a protection to the body of the inhabitant.

All the lobes, as they dip inward, are subdivided by numerous dentations, which afford points of attachment to the mantle of the animal; thus each lobe is flanked by a series of accessory lobes, and these again are provided with farther symmetrical dentations, the extremities of which produce all the beautiful appearances of complicated foliage, which prevail through the family of Ammonites, and of which we have a striking example on the surface of Pl. 38.

The extremities of the dentations are always sharp and pointed, inwards, towards the air-chamber, (Pl. 38, d. 1.;) but are smooth and rounded up. wards towards the body of the animal, (Pl. 38, S. S.,) and thus the jagged terminations of these lobes may have afforded holdfasts whereby the base of the mantle could fix itself firmly, and as it were take root, around the bottom of the external chamber.

No such dentations exist in any species of Nautilus. In the N. Pompi. lius, Mr. Owen has shown that the base of the mantle adheres to the outer shell, near its junction with the transverse plate by means of a strong horny girdle; a similar contrivance probably existed also in all the fossil species of Nautili. The sides of the mantle also of the N. Pompilius are fixed to the sides of the great external chamber by two strong broad lateral muscles, the impressions of which are visible in most specimens of this shell.

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As the animal increased in bulk, and advanced along the outer chamber of the shell, the spaces left behind it were successively converted into air-chambers, simultaneously increasing the power of the float. This float, being regulated by a pipe, passing through the whole series of the chambers, formed an hydraulic instrument of extraordinary delicacy, by which the animal could, at pleasure, control its ascent to the surface, or descent to the bottom of the

sea.

To creatures that sometimes floated, a thick and heavy shell would have been inapplicable; and as a thin shell, enclosing air, would be exposed to various, and often intense degrees of pressure at the bottom, we find a series of provisions to afford resistance to such pressure, in the mechanical construction both of the external shell, and of the internal transverse plates which formed the air-chambers. First, the shell is made up of a tube, coiled round itself and externally convex. Secondly, it is fortified by a series of ribs and vaultings disposed in the form of arches and domes on the convex surface of this tube, and still farther adding to its strength. Thirdly, the transverse plates that form the air-chambers, supply also a continuous succession of supports, extending their ramifications, with many mechanical advantages, beneath those portions of the shell which, being weakest, were most in need of them.

If the existence of contrivance proves the exercise of mind; and if higher degrees of perfection in mechanism are proof of more exalted degrees of intellect in the Author from whom they proceeded; the beautiful examples which we find in the petrified remains of these chambered shells, afford evidence coeval and coextensive with the mountains wherein they are entombed, attesting the Wisdom in which such exquisite contrivances originated, and setting forth the Providence and Care of the Creator, in regulating the structure of every creature of his hand.

THE name of Nautilus Sypho* has been applied to a very curious and beautiful chambered shell found in the Tertiary strata at Dax, near Bourdeaux; and that of Nautilus Zic Zac to a cognate shell from the London clay. (See Pl. 43, Figs. 1, 2, 3, 4.)

These fossil shells present certain deviations from the ordinary characters of the genus Nautilus, whereby they in some degree partake of the structure of an Ammonite.

These deviations involve a series of compensations and peculiar contrivances, in order to render the shell efficient in its double office of acting as a float, and also as a defence and chamber of residence to the animal by which it was constructed.

Some details of these contrivances, relating to the Nauti-lus Sypho will be found in the subjoined note.†

* This shell has been variously described by the names of Ammonites. Atun, Nautilus Sypho, and N. Zonarius. (See M. de Basterot. Mem. Geol.. de Bourdeaux.)

The transverse plates, (Pl. 43, Fig. 1, a. a1. a2.,) present a peculiarity of structure in the prolongation of the collar, or siphuncular aperture entirely across the area of the air-chambers, so that the whole series of transverse plates are connected in one continuous spiral chain. This union is effected by the cnlargement and elongation of the collar for the passage of the siphuncle into the form of a long and broad funnel, the point of which b. fits closely into the neck of the funnel next beneath it, c. whilst its inner margin, resting upon the arch of the subjacent whorl of the shell, transfers to this arch a portion of the external pressure upon the transverse plates, thereby adding to their strength..

As this structure renders it impossible for the flexible siphuncle to expand itself into the area of the air-chambers, as in other Nautili and in Ammonites, the diameter of each funnel is made large enough to allow