chanical contrivances, more obviously adapted to a definite purpose, than can be found in shells of simpler character. Secondly, because the use of many of their parts can be explained, by reference to the economy and organization of the existing animals, most nearly allied to the extinct fossil genera and species with which we are concerned. And, thirdly, because many of these chambered shells can be shown, not merely to have performed the office of ordinary shells, as a defence for the body of their inhabitants; but also to have been hydraulic instruments of nice operation, and delicate adjustment, constructed to act in subordination to those universal and unchanging Laws, which appear to have ever regulated the movement of fluids.

The history of Chambered shells illustrates also some of those phenomena of fossil conchology, which relate to the limitation of species to particular geological Formations;* and affords striking proofs of the curious fact, that many genera, and even whole families, have been called into existence, and again totally annihilated, at various and successive periods, during the progress of the construction of the crust of our globe.

The history of Chambered Shells tends farther to throw light upon a point of importance in physiology, and shows that it is not always by a regular gradation from lower to higher degrees of organization, that the progress of life has advanced, during the early epochs of which geology takes cognizance. We find that many of the more simple forms have maintained their primeval simplicity through all the varied changes the surface of the earth has undergone: whilst, in other cases, organizations of a higher order preceded many of the lower forms of animal life; some of

* Thus, the Nautilus multicarinatus is limited to strata of the Transition formation; the N. bidorsatus to the Muschelkalk; N. obesus, and N. lineatus, to the Oolite Formation; N. elegans, and N. undulatus, to the Chalk.. The divisions of the Tertiary formations have also species of Nautili pecu liar to themselves.

the latter appearing, for the first time, after the total annihilation of many species and genera of a more complex character.*

The prodigious number, variety, and beauty, of extinct Chambered shells, which prevail throughout the Transition and Secondary strata, render it imperative that we should seek for evidence in living nature, of the character and habits of the creatures by which they were formed, and of the office they held in the ancient economy of the animal world. Such evidence we may expect to find in those inhabitants of the present sea, whose shells most nearly resemble the extinct fossils under consideration, namely, in the existing Nautilus Pompilius, (See Pl. 31, Fig. 1,) and Spirula, (Pl. 44. Figs. 1, 2.†)

* The multiplication, in the Tertiary periods, of a class of animals of lower organization, viz. the carnivorous Trachelipods, (See Chap. XV. Section 1,) to fill the place which, during the Secondary periods, had been occupied by a higher order, namely, the carnivorous Cephalopods, affords an example of Retrocession which seems fatal to that doctrine of regular Progression, which is most insisted on by those who are unwilling to admit the repeated interferences of Creative power, in adjusting the successive changes that animal life has undergone.

It will appear, on examination of the shells of fossil Nautili, that they have retained through strata of all ages, their aboriginal simplicity of structure, a structure which remains fundamentally the same in the Nautilus Pompilius of our existing seas, as it was in the earliest fossil species that we find in the Transition strata. Mean time the cognate family of Ammonites, whose shells were more elaborately constructed than those of Nautili, commenced their existence at the same early period with them in the Transition strata, and became extinct at the termination of the Secondary formations. Other examples of later creations of genera and species, followed by their periodi. cal and total extinction, before, or at the same time with the cessation of the Ammonites, are afforded by those cognate Multilocular shells, namely, the Hamite, Turrilite, Scaphite, Baculite, and Belemnite, respecting each of which I shall presently notice a few particulars.

t I omit to mention the more familiar shell of the Argonauta or Paper Nautilus, because, not being a chambered species, it does not apply so directly to my present subject; and also, because doubts still exist whe

I must enter at some length into the natural history of these shells, because the conclusions to which I have been led, by a long and careful investigation of fossil species, are at variance with those of Cuvier and Lamarck, as to the fact of Ammonites being external shells, and also with the prevailing opinions as to the action of the siphon and air chambers, both in Ammonites and Nautili.

Mechanical Contrivances in the Nautilus.

The Nautilus not only exists at present in our tropical seas, but is one of those genera which occur in a fossil state in formations of every age; and the molluscous inhabitants of these shells, having been among the earliest occupants of the ancient deep, have maintained their place through all the changes that the tenants of the ocean have undergone.

The recent publication of Mr. R. Owen's excellent Memoir on the Pearly Nautilus, (Nautilus Pompilius Lin.) 1832, affords the first scientific description ever given of the animal by which this long-known shell is constructed.* This Memoir is therefore of high importance, in its relation to

ther the Sepia found within this shell be really the constructor of it, or a parasitic intruder into a shell formed by some other animal not yet discovered. Mr. Broderip, Mr. Gray, and Mr. G. Sowerby, are of opinion, that this shell is constructed by an animal allied to Carinaria.

*It is a curious fact, that although the shells of the Nautilus have been familiar to naturalists, from the days of Aristotle, and abound in every collection, the only authentic account of the animals inhabiting them, is that by Rumphius, in his history of Amboyna, accompanied by an engraving, which though tolerably correct, as far as it goes, is yet so deficient in detail that it is impossible to learn any thing from it respecting the internal organization of the animal.

I rejoice in the present opportunity of bearing testimony to the value of Mr. Owen's highly philosophical and most admirable memoir upon this subject; a work not less creditable to the author, than honourable to the Royal College of Surgeons, under whose auspices this publication has been so handsomely conducted.

geology; for it enables us to assert, with a confidence we could not otherwise have assumed, that the animals by which all fossil Nautili were constructed, belonged to the existing family of Cephalopodous Mollusks, allied to the common Cuttle Fish. It leads us farther to infer, that the infinitely more numerous species of the family of Ammonites, and other cognate genera of Multilocular shells, were also constructed by animals, in whose economy they held an office analogous to that of the existing shell of the Nautilus Pompilius. We therefore entirely concur with Mr. Owen, that not only is the acquisition of this species peculiarly acceptable, from its relation to the Cephalopods of the present creation; but that it is, at the same time, the living type of a vast tribe of organized beings, whose fossilized remains testify their existence at a remote period, and in another order of things.*

By the help of this living example, we are prepared to investigate the question of the uses, to which all fossil Chambered shells may have been subservient, and to show the existence of design and order in the mechanism, whereby they were appropriated to a peculiar and important function, in

* A farther important light is thrown upon those species of fossil Multilocular shells, e. g. Orthoceratites, Baculites, Hamites, Scaphites, Belemnites, &c. (See Pl. 44,) in which the last, or external chamber, seems to have been too small to contain the entire body of the animals that formed them, by Peron's discovery of the well-known chambered shell, the Spirula, partially enclosed within the posterior extremity of the body of a Sepia (Pl. 44, Figs. 1, 2.) Although some doubts have existed respecting the authenticity of this specimen, in consequence of a discrepance between two drawings professedly taken from it (the one published in the Encyclopédie Méthodique, the other in Peron's Voyage,) and from the loss of the specimen itself before any anatomical examination of it had been made, the subsequent discovery by Captain King of the same shell, attached to a portion of the mutilated body of some undescribed Cephalopod allied to the Sepia, leaves little doubt of the fact that the Spirula was an internal shell, having its dorsal margin only exposed, after the manner represented in both the drawings from the specimen of Peron. (See Pl. 44, Fig. 1.)

the economy of millions of creatures long since swept from the face of the living world. From the similarity of these mechanisms to those still employed in animals of the existing creation, we see that all such contrivances and adaptations, however remotely separated by time or space, indicate a common origin in the will and design of one and the same Intelligence.

We enter then upon our examination of the structure and uses of fossil Chambered shells, with a preliminary knowledge of the facts, that the recent shells, both of N. Pompilius and Spirula, are formed by existing Cephalopods; and we hope, through them, to be enabled to illustrate the history of the countless myriads of similarly constructed fossil shells whose use and office has never yet been satisfactorily explained.

We may divide these fossils into two distinct classes; the one comprising external shells, whose inhabitants resided like the inhabitant of the N. Pompilius, in the capacious cavity of their first or external chamber (Pl. 31, Fig. 1 ;) the other, comprising shells, that were wholly or partially included within the body of a Cephalopod, like the recent spirula, (Pl. 44, Figs. 1, 2.) In both these classes, the chambers of the shell appear to have performed the office of air vessels, or floats, by means of which the animal was enabled either to raise itself and float on the surface of the sea, or sink to the bottom.

It will be seen by reference to Pl. 31, Fig. 1,* that in the recent Nautilus Pompilius, the only organ connecting the air chambers, with the body of the animal, is a pipe, or siphuncle, which descends through an aperture and short projecting tube (y) in each successive transverse plate, till it ter

* The animal is copied from Pl. 1, of Mr. Owen's Memoir; the shell from a specimen in the splendid and unique collection of my friend W. J. Broderip, Esq., by whose unreserved communications of his accurate and extensive knowledge in Natural History, I have been long and largely benefited.