WE are much limited in our means of obtaining information as to the anatomical structure of those numerous tribes of extinct animals which are comprehended under Cuvier's great division of Mollusks. Their soft and perishable bodies have almost wholly disappeared, and their external shells, and, in a few cases, an internal apparatus of the nature of shell, form the only evidence of the former existence of the myriads of these creatures that occupied the ancient waters.

The enduring nature of the calcareous coverings

* See note, p. 62.

[296 MOLLUSKS AND CONCHIFERS.] which these animals had the power of secreting, has placed our knowledge of Fossil Shells almost on a footing with that of recent Conchology. But the plan of our present enquiry fbrbids us here to take more than a general review of the history, and economy of the creatures by which they were constructed.

We find many and various forms, both of Univalve and Bivalve shells, mixed with numerous remains of Articulated and Radiated animals, in the most ancient strata of the Transition period that contain any traces of organic life. Many of these shells agree so closely with existing species, that we may infer their functions to have been the same; and that they were inhabited by animals of form and habits similar to those which fabricate the living shells most nearly re sembling them.

All Turbinated and simple shells are constructed by Mollusks of a higher Order than the Conchifers, which construct Bivalves; the former have heads and eyes; the Conchifers, or constructors of bivalves, are without either of these important parts, and possess but a low degree of any other sense than touch, and taste. Thus the Mollusk, which occupies a Whelk, or a Limpet shell, is an animal of a higher Order

* See Mr. Broderip's Introduction to his Paper on some new species of Brachiopoda, Zool. Trans., vol. 1, p. 141.

[297 TWO DIVISIONS OF TRACHELIPODS.] than the Conchifer enclosed between the two valves of a Muscle or an Oyster shell.

Lainarck has divided his Order of Trachelipods* into two great sections, viz, herbivorous and carnivorous; the carnivorous are also divisible into two families of different office, the one attacking and destroying living bodies, the other eating dead bodies that have perished in the course of nature, or from accidental causes; after the manner of those species of predaceous beasts and birds, e. g. the Hyænas and Vultures, which, by preference, live on carrion. The same principle of economy in nature, which causes the dead carcases of the hosts of terrestrial herbivorous animals to be accelerated in their decomposition, by forming the food of numerous carnivora, appears also to have been applied to the submarine inhabitants of the most ancient, as well as of the existing seas; thus converting the death of one tribe into the nutriment and support of life in others.

It is stated by Mr. Dillwyn, in a paper read before the Royal Society, June 1823, that Pliny has remarked, that the animal which was supposed

* This name is derived from the position of the foot, or locomotive apparatus, on the lower surface of the neck, or of the anterior part of the body. By means of this organ Trachelipods crawl like the common garden snail (Helix aspersa). This Helix offers also a familiar example of the manner in which they have the principal viscera packed within the spiral shell.

[298 TURBINATED UNIVALVES,] to yield the Tyrian dye, obtained its food by boring into other shells by means of an elongated tongue; and Lamarck says, that all those Mollusks whose shells have a notch or canal at the base of their aperture, are furnished with a similar power of boring, by means of a retractile proboscis.* In his arrangement of invertebrate animals, they form a section of the Trachelipods, which he calls carnivorous. (Zoophages). In the other section of Trachelipods, which he calls herbivorous (Phytiphages)the aperture of the shell is entire, and the animals have jaws formed for feeding on vegetables.

Mr. Diliwyn further asserts, that every fossil Turbinated Univalve of the older beds, from the

* The proboscis, by means of which these animals are enabled to drill holes through shells, is armed with a number of minute teeth, set like the teeth of a file, upon a retractile membrane, which the animal is enabled to fix in a position adapted for boring or filing a hole from without, through the substance of shells, and through this hole to extract and feed upon the juices of the body within them. A familiar example of this organ may be seen in the retractile proboscis of Buccinum Lapillus, and Buccinum Undatum, the common whelks of our own shores. A valuable Paper on this subject has recently been published by Mr. Osler (Phil. Trans., 1832, Part 2, P. 497), in which he gives an engraved figure of the tongue of the Buccinum Undaturn, covered with its rasp, whereby it perforates the shells ot' animals destined to become its prey. Mr. Osler modifies the rule or the distinction between the shells of carnivora and herbi vora, by shewing that, although it is true that all beaked shells indicate their molluscous inhabitant to have been carnivorous, an entire aperture does not always indicate an herbivorous character.

[299 DISTRIBUTION AND FUNCTIONS.] Transition lime to the Lias, belongs to the herbivorous genera; and that the herbivorous class extends through every stratum in the entire series of geological formations, and still retains its place among the inhabitants of our existing seas. On the other hand, the shells of marine carnivorous univalves are very abundant in the Tertiary strata above the Chalk, but are extremely rare in the Secondary strata, from the Chalk downwards to the Inferior oolite; beneath which no trace of them has yet been found.

Most collectors have seen upon the sea shore numbers of dead shells, in which small circular holes have been bored by the predaceous tribes, for the purpose of feeding upon the bodies of the animals contained within them; similar holes occur in many fossil shells of the Tertiary strata, wherein the shells of carnivorous Trachelipods also abound; but perforations of this kind are extremely rare in the fossil shells of any older formation. In the Green-sand and Oolite, they have been noticed only in those few cases where they are accompanied by the shells of equally rare carnivorous Mollusks; and in the Lias, and strata below it, there are neither perforations, nor any shells having the notched mouth peculiar to perforating carnivorous species.

It should seem, from these facts, that in the economy of submarine life, the great family of carnivorous Trachelipods, performed the same

[300 TESTACEOUS CEPHALOPODS.] necessary office during the Tertiary period, which is allotted to them in the present ocean. We have further evidence to shew, that in times anterior to, and during the deposition of the Chalk, the same important functions were consigned to other carnivorous Mollusks, viz. the Testaceous Cephalopods;* these are of comparatively rare occurrence in the Tertiary strata, and in our modern seas; but, throughout the Secondary and Transition formations, where carnivorous Trachelipods are either wholly wanting, or extremely scarce, we find abundant remains of carnivorous Cephalopods, consisting of the chambered shells of Nautili and Ammonites, and many kindred extinct genera of polythalamous shells of extraordinary beauty. The Molluscous inhabitants of all these chambered shells, probably possessed the voracious habits of the modern Cuttle Fish, and by feeding like them upon young Testacea and Crustacea, restricted the excessive increase of animal life at the bottom of the more ancient seas. Their sudden and nearly total disappearance at the commencement of the Tertiary era, would have caused a blank in the "police of nature, allowing the herbivorous tribes to increase to an excess, that would ultimately have been destructive of marine vegetation, as well as of themselves, had they not been replaced by a

* See explanation of the term Cephalopod, in note at p. 303.

[301 REPLACED BY CARNIVOROUS TRACHELIPODS.] different order of carnivorous creatures, destined to perform in another manner, the office which the inhabitants of Ammonites and various extinct genera of chambered shells then ceased to discharge. From that time onwards, we have evidence of the abundance of carnivorous Trachelipods, and we see good reason to adopt the conclusion of Mr. Dillwyn, that " in the formations above the Chalk, the vast and sudden decrease of one predaceous tribe has been provided for by the creation of many new genera, and species, possessed of similar appetencies, and yet formed for obtaining their prey by habits entirely different from those of the Cephalopods." *

The design of the Creator seems at all times to have been, to fill the waters of the seas, and cover the surface of the earth with the greatest possible amount of organized beings enjoying life; and the same expedient of adapting the vegetable kingdom to become the basis of the life of animals, and of multiplying largely the amount of animal existence by the addition of Carnivora to the Herbivora, appears to have prevailed from the first commencement of organic life unto the present hour.*

* Mr. Diliwyn observes further, that all the herbivorous marine Trachelipods of the Transition and Secondary strata were furnished with an operculum, as if to protect them against the carnivorous Cephalopods which then prevailed abundantly; but that in the Tertiary formations, numerous herbivorous genera appear, which are not furnished with opercula, as if no longer requiring the protection of such a shield, after the extinction

[302 SPECIFIC GRAVITY OF SHELLS.] Mr. De la Beche has recently published a list of the specific gravities of living shells of different genera, from which he shews that their weight and strength are varied in accommodation to the habits and habitation of the animals by which they are respectively constructed; and points out evidence of design, such as are discover, in all carefully conducted investigations of the works of nature, whether among the existing or extinct forms of the animal creation.*

of the Ammonites and of many cognate genera of carnivorous Trachelipods, at the termination of the Secondary period, i. e. after the deposition of the Chalk formation.

* " It can scarcely escape the observation of the reader, that, while the specific gravities of the land shells enumerated is generally greatest, the densities of the floating marine shells are much the smallest. The design of the difference is obvious: The land shells have to contend with all changes of climate, and to resist the action of the atmosphere, while, at the same time, they are thin for the purpose of easy transport, their density is therefore greatest. The Argonaut, Nautilus, and creatures of the like habits require as light shells as may be consistent with the requisite strength; the relative specific gravity of such shells is consequently small. The greatest observed density was that of a Helix, the smallest, that of an Argonaut. The shell of the Ianthina, a floating Molluscous creature, is among the smallest densities. The specific gravity of all the land shells examined was greater than that of Carara marble; in general more approaching to Arragonite. The freshwater and marine shells, with the exception of the Argonaut, Nautilus, Ianthina, Lithodomus, Haliotis, and great radiated crystalline Teredo from the East Indies, exceeded Carara marble in density. This marble and the Haliotis are of equal specific gravities." — De la Beche's Geological Researches, 1834, p. 76.

[303 NAKED MOLLUSKS.]

It is well known that the common Cuttle Fish, and other living species of Cephalopods,* which have no external shell, are protected from their enemies by a peculiar internal provision, consisting of a bladder-shaped sac, containing a black and viscid ink, the ejection of which defends them, by rendering opaque the water in which they thus become concealed. The most familiar examples of this contrivance are found in the Sepia vulgaris, and Loligo of our own seas. (See Pl. 28, Fig. 1.)

It was hardly to be expected that we should find, amid the petrified remains of animals of the

* The figure of the common Calmar, or Squid (Loligo Vulgaris Lam. — Sepia loligo of Linnæus), see Pl. 28, Fig. 1, illustrates the origin of the term Cephalopod, a term applied to a large family of molluscous animals, from the fact of their feet being placed around their heads. The feet are lined internally with ranges of horny cups, or suckers, by which the animal seizes on its prey, and adheres to extraneous bodies. The mouth, in form and substance resembles a Parrot's beak, and is surrounded by the feet. By means of these feet and suckers the Sepia octopus, or cornmon Poulpe (the Polypus of the ancients), crawls with its head downwards, along the bottom of the sea.

[304 FOSSIL INK-BAGS.] ancient world, (remains which have been buried for countless centuries in the deep foundations of the earth,) traces of so delicate a fluid as the ink which was contained within the bodies of extinct species of Cephalopods, that perished at periods so incalculably remote; yet the preservation of this substance is established beyond the possibility of doubt, by the recent discovery of numerous specimens in the Lias of Lyme Regis,* in which the ink-bags are preserved in a fossil state, still distended, as when they formed parts of the organization of living bodies, and retaining the same juxta-position to a horny pen, which the ink-bag of the existing Loligo bears to the pen within the body of that animal. (Pl. 28, Fig. 1.)

Having before us the fact of the preservation of this fossil ink, we find a ready explanation of it, in the indestructible nature of the carbon of which it was chiefly composed. Cuvier describes the ink of the recent Cuttle Fish, as being a dense fluid of the consistence of pap, "bouillie," suspended in the cells of a thin net-work that pervades the interior of the ink-bag; it very much resembles common printers' ink. A substance of this nature would readily be transferred

* We owe this discovery to the industry and skill of Miss Mary Anning, to whom the scientific world is largely indebted, for having brought to light so many interesting remains of fossil Reptiles from the Lias at Lyme Regis.

[305 FOSSIL PENS.] to a fossil state, without much diminution of its bulk.*

Pl. 28, Fig. 5, represents an ink-bag of a recent Cuttle Fish, in which the ink is preserved in a desiccated state, being not much diminished from its original volume. Its form is similar to that of many fossil ink-bags (Pl. 29, Figs. 3-10), and the indurated ink within it differs only from the fossil ink, inasmuch as the latter is impregnated with carbonate of lime.

In a communication to the Geological Society, February 1829, I announced that these fossil ink-bags had been discovered in the Lias at Lyme Regis, in connexion with horny bodies, resembling the pen of a recent Loligo.

These fossil pens are without any trace of nacre, and are composed of a thin, laminated,

* So completely are the character and qualities of the ink retained in its fossil state, that when, in 1826, I submitted a portion of it to my friend Sir Francis Chantrey, requesting him to try its power as a pigment, and he had prepared a drawing with a triturated portion of this fossil substance; the drawing was shewn to a celebrated painter, without any information as to its origin, and he immediately pronounced it to be tinted with sepia of excellent quality, and begged to be informed by what colourman it was prepared. The common sepia used in drawing is from the ink-bag of an oriental species of cuttle-fish. The ink of the cuttle fishes, in its natural state, is said to be soluble only in water, through which it diffuses itself instantaneously; being thus remarkably adapted to its peculiar service in the only fluid wherein it is naturally employed.

[306 RESEMBLANCE TO RECENTLOLIGO.] semi-transparent substance, resembling horn. Their state of preservation is such as to admit of a minute comparison of their internal structure with that of the pen of the recent Loligo; and leads to the same result which we have collected from the examination of so many other examples of fossil organic remains; namely, that although fossil species usually differ from their living representatives, still the same principles of construction have prevailed through every cognate genus, and often also through the entire families under which these genera are comprehended.
The petrified remains of fossil Loligo, therefore, add another link to the chain of argument which we are pursuing, and aid us in connecting successive systems of creation which have followed each other upon our Planet, as parts of one grand and uniform Design. Thus the union of a bag of ink with an organ resembling a pen in the recent Loligo, is a peculiar and striking association of contrivances, affording compensation for the deficiency of an external shell, to an animal much exposed to destruction from its fellow-tenants of the deep; we find a similar association of the same organs in the petrified remains of extinct species of the same family, that are preserved in the ancient marl and limestone strata of the Lias. Cuvier drew his figures of the recent Sepia with ink extracted from its own body. I have drawings of the remains of

[307 SUDDEN INTERMENT OF FOSSIL LOLIGO.] extinct species prepared also with their own ink; with this fossil ink I might record the fact, and explain the causes of its wonderful preservation. I might register the proofs of instantaneous death detected in these ink-bags, for they contain the fluid which the living sepia emits in the moment of alarm; and might detail further evidence of their immediate burial, in the retension of the forms of these distended membranes (Pl. 29. Figs. 3-10.); since they would speedily have decayed, and have spilt their ink, had they been exposed but a few hours to decomposition in the water. The animals must therefore have died suddenly, and been quickly buried in the sediment that formed the strata, in which their petrified ink and ink-bags are thus preserved. The preservation also of so fragile a substance as the pen of a Loligo, retaining traces even of its minutest fibres of growth, is not much less remarkable than the fossil condition of the ink-bags, and leads to similar conclusions.*

* We have elsewhere applied this line of argument to prove the sudden destruction and burial of the Saurians, whose skeletons we find entire in the same Lias that contains the pens and ink-bags of Loligo. On the other hand, we have proofs of intervals between the depositions of the component strata of the Lias, in the fact, that many beds of this formation have become the repository of Coprolites, dispersed singly and irregularly at intervals far distant from one another, and at a distance from any entire skeletons of the Saurians, from which they were derived; and in the further fact, that those surfaces only of the Coprolites which lay uppermost at the bottom of the sea, have often

[308 SIMILAR REMAINS IN GERMANY.] We learn from a recent German publication (Zieten 's Versteinerungen Württembergs. Stuttgart, 1832, Pl. 25 and Pl. 37,) that similar remains of pens and ink bags are of frequent occurrence in the Lias shale of Aalen and Boll.* Hence it is clear that the same causes which produced these effects during the deposition of the Lias at Lyme Regis, produced similar and nearly contemporaneous effects, in that part of Germany which presents such identity in the character and circumstances of these delicate organic remains.

suffered partial destruction from the action of water before they were covered and protected by the muddy sediment that has afterwards permanently enveloped them. Further proof of the duration of time, during the intervals of the deposition of the Lias, is found in the innumerable multitudes of the shells of various Mollusks and Conchifers which had time to arrive at maturity, at the bottom of the sea, during the quiescent periods which intervened between the muddy invasions that destroyed, and buried suddenly the creatures inhabiting the waters, at the time and place of their arrival.

* As far as we can judge from the delineations and lines of structure in Zieten's plate, our species from Lyme Regis is the same with that which be has designated by the name of Loligo Aalensis; but I have yet seen no structure in English specimens like that of his Loligo Bollensis.

Although the resemblance between the pens of the Loligo and a feather (as might be expected from the very different uses to which they are applied) does not extend to their internal structure, we may still, for convenience of description, consider them as composed of the three following parts, which, in all our figures, will be designated by the same letters, A. B. C. First, the external filaments of the plume, (Pl. 28, 29, 30,

[309 STRUCTURE OF FOSSIL PENS.] Paley has beautifully, and with his usual felicity, described the Unity and Universality of Providential care, as extending from the construction of a ring of two hundred thousand miles diameter, to surround the body of Saturn, and be suspended, like a magnificent arch, above the heads of his inhabitants, to the concerting

A.) analogous to those of a common feather. These filaments terminate inwar(ls on a straight line, or base, where they usually form an acute angle with the outer edges of the marginal bands. Secondly, two marginal bands, B. B., dividing the base of the filaments from the body of the shaft; the surface of these bands, B., usually exhibits angular lines of growth in the smaller fossil pens (Pl. 28, Fig. 6, and Pl. 29, Fig. 2,) which become obtuse and vanish into broad curves, in larger specimens, Pl. 29, Fig. I, and Pl. 30. Thirdly, the broad shaft, which forms the middle of the pen, is divided longitudinally into two equal parts by a straight line, or axis, C.: it is made up of a number of thin plates, of a horn-like substance, laid on each other, like thin sheets of paper in pasteboard; these thin plates are composed alternately, of longitudinal, and transverse fibres; the former (Pl. 28, Fig. 7, f. f.) straight, and nearly parallel to the axis of the shaft, the latter (Pl. 28, Fig. 7, e. e.) crossing the shaft transversely in a succession of symmetrical and undulating curves. These transverse fibres do not interlace the others, as the woof interlaces the weaver's warp, but are simply laid over, and adhering to them, as in the alternate laminæ of paper made from slices of papyrus; the strength of such paper much exceeds that made from flax or cotton, in which the fibres are disposed irregularly in all directions. The fibres of both kinds are also collected at intervals into fluted fasciculi, Pl. 30, f, and e, forming a succession of grooves and ridges fitted one into another, whereby the entire surface of each plate is locked into the surface of the adjacent plate, in a manner admirably calculated to combine elasticity with strength.

[310 PROOFS OF DESIGN.] and providing an appropriate mechanism for the clasping and reclasping of the filaments in the feather of the Humming-bird. The geologist descries a no less striking assemblage of curious provisions, and delicate mechanisms, extending from the entire circumference of the crust of our planet, to the minutest curl of the smallest fibre in each component lamina of the pen of the fossil Loligo. He finds these pens uniformly associated with the same peculiar defensive provision of an internal ink-bag, which is similarly associated with the pen of the living Loligo in our actual seas; and hence he concludes, that such a union of contrivances, so nicely adjusted to the wants and weaknesses of the creatures in which they occur, could never have resulted from the blindness of chance, but could only have originated in the will and intention of the Creator.
 

I SHALL select from the family of Multilocular, or Chambered shells, the few examples which I shall introduce from mineral conchology, with

[311 CHAMBERED SHELLS.] a view of illustrating certain points that have relation to the object of the present Treatise.

I select these, first, because they afford proofs of mechanical contrivances, more obviously adapted to a definite purpose, than can be found in shells of simpler character. Secondly, be cause 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 shewn, 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

* 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. undlulatus, to the Chalk. The divisions of the Tertiary formations have also species of Nautili peculiar to themselves.

[312 PROGRESS OF' ORGANIZATION.] 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 further 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 the latter appearing, for the first time, after the total annihilation of many species and genera of a more complex character.*

* The introduction, 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

[313 FOSSIL SHELLS ILLUSTRATED BY RECENT.] 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).*

 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. Meantime 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 periodical 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.

* 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, be cause doubts still exist whether 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.

[314 EXTENT OF THE GENUS NAUTILUS.] 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.

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 Pomnpilius Lin.) 1832, affords the first scientific description ever given of the animal by which this long-known shell is constructed.* This

* 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

[315 NAUTILUS POMPILIUS.] Memoir is therefore of high importance, in its relation to 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, belong to the existing family of Cephalopodous Mollusks, allied to the common Cuttle Fish. It leads us further 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.*

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 prcsent 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.

* A further important light is thrown upon those species of fossil Multilocular shells, e. g. Orthoceratites, Baculites, Hamites,

[316 FOSSIL CHAMBERED SHELLS,] 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 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 ammals 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,

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 Encyclopædie 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.)

[317 ILLUSTRATED BY NAUTILUS POMPILIUS.] 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. Poinpilius, 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 near 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,

* The animal is copied from Pl. l. 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 benefitted.

[318 MECHANISM OF NAUTILUS POMPILIUS.] till it terminates in the smallest chamber at the inner extremity of the shell. I shall presently attempt to show how by means of a peculiar fluid, admitted into or abstracted from this pipe, the animal has the power to increase or diminish its specific gravity, and to sink or float accordingly; as the floating portion of that beautiful toy the Water balloon is made to descend or ascend by means of water forced into, or abstracted from its interior. (See P. 327.)

The motion of the Nautilus, when swimming, with its arms extended, is retrograde, like that of the naked Cuttle Fish, being produced by the reaction of water, violently ejected from the funnel (k).

The position assumed during this operation is that which is best adapted to facilitate its passage through the water, as it places foremost that part of the shell, which approaches most nearly in form to the prow of a boat. The fingers and tentacula (p, p), are here represented as closed around the beak, which is consequently invisible; when the animal is in action, they are probably spread forth like the expanded rays of the sea Anemone.

The horny beak of this recent Nautilus (See Pl. 31, Fig. 2, 3) resembles the bill of a Parrot. Each mandible is armed in front, with a hard and indented calcareous point, adapted to the office of crushing shells and crustaceous animals, of which latter, many fragments were found in the stomach of the individual here represented.

[319 RHYNCHOLITES.] As these belonged to species of hairy brachyurous crustacea,thatlive exclusively at the bottom of the sea, they shew that this Nautilus, though occasionally foraging at the surface, obtains part of its food from the bottom. As it also had a gizzard, much resembling that of a fowl, we see in this organ, further evidence that the existing Nautilus has the power of digesting hard shells.*

A similar apparatus is shewn to have existed in the beaks of the inhabitants of many species of fossil Nautili, and Ammonites, by the abundance of fossil bodies called Rhyncholites, or beak-stones, in many strata that contain these fossil shells, e. g. in the Oolite of Stonesfield, in the Lias at Lyme Regis and Bath, and in the Muschel-kalk at Luneville.

As we are warranted in drawing conclusions from the structure of the teeth in quadrupeds, and of the beak in birds, as to the nature of the

* In Pl. 31, Fig. 3 represents the lower mandible, armed in frontlike Fig. 2. with a hard and calcareous margin; and Fig. 4 represents the anterior calcareous part of the palate of the upper Mandible Fig. 2. formed of the same hard calcareous substance as its point; this substance is of the nature of shell.

These calcareous extremities of both mandlibles are of sufficient strength to break through the coverings of Crustacea and shells, and as they are placed at the extremity of a beak composed of thin and tough horn, the power of this organ is thereby materially increased.

In examining the contents of the stomach of the Sepia vulgaris, and Loligo, I have found them to contain numerous shells of small Conchifera.

[320 USE OF CHAMBERED SHELLS.] food on which they are respectively destined to feed, so we may conclude, from the resemblance of the fossil beaks, or Rhyncholites, (Pl. 31, Fig. 6-11), to the calcareous portions of the beak of the Cephalopod, inhabiting the N. Pompilius, that many of these Rhyncholites were the beaks of the cephalopodous inhabitants of the fossil shells with which they are associated; and that these Cephalopods performed the same office in restraining excessive increase among the Crustaceous and Testaceous inhabitants of the bottom of the Transition and Secondary seas, that is now discharged by the living Nautili, in conjunction with the carnivorous Trachelipods.*

Assuming, therefore, on the evidence of these analogies, that the inhabitants of the shells of the fossil Nautili and Ammonites were Cephalopods, of similar habits to those of the animal which constructs the shell of the N. Pompilius, we shall next endeavour to illustrate, by the organization and habits of the living Nautilus, the manner in which these fossil shells were adapted to the use of creatures, that sometimes moved and fed at the bottom of deep seas, and at other times rose and floated upon the surface.

The Nautili (see Pl. 31. Fig. l. and Pl. 32. Figs. l. 2.) constitute a natural genus of spiral discoidal shells, divided internally into a series

[321 CHAMBERS OP NAUTILUS.] of chambers that are separated from each other by transverse plates; these plates are perforated to admit the passage of a membranous tube or siphuncle either through their centre, or near their internal margin. (Pl. 1 . Fig. 31. Pl. 32. Fig. 2. and Pl. 33.)

The external open chamber is very large, and forms the receptacle of the body of the animal. The internal close chambers contain only air, and have no communication with the outer chamber, excepting by one small aperture in each plate for the passage of a membranous tube, which descends through the entire series of plates to the innermost extremity of the shell, (Pl. 31, y. y. a. b. c. d. e. and Pl. 32, a. b. d. e. f.). These air chambers are destined to counterbalance the weight of the shell, and thereby to render the body and shell together so nearly of the weight of water, that the difference arising from the siphuncle being either empty, or filled with a fluid, may cause the animal to swim or sink.*

As neither the siphuncle, nor the external

* The siphuncle represented in Pl. 31, Fig. 1, illustrates the structure and uses of that organ; in the smallest whorls, from d. inwards, it is enclosed by a thin and almost pulverulent calcareous covering, or sheath, of so soft a nature as to be readily scraped off by the point of a quill; this sheath may admit of the same expansion or contraction, as the membranous tube enclosed within it. In the fossil Nautili, a similar calcareous sheath is often preserved, as in Pl. 32, Figs. 2, 3, and Pl. 33, forming a connected series of tubes of carbonate of lime, closely fitted to the collar of each transverse plate. In four chambers of the recent shell (Pl. 31, Fig. 1, a. b. C. d.) this sheath is partially

[322 CHAMBERS CONTAINED ONLY AIR.] shell have any kind of aperture through which a fluid could pass into the close chambers,* it follows that these chambers contain nothing more than air, and must consequently be exposed to great pressure when at the bottom of the sea. Several contrivances are therefore in troduced to fortify them against this pressure.

removed from the desiccated menibranous pipe within it, which has assumed the condition of a black elastic substance, resembling the black continuous siphuncular pipe that is frequently preserved in a carbonaceous state in fossil Ammonites.

At that part of each transverse plate, which is perforated for the passage of the siphuncle, (Pl. 31, Fig. 1, y. y.), a portion of its shelly matter projects inwards to about one-fourth of the distance across each chamber, and forms a collar, around the membranous pipe, thus directing its passage through the transverse plates, and also affording to it, when distended with fluid, a strong support at each collar. A similar projecting collar is seen in the transverse plate of a fossil Nautilus. (Pl. 32, Fig. 2, e, and Fig. 3, e, i. and Pl. 33.) A succession of such supports placed at short intervals from one another, divides this long and thin membranaceous tube, when distended, into a series of short compartments, or small oval sacs, each sac communicating with the adjacent sacs by a contracted aperture or neck at both its ends, and being firmly supported around this neck by the collar of each transverse plate. (See Pl. 32, Figs . 2, 3, and Pl. 33.)

The strength of each sac is thus increased by the shortness of the distance between its two extremities, and the entire pipe, thus subdivided into thirty or forty distinct compartments, derives from every subdivision an accession of power to sustain the weight or pressure of any fluid that may be introduced to its interior.

* We learn from Mr. Owen, that there was no possibility of the access of water to the air chambers between the exterior of the siphuncle and the siphonic apertures of the transverse plates, because the entire circumference of the mantle in which the siphuncle originates, is firmly attached to the shell by a horny girdle, impenetrable by any fluid. — Memoir on Nautilus Ponpilius,p. 47.

[323 FORTIFICATION OF CHAMBERS.] First, the circumference of the external shell is constructed every way upon the principles of an Arch (see Pl. 31, Fig. I, and Pl. 32, Fig. 1.), so as to offer in all directions the greatest resistance to any pressure that tends to force it inwards.

Secondly, this arch is further fortified by the addition of numerous minute Ribs, which are beautifully marked in the fossil specimens represented at Pl. 32, Fig. I . In this fossil the external shell exhibits fine wavy lines of growth, which, though individually small and feeble, are collectively of much avail as ribs to increase the aggregate amount of strength. (See Pl. 32, Fig. I . a. to b.)

Thirdly, the arch is rendered still stronger by the disposition of the edges of the internal Transverse plates, nearly at right angles to the sides of the external shell, (see Pl. 32, Fig. 1, b. to c.) The course of the edges of these transverse plates beneath the ribs of the outer shell is so directed, that they act as cross braces, or spanners, to fortify the sides of the shell against the inward pressure of deep water. This contrivance is analogous to that adopted in fortifying a ship for voyages in the Arctic Seas, against the pressure of ice-bergs, by the introduction of an extraordinary number of transverse beams and bulk heads. *

* The disposition of the curvatures of the transverse ribs, or lines of growth, in a different direction from the curvatures of the internal transverse plates, affords an example of further contrivance for producing strength in the shells both of recent and

[324  ADDITION OF CHAMBERS.] We may next notice a fourth contrivance by which the apparatus that gives the shell its power of floating, is progressively enlarged in due proportion to the increasing bulk of the body of the animal, and increasing weight of the external chamber in which it resides; this is effected by successive additions of new transverse Plates across the bottom of the outer chamber, thus converting into airchambers that part of the shell, which had become too small to hold the body. This operation, repeated at intervals in due proportion to the successive stages of growth of the shell, maintains its efficacy as a float, enlarging gradually and periodically until the animal has arrived at full maturity.*

fossil Nautili. As the internal transverse plates are convex inwards, (see Pl. 32, Fig. 1, b. to c.) whilst the ribs of the outer shell are in the greater part of their course convex outwards, these ribs intersect the curved edges of the transverse plates at many points, and thus divide them into a series of curvilinear parallelograms; the two shorter sides of each parallelogram being formed by the edges of transverse plates, whilst its two longer sides are formed by segments of the external ribs. The same principle of construction here represented in our plate of Nautilus hexagonus, extends to other species of the family of Nautilus, in many of which the ribs are more minute; it is also applied in other families of fossil chambered shells; e. g. the Ammonites, Pl. 35, and Pl. 38. Scaphites, Pl. 44, Fig. 15. Hamites, Pl. 44, Fig. 8-13. Turrilites, Pl. 44, Fig. 14, and Baculites, Pl. 44, Fig. 5.

* In a young Nautilus Pompilius in the collection of Mr. Broderip, there are only seventeen Septa. Dr. Hook says that he has found in some shells as many as forty. A cast, expressing the form of a single air chamber, of the Nautilus Hexagonus is represented in Pl. 42, Fig. 1.

[325 DISTANCES OF TRANSVERSE PLATES.]

A fifth point of structure, producing mechanical advantage, is exhibited in the Distances at which these successive transverse Plates are set from one another. See Pl. 31, Fig. l. and Pl. 32, Fig. 1, 2). Had these distances increased in the same proportion as the area of the air chambers, the external shell would have been without due support beneath those sides of the largest chambers, where the pressure is greatest: for this a remedy is provided in the simple contrivance of placing the transverse plates proportionally nearer to one another, as the chambers, from becoming larger, require an increased degree of support.

Sixthly, the last contrivance, I shall here notice, is that which regulates the ascent and des cent of the animal by the mechanism of the Siphuncle. The use of this organ has never yet been satisfactorily made out; even Mr. Owen's most important Memoir leaves its manner of operation uncertain; but the appearances it occasionally presents in a fossil state, (See Pl. 32, Fig. 2, 3,* and Pl. 33,) supply evidence, which taken in conjunction with Mr. Owen's representation of its termination in a large sac (Pl. 34, p, p.) surrounding the heart of the animal (a, a.), appears sufficient to decide this long disputed question. If we suppose this sac (p, p.) to contain

* Pl. 32, Fig. 2, represents a fractured portion of the interior of a Nautilus Hexagonus, having the transverse plates (c. c'.) encrusted with calcareous spar; the Siphuncle also is similarly

[326 MANNER OF ACTION] a pericardial fluid, the place of which is alternately changed from the pericardium (p, p.) to the siphuncle (n.), we shall find in these organs an hydraulic apparatus for varying the specific gravity of the shell ; so that it sinks when the pericardial fluid is forced into the siphuncle, and becomes buoyant, when the same fluid returns to the pericardiuin. On this hypothesis also the chambers would be permanently filled with air alone, the elasticity of which would admit of the alternate expansion and contraction of the

encrusted, and distended in a manner which illustrates the action of this organ. (Pl. 32, Fig. 2, a.  a¹. a². a³. d. e. f, and Fig. 3, d. e. f). The fracture at Fig. 2, b. shews the diameter of the siphuncle,  where it passes through a transverse plate, to be much smaller than it is midway between these Plates (at d. e. f.). The transverse sections at Fig. 2, a. and b., and the longitudinal sections at Fig. 2, d. e. f. and Fig. 3, d. e. f. shew that the interior of the siphuncle is filled with stone, of the same nature with the stratum in which the shell was lodged. These earthy materials, having entered the orifice of the pipe at a in a soft and plastic state, have formed a cast which shews the interior of this pipe, when distended, to have resembled a string of oval beads, connected at their ends by a narrow neck, and enlarged at their centre to nearly double the diameter of this neck.

A similar distension of nearly the entire siphuncle by the stony material of the rock in which the shell was imbedded, is seen in the specimen of Nautilus striatus from the Lias of Whitby, represented at Pl. 33. The Lias which fills this pipe, must have entered it in the state of liquid mud, to the same extent that the pericardial fluid entered, during the hydraulic action of the siphuncle in the act of sinking; not one of the air chambers has admitted the smallest particle of this mud ; they are all filled with calcareous spar, subsequently introduced by gradual infiltration, and at successive periods which are marked by changes

[327 OF THE SIPHUNCLE.] siphuncle in the act of admitting or rejecting the pericardial fluid.

The principle to which we thus refer the rising and sinking of the living Nautilus, has been already stated (P. 318) to be the same which regulates the ascent and descent of the Water Balloon: the forcing of a quantity of water into the single air chamber of the balloon compresses the air, and increases the quantity of matter in this chamber, without enlarging the magnitude of the balloon,

in the colour of the spur. In both these fossil Nautili, the entire series of the earthy casts within the siphuncle represents the bulk of fluid which this pipe could hold.

The sections, Pl. 32, Fig. 3, d. e. f., shew the edges of the calcareous sheath surrounding the oval casts of three compartments of the expanded siphuncle. This calcareous sheath may have been flexible, like that surrounding the membranous pipe of the recent Nautilus Pompilius. (Pl. 31, Fig. 1, b. d. e.) The continuity of this sheath across the air chambers, (Pl. 32, Fig. 2, d. e. f. Fig. 3, d. e. f. and Pl. 33), shows that there was no communication for the passage of any fluid from the siphuncle into these chambers: had any such existed, some portion of the fine earthy matter, which in these two fossils forms the casts of the siphuncle, must have passed through it into these chambers. Nothing has entered them, but pure  crystallized spar, introduced by infiltration through the pores of the shell, after it had undergone sufficient decomposition to be percolated by water, holding in solution carbonate of lime.

The same argument applies to the solid casts of pure crystallized carbonate of lime, which have entirely filled the chambers of the specimen Pl. 32, Fig. 1 ; and to all fossil Nautili and Ammonites, in which the air chambers are either wholly void, or partially, or entirely filled with pure crystallized carbonate of lime. (See Pl. 42, Fig. 1, 2, 3, and Pl. 36). In all such cases, it is clear that no communication existed, by which water could pass from the interior of the siphon to the air chambers. When

[328 NAUTILUS POMPILlUS.] and thus increasing its specific gravity, causes it to sink; when the pressure is removed, the air within the chamber expands and expels the water, the specific gravity of the balloon is diminished, and it again rises.*

I shall conclude this attempt to illustrate the structure and economy of fossil Nautili by those of the living species, with shewing in what manner the chambers of the pearly Nautilus, supposing them to be permanently filled only with air, and the action of the siphuncle, supposing it to be the receptacle only of a fluid, interchanging its place alternately from the siphuncle to the pericardium, would be subsidiary to the movements of the animal, both on the surface, and at the bottom of the sea.

First, The animal captured by Mr. Bennett, was seen floating at the surface, with the upper portion of the shell raised above the water and kept in a vertical position by means of the included air (see Pl. 31, Fig. 1.); this position

the pipe was ruptured, or the external shell broken, the earthy sediment, in which such broken shells were lodged, finding through these fractures admission to the air chambers, has filled them with clay, or sand or limestone.

* See Sup. Note.

The substance of the siphuncle is a thin and strong membrane, surrounded by a coat of muscular fibres, by which it could contract or expand itself, in the process of admitting or ejecting any fluid to or from its interior. (See Owen's Memoir, p. 10.) In our first edition it was stated erroneously that the siphuncle had no appearance of muscular fibres.

See Sup. Note.

[329 ITS ACTION AT THE SURFACE.] is best adapted to the retrograde motion, which a Sepia derives from the violent ejection of water through its funnel (k);* thus far, the air chambers serve to maintain both the shell and body of the animal in a state of equilibrium at the surface.

The mode of operation of the siphuncle and air chambers, in the act of sinking suddenly from the surface to the bottom is explained in the note subjoined.

* See Sup. Note.

It appears from the figure of the animal, Pl. 34, with which I have been favoured by Mr. Owen, that the upper extremity of the siphuncle marked by the insertion of the probe, terminates in the cavity of the pericardium p, p. As this cavity contains a fluid, excreted by the glandular follicles d, d., and is apparently of such a size that its contents would suffice to fill the siphuncle, it is probable that this fluid forms the circulating medium of adjustment, and regulates the ascent or descent of the animal by its interchange of place from the pericardium to the siphuncle.

When the arms and body are expanded, the fluid remains in the pericardium, and the siphuncle is empty, and collapsed, and surrounded by the portions of air that are permanently confined within each air chamber; in this state, the specific gravity of the body and shell together is such as to cause the animal to rise, and be sustained floating at the surface.

When, on any alarm, the arms and body are contracted, and withdrawn into the shell, the retraction of these parts, causing pressure on the pericardium, forces its fluid contents into the siphuncle; and as the quantity of matter within the shell is thus increased, without increasing its magnitude, whilst the specific gravity of the body remains unaltered by the removal of this fluid from the pericardium, accompanied by a simultaneous diminution of the magnitude of the body, the specific gravity of the entire animal is increased, and it begins to sink.

[330 ACTION AT THE BOTTOM.] Thirdly, It remains to consider the effect of the air (supposing it to be retained continually within the chambers,) at the bottom of the sea. Here, if the position of the moving animal be beneath the mouth of the shell, like that of a snail as it crawls along the ground, the air within the chambers would maintain the shell, buoyant, and floating at ease above the body; and the

The air within each chamber remains under compression, as long as the siphuncle continues distended by the pericardial fluid; and returning, by its elasticity, to its former state, as soon as the pressure of the body is withdrawn from the pericardium, cooperates with the muscular coat of the siphuncle, to force the fluid back again into the pericardium; and the shell, thus diminished as to its specific gravity, has a tendency to rise.

The place of the pericardial fluid, therefore, will be always in the pericardium, excepting when it is forced into and retained in the siphuncle by pressure of the body on the pericardial sac, during the contraction of the animal within its shell. When the arms and body are expanded, either on the surface, or at the bot torn of the sea, the water will have access to the branchial chambers, and the movements of the heart proceed freely in the distended pericardium; which will have great part of its fluid with drawn at those times only, when the body is contracted into the shell, and the access of water to the branchia consequently impeded.

The following experiments shew that the weight of fluid requi site to be added to the shell of a Nautilus, in order to make it sink, is about half an ounce.

I took two perfect shells of a Nautilus Pompilius, each weigh ing about six ounces and a half in air, and measuring about seven inches across their largest diameter; and having stopped the Siphuncle with wax, I found that each shell, when placed in fresh water, required the weight of a few grains more than an ounce to make it sink. As the shell, when attached to the living animal, was probably a quarter of an ounce heavier than these dry dead

[331 OPINIONS OF HOOK AND PARKINSON.] tendency of the shell to rise to the surface would be counteracted by the strong muscular disk (Pl. 31, n.), with which the creature crawls, and adheres to the bottom, using freely its tentacula to seize its prey.*

Dr. Hook considered (Hook's Experiments, 8vo. 1726, page 308) that the air chambers were filled alternately with air or water; and Parkinson (Organic Remains, vol. iii. p. 102), admitting that these chambers were not accessible to water, thinks that the act of rising or sinking depends on the alternate introduction of air or water into the siphuncle; but he is at a loss to find the source from which this air could be obtained at the bottom of the sea, or to

shells, and the specific gravity of the body of the animal, when contracted into the shell, may have exceeded that of water to the amount of another quarter of an ounce, there remains about half an ounce for the weight of fluid, which being introduced into the siphuncle, would cause the shell to sink; and this quantity seems well proportioned to the capacity both of the pericardium, and of the distended siphuncle.

* See Sup. Note.

If the chambers were filled with water, the shell could not be thus suspended without muscular exertion, and instead of being poised vertically over the body, in a position of ease and safety, would be continually tending to fall flat upon its side thus exposing itself to injury by friction, and the animal to attacks from its enemies. Rumphius states, that at the bottom, He creeps with his boat above him, and with his head and barbs (tentacula) on the ground, making' a tolerably quick progress. The author has observed that a similar vertical position is maintained by the shell of the Planorbis corneus, whilst the animal is in the act of crawling at the bottom.

[332 CONCLUSION.] explain " in what manner the animal etlected those modifications of the tube and its contained air, on which the variation of its buoyancy depended."* The theory which supposes the chambers of the shell to be permanently  filled with air alone, and the siphuncle to be the organ which regulates the rising or sinking of the animal by changing the place of the pericardial fluid, seems adequate to satisfy every hydraulic condition of a Problem that has hitherto received no satisfactory solution.

I have dwelt thus long upon this subject, on account of its importance, in explaining the complex structure, and hitherto imperfectly understood functions, of all the numerous and widely disseminated families of fossil chambered shells, that possessed siphunculi.  If, in all these families, it can be shewn that the same principles of mechanism, under various modifications, have prevailed from the first commencement of organic life unto the present hour, we can hardly avoid the conclusion which would refer such unity of organizations to the will and agency of one and the same intelligent First Cause, and lead us to regard them all as "emanations of that Infinite Wisdom, that appears in the shape and structure of all other created beings." 

* The recent observations of Mr. Owen shew, that there is no gland connected with the siphuncle, similar to that which is supposed to secrete air in the air-bladder of fishes.

See Sup. Note.

Dr. Hook's Experiments, p. 306.

[333 AMMONITES.]
 

HAVING entered thus largely into the history of the Mechanism of the shells of Nautili, we have hereby prepared ourselves for the consideration of that of the kindred family of Ammonites, in which all the essential parts are so similar in principle to those of the shells of Nautili, as to leave no doubt that they were subservient to a like purpose in the economy of the numerous extinct species of Cephalopodous Mollusks, from which these Ammonites have been derived.

The family of Ammonites extends through the entire series of the fossiliferous Formations, from the Transition strata to the Chalk inclusive. M. Brochant, in his Translation of De la Beche's Manual of Geology, enumerates 270 species; these species differ according to the age of the strata in which they are found, and vary in

Thus one of the first forms under which this family appeared, the Ammonites Henslowi, (Pl. 40, Fig. 1), ceased with the Transifion formation; the A. Nodosus (Pl. 40, Figs. 4, 5.) began and terminated its period of existence with the Muschel-Kalk. Other genera and species of Ammonites, in like manner, begin and end with certain definite strata, in the Oolitic and Cretaceous formations; e. g. the A. Bucklandi (Pl. 37, Fig. 6.) is

[334 EXTENT AND NUMBER OF SPECIES.] size from a line to more than four feet in diameter.*

peculiar to the Lias; the A. Goodhalli to the Greensand ; and the A. Rusticus to the Chalk. There are few, if any, species which extend through the whole of the Secondary periods, or which have passed into the Secondary, from the Transition period.

The following Tabular Arrangement of the distribution of Ammonites, in different geological formations, is given by Professor Phillips in his Guide to Geology, 1834, p. 77.

" It is easy to see how important, in questions concerning the relative antiquity of stratified rocks, is a knowledge of Ammonites, since whole sections of them are characteristic of certain systems of rocks." — Phillips's Guide to Geology, 8vo. 1834, sec. 82.

The strata here termed primary are those which, in the Section, (Pt. 1), I have included in the lower region of the transition series.

* Mr. Sowerby (Mm. Conch. vol. iv. p. 79 and p. 81,) and Mr. Mantell speak of Ammonites in Chalk, having a diameter of three feet. Sir T. Harvey, and Mr. Keith Mimes, have recently measured Ammonites in the Chalk near Margate, which exceeded four feet in diameter; and this in cases where the diameter can have been in a very small degree enlarged by pressure.

[335 GEOGRAPHICAL DISTRIBUTION.] It is needless here to speculate either on the physicals or final. causes, which produced these curious changes of species, in this highest order of the Molluscous inhabitants of the seas, during some of the early and the middle ages of geological chronology; but the exquisite symmetry, beauty and minute delicacy of structure, that pervade each variation of contrivance throughout several hundred species, leave no room to doubt the exercise of Design and lntelligence in their construction ; although we cannot always point out the specific uses of each minute variation, in the arrangement of parts fundamentally the same.

The geographical distribution of Ammonites in the ancient world, seems to have partaken of that universality, we find so common in the animals and vegetables of a former condition of our globe, and which differs so remarkably from the varied distributton that prevails among existing forms of organic life. We find the same genera, and, in a few cases, the same species of Ammonites, in strata, apparently of the same age, not only throughout Europe, but also in distant regions of Asia, and of North and South America.*

* Dr. Gerard has discovered at the elevation of sixteen thousand feet in the Himmalaya Mountains, species of Ammonites e.g. A. Walcoti and A. Communis, identical with those of the Lias at Whitby and Lyme Regis. He has also found in the same parts of the Himmalaya, several species of Belemnite, with

[336 PARTS OF AN AMMONITE.] hence we infer that during the Secondary and Transition periods a more general distribution of the same species, than exists at present, prevailed in regions of the world most remotely distant from one another.

An Ammonite, like a Nautilus, is composed of three essential parts: 1st. An external shell, usually of a flat discoidal form, and having its surface strengthened and ornamented with ribs (see Pl. 36, and Pl. 37.) 2nd. A series of internal air chambers formed by transverse plates, intersecting the inner portion of the shell, (see Pl. 36 and 41). 3rd. A siphuncle, or pipe, commencing at the bottom of the outer chamber, and thence passing through the entire series of air chambers to the innermost extremity of the shell, (see Pl. 36, d. e. f. g. h. i.) In each of these parts, there are evidences of mechanism, and
 

Terebratulæ, and other Bivalves, that occur in the English Oolite; thereby establishing the existence of the Lias, and Oolite formations in that elevated and distant region of the world. He has also collected in the same Mountains, shells of the genera Spirifer, Producta, and Terebratula, which occur in the Transition formations of Europe arid America.

The Greensand of New Jersey also contains Ammonites mixed with Hamites and Scaphites, as in the Greensand of England, and Captain Beechey and Lieutenant Belcher found Arnmonites on the coast of Chili, in Lat. 36. S. in the Cliffs near Conception; a fragment of one of these Ammonites is preserved in the Museum of Hasler Hospital at Gosport.

Mr. Sowerby possesses fossil shells from Brazil resembling those of the Inferior Oolite of England.

[337 AMMONITES WERE EXTERNAL SHELLS.] consequently of design, a few of which I shall endeavour briefly to point out.

The use and place of the shells of Ammonites has much perplexed geologists and conchologists. Cuvier and Lamarck, guided by the analogies afforded by the Spirula, supposed them to be internal shells.* There is, however, good reason to believe that they were entirely external, and that the position of the body of the animal within these shells was analogous to that of the inhabitant of the Nautilus Pompilius. (See Pl. 31, Fig. 1).

* The smallness of the outer chamber, or place of lodgment for the animal, is advanced by Cuvier in favour of his opinion that Ammonites, like the Spirula, were internal shells. This reason is probably founded on observations made upon imperfect specimens. The outer chamber of Ammonites is very seldom preserved in a perfect state, but when this happens, it is found to bear at least as large a proportion to the chambered part of the shell, as the outer cell of the N. Pompilius bears to the chambered interior of that shell. It often occupies more than half, (see Pl. 36. a. b. c. d.) and, in some cases, the whole circumference of the outer whorl. This open chamber is not thin and feeble, like the long anterior chamber of the Spirula, which is placed within the body of the animal producing this shell; but is nearly of equal thickness with the sides of the close chambers of the Ammonite.

Moreover, the margin of the mature Ammonite is in some species reflected in a kind of scroll, like the thickened margin of the shell of the garden snail, giving to this part a strength which would apparently be needless to an internal shell. (See Pl. 37. Fig. 3. d.)

The presence of spines also in certain species, (as in A.

[338 ANIMAL OCCUPIED THE LAST CHAMBER.] Mr. De la Beche has shewn that the mineral condition of the outer chamber of many Ammonites, from the Lias at Lyme Regis, proves that the entire body was contained within it; and that these animals were suddenly destroyed and buried in the earthy sediment of which the lias is composed, before their bodies had either undergone decay, or been devoured by the crustaceous Carnivora with which the bottom of the sea then abounded.*

As all these shells served the double office of affording protection, and acting as floats, it was necessary that they should be thin, or they would have been too heavy to rise to the surface: it was not less necessary that they should be strong, to resist pressure at the bottom of the sea; and accordingly we find them fitted for this double function, by the disposition of their materials,

Armatus, A. Sowerbii,) affords a strong argument against the theory of their having been internal shells. These spines which have an obvious use for protection, if placed externally, would seem to have been useless, and perhaps noxious in an internal position, and are without example in any internal structure with which we are acquainted.

* In the Ammonites in question, the outer extremity of the first great chamber in which the body of the animal was contained, is filled with stone only to a small depth, (see Pl. 36, from a. to b.); the remainder of this chamber from b. to c., is occupied by brown calcareous spar, which has been ascertained by Dr. Prout to owe its colour to the presence of animal matter, whilst the internal air chambers and siphuncle are filled with pure white spar. The extent of the brown calcareous spar, therefore, in the outer chamber, represents the space which was

[339 FORTIFICATION OF AMMONITES.] in a manner calculated to combine lightness and buoyancy with strength.

First, The entire shell, (Pl. 35,) is one continuous arch, coiled spirally around itself in such a manner, that the base of the outer whorls rests upon the crown of the inner whorls, and thus the keel or back is calculated to resist pressure, in the same manner as the shell of a common hen's egg resists great force, if applied in the direction of its longitudinal diameter.

Secondly, besides this general arch-like form, the shell is further strengthened by the insertion of ribs, or transverse arches, which give to many of the species their most characteristic feature, and produce in all, that peculiar beauty which invariably accompanies the symmetrical repetition of a series of spiral curves. (See Pl. 37, Figs. 1-10.)

From the disposition of these ribs over the

occupied by the body of the animal after it had shrunk within its shell, at the moment of its death, leaving void the outer portion only of its chamber, from a. to b., to receive the muddy sediment in which the shell was imbedded.

I have many specimens from the lias of Whitby, of the Ammonites Communis, in which the outer chamber thus filled with spar, occupies nearly the entire last whorl of the shell, its largest extremity only being filled with lias. From specimens of this kind we also learn, that the animal inhabiting the shell of an Ammonite, had no ink bag; if such an organ existed, traces of its colour must have been found within the cavity which contained the body of the animal at the moment of its death. The protection of a shell seems to have rendered the presence of an ink bag superfluous.

[340 FLUTED FORM OF RIBS.] surface of the external shell, there arise mechanical advantages for increasing its strength, founded on a principle that is practically applied in works of human art. The principle I allude to, is that by which the strength and stiffness of a thin metallic plate are much increased by corrugating, or applying flutings to its surface. A common pencil-case, if made of corrugated or fluted metal, is stronger than if the same quantity of metal were disposed in a simple tube. Culinary moulds of tin and copper are in the same way strengthened, by folds or flutings around their margin, or on their convex surfaces. The recent application of thin plates of corrugated iron to the purpose of making self-supporting roofs, in which the corrugations of the iron supply the place, and combine the power of beams and rafters, is founded on the same principle that strengthens the vaulted shells of Ammonites. In all these cases, the ribs or elevated portions, add to the plates of shell, or metal, the strength resulting from the convex form of an arch, without materially increasing their weight; whilst the intermediate depressed parts between these arches, are suspended and supported by the tenacity and strength of the material. (See Pl. 37, Figs. 1-10.*)

The figures engraved at Pl. 37, afford examples of various contrivances to give strength and beauty to the external shell. The first and simplest mode, is that represented in Pl. 35 and

[341 SUBDIVISION OF RIBS.] The general principle of dividing and subdividing the ribs, in order to multiply supports as the vault enlarges, is conducted nearly on the same plan, and for the same purpose, as the divisions and subdivisions of the ribs beneath the groin work, in the flat vaulted roofs of the florid Gothic Architecture.

Another source of strength is introduced in many species of Ammonites by the elevation of parts of the ribs into little dome-shaped tubercules,

Pl. 37, Fig. 1 and 6. Here each rib is single, and extends over the whole surface, becoming gradually wider, as the space enlarges towards the outer margin, or back of the shell.

The next variation is that represented (Pl. 37, Figs. 2, 7, 9,) where the ribs, originating singly on the inner margin, soon bifurcate into two ribs that extend outwards, and terminate upon the dorsal keel.

In the third case, (Pl. 37. Fig. 4), the ribs, originate simply, and bifurcating as the shell enlarges, extend this bifurcation entirely around its circular back. Between each pair of bifurcated ribs, a third or auxiliary short rib is interposed, to fill up the enlarged space on the dorsal portion where the shell is broadest.

In a fourth modification, (Pl. 37, Fig. 3), the ribs, originating singly on the internal margin, soon become trifurcate, and expand outwards, around the circular back of the shell. A perfect mouth of this shell is represented at Pl. 37, Fig. 3, d.

A fifth case is that (Pl. 37, Fig. 5,) in which the simple rib becomes trifurcate as the space enlarges, and one or more auxiliary short ribs are also interposed, between each trifurcation. These subdivisions are not always maintained with numerical fidelity through every individual of the same species, nor over the whole surface of the same shell; their use, however, is always the same, viz, to cover and strengthen those spaces which the expansion of the shell towards its outer circumference, would have rendered weak without the aid of some such compensation.

[342 VAULTED DOMES AND BOSSES.] or bosses, thus superadding the strength of a dome to that of the simple arch, at each point where these bosses are inserted.*

The bosses thus often introduced at the origin, division, and termination of the ribs, resemble those applied by architects to the intersections of the ribs in Gothic roofs, and are much more efficient in producing strength. These tubercules have the effect of little vaults or domes; and they are usually placed at those parts of the external shell, beneath which there is no immediate support from the internal transverse plates (see Pl. 37, Fig. 8. Pl. 42, Fig. 3. c. d. e. and Pl. 40, Fig. 5.)

* These places are usually either at the point of bifurcation, as in Pl. 37, Figs. 2, 7, 9, 10, or at the point of trifurcation, as in Fig. 3.

The ribs and bosses in vaulted roofs project beneath the under surface of the arch; in the shells of Ammonites, they are raised above the convex surface.

In Pl. 37, Fig. 9 (A. varians), the strength of the ribs and proportions of the tubercies are variable, but the general character exhibits a triple series of large tubercles, rising from the surface of the transverse ribs. Each of these ribs commences with a small tubercle near the inner margin of the shell. At a short distance outwards is a second and larger tubercle, from which the rib bifurcates, and terminates in a third tubercle, raised at the extremity of each fork upon the dorsal margin.

Many species of Ammonites have also a dorsal ridge or keel, (Pl. 37, Figs. l. 2. 6.) passing along the back of the shell, immediately over the siphuncle, and apparently answering, in some cases, the further purpose of a cut-water, and keel (Pl. 37, Figs. 1, 2.). In certain species, e. g. in the A. lautus (Pl. 37,

[343 ECONOMY AND VARIETY OF COMPENSATiONS.] Similar tubercles are introduced with the same advantage of adding Strength as well as Beauty in many other cognate genera of chambered shells. (Pl. 44, Fig. 9. 10. 14. 15.)

In all these cases, we recognize the exercise of Discretion and Economy in the midst of Abundance; distributing internal supports but sparingly, to parts which, from their external form, were already strong, and dispensing them

Fig. 7, a. c.) there is a double keel, produced by a deep depression along the dorsal margin; and the keels are fortified by a line of tubercles placed at the extremity of the transverse ribs. In the A. varians (Pl. 37, 9. a. b. c.) which has a triple keel, the two external ones are fortified by tubercles, as in Fig. 7, and the central keel is a simple convex arch .

Pl. 37, Fig. 8, offers an example of domes, or bosses, compensating the weakness that, without them, would exist in the A. catena, from the minuteness of its ribs, and the flatness of the sides of the shell. These flat parts are all supported by an abundant distribution of the edges of the transverse plates directly beneath them, whilst those parts which are elevated into bosses, being sufficiently strong, are but slightly provided with any other support. The back of this shell also, being nearly flat, (Pl. 37, Fig. 8. b. c.) is strongly supported by ramifications of the transverse plates.

In Pl. 37, Fig. 6, which has a triple keel, (that in the centre passing over the siphuncle,) this triple elevation affords compensation for the weakness that would otherwise arise from the great breadth and flatness of the dorsal portion of this species. Between these three keels, or ridges, are two depressions or dorsal furrows, and as these furrows form the weakest portion of the shell, a compensation is provided by conducting beneath them the denticulated edges of the transverse plates, so that they present long lines of resistance to external pressure.

[344 TRANSVERSE PLATES ANi) AIR CHAMBERS.]

abundantly beneath those parts only, which without them, would have been weak.

We find an infinity of variations in the form and sculpture of the external shell, and a not less beautiful variety in the methods of internal fortification, all adapted, with architectural advantage, to produce a combination of Ornament with Utility. The ribs also are variously multiplied, as the increasing space demands increased support; and are variously adorned and armed with domes and bosses, wherever there is need of more than ordinary strength .

The uses of the internal air chambers will best be understood by reference to our figures. Pl. 36 represents a longitudinal section of an Ammonite bisecting the transverse plates in the central line where their curvature is most simple. On each side of this line, the curvature of these plates become more complicated, until, at their termination in the external shell, they assume a beautifully sinuous, or foliated arrangement, resembling the edges of a parsley leaf, (Pl. 38), the uses of which, in resisting pressure, I shall further illustrate by the aid of graphic representations .

At Pl. 35, from d. to e. we see the edges of the same transverse plates which, in Pl. 36,

[345 THEIR USE IN RESISTING PRESSURE.] are simple curves, becoming foliated at their junction with the outer shell, and thus distributing their support more equally beneath all its parts, than if these simple curves had been continued to the extremity of the transverse plates. In more than two hundred known species of Aminonites, the transverse plates pre sent some beautifully varied modifications of this foliated expansion at their edges; the effect of which, in every case, is to increase the strength of the outer shell, by multiplying the subjacent points of resistance to external pressure. We know that the pressure of the sea, at no great depth, will force a cork into a bottle filled with air, or crush a hollow cylinder or sphere of thin copper; and as the air chambers of Ammonites were subject to similar pressure, whilst at the bottom of the Sea, they required some peculiar provision to preserve them from destruction,* more especially as most zoologists

Captain Sinyth found, on two trials, that the cylindrical copper air tube, under the vane attached to Massey's patent log, collapsed, and was crushed quite flat under a pressure of about three hundred fathoms. A claret bottle, filled with air, and well corked, was burst before it had descended four hundred fathoms. He also found that a bottle filled with fresh water, and corked, had the cork forced at about a hundred and eighty fathoms below the surface; in such cases, the fluid sent down is replaced by salt water, and the cork which had been forced in, is sometimes inverted.

Captain Beaufort also informs me, that he has frequently sunk corked bottles in the sea more than a hundred fathoms deep,

[346 CURVATURES OF TRANSVERSE PLATES.] agree that they existed at great depths, "dans les grandes profondeurs des mers." *

Here again we find the inventions of art anticipated in the works of nature, and the same principle applied to resist the inward pressure of the sea upon the shells of Ammonites, that an engineer makes use of in fixing transverse stays beneath the planks of the wooden centre on which he builds his arch of stone.

The disposition of these supports assumes throughout the family of Ammonites a different arrangement from the more simple curvature of the edges of the transverse plates within the shells of Nautili; and we find a probable cause for this variation, in the comparative thinness of the outer shells of many Ammonites; since this external weakness creates a need of more internal support under the pressure of deep water, than was requisite in the stronger and thicker shells of Nautili.

This support is effected by causing the edges of the transverse plates to deviate from a simple

some of them empty, and others containing a fluid. The empty bottles were sometimes crushed, at other times, the cork was forced in, and the bottle returned full of sea water. The cork of the bottles containing a fluid was uniformly forced in, and the fluid exchanged for sea water; the cork was always returned to the neck of the bottle, sometimes, but not always, in an inverted position.

* See Lamarck, who cites Bruguières with approbation on this point. — Animaux sans: Vert: vol. vii. p. 635.

[347 SINUOUS EDGES OF TRANSVERSE PLATES.] curve, into a variety of attenuated ramifications and undulating sutures. (See Pl. 38. and Pl. 37, Figs. 6, 8). Nothing can be more beautiful than the sinuous windings of these sutures in many species, at their union with the exterior shell; adorning it with a succession of most graceful forms, resembling festoons of foliage, and elegant embroidery. When these thin septa are converted into iron pyrites, their edges appear like golden filigrane work, meandering amid the pellucid spar, that fills the chambers of the shell.*

* The A. Heterophyllus, (Pl. 38), is so called from the apparent occurrence of two different forms of foliage; its laws of dentation are the same as in other Ammonites, but the ascending secondary saddles (Pl. 38. S. S.) which, in all Ammonites are round, are in this species longer than ordinary, and catch attention more than the descending points of the lobes, (Pl. 38. d. I.)

The figures of the edge of one transverse plate are repeated in each successive plate. The animal, as it enlarged its shell, thus leaving behind it a new chamber, more capacious than the last, so that the edges of the plates never interfere or become entangled.

Although the pattern on the surface of this Ammonite is apparently so complicated, the number of transverse plates is but sixteen in one revolution of the shell; in this, as in almost all other cases, the extreme beauty and elegance of the foliations result from the repetition, at regular intervals, of one symmetrical system of forms, viz, those presented by the external margin of a single transverse plate. No trace of these foliations is seen on the outer surface of the external shell. (See Pl. 38, c.)

The figures of A. obtusus, (Pl. 35 and Pl. 36), shew the relations between the external shell and the internal transverse

[348 VARIED PROPORTIONS OF SUPPORT.] The shell of the Ammonites Heterophyllus (Pl. 38, and Pl. 39,) affords beautiful exemplifications of the manner in which the mechanical strength of each transverse plate is so disposed, as to vary its support in proportion to the different degrees of necessity that exist for it in different parts of the same shell.*

partitions of an Ammonite. Pl. 35 represents the form of the external shell, wherein the body occupied the space extending from a. to c., and corresponding with the same letters in Pl. E. 36.

This species has a single series of strong ribs passing obliquely across the shell of the outer chamber, and also across the air chambers. From c. to the inmost extremity of the shell, these ribs intersect, and rest on the sinuous edges of the transverse plates which form the air chambers. These edges are not seen where the outer shell is not removed. (Pl. 35, e.) A small portion of the shell is also preserved at Pl. 35, b.

From d. inwards, these sinuous lines mark the terminations of the transverse plates at their junction with the external shell; they are not coincident with the direction of the ribs, and therefore more effectually co-operate with them in adding strength to the shell, by affording it the support of a series of various props and buttresses, set nearly at right angles to its internal surface.

Thus on the back or keel, Pl. 39, from V. to B., where the shell is narrow, and the strength of its arch greatest, the intervals between the septa are also greatest, and their sinuosities comparatively distant; but as soon as the flattened sides of the same shell, Pl. 38, assume a form that offers less resistance to external pressure, the foliations at the edges of the transverse plates approximate more closely; as in the flatter forms of a Gothic roof, the ribs are more numerous, and the tracery more complex, than in the stronger and more simple forms of the pointed arch.

The same principle of multiplying and extending the ramifications of the edges of the transverse plates, is applied to other species of Aminonites, in which the sides are flat, and require a

[349 DOUBLY VAULTED INTERNAL ARCHES.] At Plate 41. we have a rare and most beautiful example of the preservation of the transverse plates of the Aminonites giganteus converted to chalcedony, without the introduction of any earthy matter into the area of the air-chambers.

This shell is so laid open as to shew the manner in which each transverse plate forms a tortuous partition between the successive air-chambers. By means of these winding plates, the external shell, being itself a continuous arch, is further fortified with a succession of compound arches, passing transversely across its internal cavity; each arch being disposed in the form of a double tunnel, vaulted not only at the top, but having a corresponding series of inverted arches along the bottom.

We can scarcely imagine a more perfect instrument than this for affording universal resistance to external pressure, in which the greatest possible degree of lightness is combined with the greatest strength.

similar increase of support; whilst in those species to which the more circular form of the sides gives greater strength (as in A. obtusus, Pl. 35.) the sinuosities of the septa are proportionately few.

It seems probable that some improvement might be made, in fortifying the cylindrical air-tube of Massey's Patent Log for taking soundings at great depths, by the introduction of transverse plates, acting on the principle of the transverse plates of the chambered portion of the shells of Nautili and Ammonites, or rather of Orthoceratites, and Baculites, (see Pl. 44, Figs. 4. and 5.)

[350 COMPLEX FORM OF AIR CHAMBERS.] The form of the air-chambers in Ammonites is much more complex than in the Nautili, in consequence  of the tortuous windings of the foliated margin of the transverse plates.*

It remains to consider the mechanism of the Siphuncle, that important organ of hydraulic adjustment, by means of which the specific gravity of the Ammonites was regulated. Its

Pl. 42, Fig. 1, represents the cast of a single chamber of N. Hexagonus, convex inwards, and concave outwards, and bounded at its margin by lines of simple curvature. In a few species only of Nautilus the margin is undulated, (as in Pl. 43, Fig. 3,4,) but it is never jagged, or denticulated like the margin of the casts of the chambers of Ammonites.

In Ammonites, the chambers have a double curvature, and are, at their centre, convex outwards (see Pl. 36. d. and Pl. 39. d. V.). Pl. 42, Fig. 2, represents the front view of the cast of a single chamber of A. excavatus; d, is the dorsal lobe enclosing the siphuncle, and e. f. the auxiliary ventral lobes, which open to receive the inner whorl of the shell. Pl. 42. Fig. 3. represents a cast of three chambers of A. catena, having two transverse plates still retained in their proper place between them. The foliated edges of these transverse plates have regulated the foliations of the calcareous casts, which, after the shell has perished, remain locked into one another, like the sutures of a skull.

The substance of the casts in all these cases is pure crystalline carbonate of lime, introduced by infiltration through the pores of the decaying shell. Each species of Ammonite has its peculiar form of air-chamber, depending on the specific form of its transverse plates. Analogous variations in the form of the air-chambers are co-extensive with the entire range of species in the family of Nautili.

[351 HYDRAULIC ACTION OF SIPHUNCLE.] mode of Operation as a pipe, admitting or rejecting a fluid, seems to have been the same as that we have already considered in the case of Nautili.*

The universal prevalence of such delicate hydraulic contrivances in the Siphuncle, and of such undeviating and systematic 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

* In the family of Ammonites, the place of the Siphuncle is always upon the exterior, or dorsal margin of the transverse plates. (See Pl. 36. d. e. f. g. h. i., and Pl. 42, Fig. 3. a, b.) It is conducted through them by a ring, or collar, projecting outwards; this collar is seen, well preserved, at the margin of all the transverse plates in Pl. 36. In Nautili, the collar projects uniformly inwards, and its place is either at the centre, or near the inner margin of the transverse plates. (See Pl. 31, Fig. l. y. and Pl. 42. 1.)

The Siphuncle represented at Pl. 36, is preserved in a black carbonaceous state, and passes from the bottom of the external chamber (d.) to the inner extremity of the shell. At e. f. g. h. its interior is exposed by section, and appears filled, like the adjacent air-chambers, with a cast of pure calcareous spar. At Pl. 42. Fig. 3. b. a similar cast fills the tube of the Siphuncle, and also the air-chambers. Here again, as in Pl. 36, its diameter is contracted at its passage through the collar of each transverse plate, with the same mechanical advantages as in the Nautilus.

The shell engraved at Pl. 42. Fig. 4. from a specimen found by the Marquis of Northampton in the Green sand of Earl Stoke, near Devizes, and of which Figs. 5. 6. are fragments, is remarkable for the preservation of its Siphuncle, distended and empty, and still fixed in its place along the interior of the dorsal margin of the shell. This Siphuncle, and also the shell and transverse

[352 SPECIFIC GRAVITY REGULATED BY SIPHUNCLE.] 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.

Besides the uses we have attributed to the sinuous arrangement of the transverse septa of Ammonites, in giving strength to the shell to

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, shews 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.

[353 VON BUCH'S THEORY OF AMMONITES.] resist the pressure of deep water, M. Von Buch has suggested a further use of the lobes thus 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 generally concave, and without any jagged termination, or sinuous fiexure, 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 (I), next above the ventral lobe.

The separations between these lobes form seats, or saddles,

[364 USES OF LOBES IN AMMONITES.] 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 increases our admiration of the Wisdom in which it was contrived.

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 furnisbed with small auxiliary lobes, varying with the growth of the Ammonite to the number of three, four, or five pairs. (Pl. 39, a. I, a. 2, a. 3, a. 4, a. 5.)

All the lobes, as they dip inwards, 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 further 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

[355 PROOFS OF DESIGN IN AMMONITES.]

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 its inhabitant.

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

and rounded upwards 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. Pompilius, Mr. Owen has shewn 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.

[356 CONCLUSION.] 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, inclosing 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 further 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 co-extensive with the mountains wherein they are entombed, attesting

[357 NAUTILUS SYPHO.] 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.