in natural history, a hard, and, as it were, flaky covering, with which certain animals are defended, and thence called shellfish.

The singular regularity, beauty, and delicacy in the formation of the shells of animals, and the variety and brilliancy in the colouring of many of them, at the same time that they strike the attention of the most curious observers, have at all times excited philosophers to inquire into and detect, if possible, the causes and manner of their formation. But the attempts of naturalists, ancient and modern, to discover this process, have constantly proved unsuccessful. M. de Reaumur hitherto appears alone to have given a plausible account, at least, of the formation of the shell of the garden-snail, in particular, founded on a course of very ingenious experiments, related in the Paris Memoirs*. He there* See Mem. endeavours to show, that this substance is produced merely by the perspirable matter of the animal condensed, sung and afterwards hardening on its surface, and accordingly taking the figure of its body, which has performed ed the office of a mould to it; in short, that the shell is made of a snail, and, as he supposed, of all other animals performed. fessed of shells, was only the product of a viscous transmutation from the body of the animal, containing earthy particles united by mere juxtaposition. This hypothesis, however, is liable to very great and insurmountable difficulties, if we apply it to the formation of some of the most common shells; for how, according to this system, it may be asked, can the oyster, for instance, considered simply as a mould, form to itself a covering so much exceeding its own body in dimensions?

M. Hercifant, in the Memoirs of the Academy of Sciences for 1766, has discovered the structure of shells to be organic. In the numerous experiments that he made on an immense number, and a very great variety, of animal shells, he constantly found that they were composed of two distinct substances; one of which is a cretaceous or earthy matter; and the other appeared, from many experiments made upon it by burning, distillation, and otherwise, to be evidently of an animal nature. These two substances he dexterously separated from each other by a very easy chemical analysis; by the gentle operation of which they were exhibited distinctly to view, without any material alteration from the action of the solvent, or instrument employed for that purpose. On an entire shell or a fragment of one, contained in a glass vessel, he poured a sufficient quantity of the nitrous acid, considerably diluted either with water or spirit of wine. After the liquor had dissolved all the earthy part of the shell (which may be collected after precipitation by a fixed or volatile alkali), there remained floating in it a soft substance, consisting of innumerable membranes of a retiform appearance, and disposed, in different shells, in a variety of positions, which constitutes the animal part of it. This, as it has not been affected by the solvent, retains the exact figure of the shell; and, on being viewed through a microscope, exhibits satisfactory proofs of a vascular and organic structure. He shows that this membranous substance is an appendix to the body of the animal, or a continuation of the tendinous fibres that compose the ligaments by which it is fixed to its shell; and that this last owes its hardness to the earthy particles conveyed through the vessels of the animal, which fix themselves into, and incrust, as it were, the meshes formed by the reticular filaments of which this membranous substance is composed. In the shell called porcelain, in particular, the delicacy of these membranes was so great, that he was obliged to put it into spirit of wine, to which he had the patience to add a minute drop of spirit of nitre day by day, for the space of two months; lest the air generated, or let loose by the action of the acid on the earthy substance, should tear the compases of its fine membranous structure into shatters; as it certainly would have done in a more hasty and less gentle dissolution. The delicate reticulated film, left after this operation, had all the tenacity of a spider's web; and accordingly he does not attempt to delineate its organization. In other shells he employed even five or six months in demonstrating the complicated membranous structure of this animal-substance by this kind of chemical anatomy. In general, however, the process does not require much time.

Of the many angular configurations and appearances of the membranous part of different shells, which are described in this memoir, and are delineated in several well executed plates, we shall mention only, as a specimen, the curious membranous structure observed in the laminae of mother-of-pearl, and other shells of the same kind, after having been exposed to the operation of the author's solvent. Beside the great variety of fixed or permanent colours with which he found the animal-filaments of these shells to be adorned, it is known, that the shell itself presents to the view a succession of rich and changeable colours, the production of which he easily explains from the configurations of their membranes. Nature, he observes, always magnificent in her designs, but singularly frugal in the execution of them, produces these brilliant decorations at a very small expense. The membranous substance above-mentioned is plaited and lumped, as it were, in such a manner, that its exterior lamina, incrusted with their earthy and semi-transparent matter, form an infinite number of little prisms, placed in all kinds of directions, which reflect the rays of light, and produce all the changes of colour observable in these shells.

With respect to the figures and colours of shells, it is observed, that river shells have not so agreeable or diversified a colour as the land and sea shells; but the variety in the figure, colours, and other characters of sea shells, is almost infinite. The number of distinct species we find in the cabinets of the curious is very great; and doubtless the deep bottoms of the sea, and the shores yet unexplored contain multitudes still unknown to us. Even the same species differ in some degree in almost every individual; so that it is rare to find any two shells which are alike in all respects.

This wonderful variety, however, is not all the produce of one sea or one country; the different parts of the world afford us their different beauties. Bonanni observes, that the most beautiful shells we are acquainted with come from the East Indies and from the Red Sea. This is in some degree countenanced by what is found to this day; and from the general observations of the curious, it seems, that the sun, by the great heat that it gives to the countries near the line, exalts the colours of the shells produced there, and gives them a lustre and brilliancy that those of colder climates always want; and it may be, that the waters of those vast seas, which are not subject to be weakened by fresh rivers, give a nourishment to the fish, that may add to the brilliancy of their shells.

The shores of Asia furnish us with the pearl-oysters and scallops in great perfection. About Amboyna are found the most beautiful specimens of the cabbage-shell, Asia, the arrofoir, the ducal mantle, and the coral oysters, or echinated oysters. Here also are found a great variety of extremely beautiful mussels, telling, and volute; some fine buccinums, and the shell called the Ethiopian crown, in its greatest perfection. The dolia, the murices, and the caffandra, are also found on these coasts in great beauty. Many elegant snails and terebr-shells are also brought from thence; and finally, the serapion and spider-shells. The Maldiva and Philippine islands, Bengal, and the coast of Malabar, abound with the most elegant of all the species of snails, and furnish many other kinds of shells in great abundance and perfection. China abounds in the finest species of porcelain shells, and has also a great variety of beautiful snails. Japan furnishes us with all the thicker and larger bivalves; and the isle of Cyprus is famous above all other parts of the world for the beauty and variety of the patella or limpet found there. America affords many very elegant shells, but neither in so great abundance nor beauty as the shores of Asia. Panama is famous for the cylinders or rhombi, and we have beside, from the same place, some good porcelains, and a very fine species of dolium, or concha globosa, called from this place the Panama purple shell. One of the most beautiful of the cylinders is also known among our naturalists under the name of the Panama shell. About Brazil, and in the gulf of Mexico, there are found murices and dolia of extreme beauty; and also a great variety of porcelains, purpurea, pectens, nerite, buccinaria, or heart-shells, and elegant limpets. The isle of Cayenne affords one of the most beautiful of the Buccinum kind, and the Midas ear is found principally about this place. Jamaica and the island of Barbadoes have their shores covered with porcelains, chameæ, and buccina; and at St Domingo there are found almost all the same species of shells that we have from the East Indies; only they are less beautiful, and the colours more pale and dead. The pearl-oyster is found also on this coast, but smaller than in the Persian gulf. At Martinique there are found in general the same shells as at St Domingo, but yet less beautiful. About Canada are found the violet chameæ, and the lakes of that country abound with mussels of a very elegant pale blue and pale red colours. Some species of these are remarkably light and thin; others are very thick and heavy. The Great Bank of Newfoundland is very barren in shells: the principal kind found there are mussels of several species, some of which are of considerable beauty. About Carthagena there are many mother-of-pearl shells, but they are not of so brilliant colours as those of the Persian gulf. The island of Magellan, at the southern point of America, furnishes us with a very remarkable species of mussel called by its name; and several very elegant species of limpets are found there, particularly the pyramidal.

In Africa, on the coast of Guinea, there is a prodigious quantity of that small species of porcelain which is used there as money; and there is another species of porcelain on the same coast which is all over white: the women make bracelets of these, and the people of the Levant adorn their hair with them. The coast of Zanzibar is very rich in shells: we find there a vast variety of the large porcelains, many of them of great beauty; and the nux maris or sea-nut is very frequent there. Beside these, and many other shells, there are found on this coast all the species of nautili, many of which are very beautiful. The Canary islands abound with a vast variety of the murices, and some other good shells; and we have from Madeira great variety of the echini or sea-eggs different from those of the European seas. Several species of mussels are also common there, and the auris marina is nowhere more abundant. The Red sea is beyond all other parts of the world abundant in shells, scarce any kind is wanting there; but what we principally have from thence are the purpurea, porcelains, and echini marini.

The Mediterranean and Northern ocean contain a great variety of shells, and many of very remarkable elegance and beauty; they are upon the whole, however, greatly inferior to those of the East Indies. The Mediterranean abounds much more in shells than the Ocean. The gulf of Taranto affords great variety of purpurea, of porcelains, nautili, and elegant oysters; the coasts of Naples and Sardinia afford also the same, and with them a vast number of the folens of all the known species. The island of Sicily is famous for a very elegant kind of oyster which is white all over; pinnae marinæ and porcelains are also found in great plenty there, with tellinæ and chameæ of many species, and a great variety of other beautiful shells. Corfu is famous, beyond all other places, for vast quantities of the pinnae marinæ; and many other very beautiful shells are found there. (Lister, Hist. Conchyli.) About Syracuse are found the gondola shell, the alated murex, and a great variety of elegant snails, with some of the dolia and nerite. The Adriatic sea, or gulf of Venice, is less furnished with shells than almost any of the seas thereabout. Muscles and oysters of several species are however found there, and some of the cordiform or heart-shells; there are also some tellinæ. About Ancona there are found vast numbers of the pholades buried in stone; and the aures marinæ are particularly frequent about Puzzoli. (Bonani, Recreat. Ment. et Occul.)

The ports of Marfeilles, Toulon, and Antibes, are on the full of pinnae marinæ, mussels, tellinæ, and chameæ. The coasts of Bretagne afford great numbers of the conchæ anatitæ and pouffepieds; they are found on old rotten boards, on sea substances, and among clusters of sponges. The other ports of France, as Rochelle, Dunkirk, Brett, St Malo, and others, furnish oysters excellent for the table, but of the common kind, and of no beauty in their shells; great numbers of mussels are also found there; and the common tellinæ, the onion-peel oysters, the folens, and conchæ anatitæ, are also frequent there. At Granville, in Lower Normandy, there are found very beautiful pectens, and some of the cordiform or heart-shells.

Our own English coasts are not the least fruitful in Of Britain's shells, tho' they do not produce such elegantly painted ones as the Indies. About Plymouth are found oysters, mussels, and folens, in great abundance; and there, and on most of our other shores, are numbers of the aures marinæ and dentalia, with pectens, which are excellent food; and many elegant species of the chameæ and tellinæ are fished up in the sea about Scarborough and other places. Ireland affords us great numbers of mussels, and some very elegant scallop-shells in great abundance, and the pholades are frequent on most of our shores. We have also great variety of the buccina and cochleæ, some voluteæ; and, on the Guernsey coast, a peculiarly beautiful snail, called thence the Guernsey snail.

The coasts of Spain and Portugal afford much the same species of shells with the East Indies, but they are of much fainter colours, and greatly inferior in beauty, gal., &c. There are, according to Tavernier and others, some rivers in Bavaria in which there are found pearls of a fine water. About Cadiz there are found very large pinnae marinæ, and some fine buccina. The isles of Majorca and Minorca afford a great variety of extremely elegant shells. The pinnae marinæ are also very numerous there, and their silk is wrought into gloves, stockings, and other things. The Baltic affords a great many beautiful species, but particularly an orange-coloured pecten, or scallop-shell, which is not found in any other part of the world.

The fresh water shells are found much more frequently, and in much greater plenty than the sea shells. There is scarce a pond, a ditch, or a river of fresh water in any part of the world in which there are