Testaceous animals form the principal subsistence of an immense number of savage nations, inhabitants of the sea-board. On the coast of Western Africa, of Chili, of New Holland, and in the clustered and populous islands of the Southern seas, how vast an item is the apparently unimportant shell-fish in the wealth and happiness of man! In more civilized countries it often supplies the table with a delicate luxury. Nor must we forget the services of the pinna with its web, nor of the purpura with its brilliant and once valuable dye, nor omit to speak of the pearl-oyster, with the radiant nacre, and the gem which it produces, and the world of industry which it sets in action as minister to the luxury which it stimulates.
Shells, too, being composed of particles already in natural combination, have not within them, like flowers and animals, the seed of dissolution. While the preparation of a specimen for the cabinet is a simple operation, a conchological collection will yet remain perfect for ages. These important circumstances being duly considered, in connexion with the universally acknowledged beauty and variety, both of form and colour, so strikingly observable in shells, it is a matter for neither wonder nor regret that these magnificent exuviæ, even regarded merely as such, should have attracted, in a very exclusive degree, the attention and the admiration of the naturalist. The study of Conchology, however, when legitimately directed, and when regarding these exuviæ in their natural point of view, as the habitations, wonderfully constructed, of an immensely numerous and vastly important branch of the animal creation, will lead the mind of the investigator through paths hitherto but imperfectly trodden, to many novel contemplations of Almighty Beneficence and Design.
But it is, beyond all doubt, in a geological point of view that Conchology offers the most of interest to the student; and here, by reference to the fair pages of a profound and mighty knowledge to which it has pointed out the searcher after truth, are triumphantly refuted all charges brought against it of insignificance or frivolity.
“In fine, the relations of the mollusca,” says De Blainville, “with the mineral kingdom, and consequently with the mass of the earth which they contribute to form, are not devoid of interest, for without seeking here to resolve the physiological question—whether the conchyliferous mollusca borrow of the inorganic kingdom the calcareous matter which composes their shells, or whether they form it of themselves, it is still certain that they produce, at least, changes upon the surface of the earth by accumulating this material in some places more than in others, and in consequence that they alter the physiognomy of the superficial structure of the globe, the study of which constitutes geognosy.”
“By this,” says Parkinson, “we are taught that innumerable beings have lived, of which not one of the same kind does any longer exist—that immense beds composed of the spoils of these animals, extending for many miles under ground, are met with in many parts of the globe—that enormous chains of mountains, which seem to load the surface of the earth, are vast monuments, in which these remains of former ages are entombed—that, though lying thus crushed together, in a rude and confused mass, they are hourly suffering those changes, by which, after thousands of years, they become the chief constituent parts of gems, the limestone which forms the humble cottage of the peasant, or the marble which adorns the splendid palace of the prince.” Fossil, wood, coral, and shells, are, indeed, as Bergman very forcibly observes, the only true remaining “medals of Creation.”
EXPLANATION OF THE PARTS OF SHELLS.
MULTIVALVE.
A MULTIVALVE shell is composed of more parts than two. Every part of a shell which is connected by a cartilage, ligament, hinge, or tooth, is called a valve of such shell; thus, the Chitons have eight transverse, broad, but very short valves, placed on the back of the animal, and inserted at their sides into a marginal tough ligament. Plate [I]. fig. 11, a a a.
Operculum consists of four small valves on the summit of the Lepas, which shut up the superior orifice; it is in a certain degree stationary, and different from the operculum of univalve shells, which will hereafter be described. Plate [I]. fig. 1, A. Fig. 9 represents a profile view of the operculum removed from its place, a the front valves, b the back valves. Fig. 10 a front view of the operculum.
Base is that part of the shell by which it is fixed to rocks and other bodies. Plate [I]. fig. 1 and 2, B B B.—H is a piece of stone to which the base is fixed, and G a piece of wood to which the shells of this section are generally attached.