panied by two external impressions, one of these, the Fig. 70. First. pos Those which are furnished with internal teeth at the hinge, but which are not inserted into the opposite valves, as in fig. 70. The genus Mya, (to which belongs common long clam,) and Solen, (razor shell,) are exles. o the Mya genus, belongs the Pearl Gaper, (Mya garitifera,) a beautiful shell with a pearly lustre, and h occasionally produces pearls of great value. It is d in the large rivers of the northern latitudes, and is the shell which is the object of the regular pearl ers. "o this genus also, belongs some shells in considerable est among collectors: but on the whole, the genus is remarkable for the beauty of many of its species. ich is well known in our markets, under the name of und clam, and which are taken in great abundance on e shores of Long Island, and sold as an article of food. Third. Shells, having a hinge, without teeth, as in the ell known shells, the oyster and scallop. The generic distinctions of the bivalves, depending enely on their teeth, and their genera in the Linnæan sysm amounting to only thirteen in number, they are easily stinguished from each other. The species depending on e forms and markings are not so readily distinguished. 3. UNIVALVES. This is much the largest class, and ontains a great proportion of the shells which collectors eek after with so much avidity, and many of which are xceedingly beautiful in their forms and colors. Univalves differ greatly from each other in form, size, nd coloring. Like the bivalves, their different parts are istinguished by peculiar names, which are applied in scientific descriptions, and by means of which conchologists are enabled to understand each other. Only the most necessary and common of these terms can here be explained. The univalves are distinguished chiefly by the form, size, and direction of their apertures, but sometimes by the conformation of the shell. The univalves are exceedingly numerous, of a great variety of forms; and some of them remarkably beautiful, both in shape and color. The names of the several parts of a univalve will be distinguished by the annexed cut. Fig. 72. d The spire, a, in the univalve, fig. 72, is formed by the union of the turns, or whorls, b, which are counted by reckoning the lower turn, containing the opening below, as the first, and counting on the same line to the top of the spire. The turns in most shells go from the right to the left; when they pass from left to right, which rarely happens, the shell is said to be reversed. The line passing round the shell like a screw, and at which horls are united to each other, is termed the suture. horls are plain, grooved, crenulated, crowned with &c. back of the shell, c, is the external, tumid part, on posite side, and above the aperture. The body conf the whole of the tumid part, c, which forms the horl. The opening, or aperture, e, is circular, oval, ar, &c., and it is often the form of this part which dees the genus of the shell. This opening terminates roove or notch, which is either straight or turned to ght or left, or backwards. When the opening is than wide, it is said to be longitudinal; and when than long, transverse. The edge or margin of the ng is divided into right and left lips. The right, or lip, d, reaches from the body, or first turn of the shell, base. The left lip, g, is on the other side of the ng, and is of small extent in those shells, the openings ich are entire. This opening is filled with a body osed of shell, or cartilage, which is attached to the l, and with which he can close the opening at pleasy drawing it in. This is termed the operculum. e little white bodies, popularly called eye-stones, are ulums. ivalves are distinguished into two kinds. gener now l both m F a my pene ig. 73. Fig. 74. First. Those which are furnished with a spire, as fig 73, and those having no spire. Those furnished with spires, are again divided into such as have, 1st, their apertures effuse, that is, having the lips separated by a sinus, or gutter, so that if filled with water, it would flow out at the back part, as the conus, cypræa, bulla and voluta. 2d. Such as have their apertures canaliculate, or like a canal, as buccinum, strombus, and murex. 3d. Such as have their apertures coarctate, or contracted, opposed to effuse, as helix, turbo, and nerita. Second. Those either having no spires, or irregular, or imperfect ones. The patella, or limpet, fig. 74, is an example. In this epitome of conchology, we shall describe a part, but not the whole of the thirty-six Linnæan ra, at the same time indicating which are recent, or living; which are fossil, or extinct; and which are recent and fossil. Fig. 75. MULTIVALVES. Genus Pholat, fig. 75. Shell bivalve, inequilateral, and gaping; having small accessory valves, a, situated on the hinge and posterior slope; hinge recurved and furnished with a tooth. The name Pholades, imports seek a hiding, in reference to the habits of the animals, which live in limestone rocks, or wood, entering when small, and gradually increasing their cells, according to their growth. The largest specimens are found in chalk, which being a soft rock, perhaps admits of a larger growth, in consequence of the ease with which the animal enlarges his cell. There is ystery concerning the means by which these animals 11 e size of the aperture must be done when they are very ung. The animal undoubtedly has the power of disIving the stone and wood by means unknown to man. he idea of friction with the shell, is untenable, since this covered with raised net work, with the points sharply fined. This shell has not been found in the fossil state. Fig. 76. BIVALVES. Genus Mytilus, fig. 76. Shell longitudinal, equivalved; the beaks nearly straight, terminal and pointed; hinge without teeth. Shape either folded or lobed, crested or attenuated towards the apex. This is the muscle of common language. To this genus belongs the pearl-bearing shell, (mytilus marritiferus,) of the Indian fisheries. The whole genus e inseparably attached to other substances. The species in which pearls are found, are most abunnt, and in the greatest perfection, on the coast of the rsian gulf and of the island of Ceylon. The term arl oyster is commonly applied to this shell, but incorctly, as is obvious, since the genus is Mytilus, and not trea. In the great pearl fisheries which supply the eastern arkets, the number of fish annually brought up by dirs, is almost incredible. Many of the shells contain pearls, but some contain two or three. Those of two ains, sell from about 1.50 to 2 dollars each, those of five ains, from 8 to 10 dollars each: those of eight or nine ains are of arbitrary value, because they are very rare. he finest specimens sometimes, bring enormous prices, ing considered invaluable, and fit only to adorn the rsons of eastern potentates. Of the Mytilus, there are about forty recent, and two sil species. Fig. 77 Genus Ostrea. Shell bivalve, gen |