Pecten maximus.Malleus albus.
The power of locomotion appears to be very considerable in some species of the Pectens; it is said the animal can raise itself up in the water, and even reach the surface, by moving the two valves of its shell; but this is a fact not quite established, as but little is known of its habits. It is sometimes used as an article of food; but to render it tolerably palatable it requires cooking.
In some countries, the shells of the larger species are used by the poorer classes instead of plates. In Paris, the restaurateurs employ them for the same purpose when serving up a certain preparation of mushrooms; in England, they are employed in cooking scalloped oysters, and the shell is consequently known as the Scallop Shell.
The Pearl Oyster, ([Meleagrina margaritifera].)
The animal of this shell, although popularly called an oyster, is very different in structure, bearing greater resemblance, in some parts of its formation, to the mussel, particularly in possessing a byssus, or beard; it is the shell in which the famous oriental pearls are found. There are but two known species of the Meleagrina, which are chiefly found in the Persian Gulf, and at Ceylon, or in some of the seas of Australasia.
The cause of the formation of pearl in the shells of this and other inhabitants of the water, has been the occasion of considerable dispute, but it is now pretty well ascertained.
The inner portion of the shell of the Meleagrina is lined with a pearly substance, which is called mother-of-pearl; this is formed by an animal deposit, and is in thin layers. If, by any accident, the inner surface of the shell is injured, so as to cause a fracture of the mother-of-pearl, the deposit, in that place, becomes for the future irregular, and a bump is gradually formed. Accidental circumstances cause this bump to assume various shapes; sometimes it is oval, sometimes globular, and at others pear-shaped. This kind of pearl is always originally found attached to the shell by means of a small neck, or footstalk, and the spot at which this neck was placed can always be traced on the pearl itself.