PEARL BARLEY. See BARLEY.
PEARL OYSTER„4vicula or Mdeagrina margaritifera, a lamellibranehiate mollusk, of the family Aricalido, generally found—great numbers togethe•—attached to sub marine rocks at a considerable depth on the coasts of tropical countries, and important as producing almost all the pearls and all the mother-of-pearl of commerce. It is some times called the PEARL MussEL,• but the family to which it belongs differs considerably both from that of mussels and from that of oysters, the valves of the shell being unequal, the hinge-line straight and long, and the animal furnished with two adductor muscles, one of them small. and with a foot by which it produces a byssus. The pearl oyster is of an oblique oval form, longitudinally ribbed, and with concentric foliations when young which disappear when it is old. It attains a large size, and there are sev eral varieties, the most important of which are noticed in the article 31ornER-OF-PEABL. The whole inside of the shell is covered with a thick layer of nacre or mother-of-pearl.
compact and beautiful, forming indeed the chief part of the shell, and exhibiting very considerable variety of color, most frequently white, but sometimes blood-red. Pearls are formed of the same substance (see PEARL) and are generally, if not always, pro duced by eggs which have become abortive, and which remain lodged within the mid dusk instead of being ejected into the•sea.
The pearl oyster is too rank and coarse to be eaten. When taken from the sea it is commonly laid out in the sun to die, that the pearls may be sought for after the shell opens.
The pearl oyster is not the Only mullusk which produces pearls. The Placura pla centa—an oyster (family Ostreack) with thin transparent shell, which is used in China and elsewhere as a substitute for window glass—produces diminutive pearls. The fresh water mussel (q.v.) of Britain produces pearls sometimes of considerable beauty and value; and instances have occurred of pearls being found in pinnw, etc., and even in limpets.