Besides the pearl-mussel, a species of large clam is found in the lagoons of many of the Pacific Islands, affording pearls of unusual value. They are of two kinds, and are locally called paahua or tridachna ; one grows chiefly on the solid coral, and does not attain so great size as the other, which is found not only on the hard reef, but bound to loose rocks, or lodged upon the sandy bottom. The latter attains enormous proportions, and is the kind which yields pearls. These are found in the body of the animal, and are so common that 100 may be gathered in a day's fishing, but they are generally of irregular shape and quite opaque ; they are never sought after by the fishermen, and valuable ones are rare, but their systematic search would probably be highly remunerative. Yet another pearl-yielding mollusc inhabits these seas, with a shell like that of an oyster. It is always firmly attached to the rock, and is found singly, so that it is scarce ; but it affords perfectly round, lustrous, golden-coloured pearls, about as large as peas.
The Central American pearl-fisheries lie on both the Atlantic and Pacific aides. They occur in the Bay of Panama, about the Pearl Islands, of which St. Joseph is the most important, whence 800-1000 tons of shell have been taken annually. In 1869, we imported pearls to the value of about 40,000/. from New Granada, the Atlantic ports of America, and St. Thomas ; and the average annual value of the Panama fishery has been estimated at about 25,000/. In the lower part of the Bay of Mulege, in the Gulf of California, near Los Coyetes, pearls have been found of great value ; and it is generally believed that a series of beds extend from the Gulf of Darien to the Gulf of California. lu the latter, and along the shores of Central Mexico 'and Costa Rica, pearl-fishing has long been a lucrative occupation. There is great variety in the quality of the shells from different localities. The chief fishery on the Mexican coast is between Mulege and Cape San Lucas, and in a lesser degree around the Islas tree Marias, and in the neighbourhood of Acapulco. The molluscs here met with are the concha nacar or mother-of-pearl mussel (Meleagrina margaritifera), and ear-shells (Haliotis rufescens). The fishery is carried on during July-October, wind and cold preventing it at other seasons. The use of diving apparatus is coming largely into vogue. The mother-of-pearl found in the Gulf of California is white, with blue-black or yellow bands, and 3-6 in. across. The size and number have much decreased of late years, on account of reckless fishing, without giving time for the beds to recover ; also, it is thought, from the damage done to young molluscs by the heavily-weighted hoots of the divers. It has recently been determined to suspend operations, and open the fishery only once in every four years. The Californian shells go almost exclusively to Hamburg, whence Austria, France, and England draw their supplies. The pearls go mostly to Paris, but also to Fraukfort-on-Maine and Hamburg. The total Californian fishery is reckoned to produce 6000-7000 cwt. of mother-of-pearl annually. The exports of mother of-pearl from Costa Rica were 2042 lb. in 1875, 4425 lb. in 1876, 42,446 lb. in 1877, 6750 lb. in 1878, and 3549 lb. in 1879 ; the value rose from 2c. to 10c. a lb. Panama, in 1879, shipped 7000/. worth
of pearls to the United States. Guayaquil shipped at the rate of 13-14 tons yearly of mother of-pearl about 1871.
In the Bahamas, conch-fishing is an important industry. The only species affording pearl is the common pink conch (Strombus gigas). The pearls taken from under its apron are pink, yellow, or black, the first-named alone having any value. They possess a delicate pink tint, and are often beautifully waterlined, which, with their size and colour, determines their worth.. They are readily saleable in Nassau (Bahamas), at figures occasionally reaching 20/. The value of the total annual export is estimated at 10,000/.
Ohio, one of the States of the American Union, is remarkable for an extensive fishery of a kind of river-pearl, in the Little Miami river, Warren County. The fishing season lasts from June till October. Men and boys wade over the banks in the river, and raise the shells with their feet, so as to avoid putting the bead under water. The shells are opened with a knife, and in about one case out of 150, pearls—sometimes to the number of three—are found between the shell and the membrane that lines it.
Qualities, Values, and Commerce.—The qualities of pearls and mother-of-pearl vary widely. The best pearls are of a clear, bright whiteness, smooth and glossy, and free from spot or stain. The globular form is most generally eateemed, but pear-shaped ones of large size make handsome earrings. Pearls of dark colour are in little favour. The value, other conditions being equal, increases geometrically with the size. Thus a pearl of 3 gr. is worth about 198. ; 4 gr., 32s. ; 5 gr., 47s. ; 6 gr., 758. ; 8 gr., 114s. ; 10 gr., 11/. ; 12 gr., 16/. ; 14 gr., 20/. ; 16 gr., 30/. ; 18 gr., 40/. ; 20 gr., 50/. ; 24 gr., 721. ; 30 gr., 1001. When two or more pearls possess identity of form, size, colour, &o., they aasume a fancy value beyond all rules. Mother-of-pearl owes its beauty to the minute corru gations of its surface, which cause the much-admired iridescence. The shells, as imported, are of various sizes and values. The smallest are Panama, weighing about lb. the single valve ; Bombay and Egyptian weigh about I lb. ; black-edged South Sea, 1 lb. ; Manila, Singapore, and Australian, 11-3 lb. The medium and small shells, being cleanest, bring higher rates in com parison with the larger. The approximate London market values are :—Panama, 60-858. a cwt. ; black-edged S. Sea, 65-130s. ; Bombay and Egypt, 958.-132s. 6d. ; Manila, 135-1608. ; Australian, 130-220s. Pearls are used exclusively for jewellery in Europe and America. Mother-of-pearl has very wide applications for ornamental purposes, such as fans, studs, buttons (see p. 558), card-cases, and multifarious toilet articles, as well as in cabinet-making, inlaying, and papier-mach6 work. In 1870 (the latest detailed Return), we imported 26,197 cwt. of mother-of-pearl, value 76,4891., and 16,6751. worth of pearls. In the ten years ending 1876, France imported 1,376,132 kilo. of mother-of-pearl, value 3,159,943 fr., and 118,078 gm. of pearls, value 2,007,333 fr.; France also now imports about 125,000 kilo. annually of ear-shells (Haliotis). The imports of mother-of-pearl at Hamburg were 7600 cwt. in 1875, 600 cwt. in 1876, and 3300 cwt. in 1877.