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GENESIS OF PEARLS
Pearls are found in certain marine and fresh­water mollusks. The former are usually termed oysters, though zoologists regard it in some instances as a misnomer. The sea-fish is the avicula margaritifera, a bivalve of which there are many varieties, all of similar shape and nature but differing widely in the size, weight, coloring, and quality of the shell.
Of them, the genus "meleagrina" is the largest, has the heaviest shell, and furnishes the greatest quantity of the beautiful substance known as mother-of-pearl. The other extreme is the small, frail-shelled variety taken off the coast of Venezuela, called sometimes avicula squamulosa. Similar to this is the margari­tifera vulgaris^ or avicula fucata, of Ceylon. The pearl oyster of the Persian Gulf though similar is somewhat larger.
Exact and uniform classification of the pearl-bearing mollusks of the sea does not exist, nor is it necessary in this connection, as the
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