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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