70 THE BOOK OF THE PEARL
large species of pearl-oyster, Margaritifera maxima, obtained
off the north and west coasts of Australia, among the Sulu Islands, and
elsewhere in the Malay Archipelago. In the fisheries for this species,
the mother-of-pearl is the principal object sought, and the pearls are
obtained incidentally. It is the largest of all the members of this
family, reaching in exceptional cases twelve or thirteen inches in
diameter, and weighing upward of twelve pounds ; while the Ceylon
oyster rarely exceeds four ounces in weight. So marked is this
difference, that the Australian species is often designated the
"mother-of-pearl oyster," and the Ceylon species the "pearl-oyster."
Jameson notes that it differs from the Margaritifera margaritifera, its
nearest competitor in size, in its much longer hinge, its shape, its
lesser convexity, and in its color and markings. As described by him,
the color ranges from pale yellowish brown to deep brown, with traces
of radial markings of dark brown, green, or red in the umbonal area. In
its marginal region, the shell is marked by a series of circumferential
lines about one third of a millimeter apart.
Several
geographical varieties of this species are recognized in the
mother-of-pearl trade, differing principally in the coloring of the
interior surface. The chief commercial varieties are "Sydney" or
"Queensland," "Port Darwin," "West Australian," "New Guinea," "Manila,"
"Macassar," and "Mergui." The nacre of those from the Australian coast
is almost uniformly silvery white. That of the "Manila shell" is
characterized by a broad golden border surrounding the silvery white
nacre. The "Macassar shell" lacks the golden border of the "Manila
shell," and is similar in its uniform whiteness to the "Sydney shell,"
but its iridescence is much greater.
The Margaritifera carcharium, from
Sharks Bay, on the coast of Australia, yields yellow pearls and small
quantities of mother-of-pearl. This species is small—three or four
inches in diameter. The color is grayish or greenish yellow, with
several somewhat indistinct radial bands of brownish green. The nacre
has a yellowish green tint, with a margin of pale yellow, with brown
markings.
In the West Indies and on the Atlantic coast of tropical America, especially the coast of Venezuela, occurs the Margaritifera radiata. This
species is quite small, and seems to be closely allied to the Ceylon
oyster. Like the latter, the nacreous interior is rich and brilliant,
but owing to its small size, the shell is wholly valueless as
mother-of-pearl. The principal and almost the only fishery for this
species is on the Venezuelan coast, in the vicinity of Margarita
Island, the islands of Cubagua, and Coche.
The coast of Japan yields the Margaritifera martensi, which occurs among the numerous islands in the southern part of the empire, but
