whence
large quantities of the shell are exported under the name of "Lingah
shell." The Ceylon variety has the nacreous lining almost uniformly
white over the entire surface, only the lip having a slightly pinkish
ground color. The exterior is marked by seven or eight reddish brown
radial bands on a pale yellow ground. In addition to its greater size,
the Persian variety is darker, and the lip of the shell has a reddish
tinge.
For centuries the Margaritifera vulgaris has
sustained the great pearl fisheries of Ceylon, India, and Persia, and
at present yields the bulk of pearls on the market, especially the
seed-pearls and also those of medium size. It produces relatively few
large ones, rarely exceeding twelve grains in weight. These pearls are
commonly silvery white, and for their size command the highest prices,
because of their beautiful form and superior luster. Excepting the
Venezuelan species, this is the only pearl-oyster which at present
supports extensive fisheries exclusively for pearls; in the fisheries
for all other species the value of the shells furnishes considerable
revenue, and in some localities this represents several times as much
as the income from the pearls.
Ranking next to Margaritifera vulgaris in extent of pearl-production is the Margaritifera margaritifera, which
is widely distributed about the tropical inshore waters of the Pacific
and Indian oceans. It is very much larger than the Lingah oyster, good
specimens measuring seven or eight inches in diameter, and the
nacreous interior is usually of a darker color. In addition to its
yield of pearls, the shell of this species is of value in the
mother-of-pearl trade, and contributes largely to the economic results
of the fisheries. Indeed, in several regions the shell is of more value
than the pearls, which represent only an incidental yield. As Jameson
notes, the color and markings of the shell, though extremely variable,
generally suffice to distinguish this species. The ground color of the
exterior ranges through various shades from yellowish brown to very
dark brown. Its characteristic markings consist of from ten to eighteen
radial rows of white and yellow spots, running from the umbo, or hinge,
to the margin.
Several varieties of Margaritifera margaritifera are
recognized. The type species occurs along the north coast of Australia,
from Brisbane on the east to Sharks Bay on the west ; on the New
Guinea coast ; at Formosa ; and about many of the islands of the
Pacific. The well-known "black-lip shell" of Australian waters is of
this species; it shows a greenish black on the margin of the nacre. The
yield of this is very small compared with that of the large
pearl-oyster of Australia.
The Margaritifera margaritifera occurs on the eastern coast of Arabia in two varieties, which differ somewhat from the type species.
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