and
sometimes twenty or more inches in length, constituting the bys-sus, a
remarkable provision by means of which it anchors itself to the bottom
and thus outrides the storm. Formerly the byssus was gathered in
Sicily, washed in soap and water, dried, corded, and fabricated into
gloves and similar articles of a fine texture. The finished garments
were of a beautiful golden brown color, resembling the burnished gold
on the backs of some splendid flies or beetles.
The yield of Pinna pearls
is very small. A few are obtained from the Mediterranean, especially on
the Adriatic coast. These are usually rose-tinted or reddish in color,
but of diminished orient, and inferior in size. Pinna pearls
are also reported from the Isle of Pines and from New Caledonia, where
they are commonly very dark, almost black in color.
The window-glass shell (Placuna placenta), the vitre chinoise of
some writers, yields a few small, irregularly shaped pearls of a dull
leaden color. It occurs in the inshore waters of the Indian and the
southwestern Pacific oceans; fisheries are prosecuted in Tablegram
Lake, near Trincomali, on the northeast coast of Ceylon ; on the coast
of Borneo, especially at Pados Bay, and to a less extent in some other
localities. This mollusk is quite distinct from the true pearl-oyster,
and in adult life is devoid of the byssus, living on the muddy bottom
of the shallow waters. The shell is almost circular, the right valve is
quite flat, and the left only slightly convex. It is remarkable for its
transparency, especially in the first year of growth, when the beating
of the heart of the mollusk is visible through it. Reaching maturity
in about two years, the shell becomes white and translucent,
resembling pressed isinglass somewhat in its texture. It then measures
about six or seven inches in length, and nearly the same in width. The
outside is rough ; the interior is glazed over and has a subdued
pearly luster. It is so thin and transparent that with a strong light
very coarse print can be read through it. It is commonly used in the
East Indies as a substitute for glass in windows, admitting a soft
mellow light into the room. For this purpose it is usually cut into
small rectangular or diamond-shaped pieces, about five or six square
inches in area, and these are inserted into sash frames. It forms a
good economical substitute for glass, not only in windows of native
residences, but also in lanterns and the like.
The giant clam (Tridacna gigas) of
tropical waters yields a few large opal-white symmetrical pearls, with
faint luster and of little value. The transversely oval shell of the Tridacna, with
its great squamous ribs, is probably the largest and heaviest in
existence, single pairs weighing upward of 500 pounds. It is found in
tropical seas, and especially in the Indian Ocean. It is much used for
ornament,
