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374 American Seashells
Ostrea permollis Sowerby Sponge Oyster
North Carolina to Florida and the West Indies.
Plate 28b
Rarely over 3 inches in size. Lives embedded in sponges with only the
margins of the valves showing. The surface of the valves has a soft, silky
appearance. Beak twisted back into a strong spiral. Exterior light-orange to
tan; interior white. Inner margins with numerous small, round denticles.
Common.
Another flat, but larger and light-shelled oyster, Pycnodonta hyotis
Linne, is found in deep water attached to old wrecks off Florida and in the
West Indies. It is immediately recognized by the peculiar structure of the
shell which under a lens appears to be filled with numerous bubbles or empty
cells, much like a bath sponge. It reaches a diameter of 3 or 4 inches, is
generally circular in outline and may be colored whitish cream, brownish or
even lavender. Ostrea thovmsi McLean is this species according to the French
worker, Gilbert Ranson.
Ostrea lurida Carpenter Native Pacific Oyster
Alaska to Lower California.
Plate igi
2 to 3 inches in length, of various shapes; generally rough with coarse
concentric growth lines, but sometimes smoothish. Interior usually stained
with various shades of olive-green, and sometimes with a slight metallic
sheen. It occasionally has purplish brown to brown axial color bands on the
exterior. This is the common intertidal native species of the Pacific Coast.
A number of ecological forms have been described: expansa Carpenter,
rufoides Cpr. and possibly conchaphila Cpr.
Genus Crassostrea Sacco 1897
This genus includes the commercially important American Oyster, C.
virginica Gmehn, which was formerly placed in the genus Ostrea. In
Crassostrea, the left or attached valve is larger than the right. The inner
margin is smooth. The eggs are small, produced in large numbers at one
spawning (over 50 million), and are fertilized and develop in the open wa-
ters outside of the parents. The muscle scar is usually colored. The prodisso-
conch hinge is short, and the valves asymmetrical. The Japanese Oyster (C.
gigas)^ introduced to west American shores, the Portuguese Oyster (C angu-
lata Lamarck), and C. rhizophorae Guilding from Cuba also belong to this
genus. Gryphaea Lamarck is a fossil genus which should not be associated
with this genus.