374 American Seashells 



Ostrea permollis Sowerby Sponge Oyster 



Plate 28b 



North Carolina to Florida and the West Indies. 



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 



Plate igi 

 Alaska to Lower California. 



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. 



