Page:American Seashells (1954).djvu/457

Rh Crassostrea virginica Gmelin Eastern Oyster Plate 28a Gulf of St. Lawrence to the Gulf of Mexico and the West Indies. 2 to 6 inches in length. This is the familiar edible oyster which varies greatly in size and shape. The valve margins are only slightly undulating or are straight. The muscle scar is usually colored a deep purple, the rest of the shell being white inside and dirty-gray exteriorly. Beaks usually long and strongly curved. "Blue Points," a form originally harvested at Blue Point, Long Island, are rounded in shape and with a rather deep, lower valve. "Lynnhavens" arc broad, elongate forms originally harvested at Lynnhaven Bay, Virginia. These variations are due to environmental differences. C. brasiliana Lamarck and C. floridensis Sowerby are this species. Crassostrea rhizophorae Guilding (brasiliana of authors) is found in the Caribbean region, and it is a lightweight shell, deep-cupped, with a flat upper valve small and fitting well down into the lower valve. The inner margin of the lower, attached valve is splotched with bluish purple. Common. Crassostrea gigas Thunberg Giant Pacific Oyster Plate 29g British Columbia to California. Japan. 3 to 12 inches in length, of various shapes, but generally characterized by its large size, its coarse, widely spaced, concentric lamellae or very coarse longitudinal flutings or ridges on the outside. Interior enamel white, often with a faint purplish stain on the muscle scar or near the edges of the shell. Very rarely with a greenish stain. A common, large and marketable oyster introduced yearly into Canada and the United States from Japan. The form lapermisi Schrenck is round. The typical gigas is the long, strap-like form. O. gigas Aleuschen is an invalid name and does not preoccupy that of Thun- berg's. Also known as the Japanese Oyster. Order EULAMELLIBRANCHIA Suborder HETERODONTA S7iperfa77nly ASTARTACEA Family ASTARTIDAE Genus Astarte Sowerby 18 16 Astarte borealis Schumacher Boreal Astarte Plate 28q Arctic Seas to Massachusetts Bay. Alaska. I to 2 inches in length, ovate, moderately compressed. External liga- ment large. Concentric ridges strong near the beaks but disappearing near