Page:American Seashells (1954).djvu/544

446 Up to I % inches in length, moderately fragile, moderately elongate and with the beaks central. Characterized by pecuhar, concentric undulations on the beaks. This small species of Mactra is common in lagoons and bays of southern California. It lives 3 to 6 inches below the surface of the sand. Mactra nasuta Gould Gould's Pacific Mactra San Pedro, California, to Mazatlan, Mexico. Up to 3/4 inches in length, similar to calif ornica, but more oval at the ventral margin, without concentric undulations on the beaks, and with 2 very distinct, raised, radial ridges on the posterior dorsal margin. The whitish shell is glossy and the periostracum is shiny and yellowish tan. Not very common. Genus Spisula Gray 1837 Spisiila soUdissima Dillwyn Atlantic Surf Clam Plate 32P Nova Scotia to South Carolina. Up to 7 inches in length (usually about 4 or 5 inches), strong, oval and smoothish, except for small, irregular growth lines. The lateral teeth bear very tiny, saw-tooth ridges. Color yellowish white with a thin yellowish brown periostracum. Common below low-water mark on ocean beaches. After violent winter storms, these clams are cast ashore in incredible num- bers, some estimates giving an approximate count of 50 million clams along a ten-mile stretch. The subspecies shnilis Say (Cape Cod to both sides of Florida and to Texas) is more elongate, its anterior slope flatter, and its pallial sinus longer and not sloping slightly upward. In the left valve, the tiny double tooth, just anterior to the spoon-shaped chondrophore, is usually much larger and stronger. Moderately common, and commonly existing with the typical spe- cies in the northern part of its range. Compare with polynyma which has a larger pallial sinus. Spisula polynyma Stimpson Stimpson's Surf Clam Plate 31W; figure 26k Arctic Seas to Rhode Island. Arctic Seas to Puget Sound. Also Japan. 3 to 5 inches in length, beaks very near the middle of the valve. Anterior