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Rh 1% to 2 inches in length, extremely close to Protothaca sta?mnea and grata Sowerby (the latter's range is from the Gulf of California to Panama), but differing from both in being much more elongate and more compressed. Its lunule and small escutcheon are more distinct and quite smooth as com- pared to those of stavnnea. The hinges are extremely similar. P. grata differs in having tiny, distinct crenulations on the inside of the anterior dorsal margin. T. seviideciissata Reeve appears to be the same as this introduced species. Its colors are variable and commonly variegated. Alias T. bifurcata Quayle 1938. Genus Compsomyax R. Stewart 1930 Co7npso7nyax subdiaphana Carpenter Alaska to Lower California. Milky Pacific Venus Plate 3 if; figure 8ia, b 1/4 to 2/4 inches in length, elongate-ovate, moderately inflated; beaks anterior and pointing forward. Sculpture of fine, irregular, concentric lines of growth, otherwise rather smoothish. Lunule poorly defined. 3 cardinal teeth in each valve, the most posterior one in the right valve deeply split. Color usually chalky-white, but younger specimens are yellowish white and semi-glossy. Interior white. Dredged in soft mud from 5 to 25 fathoms. Abundant in some Californian localities. Formerly placed in the genus CI 677 jentia.

Figure 82. Psephidia of the Pacific Coast, a-b, P. lordi Baird; c, P. nvctUs Dall. Both % inch. Genus Psephidia Dall 1902 Psephidia lordi Baird Lord's Dwarf Venus Figure 82a Alaska to San Diego, California. % inch in length, ovate, compressed or slightly fattened; beaks small; sculpture of microscopic, concentric growth lines. 3 cardinals in hinge of each valve. No laterals. On the dorsal margin there is a microscopic groove parallel to the edge. Color whitish to greenish white, commonly with darker, concentric color bands. Tiny young shells may be found inside the adult clams in the summer and spring months. Common.