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VENERIDAE 411
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
CI677jentia.
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
Alaska to San Diego, California.
Figure 82a
% 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.