CLASS PELECYPODA 
197 
two obscure teeth; no lateral teeth; pallial sinus deep. (Tryon. S. S. 
Conch.) 
Type. Mya nitens Montagu, 1808. 
Distribution. West Indies, Britain, Canaries, Mediterranean, Red 
Sea, West Coast of America. 
Ervilia californica Dali, 1916. 
Proc. U. S . N. M., 52:414. 
Shell small, ovate, white with a rosy flush, inequilateral, the posterior 
end shorter; the beaks inconspicuous, the ends rounded, the basal margin 
arcuate; sculpture of fine close-set, regular, uniform concentric threads 
over the whole surface; hinge strong, pallial sinus small. Length, 7; 
height, 4.5; diameter, 2 mm. (Dali.) 
Type in U. S. N. M., No. 151419. Type locality, San Pedro, California. 
Range. San Pedro to San Diego, California. 
Family MYACID^E. 
Genus MYA (L.) Lamarck, 1799. 
Shell oblong, inequivalve, gaping at the ends; left valve smallest, with 
a large flattened cartilage-process; pallial sinus large. (Tryon. S. S. 
Conch.) 
Type. My a trune at a Linnaeus, 1758. 
Distribution. Northern seas, West Africa, Philippines, Australia, 
California. 
Mya truncata Linnaeus, 1758. 
Plate 10, fig. 4. 
Syst. Nat. ed. 10, p. 670. Binney and Gould’s Invert. Mass., p. 59, fig. 376. 
M. testa ovata postice truncata, cardinis dente antrorsum porrecto 
obtusissimo. (Linnaeus.) 
Shell oblong, inequipartite, longest and rounded before, narrower and 
abruptly cut off, generally obliquely, behind; valves are strong, deeply 
concave and often unequal, but sometimes the right valve, and sometimes 
the left, is most prolonged; surface irregularly ridged along the lines of 
growth; color dingy white, covered with a thick, tough, yellowish, wrinkled 
epidermis, which folds over the edges of the shell, and is greatly pro¬ 
longed posteriorly, forming a tube six or eight inches long, supplying in 
some measure the apparent loss of protection to the animal by the trunca¬ 
tion of the shell; the truncated edges are a little flaring, and the shell is 
left wide open behind; beaks moderately prominent, turning slightly 
forward; teeth broader than long, projecting a little inward; inner face 
smooth, and nearly flat; outer face similar to that of M. arenaria, but the 
