CLASS PELECYPODA 
177 
Macoma yoldiformis Carpenter, 1864. 
Plate 44, fig. 6. 
Suppl. Rep. Brit. Assoc., p. 630. Proc. Acad. Nat. Sci. Phila., 1865, p. 55. 
M. t. parva, valde transversa, subplanata, yoldiformi; alba, tenua, 
subdiaphana, politissima; epidermide nitente, pallide straminea induta; 
lineis incrementi, postice conspicuis, exceptis, laevi; parum inaequilaterali, 
umbonibus postice inflectis; marginibus undique (regione ligamenti 
excepta) regulariter excurvatis; intus nympha ligamentali concava, sub- 
celata; postice secta, dein parum alata; dentibus cardinalibus valva 
sinistrali ii., quorum unus bifidis; margine dorsali antico excurvato; sinu 
pallii obscure triangulato, paulo plus quam duas trientes interstitii inter 
cicatrices adductores minores porrecto. Long. .68; lat. .4; alt. .15. (Car¬ 
penter.) 
Shell small, subelliptical, compressed, very thin and fragile; umbones 
slightly posterior to center; anterior end evenly rounded, longer than 
posterior side, which is very faintly folded, biangular and more cuneiform; 
surface smooth, except for very fine incremental lines; ligamental area 
scooped out about one-half length of posterior end; teeth very small. 
(Arnold.) 
Type locality, Boreal, Pacific. 
Range. Puget Sound to San Diego, California. In the Pleistocene 
at San Pedro, California. 
Macoma truncaria Dali, 1916. 
Proc. U. S. N. M., 52 :414. 
Shell small, subquadrate, white, nearly equilateral, the posterior end 
slightly shorter, attenuated subtruncate; basal margin nearly straight, 
anterior end evenly rounded, beaks not prominent, dorsal slopes subequal, 
the posterior steepest; sculpture only of incremental lines irregularly 
prominent; hinge teeth feeble; interior chalky white, the pallial sinus 
reaching only to the vertical of the beak, rounded, free from the pallial 
line. Length, 15; height, 10; diameter, 4 mm. (Dali.) 
Type in U. S. N. M. No. 210916. Type locality, Arctic coast between 
Cape Halkett and Gary River. 
Range. Known only from the type locality. 
Macoma alaskana Dali, 1900. 
Plate 13, fig. 14. 
Proc. U. S. N. M., 23:323; pi. 3, fig. 5. 
Shell small, very inequilateral, moderately inflated, white, with a pol¬ 
ished pale-green periostracum; beaks low but acute, two-fifths of the 
whole length of the shell from the posterior end; anterior end produced, 
evenly rounded, posterior end descending rapidly to a rather blunt point; 
