30 
MARINE SHELLS OF WEST COAST OF NORTH AMERICA 
more acute. Hinder dorsal slope nearly rectilinear, scarcely arcuate, area 
distinct. Length, 12; width, 22; diameter, 6 mm. 
Type in British Museum. Type locality, Vancouver Island, British 
Columbia. 
Range. Vancouver Island. 
SECTION YOLDIA s. s. 
Yoldia myalis Couthouy, 1838. 
Plate 5, fig. 8. 
Boston Jour . Nat . History, 2:62; pi. 3, fig. 7. 
Shell ovate, nearly equilateral, slightly gaping at both extremities, 
moderately convex, with numerous ridges of growth; summits antero- 
dorsal; posterior side rather more than half the whole length, posterior 
superior margin somewhat depressed, inferior rounded; anteriorly sub- 
rostrate, not truncated, slightly compressed laterally and superiorly, an¬ 
terior dorsal area lanceolate, smooth, shiny, carinated and rectilinear in 
its whole extent from the beaks to the extremity, posterior dorsal area 
superficial, elliptical and finely striated; basal margin regularly curved 
and entire; ligamentary fossa median, triangular and profound; teeth 
from 20 to 22, posteriorly rectilinear, angulated anteriorly or internally and 
slightly inclined to the summits; color of the interior dull yellowish- 
white; muscular impression well defined, bi-partite, the anterior one 
rounded or oval, posterior subtriangular; epidermis thin, smooth, dark olive 
with paler zones interposed between the incremental lines. Long., 2 % 0 5 
lat -> V 20 ; alt., 12 / 20 of an inch. (Couthouy.) (Naucula myalis.) 
Type in Bost. Soc. Nat. History? Type locality, Massachusetts Bay. 
Range. Arctic Ocean to Puget Sound. 
Yoldia cooperi Gabb, 1865. 
Plate 1, fig. 1, and plate 37, fig. 9. 
Proc. Cal. Acad. Sci., 3:189. Pal. California, 2; pi. 9, fig. 54. 
Shell thin, subcompressed, very inequilateral; beaks minutely placed 
in advance of the middle, becoming more anterior as the shell increases 
in size; anterior end narrow subacuminate; posterior end broadly rounded; 
base most prominent behind the middle, curving upward to the anterior 
end, surface sculptured by numerous small concentric ribs, rarely dichot¬ 
omous, abrupt on the upper side, and sloping downward on the side 
toward the base, muscular scars large, the posterior a third the largest, 
broadly suboval, anterior triangular. Length, 50; height, 25; diameter, 
9 mm. (Gabb.) 
Type in Cooper collection, University of California. Type locality, 
Monterey, California. 
