84 
MARINE SHELLS OF WEST COAST OF NORTH AMERICA 
Type. Thracia corbuloides Blainville. 
Distribution. Greenland, United States, Norway, Britain, Mediter¬ 
ranean, Canaries, China. 
Range in time. In the Triassic and Pleistocene. 
Thracia curta Conrad, 1837. 
Plate 43, fig. 6. 
Jour. Acad. Nat. Set., Phila., 7:248; pi. 19, fig. 8. 
Shell sub-oval; anterior margin obtusely rounded; posterior margin 
direct, sub-rectilinear; umbonal slope angular. Additional description: 
shell chalky white, with a dehiscent brownish periostracum slightly inequi- 
valve. Length, 30; height, 20; diameter, 13 mm. (Conrad.) 
Type in Acad. Nat. Sci. Phila.? Type locality, near Santa Barbara, 
California. 
Range. Icy Cape, Arctic Ocean, Bering Sea, to San Diego, California. 
Thracia trapezoides Conrad, 1840. 
Plate 43, fig. 8. 
Wilkes Exped., p. 723; Atlas, pi. 17, fig. 6. 
Trapezoidal; ventricose; flank flattened, carinate, side anteriorly com¬ 
pressed. Surface faintly, concentrically undulate, and neatly but unequally 
marked with concentric striae. Beaks prominent, medial. Posterior 
margin truncated, basal margin tumid at middle. Described from a 
fossil. Length, 48; height, 38; diameter, 16 mm. (Conrad.) 
Type in U. S. N. M. ? Type locality, Astoria, Oregon, Miocene. 
Range. Living in Puget Sound. Fossil in the Pliocene at Eagle 
Prairie, Humboldt County, and San Pedro, California. In the Miocene 
in Oregon, and at Blakely, near Seattle, Washington. 
Thracia challisiana Dali, 1915. 
Plate 43, fig. 7. 
Proc. U. S. N. M., 49:443. Rep. Puget Sound Moll.; pi. 7, fig. 1. 
Shell large, chalky, sub-quadrate, almost equivalve, the posterior end 
longer, surface covered with a coarse, almost imbricating granulation, 
without radial elevations or defined dorsal areas. Both ends are rounded; 
there is no distinct posterior truncation, though that end is blunter than 
the anterior; resilium and ligament marginal, inconspicuous, with no 
indication of a lithodesma; pallial sinus wide, shallow, reaching only 
halfway from the posterior end to the vertical of the beaks. Length, 45 ; 
height, 33; diameter, 20; vertical from the beaks 25 mm. in front of the 
posterior end. (Dali.) 
