120 
MARINE SHELLS OF WEST COAST OF NORTH AMERICA 
Thyasira bisecta Conrad, 1849. 
Plate 10, fig. 1. 
Rep. U. S. Exp., 10:724; pi. 17, fig. 10. 
Shell large, subquadrate, convex, of medium thickness, equivalve, ine¬ 
quilateral; beaks terminal, anterior; anterior end abruptly and angularly 
truncated; posterior dorsal margin arcuate, sloping down toward posterior 
extremity; surface marked only by lines of growth except near the 
posterior part. Where the peculiar truncation takes place, the surface 
suddenly descending at right angles to the curve of the shell, for a short 
distance, and then resuming its former direction; ligament long and 
elliptical; large lunular area in front of the beaks. Length, 72; height, 65; 
diameter, 45 mm. (Conrad.) 
Type in U. S. N. M. ? Type locality, Miocene of Washington. 
Range. Off Alaska Peninsula to Puget Sound. In the Pliocene of 
California and Washington and Miocene of same range. 
Thyasira barbarensis Dali, 1889. 
Plate 53, fig. 3. 
Proc. U. S. N. M., 12:261; pi. 8, fig. 9. 
Shell white, superficially chalky, rather compressed, rounded below, 
the beaks not very prominent; the surface is sculptured only with incre¬ 
mental lines; there is a rather large impressed lunular area not circum¬ 
scribed by a line; behind there is an upper, narrow and deep radial 
depression with a lower, wider and less marked second one, with cor¬ 
responding flexuosities of the posterior margin; a narrow rather deep 
groove runs near the margin outside the ligament marking off a narrow 
elongate escutcheon ; interior white, unpolished; hinge edentulous. Length, 
5; height, 5.1; diameter, 3 mm. (Dali.) 
Type in U. S. N. M., No. 96973. Type locality, Station 2840, Santa 
Barbara Islands. 
Range. Strait of Juan de Fuca to the Gulf of California. 
Thyasira gouldii Philippi, 1845. 
Plate 34, fig. 5. 
Zeitschr. Mai., 2:74. Binney and Gould, Inv. of Mass., p. 100; fig. 206. 
Shell small, globular, posterior side angulated or furrowed; umbones 
much recurved; surface sculptured with fine incremental lines; lunule 
indistinct, depressed in front of beaks; ligament external, placed in a 
groove on the hinge line and outside the hinge plate; teeth wanting. 
Length, 9.5; height, 11; diameter, 8 mm. 
Type in State Museum, Albany, New York. Type locality, Massachu¬ 
setts Bay. 
