CLASS PELECYPODA 
195 
Spisula falcata Gould, 1850. 
Plate 20, figs. 1, 2, 3. 
Proc. Boston Soc. Nat. Hist., 3:216. Rep. U. S. Expl. Exp., Moll., p. 393; figs. 
506, a-b. 
Shell large, solid, transversely ovate-triangular, sub-falcate, inequi¬ 
lateral, hinder end shorter, moderately gaping, white, covered with a thick, 
shining, dusky, straw-colored epidermis; surface delicately marked by 
incremental lines, with obscure, distant, radiating ridges; beaks acute, 
nearly touching, post-median, rather compressed; anterior end narrower 
than posterior, triangular, somewhat ascendant, extremity rather acute; 
posterior end broadly rounded, truncate at tip, in young specimens more 
triangular; basal edge regularly arcuate; anterior dorsal edge rectilinear, 
presenting a plane lanceolate space in front of the beaks; posterior dorsal 
edge rounded, with a coarse, loose, dusky epidermis. Valves slightly 
convex; within milk-white; siphonal sinus reaching as far as the beak. 
Cardinal areas large; ligamentary pit large, oblique, shallow; sides of 
V-tooth very unequal, strong; lateral teeth thin, elevated, anterior one 
of left valve bilobate. Length, ; height, ; diameter, iy% inches. 
(Gould.) 
Type locality, Puget Sound, Washington. 
Range. Puget Sound to Cortez Bank and Coronados Islands, Lower 
California. In the Pleistocene at San Pedro and San Diego; the Pliocene, 
at Eagle Prairie, Humboldt County, and Kirker’s Pass, Contra Costa 
County; the Miocene, at Martinez, Contra Costa County, Half Moon Bay, 
San Mateo County, Sunol, Alameda County, Siebeck’s, Santa Clara 
County, Griswold's, San Benito County, Foxen’s, Santa Barbara County, 
San Diego and Los Angeles, California. 
Subgenus Symmorphomactra Dali, 1894. 
Spisula planulata Conrad, 1837. 
Jour. Acad. Nat. Sci. Phila., 7 :240. 
Shell triangular, much compressed, sub-equilateral; the posterior side 
rather shorter than the anterior; anterior side sub-cuneiform; posterior 
side with an obscure sub-marginal line, extremity rounded; beaks elevated; 
epidermis smooth, shining. Length, 1inch. (Conrad.) 
Type locality, near Santa Barbara, California. 
Range. Monterey, California, to Cape San Lucas, Lower California. 
Genus SCHIZOTHiERUS Conrad, 1853. 
Very closely allied to Tresits, with a deep channel on either side of the 
cardinal tooth. The terminations of the siphons are protected by two 
solid valves. 
