210 
MARINE SHELLS OF WEST COAST OF NORTH AMERICA 
Genus ZIRFiEA (Leach) Gray, 1847. 
Shell oval, cardinal margin scarcely reflected, no accessory valves, the 
beaks protected by a membrane; usually a thin fugacious epidermis; 
anteriorly greatly gaping. (Tryon. S. S. Conch.) 
Shell with a radial sulcus dividing the valves into two areas; accessory 
plates rudimentary or wanting; anterior gape large. (Dali.) 
Type. Pholas crispata Linnaeus. 
Distribution. Europe, United States, Senegal, Straits of Sunda, 
Japan. 
Zirfaea gabbi Tryon, 186;3. 
Plate 36, fig. 1. 
Proc. Acad. Nat. Sci. Phila ., 15:144; pi. 1, fig. 1. 
Shell large, transverse, obliquely divided by a deep furrow proceeding 
from the umbonal apex to the basal margin and forming a corresponding 
rib on the internal surface of the valve. Posteriorly to the furrow the 
shell is marked only by growth lines which, in crossing it, are elevated into 
sharp ribs, in which character they are continued to the anterior margin. 
The portion of the shell anterior to the radiating furrow is ornamented 
with numerous longitudinal ribs, approximating in pairs and rendered 
acutely scabrous at the intersection of the rib-like growth lines. Ventral 
anterior margin emarginate. Dorsal anterior margin reflected and closely 
appressed over the beaks. Posterior dorsal margin declining somewhat 
to the quadrately rounded posterior lateral end. Color white. Length, 1^4 
inch; breadth, V/ 2 inch; breadth anterior to furrow, % 0 inch, posterior to 
the furrow, \ l / 2 inch. (Tryon.) 
Type in Acad. Sci. Phila. Type locality given by W. M. Gabb as Japan. 
Range. Bering Sea and islands south to San Diego, California. Also 
Japan. In the Pleistocene at San Pedro and Santa Barbara, California. 
Genus PARAPHOLAS Conrad, 1848. 
Shell oval-oblong; anterior gape closed by a thin, swollen, globose, 
callous plate; valves equal, divided by two radiating grooves into three 
portions; two dorsal valves. 
Type. Pholas califomica Conrad. 
Distribution. California, Australia. Fossil, Cretaceous. 
Range in time. From the Cretaceous. 
Parapholas californica Conrad, 1837. 
Plate 22, figs. 7, 13, and plate 36, figs. 2a, 2b. 
Jour. Acad. Nat. Sci. Phila., 7:236; pi. 18, fig. 5. 
Shell elongated, with eight accessory valves, two of which are on the 
basal margin, extending nearly its entire length; anterior side gibbous, 
