CLASS PELECYPODA 
211 
with the concentric lines lamellar, crowded, undulated and crossed by 
numerous impressed lines; valves much contracted sub-medially, with an 
oblique groove; umbonal slope angulated; posterior side with elevated 
laminae; extremity truncated; apophysis oblique, dilated; hinge margin 
within greatly thickened posteriorly. Length, 4 inches. (Conrad.) 
Type locality, San Diego, California. 
Range. Monterey to San Diego, California. 
Genus PHOLADIDEA Turton, 1819. 
Shell globose-oblong, with a transverse furrow; anterior gape large, 
closed in the adult by a callous plate; two minute accessory valves in 
front of the beaks. (Tryon. S. S. Conch.) 
Type. Pholadidea loscombiana Goodall. 
Distribution. Britain, New Zealand, Ecuador, West Coast of United 
States. 
Pholadidea penita Conrad, 1837. 
Plate 21, fig. 10, and plate 51, figs. 3a, 3b. 
Jour. Acad. Nat. Sci., Philo., 7 :237; pi. 18, fig. 7. 
Shell ovate, elongated, contracted sub-medially and grooved; anterior 
side inflated, with decussating lines, the radiating striae having a granulated 
appearance, posterior side sub-cuneiform, extremity truncated, with a 
membranous expansion or appendage; apophysis oblique, slender, spoon¬ 
shaped at the extremity. (Conrad.) 
Type locality, near San Diego, California. 
Range. Chirikoff Islands, Alaska, to San Pedro and San Diego, 
California. 
Pholadidea penita concamerata Deshayes, 1839. 
Plate 22, figs. 4, 5. 
Rev. Zool. Soc. Cuvierienne , p. 324. Guerin, Mag. Zool. 1840, Mol., pi. 17. 
Shell ventricose, closed, obliquely divided; anterior part inflated, radi- 
ately ribbed, ribs imbricated, dorsal margins widely reflected; posterior 
part striated, sub-quadrate at the end, produced into a horny cup divided 
at the sides; a large sub-quadrate, posteriorly acuminated sub-quadrate 
lamnia at the umbos, then two wide laminae confluent with the terminal 
margins of the shell. (Conch. Iconica.) 
Type in British Museum. Type locality, Monterey, California. 
Range. Bering Sea and Islands to San Diego, California. In the 
Pleistocene at Santa Barbara and Plarris’s Ranch, Santa Barbara County 
and San Pedro, California. 
