ARNOLD — THE PALEONTOLOGY AND STRATIGEAPHY OF SAN PEDKO. 167 



The specimen figured is not the type, which is larger, and is in the United 

 States National Mnseum. The specimen fignred came from the lower San Pedro 

 Series at Deadman Island, and is now in the collection of Delos Arnold. 



Living. — Monterey (Dall). 



Pleistocene. — San Pedro (Arnold). 



Genus Cumingia Soiverbj. 



Shell transversely oval, equivalve, rounded in front, subrostrated and slightly gaping behind; 

 small, thin, often irregular in form; hinge with a spoon-shaped cartilage-pit, and a small anterior 

 cardinal tooth in each valve; two elongated lateral teeth in the right valve, less developed in the left; 

 beaks small; surface concentrically ridged; pallial sinus very wide. 



Type, Cianingia mutica Sowerby. 



114. Cumingia calif ornica Conrad. 



Cumingia californica Con., Jour. Phil. Acad. Sci., Vol. VII, 1837, p. 234, PI. XVII, fig. 12. Car- 

 penter, Brit. Assn. Rept., 1863, p'. 640. Gabb, Pal. Cal., Vol. II, 1869, p. 94. 

 Cooper, 7th Ann. Rept. Cal. St. Min., 1888, p. 238. Keep, West Coast Shells, p. 196, 

 fig. 168, 1892. Williamson, Proc. U. S. Nat. Mas., Vol. XV, 1892, p. 186. 

 ^C. similis A. Ad. {Jide Dall, Trans. Wagner Inst. Sci., Vol. Ill, part 5, 1900, 

 p. 100 1 ). 



Shell of medium size, transversely oval, slightly venlricose, thin; umbones small, incon- 

 spicuous; anterior margin evenly rounded; posterior sloping from umbo at an angle of about 45 

 degrees, straight; posterior end somewhat obliquely truncated; surface sculptured by numerous, 

 about equidistant, sharp, narrow, concenlric ridges or frills; hinge with a triangular, spoon-shaped 

 cartilage-pit and a small anterior cardinal tooth in each valve; two elongated lateral teeth in right 

 valve, less developed in the left; pallial sinus very wide, expanded interiorly and deep. 



Dimensions. — Long. 24.5 mm.; alt. 18 mm.; diam. 4.9 mm. 



Resembles Macoma nasuta in general outline, but is easily distinguishable by 

 the sharp, concentric ridges. Specimens identified by Dr. Dall. 



Found in the lower San Pedro series at Deadman Island and San Pedro, and 

 in the upper San Pedro series at Deadman Island, Crawfish George's, and San Pedro. 



Living. — Monterey to San Diego; Mazatlan (Cooper): Japan (Stimson). 



Pleistocene. — Santa Barbara; San Diego (Cooper): San Pedro (Arnold). 



Family XXXII. PSAMMOBIID.E. 



Genus Psammobia (Lamarck) Bowdich. 



Subgenus Psammobia s. s. 



Shell elongated, more or less pointed behind; compressed; somewhat rudely concentrically 

 sculptured; the posterior dorsal area frequently sculptured diversely from the disc; the pallial sinus 

 elongated and for the most part coalescent below with the pallial line. 



Type, Psammohia feroehsis Grael. 



