462 



CALIFORNIA ACADEMY OF SCIENCES 



[Proc. 4th Ser. 



nally ribbed and pitted, usually worn almost smooth ; tail valve 

 large, with central mucro ; sutural laminae sinuous, triangular, 

 with steep inner slopes ; sinus wide, with a small notch at each 

 side; teeth sharp and moderately long, but covered by the 

 strongly projecting, solid eaves; slits 8 to 9, 1-1, 10 to 11. 



Recorded Range: 



Pleistocene: Lower San Pedro Series — Nob Hill Cut, 

 San Pedro, California ( !). 



Formation doubtful — Deadman Island, San Pedro, Cal- 

 ifornia ( !). 



Living: Fort Bragg, California (!), to Santa Barbara 

 Channel, California; shore to 15 fathoms. 



Material Examined. 



Remarks: The discovery of unmistakeable specimens of this 

 little known Central California species in the southern fossil 

 beds was a considerable surprise, but I feel reasonably confident 

 of the identification. The peculiar features are the roundly 

 arched outline and single slitting of the central valves, the ter- 

 raced appearance of the lateral and terminal areas due to the 

 very strong growth lines, the fine, wrinkly, radiating sculpture 

 of these regions, and the very even and delicate ribbing and 

 pitting of the central areas, though the ribs are hardly evident 

 without a lens. All of these characteristics serve to separate 

 fallax from magdalenensis and young conspicuus, with which 

 it is alone likely to be confounded. Two of the fossils are beauti- 

 fully preserved and check up well with the recent specimens, but 

 the third is so badly worn there is perhaps some question re- 

 garding it. 



