192 SHELLS OF SAN PEDRO BAY—WILLIAMSON. 
Modiola modiolus Linné. 
Two or three young specimens found in San Pedro Bay. 
Modiola recta Conr. 
Not many found. None exceeding three inches in length. 
Subgenus ApULA H. & A. Ad. 
Modiola (Adula) falcata Gld. 
Two or three, in soft rock; none large. 
Genus LITHOPHAGUS Megerle. 
Lithophagus plumula Hanl. 
A few; living. 
Family ARCID. 
Genus ARCA Linné. 
Arca mutabilis Sby. 
One badly sea-worn valve. ‘Probably adventitious, as we do noi 
know of it from north of the gulf.” (W. H. D.) 
Arca multicostata Sby. 
Single valve; Catalina Island. ‘‘Commonly found along the coast 
of Lower California.” (R. E. C. 8.) 
Genus AXINAGA Poli. 
Axinza intermedia Brod. 
One found in the bay. ‘‘ Very fine, highly colored specimen.” (W. 
H. D.) Miss Monks. 
Family NUCULID 2. 
Genus NUCULA Lam. 
Subgenus AcILA H. & A. Ads. 
Nucula (Acila) castrensis Hinds. 
Single valves (all fossil?) Dead Man’s Island. 
Family LEDID. 
Genus LEDA Schumacher. 
Leda celata Hds. 
Odd valves reported. 
Genus YOLDIA Morch. 
Yoldia Cooperi Gabb. 
Valves washed ashore in the beach drift. ‘May be identical with 
the fossil Y. impressa,” Conr. (J. G. C.) 
