— 4 — 



Some idea of the economic importance of the California mollusks may 

 be gathered from the amounts marketed during the past four years, 

 according to statistics gathered by the Fish and Game Commission: 



♦Estimated. The return for "mixed clams" was divided between tlie Washington 

 clam and the soft-shell in the proportion of two to one. The statistics of the native 

 and Eastern oyster are omitted as they are reported by number, not weight. 



To these must be added the clams used locally by residents and 

 campers, a quantity not possible to estimate accurately but which 

 would nearly double the yield of certain species and includes a number 

 of forms not listed above. 



The present paper is a result of tlic policy of the Fish and Game 

 Commission to investigate the marine resources of California In 

 1910 jMr. Will F. Thompson traversed the entire coast north of San 

 Francisco and made a careful survey of this region. In 1916 Dr. Har- 

 old Heath of Stanford University made an examination of the Cali- 

 fornia coast south of San Francisco. In 1916 Mr. Carl L. Hubbs, now 

 of the University of INIichigan, Ann Arbor, IMichigan, collected in the 

 same region. In the spring of 1919 the writer made a survey of the 

 southern part of the state, particularly tliat portion from San Pedro 

 south, which had not previously received much attention, and in the 

 fall of the same year reexamined San Francisco and Humboldt Bays). 

 The present paper represents the data collected by all these workers 

 and has been put in its present form by the writer with the advice and 

 assistance of Mr. Thompson. For the plates, key and the general 

 discussion of distribution the writer is responsible. Locality records 

 where resting on the authority of a single observer are initialed, other- 

 wise they are to be considered as matters of general knowledge or are 

 the observation of the present writer. To various deputies of the Fish 

 and Game Commission and to many clam diggers the writer wishes to 

 acknowledge his indebtedness for iniiform conrtesy in furnishing 

 information and material. Thanks are due IMrs. Oldroyd of Stanford 

 University for the opportunity of examining her collection and for 

 material. The work has been done partly at the State Fisheries 

 Laboratory at Long Beach and partly at the Hopkins Marine Station 

 of Stanford University at Pacific Grove ; to Dr. W. K. Fisher, Director 

 of the latter institution, the writer wishes to express his appreciation 

 of the facilities extended. Acknowledgment is here made to Alice 

 Jenkins Weymouth for assistance in the preparation and revision of 

 the manuscript of the present paper. 



