1918] Packard: Quantitative Analysis of Molluscan Fauna 331 



SUMMARY 



The orange-peel bucket dredge, used for the first time for purposes 

 of biological investigation, has been employed by U. S. S. "Albatross" 

 at forty-three stations within San Francisco Bay. 



Twenty-three species of Pelecypoda and twelve of Gastropoda were 

 taken by means of this dredge. The ten species that were taken at 

 more than one-fourth of the hauls represent the most adaptable forms 

 of the molluscan fauna. 



The middle division of the bay is a more favorable habitat for the 

 Mollusca than either of the other two divisions. 



Depth has little significance in determining the distribution of the 

 local forms. 



The character of the bottom is an important distributional factor. 

 The most favorable bottom appears to be composed of sand and shells, 

 the shells serving as supports for sessile forms. 



A low salt concentration or a large annual range of salinity appear 

 to be unfavorable to an abundant local molluscan life. 



The regions in which the annual range of temperature is not great 

 nor the maximum high during July and October support the larger 

 number of mollusks per unit area. Nevertheless the significance of 

 the temperature factor is obscure. 



Several species of edible clams live within San Francisco Bay. 

 Of these, Mya arenaria is most important. The present production of 

 the bay is probably considerably less than it was a decade ago. The 

 bay, under the improved methods of farming, would support an an- 

 nual yield of more than four billion bushels of this clam. Such an 

 industry should be established only after a detailed survey has been 

 made and many of the outstanding problems solved. Laws should 

 also be enacted which give private control to certain tracts suitable 

 to clam farming. 



