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. 8. ‘‘ Albatross”’ 
at forty-three stations within San Francisco Bay. 
Twenty-three species of Peleeypoda 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 mollusean fauna. 
The middle division of the bay is a more favorable habitat for the 
Mollusea 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 thari 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. . 
