244 University of California Publications in Zoology (Vou. 14 
The quantitative work by Rankin and Kofoid indicate that the 
plankton of the bay is everywhere rich enough to supply the mollusk 
with the requisite amount of food. 
The conclusions of the quantitative work parallel in the main 
those derived from the less accurate qualitative work; the differences 
in results are generally to be accounted for on the basis of the differ- 
ences of procedure followed in the two cases. 
SUMMARY 
San Francisco Bay receives the discharge of the Sacramento and 
San Joaquin rivers. This affects the salinity, temperature, and the 
bottom conditions prevailing within those waters. These factors have 
elsewhere been shown to vary considerably within the bay, producing 
a number of environments. Only the more important physical factors 
have been considered in this paper. 
The molluscan fauna taken by the Survey comprises 112 species 
and 3 varieties. This number equals but 65 per cent of the reported 
fauna from San Francisco and immediate vicinity. 
The fauna obtained in the open ocean off San Francisco comprises 
64 determined species, of which 30 are pelecypods, 32 gastropods, and 
2 scaphopods. : 
A consideration of the average number of species per station in- 
dicates that the waters of the open ocean are more favorable to a 
varied mollusean life than those of the bay. The average number of 
individuals represented by living specimens per station is more than 
three times as great in the group of stations in the former region as 
it is within the upper division of San Francisco Bay. 
‘The fauna obtained by the Survey within San Francisco Bay 
comprises 81 species and varieties, of which 43 are pelecypods, 31 
gastropods, and 7 chitons. Fifty-nine per cent of this fauna was taken 
exclusively within those waters. 
Since 76 species of the entire fauna obtained by the ‘‘ Albatross’’ 
are predominately northward ranging, whereas only 53 are predomi- 
nately southward ranging, the San Franciscan fauna appears to be 
more closely related to the northern one. 
Two new mollusean species that were taken by the Survey have 
been described by Dr. Bartsch (Odostomia franciscana Bartsch and 
Turbonilla franciscana Bartsch). Two heretofore unreported exotic 
species were obtained by the ‘‘ Albatross.”’ 
