214 University of California Publications in Zoology | Vou. 14 
undoubtedly varies somewhat within the different regions of the bay. 
Recent studies made by Mr. E. P. Rankin show that the number of 
species and individuals of diatoms decreases as one passes from the 
middle to the upper division of the bay. If these data were plotted, 
relationships of some of the bivalves to distribution might be expected, 
unless everywhere within the bay the plankton is present in quantities 
above the requirements of the mollusks. The latter is likely to be 
the case, since Professor Kofoid’s studies show that the plankton of 
the bay is relatively rich. 
For the predatory gastropods the optimum habitat is, of course, 
determined by the presence of their. prey. Thus the distribution pat- 
terns of Urosalpinx and Ilyanassa are similar to those of the native 
and eastern oysters. 
THE OPEN OCEAN 
The investigations of the ‘‘ Albatross’’ outside the Golden Gate were 
confined, during this Survey, to the waters lying between the San 
Francisco Peninsula and the Farallon Islands, with the exception of 
a single bottom sample taken west of the Farallones. Excepting this 
latter locality, the water ranged in depth from 81% to 68 fathoms. 
Just outside the Golden Gate is a shoal, known as the ‘‘Bar,’’ upon 
which depths of only 5 fathoms are encountered at a distance of five 
miles offshore. 
The annual mean temperature for the ocean off San Francisco is 
given by Sumner et al. (1914, p. 52) as 12°86C. The.range for the 
years is about 3°C, the lowest temperatures occurring in April and 
the highest in October. The mean annual salinity for the offshore 
stations is 34.04 per mille. 
No attempt has been made to make a detailed investigation of the 
character of the offshore bottom. The field descriptions of the samples 
obtained from each dredge haul indicate that the bottom is predomi- 
nantly of a dark greenish sand. 
GENERAL CHARACTER OF THE FAUNA 
The mollusean fauna taken by the Biological Survey within San 
Francisco Bay and adjacent waters comprises 112 species and 2 
varieties. These are distributed among 3 classes representing 49 
families and 78 genera. A little over 50 per cent are bivalves. The 
gastropods are represented by 47 species and 1 variety, the seapho- 
pods by 2 species, and the chitons by 6 species and 1 variety. 
