84 Umversity of California Publications in Zoology [ Vou. 14 
Two stations in the central division of the bay, near the Golden 
Gate and near Goat Island, respectively, were likewise visited on March 
6, 1914, at both the flood and the ebb tides (H. 5358, 5359, 5364, 5365). 
The mean figure for the four surface samples here taken was 13.08, 
that for the four bottom samples being 30.18. Since no earlier samples 
had been obtained at these stations, for the same time of the year, it is 
impossible to make comparisons. 
It is thus plain that the salinity figures which we have earlier 
recorded, for the spring months at least, do not fairly represent the 
condition of San Francisco Bay after a season of high rainfall, and 
they are doubtless considerably higher than would have been obtained 
after a season of even average precipitation. 
The two series of shoal water stations across the upper and lower 
portions of the bay, in July, 1913 (see p. 47), gave results which are 
perhaps not wholly comparable. The three hydrographic stations 
5348 to 5350, in the shoal waters of the southern arm of the bay, gave 
a mean salinity (surface and bottom) of 27.57, while four samples, 
taken at practically the same time at station 5001, in the main channel, 
gave a mean salinity of 27.83. These differences may have no special 
significance. 
A much greater difference was found in San Pablo Bay. where the 
mean salinity (surface and bottom) of five stations, extending through 
its region of greatest breadth, was 22.67 during the flood tide, while 
that of eight samples taken at station 5330 (= 4981) during the same 
period, was 27.86. This is not quite a fair comparison, however, since 
the last-named station was situated at the lower end of San Pablo 
Bay, while the line of shoal-water stations crossed the latter at a 
distance of some miles to the north. But even when due allowance 
is made for the difference in the stage of the tide, the lower salinity 
of the shoal water area is still sufficiently striking. It is doubtless 
due to the fresh water discharged by certain estuaries. 
Owing to the courtesy of the Morgan Oyster Company, we are 
able to present salinity figures for two of that company’s principal 
beds, based upon samples collected throughout a considerable part 
of one year. The results of these titrations are presented in table 
22. For the months of March, April, May and June, each figure 
civen is the mean derived from four samples taken at two-weeks’ 
intervals, and at both high and low-water. The remaining figures 
are based upon only two titrations each, with the exception of one, 
which is based upon ten. 
