70 University of California Publications in Zoology [ Vou. 14 
The range is, as might have been expected, least near the Golden 
Gate, where it is less than 4 per mille, and it does not rise much 
higher than this throughout the lower portion of the bay. Another 
region showing a comparatively slight annual range of salinity was 
found at Carquinez Strait. The reason for this is not evident. 
Ss 1 ae 
Feb. Mor. Apr May Jun. Jul Aug. Sept. Oct. Nov. Dec. van. 
Fig. O. Annual salinity curves for entire bay. The continuous line is 
based on surface figures, the broken line upon bottom ones. 
Figure O shows the mean salinity of the bay as a whole through- 
out the annual cycle. Separate curves have here been plotted for the 
surface and bottom water. The time of minimum salinity during our 
observations occurred in the second period (April-May), the curves 
rising to a maximum in the fourth period (October). The effects of 
the rainy and dry seasons are obvious in a general way. These rela- 
tions will be discussed more fully below. 
The relations between the curves for surface and bottom salinity 
offer some features of interest. The distance between the two is 
greatest during the period of lowest salinity, 1.e., at the time when 
the largest amount of fresh water enters the bay. On the other hand, 
this difference is least during the period of highest salinity, in 
October. These conditions, like many others which we have observed, 
might well have been predicted in advance. 
A relation the reason for which is less obvious is shown in figure P, 
representing annual salinity curves based upon the ebb and flood 
observations respectively. It is, on first thought, surprising to find 
the mean salinities for the flood tide to be lower than those for the 
ebb in five out of six of the periods of observation. The mean figures 
for the year as a whole, as will be seen by reference to Table 18, are: 
