30-1 University of California Publications in Zoology [Vol.22 



records show a mean salinity of from 28.47 to 29.14 at eight different 

 stations south of Goat Island, the lowest figure recorded during a 

 one-year period being 24.85 as compared with a maximum of 31.36 

 at the same station. For a very large stretch of water at the southern 

 end of the bay no salinity records are available, but we are fairly 

 safe in assuming that they would be consistent with the above figures, 

 with possibly a slight increase in the mean during the summer, owing 

 to the effect of evaporation 1 (Sumner, et al., 1914, p. 85), and the 

 opposite effect of seepage during and after the maximum run-off. 



The temperature range is notably greater here than in the middle 

 bay, owing largely to the influence of air temperatures on so large 

 an expanse of relative!}' shallow water ; but less, on the other hand, 

 than in the upper bay, whose temperatures depend in considerable 

 measure on those of the rivers tributary to it. 



Temperature ranges in the three divisions of the bay can best be 

 compared by reference to text figure C, where they are graphically 

 represented. 



Depth is a factor which we have usually not taken into account ; 

 this will be briefly discussed farther on. The effect of sewage (oxygen 

 content) has also been disregarded, owing to the difficulty of obtain- 

 ing quantitative data; in this connection it is to be remembered 

 further that the greatest sewage contamination occurs in the middle 

 bay, where volume of water and tidal action are greatest, both tending 

 to counteract the effect of sewage; if contamination of this sort has 

 any influence on Teredo, such influence probably occurs only actually 

 at or near the mouths of sewers. 



In order that any effect of environment in producing variation 

 might be observed in its maximal expression, we selected for this 



1 A few water samples taken at scattered intervals at Dumbarton by the writer 

 suggest that salinities at this point are not so high as Sumner (loc. cit.) has sup- 

 posed. Below are tabulated our findings, together with salinities on or near the 

 same dates at Tiburon, in the middle bay. It will be seen that the figures for the 

 latter station are notably higher, even though Tiburon is not a locality of maximal 

 salinities in this sector of the bay. 



Comparison of Surface Salinities at Dumbarton and Tiburon during the 

 Summer of 1922 



The samples at Dumbarton were taken in the main channel, where the depth 

 is about 50 feet, and the tidal flow very great. It does not appear that evapora- 

 tion has had any appreciable effect in increasing salinities in this region during 

 the period in question, unless it be in very shallow slack water along the shores. 



