36 University of California Publications in Zoology [Vol. 18 



may have been so frequently repeated during the later months of the 

 flood season as the discharge of fresh water reached its height as to 

 have presented salinity conditions during a considerable portion of 

 the year which would be inimical to the life of Teredo. 



Temperature Conditions in San Pciblo Bay. — Since the temperature 

 may in a general way be of influence in determining the rate of 

 activity of these borers, the following table is appended of temper- 

 atures taken at the same stations and at the same times as the obser- 

 vations for salinity. It is not presumable, however, that a difference 

 in temperature of less than a degree between the temperature at the 

 surface and at the bottom at these stations should be sufficient to cause 

 so marked a difference in the activity of the borers as has been noted. 

 A difference of average annual temperature amounting to 5° C or 

 more between this general region and some other region may, however, 

 be sufficient to cause a marked difference in the activity of marine 

 borers even if the same species of borer be present in both cases. 



TEMPERATUEE OF SELECTED STATIONS TN SAN PABLO BAY 

 In Degrees Centigrade 



Av. for entire year, 13.15 13.14 .... 13.04 13.08 .... 13.34 13.23 .11 



Rel.vtion of Teredo to Salinity 



It remains now to determine as closely as possible from these data, 

 so fortunately available, approximately the conditions of salinity which 

 seem to be required by this species of Teredo. 



The lowest surface salinity observed at any of these stations during 

 1912 and 1913 was 9.08 parts per 1000 and the lowest bottom salinity 

 was 10.89, both observations occurring during the period April 23- 

 May 6 in the season of maximum discharge of fresh water for that 

 year. While we do not have the actual observations upon the salinity 

 at these stations for the full year 1913, it is presumable, since the total 

 discharge of fresh water was about the same for both years, 1912 and 

 1913, that the salinity could not have fallen much lower at any time 



