1922] Miller: Variations in Teredo naval is in San Francisco Bay 307 



With the foregoing facts in mind, we naturally infer that the 

 combination of conditions occurring in the upper bay tends to pro- 

 duce certain changes in the physiological cycle of ridge deposition, 

 the net result of which is a lesser number of ridges per unit area 

 of the shell than we find to be the case under the conditions prevail- 

 ing in the middle and the lower bay. This corresponds with the 



Mean Mode 

 Crockett - 14. 5 14 

 Dumbarton- 15. 4 14 

 Goat Is. - 16. 6 15 



Pig. D. Curves showing number of ridges per millimeter on the shell of Teredo 

 from three different stations. 



results of tables 1 and 2, which indicate a fewer number of ridges 

 per unit of time for shells from the upper bay. That is, in the Car- 

 quinez Straits region, Teredo deposits ridges farther apart and at 

 wider intervals of time than at stations down the bay. 



A further note of interest on the effect ou Teredo of lowered 

 salinity and fluctuating temperature is the difference to be observed 

 between shells at different levels of the same pile in the upper bay. 



