1922] Miller: Variations in Teredo navalis in San Francisco Bay 317 



SUMMARY 



1. A study of the growth of the shell of Teredo navalis in San 

 Francisco Bay indicates that 8 or 9 cutting ridges are normally 

 deposited during the first month of boring life, and 2 to 4 ridges per 

 month thereafter. The rate of deposition of ridges tends to be lower 

 in the less saline waters. Also, growth may be hindered or stopped 

 as a result of crowding. 



2. Teredo navalis, as occurring in San Francisco Bay, exhibits 

 an extremely wide range of variation, involving practically every 

 feature of the shell. The more salient of these variations — number 

 of ridges per unit area of the shell, size of the auricle, prominence 

 of the denticles, thickness of the periostracum, and amount of color 

 present — have been found to be definitely correlated with factors of 

 the environment, especially salinity and temperature. 



3. The general trend of evidence is that these variations owe their 

 origin immediately to environmental conditions, and are not inherited. 



4. The local variates of Teredo navalis in San Francisco Bay, 

 including oeachi Bartsch, have not been found sufficiently well differ- 

 entiated from each other to warrant their being classified as sub- 

 species. Much less justification exists for assigning to any one of 

 them a specific rank. 



Zoological Laboratory, 



University of California. 



Transmitted July SI, 1922. 



