294 University of California Publications in Zoology [Vol. 22 



INTRODUCTION 



In investigating the activity of Teredo navalis in San Francisco 

 Bay, it was early noted that this species presents locally a wide range 

 of variation, particularly in the outlines and sculpture of the shell. 

 At various points about the bay specimens were taken from time to 

 time which differed so considerably in these respects as to suggest 

 at least the possibility that they might represent distinct species. 

 But further collecting continually brought to light intermediate 

 forms, and, as these accumulated, they were found to link together 

 the aberrant types by a large series of almost insensible gradations, 

 so that there could no longer be any doubt that all were representa- 

 tives of a single species. This species was identified by Kofoid 

 (1921) as Teredo navalis Linn., and was shown in a later paper 

 (Kofoid and Miller, 1922) to be identical with that species from 

 European waters. 



The present study has been undertaken with a view to pointing 

 out the range of such variations under the conditions occurring in 

 San Francisco Bay, and, so far as possible, to correlate them with 

 certain known factors of environment. 



I am indebted to Professor C. A. Kofoid for invaluable direction 

 and advice during the progress of this work. I am further grateful 

 for the cooperation of the U. S. Lighthouse Service, the U. S. Navy 

 Yard at Mare Island, the Board of State Harbor Commissioners, the 

 Southern Pacific Railroad Company, the California and Hawaiian 

 Sugar Refining Corporation, and the various members of the San 

 Francisco Bay Marine Piling Committee, through whose assistance 

 more than two thousand shells have been made available for our 

 study. 



The material at hand has been carefully worked over as a whole 

 and certain selections with respect to age and locality have been 

 made. The present paper represents a detailed study of about 800 

 shells. 



