1922] Miller: Variations in Teredo navalis in San Francisco Bay 313 



bay would be lighter, owing to the white prismatic layer showing 

 through the thinner epidermis. 



That coloration is, however, in considerable measure directly 

 dependent on immediate factors of environment, independent of the 

 thickness of the periostracum, becomes evident from certain types 

 of what we may term "accidental" coloration that have been occa- 

 sionally observed. 



In two different instances we have found that a nail driven into 

 a redwood timber below water line has produced an area of black 

 discoloration (ferric tannate) through the action on the iron of the 

 tannic acid in the wood. Teredos were working successfully in this 

 discolored area, but their bodies and shells were deeply stained with 

 blue (pi. 17, fig. 6). Teredos working elsewhere in the same piece of 

 wood were not so colored. 



In a number of instances we have found that the shells of T< rt do 

 left in stagnant water in our aquaria were colored almost entirely 

 black by the action of sulphur bacteria (pi. 17, fig. 5). This must 

 have been due to some physiological cause, as the shells of dead 

 teredos under the same circumstances were not discolored. 



SYSTEMATIC BEARING OF VARIATIONS 



The data presented in the foregoing pages appear to demonstrate 

 that certain variations occurring in the shell of Teredo navalis in San 

 Francisco Bay have a definite and causal relation to corresponding 

 ecological conditions. This inevitably suggests some discussion of 

 the systematic treatment to be accorded such environmental forms. 



The type of variate occurring in the upper bay has been described 

 by Bartsch (1921) as Teredo beachi, n. sp., San Pablo Bay being 

 designated as the type locality. The diagnostic characters which dis- 

 tinguish this form from the type of Teredo navalis are not definitely 

 stated. But we note in the description mention of "a strong posterior 

 auricle . . . umbones and a streak in the middle median portion . . . 

 rose colored . . . dental ridges . . . very strongly denticulated . . . 

 strong auricle . . . marked by rough lines of growth . . . center of the 

 median portion is marked by a roughened area . . . auricle is marked 

 by strong, curved lines of growth ..." etc. The emphasis on the 

 large auricle, color, strong denticulation, median roughened area, and 

 prominent lines of growth, as well as the type locality given, identify 



