314 University of California Publications in Zoology [Vol. 22 



this teredo as the environmental form which we have considered 

 typical of the upper bay. The wide variation we have described in 

 these characters obviously precludes such variants from specific rank. 

 The question remains as to whether oeachi should be retained as a 

 subspecies, or included in the synonomy of navalis. In case of the 

 former alternative, a subspecies would have likewise to be established 

 for the form from the lower bay and perhaps, also, as further study 

 might show, for each of several intermediate environmental forms 

 at other localities, the Goat Island form being considered typical. It 

 might even be necessary in some cases to establish subspecies for 

 teredos from the top and the bottom of the same pile. 



It will be recalled that the localities from which shells were taken 

 for this study were chosen as representing the extremes of environ- 

 ment in which Teredo occurs in San Francisco Bay. And in attempt- 

 ing to establish the effect of environmental conditions in producing 

 variation, we have naturally and legitimately emphasized the differ- 

 ences rather than the similarities observed among specimens from the 

 localities in question. We would call attention to the fact that, while 

 the extreme differences are rather marked, the mean differences 

 among shells even from these specially selected localities are com- 

 paratively slight. In many, indeed, in most, cases it is impossible 

 to take an isolated unmarked shell and declare from what locality it 

 has come. By referring again to figure D it will be seen that shells 

 having from 13 to 18 ridges per millimeter might come from any of 

 the three localities considered, the curves overlapping to this extent. 

 Prom figure P it is evident that the index of the auricle may range 

 from 30 to 70 without indicating the locality from which a shell has 

 come. A similar statement may be made regarding the other points 

 of difference noted among these three environmental races. It is only 

 in the case of the extreme variates that a locality diagnosis can be 

 made on the basis of intrinsic characters of the shell. 



Furthermore, as we depart from the extremes of environment, 

 the differences mentioned appear to become more and more obscure, 

 until they are entirely lost, the various races merging with each other 

 at intermediate points. Sufficient material is not available adequately 

 to illustrate this, but a few specimens are at hand from stations 

 between Crockett and Goat Island which indicate at least the trend 

 to such coalescence. From Oleum (see map) we find in 25 shells a 

 variation of from 14 to 20 ridges per millimeter on the anterior 

 median, and a range of from 28 to 67 in the index of the auricle, 



