316 University of California Publications in Zoology [Vol. 22 



They serve to illustrate, however, the degree to which variations in 

 the shell of Teredo are immediately dependent on conditions of the 

 environment. 



The non-genetic nature of such variations is further indicated by 

 the fact noted above (p. 308) that, under certain conditions, rather 

 marked differences may occur between shells from near the upper 

 and lower ends of the same pile. 



Variation among the Mollusca in general is a conspicuous and 

 well-known phenomenon, which cannot but impress itself upon every 

 student of shells. A correlation of variation and environment has 

 furthermore long been recognized and commented upon by a number 

 of writers. As early as 1818 we find Burrow (p. 38) announcing 

 that "varieties are formed, usually, by adventitious circumstances." 

 Bateson (1889), Locard (1892), Clessin (1897), Davenport (1904), 

 Bartsch (1906), Geyer (1909), Pilsbry (1912), and others have 

 pointed out certain effects of the conditions of life on the characters 

 of molluscan shells. Detailed studies of variation among certain 

 groups with reference to environment have lately appeared, such as 

 those by Adams (1915), Grier (1919 and 1920), Ball (1922), and 

 Colton (1922). These writers are in general agreement that varia- 

 tions of a number of different types are definitely correlated with 

 station, and hence are the result, at least in considerable measure, 

 of the ecological conditions. 



In the case of intra-specific variation which proceeds along suf- 

 ficiently distinct and disjoined lines, and especially where the differ- 

 ences appear to be hereditary (Lang, 1906; Colton, 1922), there is 

 doubtless ample reason for the establishment of appropriate sub- 

 species. But variations such as those noted for Teredo navalis in 

 San Francisco Bay, which apparently represent the immediate im- 

 press of the environment on the individual, afford an extremely 

 precarious basis for the formation of new systematic groups. To 

 recognize beachi or other local environmental forms of such indefinite 

 claims is profitless to present investigators and can serve only to call 

 upon our heads the anathemas of future workers in this field. 



