PRESIDENTIAL ADDRESS. 15 



certain proportion of Archibenthal species in any given area, 

 identical with or closely related to the analogous Literal region 

 forms of the adjacent shores. 



In the Abyssal region alone should we expect to find that 

 any considerable proportion of the fauna has lost all its litoral 

 characteristics, assumed characters in keeping with its environ 

 ment and become disseminated over the ocean bottom through 

 out a large part of its extent. These expectations in the main 

 are fairly satisfied by the facts as far as the latter are positively 

 ascertained. 



With the lesser need of protection from enemies and competi 

 tors would necessarily be related a less rigorous elimination of 

 characters which in struggle and competition might prove 

 sources of weakness. The limits of uninjurious variation 

 would be relaxed at the same time and to the same extent. 

 We find as we should expect that the deep sea mollusks are 

 more variable in their ornamentation and other superficial 

 characters than those from shallow water. In some species the 

 balance of characters is fairly well maintained ; in others vari 

 ation runs riot, and it is impossible to say what amount of it 

 should constitute a basis for specific subdivisions among indi 

 viduals. 



In general deep sea shells present pale or delicately tinted 

 color patterns, are white, or owe their color to the tinting of 

 the epidermis. This may be due directly to the absence of 

 light. Sunlight, when present, seems to have a stimulating 

 effect in developing colors as is shown by the greater bright 

 ness of tropical litoral shells whatever their colors. It ope 

 rates indirectly by promoting the development of color in algae 

 which are fed upon by phytophagous mollusks, and affect the 

 coloration of the latter directly through the assimilation of the 

 coloring matter of the food, mechanically. 



