DEEP SEA MOLLUSKS AND THE CONDITIONS 

 UNDER WHICH THEY EXIST.* 



By William Healey Dall. 



I propose on the present occasion to lay before you a state- 

 ment of the conditions which characterize the life of Mollusks 

 in the Deep Sea, so far as they are known to us, and to discuss 

 briefly the effect of these conditions upon the animals subjected 

 to them; the contrast which their life presents to that of shallow- 

 water mollusks ; the peculiarities preserved or the modifications 

 induced by the special environment ; together with some notes 

 on interesting or remarkable forms discovered in deep water. 



Once for all, it must be understood that exploration of the 

 deep sea fauna has only begun ; that the area swept by the 

 trawl and dredge compared with that which remains unknown, 

 is almost infinitesimal ; and, of the material secured by 

 dredging, a large portion is fragmentary and imperfect. In 

 short what we know about the deep-sea mollusks can only be 

 regarded as a foretaste of that knowledge which future years 

 may be expected to supply. 



In an address of this sort bibliographical references would be 

 out of place. I will only say that the literature of the subject is 

 almost wholly confined to the publications of the last twenty 

 3'ears, and consists in large part of the reports by various spec- 



* Annual Presidential Address delivered at the Ninth Anniversary 

 Meetiug of the Biological Society, November 16, 1889, in the law lecture 

 room of the Columbian University. 



