

SCIENTIFIC RESULTS OF EXPLORATIONS BY THE U. S. FISH 

 COMMISSION STEAMER ALBATROSS. 



[Published by permission of lion. Marshall McDonald, Commissioner of Fisheries.] 



No. VII.— PRELIMINARY REPORT ON THE COLLECTION OF MOLLUSCA 

 AND BRACHIOPODA OBTAINED IN 1887-'S8. 



BY 



William Healev Dall, A. M.. 



Curator of the Department of Mollusks. 

 (With Plates V to XIV.) 



Before proceeding to discuss the particular specimens obtained on the 

 voyage of the U. S. Fish Commission steamer Albatross from Fortress 

 Monroe in Chesapeake Bay to Magellan Straits and northward to Cal- 

 ifornia, it may not be improper to say a few words on the conditions 

 under which the deep-sea Mollusks exist, and the reasons why a study 

 of these animals is important for science. 



In order that their existence may be maintained, the abyssal mollusks 

 require oxygen to aerate their circulation, food to eat, and a foot-hold 

 upon which they may establish themselves. It is necessary that the 

 conditions should be such as will not prevent the development of the 

 eggs by which successive generations are propagated. That they do 

 permit it may be assumed from the very fact that mollusks in large 

 uumbers have been shown beyond all question to exist on the oceanic 

 floor wherever it has been explored. 



Formerly, when dredging with the usual appliances in small boats, 

 100 fathoms (GOO feet) was considered extremely deep. If one stauds 

 at the foot of the great Washington obelisk and looks up, the idea of 

 collecting a satisfactory representation of the insects and plants on the 

 ground at its base by dragging a 0-foot trawl or dredge by a line let 

 down from the apex of the monument strikes one as preposterous. Yet 

 the monumeut is less than 100 fathoms high. Multiply this height ten 

 or fifteen times aud the idea seems, if possible, still more unreasonable; 

 yet it is a fact that successful dredging has been done from a height 

 above the sea bottom of not less than twenty-five times the height of 

 the Washington Monument. Living animals have been secured from a 

 depth equalling the distance from the Capitol to Rock Creek, or from 

 the Washington Monument to the Mansion at Arlington — that is to say, 

 about 2i miles. 



219 



Proceedings of the National Museum Vol. XII— No. 773. 



