164 Natural History Bulleiin. 



of being stout and strong. This is probably a reminiscence 

 of the time when their distant progenitors were shallow water 

 animals." ^ 



The opinion seems quite general among those who have 

 studied the animal life of the deep sea, that it has been peo- 

 pled in a general way by a gradual invasion of forms which, 

 originally adapted to the conditions of littoral surroundings, 

 have encroached more and more upon the unoccupied terri- 

 tory in deeper water, where they were, for a time at least, 

 free from the tierce competition to which shallow water forms 

 are subjected. We can account, on this principle, for the 

 ornamentation of the deep-water Mollusca by regarding it as 

 merelv the remnant of more conspicuous characters which 

 have been of use to the ancestors of these forms before they 

 retreated from the shallow water, where the structures form- 

 ing the ornamentation were of use either as protective con- 

 trivances or as a means to attract the opposite sex. 



The broken shell of an Argoiiania {^ir^vf) was all that we 

 obtained during the cruise to represent these exquisitely deli- 

 cate and beautiful animals. Indeed, it was the onl}- Cephalo- 

 pod found on the Pourtales Plateau. The whole great group 

 of Pteropods is also unrepresented in our collections, although 

 we had expected surely to encounter some of them in this 

 region. 



Great numbers of Crinoids were collected here, but the 

 species were comparatively few. The two common West 

 Indian genera were represented, but none of the rarer forms 

 were obtained. We especially regretted our failure to secure 

 specimens of Rliizocriiius, a genus which is represented by 

 abundant individuals in certain deiinite spots on the Pourtales 

 Plateau. 



That there are portions of the sea bottom covered with as 



dense a growth of crinoids as any that flourished in Paleozoic 



seas, has been proved more than once bv recent deep-sea 



explorations. We had ample demonstration of this fact on 



.several occasions, notably when the tai]gles came up after a 



' 15ulletiii Mus. Comp. Zoiil., N'ol. XII, No. 6, ]iage 1S4. 



