"""iggay'l PROCEEDINGS OF THE NATIONAL MUSEUM. 455 



cies of Cuvierina, as also six of the fourteen species of Clio, couutiiig, 

 however, vh-yula from farther north; and lastly that from none of the 

 deeper water drcdjiiiij^s in the Pacitic are reported deposit shells, 

 although at times dredgings were there taken in the same region with 

 the surface collections which secured them; also that Limacina occur- 

 red only at considerable d<^i)ths botli alive and as deposit shells. 



From the work of the steamer lilalxe Alexander Agassiz concludes 

 that bottom distribution is largely determined by the course of the 

 ocean currents, so that by means of pelagic faunte and tlieir bottom 

 distribution, light may be throMai upon the course of tlie currents.* 

 To this cause he ascribes the presence of Arctic i^teropods along the 

 New England coast, from the course of the Labrador currents. In this 

 way also an ex]>lanation is found why surface collections of pteropods 

 may be abundant over deep waters while the bottom distribution must 

 be looked for elsewhere along the ocean current which sweeps the re- 

 gion; such doubtless is the case with regard to the surface collections 

 of the Albatross on this voyage in the Gulf of Panama and at the Gala- 

 pagos Islands. As has also been stated from the evidence of these 

 collections, forms of Clio are more abundant in the more northern sta- 

 tions than rejn'esentatives of CuroUniu. If therefoie we regard the 

 equatorial seas of the West Indian and Caribbean regions as offering 

 the most favorable conditions for the growth of these pelagic molluscs, 

 it may be readily seen that they would be largely distribnted from 

 these areas to the northward u])on the surface of the Gulf Stream; 

 while in the new conditions thus encountered the abundance of the 

 Cavolinia forms might succumb first, and that the species of Clio might 

 be enabled to hold their own longer in the struggle and so be carried 

 farther into the temperate waters of the Northern Atlantic. 



So also in the distribution of these molluscs south from these equa- 

 torial areas named, the P>razil current and the other currents running 

 southward along the coast of South America doubtless carry quantities 

 of pteropod shells far from the habitat of the animals when living be- 

 fore their final (le])osition u])on the bottoin; but the bottom accumula- 

 tions may at the same time be augmented by the shells of the same 

 species borne alive fipon the surface of the current until such conditions 

 were entered as to cause their wholesale destruction, pro<lucing a com- 

 paratively sudden precipitation, as it were, of some of the classes of 

 living organisms as soon as they are swept into the regions in question. 



At any rate from these or other (causes large deposits of pteropod 

 ooze were encountered by the Albatross in her course along the South 

 American waters. Such an ooze was discovered at station 27G0, the 

 study of which has some evidence for a distribution of the family 

 Caroliniidiv as heretofore outlined; that is to say, the accumulation of 

 mollusc shells upon the floor of the ocean is some evidence of the 

 relative kind and abundance of the molluscan life inhabiting the 



*Three cruises of the Blukt, by Alcxauder Agussiz. Vol. i, pp. 120-121. 



