1NTR0D1 CTION. \ 



and Crustacea, with the hauls in deep water, al special localities, made up 

 entirely of thousands of specimens of single species, either of Ophiurans, 

 of Echini, of ComatuUe, of Crustaceans, or of Gorgoniae. 



Take again the bottom along the ridges between the West India Islands, 

 or along the course of the Gulf Stream off the Carolinas, which are swepl 

 urarh clear of all animal life, and compare thai to the rich ami varied Fauna 

 found at the same depths along the continental shelf farther north, and 

 along the western shelf of the Windward Islam!-, on the lee side, in the 

 Caribbean; or compare these Fauna' in turn with the mass ol animal life, 

 mainly composed of GorgoniaB, of Calcareous and Horn} Sponges, 

 upon the great plateau on the west of Florida and on the Yucatan Bank; 

 there can be no greater contrasts within the narrowly circumscribed areas 

 I have mentioned, all belonging to the West Indian Fauna taken as a 

 whole. This clearly indicates great faunal contrast- in very limited areas 

 differing principally in the character of the bottom, and where the physical 

 conditions, such a- temperature, depending mainly upon currents and winds, 

 are in .striking opposition within comparatively moderate distances. 



ALEXANDEB AGASSIZ. 



Cambridge, Mass., September 1. 1SS3. 



