INTRODUCTION. V 
!ind Crustacea, with the hauls in deep water, at special localities, made up 
entirely of thousands of specimens of single species, either of Ophiurans, 
of Echini, of Comatula^, of Crustaceans, or of Gorgonia^. 
Take again the bottom along the rid<j;es between the West India Islands, 
or along the coui'se of the Gulf Stream oft" the Carolinas, which are swept 
nearly clear of all animal life, and compare that to the rich and varied Fauna 
found at the same depths along the continental shelf j'arther north, and 
along the western shelf of the Windward Islands, on the lee side, in the 
Caribbean; or coinpare these Faunif in turn witli the mass of animal life, 
mainly composed of Gorgoniaj, of Calcareous and Horn\' Sponges, found 
upon the great plateau on the west of Florida and on the Yucatan Bank ; 
there can be no greater contrasts within the narrowlv circumscribed areas 
I have mentioned, all belonging to the West Indian Fauna taken as a 
whole. This clearly indicates great faunal contrasts in very limited areas, 
differing principally in the character of the bottom, and where the physical 
conditions, such as temperature, depending mainlj- upon currents and winds, 
are in striking opposition within comparatively moderate distances. 
ALEXANDER AGASSIZ. 
Cambridge, Mass., September 1, 1883. 
