THE WEST INDIAN FAUNA. 11 



stations occupied during one season's work. Nearly all of them 

 were in comparatively shallow water, i. e. in depths of* less than 

 two hundred fathoms. On three occasions the depth exceeded 

 three hundred fathoms. 



These facts agree well with the results of the " Challenger " 

 dredgings, which yielded Comatuhe at twenty stations only 

 where the depth was more than two hundred fathoms. One 

 may fairly conclude, therefore, that these animals are essentially 

 inhabitants of shallow water. The crinoids form a striking 

 exception to the rule, which holds good among many of the 

 other groups, that the more ancient types also have a wide 

 range in depth. 



The bathymetrical distribution of the corals is such that we 

 can readily separate the species found in depths of less than one 

 hundred fathoms, where they live in the region of debris which 

 lies between the reefs and the rocky or muddy bottoms. But 

 here again there is no sharp line of demarcation in the distribu- 

 tion between the continental and the deeper zones, though the 

 abyssal regions contain a comparatively smaller number of spe- 

 cies than the continental slope. They flourish upon the continen- 

 tal slope only on sea bottoms which are free from accumulating 

 silt, and remote from flat muddy shores and from the influence 

 of great rivers ; the branching types prefer a rocky or stony 

 bottom, while the simple types thrive on shelly or oozy bottom. 

 It is on this slope that we also meet with the greatest number 

 of novelties among the gorgonians and pennatulids, while spe- 

 cially characteristic of the deeper regions is the family of Um- 

 bellulae. 



The calcareous and horny sponges, of which our commercial 

 sponge is a good representative, are eminently littoral forms. 

 Beyond that depth the bright-colored sponges are replaced by 

 the hosts of siliceous sponges which live buried in the mud, some 

 of them anchored by their bundles of gigantic spicules deep in 

 the ooze, which also envelops them in a thick coating of fine 

 mud so closely held by the network of the skeleton that care- 

 ful preparation alone brings out the wonderful beauty of their 

 structure. An Euplectella when first brought up looks like a 

 mere mud-lined cylinder, and gives no idea of the exquisite tra- 

 cery formed by the siliceous skeleton. 



