THE WEST INDIAN FAUNA. 11 
stations occupied during one season's work. Nearly all of them 
were in comparatively shallow water, ¿. e. in depths of less than 
two hundred fethoms. On three occasions the depth exceeded _ 
three hundred fathoms. 
These facts agree well with the results of the * Challenger ” 
dredgings, which yielded Comatule 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 erinoids 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 débris 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 óozy 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- 
bellule. 
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. 
