THE WEST INDIAN FAUNA. 7 



cruise our collection of Pentacrini became very extensive ; we 

 found them at Montserrat, St. Vincent, Grenada, Guadeloupe, 

 and Barbados, in such numbers that on one occasion we brought 

 up no less than one hundred and twenty-four at a single haul 

 of the bar and tangles. We must indeed have swept over 

 actual forests of Pentacrini, crowded together much as they 

 may have lived, at certain localities, both in Europe and Amer- 

 ica, during the palaeozoic period. 



The monograph of Allman on the deep-sea hydroids of Flo- 

 rida gave us the first intimation of the wealth of forms which 

 flourished in deep water, forming, as Allman says, a special 

 province in the geographical distribution of the Hydroida. 

 The collection was noted for the large number of undescribed 

 species, and the small percentage which could be referred to 

 forms existing on the European side of the Atlantic. 



Previous to the deep-sea explorations we knew only the shal- 

 low-water reef corals. The expeditions of Pourtales, of the 

 " Hassler " and the " Blake," have revealed to us a whole fauna 

 of simple corals separated from the reef district by a barren 

 zone, with not a species in common between the two districts. 

 There are now over sixty simple deep-sea corals known from the 

 Caribbean district, nearly as many species as there are from 

 the reef area. 



It is natural that, as we pass from the littoral to the conti- 

 nental, and finally to the abyssal regions, we should find a grad- 

 ual diminution of those physical causes which we are accus- 

 tomed to consider as influencing the variation of individuals, 

 so that persistent types, as they have been called, may owe 

 their origin either to an absence of modifying causes, or to an 

 inherent tendency to retain unchanged their original organiza- 

 tion. The animals we dredge from deep water cannot, from 

 the nature of their surroundings, be affected, or only in a less 

 degree, in the many ways which influence their shallow-water 

 allies. We cannot suppose that they are subject at great depths 

 to any of the causes which affect so powerfully the changing 

 chromatophores of the littoral species ; such adaptations as 

 those which we find in the animals of the sargasso weed, 

 for instance, or the littoral algae, or those living on sandy or 



