INTRODUCTORY. 33 
It is thus obvious that the region from which the present collection has 
been obtained, and which includes an area between the Florida Reef on 
the north and west, and Cuba, the Salt Key, and Bahama Banks on the 
south and east, is characterized by a very distinct hydroid fauna, and must 
form part of a special province in the geographical distribution of the 
Hydroida. How far the same forms will be found to extend beyond the 
limits of the exploration must remain for future researches to decide. 
The European species which was met with in greatest abundance over 
this area is the Sertularella Gayi, which occurred chiefly in the condition of 
the strong irregularly branched variety already referred to. It was among 
the most widely distributed species of the area, and was obtained from no 
less than nineteen different dredgings. 
Among the specimens of Gymnoblastea the gonosome is present in a 
considerable proportion of species. So also a large proportion of the 
Plumularidx is provided with the gonosome, and presents some interest- 
ing and beautiful modifications of this part of the hydroid colony. From 
the other Calyptoblastic forms, however, the gonosome is in almost every 
instance absent. The very rare cases in which it is present are from some 
of the deepest dredgings made. 
Among the new species are many which must be regarded as representa- 
tives of new generic groups. Indeed, throughout the whole collection we 
meet with features many of which are of great interest and significance in 
their general bearing on hydroid morphology. 
Bathymetrical Distribution. — With very few exceptions a careful record had 
been kept of the depths from which the specimens had been dredged. 
These depths varied from that of quite shallow water to four hundred and 
seventy-one fathoms. The following table will show at a glance the relative 
richness in hydroid life of the various depths explored: — 
Species whose Species whose 
depths have Depths from which the species have depths have Depths from which the species have 
been recorded. been dredged. been recorded. been dredged. 
10 Between 1 and 10 fathoms. 0 Between 200 and 250 fathoms. 
2 “ 10 “ 95 oo 6 “ 950 “ 300 “ 
5 “ 20 “ 50 “ 2 “ 300 “ 350 “ 
13 oe 50 “ 100 ce 0 o 350 “ 400 s 
10 Bs 100 “ 150 ce i oe 400 “ 450 U3 
6 cS 150 “ 200 ee 2 Us 450 “ 500 re 
