INTRODUCTORY. 



3 



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 Sertvlarella Ga?/i, 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 

 Plumularidae 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 morpholog}'. 



Batht/metrical Distrihidmn. — 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: — 



Depths from which the species hare 

 beeu dredged. 



Between 200 and 250 fathoms. 

 " 250 " 300 



