7<i THE VOYAGE OF H.M.S. CHALLENGER. 



relied chiefly on the mode of branching for specific purposes. Iu order to avoid a need- 

 less multiplication of genera, I have adopted one uniform course in the systematic section 

 of this Eeport, in endeavouring to refer the various species to their respective genera. 

 This may be shortly stated as follows : — 



1. The species of which I have been enabled to examine the polyps have been referred 

 without query to their respective genera. 



2. A considerable number of species have been provisionally referred to one or other of 

 the genera now proposed. These include many species of which figures or descriptions 

 of the external appearance of the polyps have been given by Pourtales and others ; also 

 a number of species the polyps of which are not known, but in which the mode of 

 branching and type of spine appear to indicate an affinity to some better known form. 

 In such cases a query has been added after the generic name when necessary. 



3. Finally, a large number of species still remain which, in the absence of information 

 concerning the polyps, have not appeared to possess sufficient characters in common with 

 better known forms to justify their inclusion in any of the genera proposed. These have 

 all been included as species incertse sedis, but the section has been divided into two 

 parts. The first includes those which appear to be good species, and the second those 

 which are too imperfectly described for identification and the types of which I have not 

 seen. 



