1 1 6 Proceedings of the Royal Irish Academy. 



regard to the spicules of this group, we also made the following observation : — 

 " Distinctions based on spicules alone are very unsatisfactory in this group 

 (Gorgonella and Verrucella), because the spieulation varies at different levels ; 

 and transition forms are so numerous and varied that it is sometimes almost 

 impossible to distinguish between double-spheres, double-stars, and double- 

 clubs, each in turn passing gradually to double-spindles. In Verrucella . . . 

 there are double-stars ; in Gorgonella . . . double-spheres occur." 



As I have elsewhere pointed out, I doubt very much the validity of 

 these two genera, on the present spicular distinction, but await a revision of 

 the known species for a solution of the difficulty. 



(b) Classification of tlie Species with emended Diagnoses. 

 On this basis four species may be recognized, and are included in this 

 report. These are : — 



iV. dichotoraa Gray. 



N. flahellata (Whitelegge). 



N. reticulata Thomson and Simpson. 



N. monUifwme (Wright and Studer). 



The following short specific diagnoses may prove useful : — 



Nicella fiMbellata. 



The colony is branched in one plane ; the smaller branches tend to arise 

 from one side of the larger. The coeuenehyma is moderately thin, and often 

 presents a ridged appearance due to segregations of spicules. The polyps are 

 disposed in two longitudinal series; in the younger part they occur in a 

 sinuous row on either side of the branch ; but in the older portions they are 

 more numerous and may encroach slightly on the median bare spaces. The 

 venucae vary in shape and size according to the stage of retraction ; when 

 expanded they are prominent, and show an eight-i"ayed figure at the summit ; 

 when retracted they appear as low conical warts, and there is no trace of an 

 octo-radiate structure. The axis is composed of concentric laminae ; and the 

 surface is marked by longitudinal striae. 



The spicules consist of (1) small double-clubs, {2} small double-wheels, 

 (3) elongated double-clubs, (4) long, massive, bluntly terminating double- 

 spindles, (5) long, slender simple-spindles. (See fig. 115.) 



Nicella reticulata. 



Colony branched in one plane, with abundant anastomosis ; ilie branches 

 and twigs are \ery slender, so that the colony is extremely reticulate and 

 fiabelliform. The coenenchyma is thin and finely granular. The polyps are 



