362 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 spiculation varies at different levels ; 

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

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

 clubs, each in turn passing gradually to double-spindles. In A^crrucella . . . 

 there are double-stare ; in Goi-gonella . . . double-spheres occur." 



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

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

 the known species for a solution of tlie ditticulty. 



(b) Chssifimtion of the Specks jcith emended Diagnoses. 



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

 report. These are: — 



N. dichotoma Gray. 



N. Jlahellata (Whitelegge). 



N, reticulata Thomson and Simpson. 



N. moniliforme (Wright and Studcr). 



The following short specific diagnoses may prove useful : — 



Kieella JlaMlata. 



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

 from one side of the larger. Tiic cocnenchyma is moderately thin, and often 

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

 disposed in two longitudinal series; in tlie 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 ou the median bare spaces. Tlie 

 verrucae vary in siiape and size according to the stage of retraction ; when 

 expanded they are prominent, and show an eight-rayed figure at the summit ; 

 when retracted tlicy api)ear 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 reticidala. 



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

 and twigs are very slender, so tliat the colony is extremely reticulate and 

 tiabelliform. The cocnenchyma is thin and finely granular. The polyps are 



