142 SIDNEY P. HARMER. 



zooecium by means of a basal piece which is quite similar to 

 that of a normal branch. 



The spines shown in fig. 4 have been artificially bent back- 

 wards ; in their normal position they curve over the front of 

 the branches. 



The number of spines developed on a colony is extremely 

 variable ; in a few cases spines are altogether absent, and the 

 species could then hardly be distinguished with certainty from 

 C. ramosa, were it not for the presence of the characteristic 

 ovicells. Although, in one or two cases observed, an interuode 

 had developed spines on all or nearly all its zooecia,it is not usual 

 to find more than one or two spines on a single internode, 

 while a large proportion of the internodes of a colony do not 

 develop any of these structures. The spines most commonly 

 occur on the lower zooecia of an internode, and are commonly 

 in the position — 



or (« + *i + «2 + r^); 



being found on the abaxial side if the internode is, as is often 

 the case, the basal member of a branch. 



The spines may, however, be developed in other positions; 

 thus it often happens that the last structure developed at the 

 apex of a branch, before the growing-point ceases to grow, 

 is a spine,^ which is situated on the axial side of the last 

 zooecium, and is consequently in the position of the terminal 

 zooecium of the branch to the right of the ovicell in fig. 4. 



In the specimens (most of them from Plymouth or RoscofiF) 

 which have come under my notice the presence of a single spine 

 on a colony has been quite sufficient to enable the species to be 

 identified with certainty as C. aculeata. It is perfectly true 

 that the lower parts of the zoarium may have an eburnea- 

 like appearance ; but the colony, if well grown, seems always 

 to acquire the aculeata form of the zooecia and internodes 

 towards the ends of the branches. 



I have in no case found an ovicell of the type shown in fig. 6 



> Cf. C. acuminata, Busk, '"Challenger" Eep.,' part 50, pi. iii, fig. 1. 



