EUPLECTELLA. 51 



Hexasters, — These are, according to my conception, minute 

 liexactins wliicli are invariably characterized by the presence of 

 a number of slender, radiall}^ disposed secondary appendages — 

 the terminal rays — at the outer end of each ray. The axial 

 canal (PI. IV, fig. 20 ; PL V, figs. 30-34) is confined to the 

 latter, which is called the principal ray, and never extends into 

 the terminal ray, as can be easily demonstrated by examining 

 the spicule in a medium whose refractive index approaches that 

 of the siliceous matter. Not unfrequently the principal possesses 

 but a single terminal by reduction, and w^hen the two are in a 

 straight line, as is often the case, the external appearance is 

 exactly like that of a simple primary ray. However, the ex- 

 clusive presence of the axial canal only at the base will at once 

 reveal the composite nature of such an apparently simple ray. 



The most constant form of hexasters in Eupledella is the 

 floricome, which I regard as a variety of discohexasters. The 

 terminal disc, instead of being uniformly developed all around, 

 possesses strong marginal prongs only on the side turned away 

 from the axis of the perianth of the terminals, while on the 

 opposite inner side the disc-edge remains smooth and obtusely 

 rounded, being only indicated by a hump-like curvature of the 

 surf\ice (PI. II, fig. 14, d ; &c.). A parallel case of the same 

 modification is found in a new octasterophorous Kossellid, which 

 will be described under the name of Rhabdocalyptus ungui- 

 culatus ; in this, the discoctaster exhibits a similar hand-like 

 development of the terminal discs. 



In their general shape the floricomes show no noteworthy 

 variation in the different species of the genus. Therefore, in this 

 respect, as also in that of the number of terminals in a perianth 

 or of marginal prongs on the terminal plate, they are scarcely 



