392 ECHINAXIA AND RHABDOSIGMA, 



names oi Raspailia hirsuta and R./oliitm; but whether these also 

 agree therewith (or with one another) sufficiently to necessitate 

 their inclusion in the same genus is not quite certain, owing to 

 the inadequacy of their descriptions. As, however, they certainly 

 do not belong to Raspailia, and the establishment of a sepaiate 

 genus for their reception would be premature, I propose that 

 they be referred (provisionally, at least) to Echinaxia, and have 

 attempted to define the genus accordingly. With respect to 

 certain features of the skeleton, the differences between the three 

 species are rather considerable. In E. hirsuta, according to 

 Thiele's description, the skeleton consists axially of a network 

 of horny fibres cored by the smaller smooth styli and echinated by 

 more abundant acanthostyli, and the extra-axial fibres are pro- 

 vided with projecting long styli apparently throughout their entire 

 length. On the other hand, in E.frondula the axial skeleton is 

 a dense and nearly subrenieroid reticulation composed almost 

 entirely of the smaller smooth styli (spongin being present only in 

 very minute quantity, and the acanthostyli scarce), while the 

 extra-axial fibres are provided with projecting long styli only 

 towards their outer extremities. Regarding the arrangement of 

 the skeleton in E.foliunn, no definite information is available, but 

 apparently it is reticulate throughout; in this species also, how- 

 ever, long smooth styli project far beyond the surface of the 

 sponge, and it is presumable that these are the terminal spicules 

 of fibres corresponding to the extra-axial fibres of the other 

 species. In E. froudula more especially, the intrafibral smooth 

 styli approximate rather closely both in size and shape to the 

 acanthostyli, conveying the suggestion of their original deriva- 

 tion therefrom; and this view of their origin is further supported 

 by the fact that, in E. hirsuta, they occasionally exhibit a slight 

 roughness of the surface, suggestive of a vestigial spination. 



Acanthostyli similar to those of Echinaxia are characteristic 

 also of the genus Raspaxilla, lately proposed by Topsent(lO) for 

 a new species from the Antarctic; and this genus (as exemplified 

 by its single known species) further resembles Echinaxia in the 

 possession of a skeleton condensed axially and consisting extra- 

 axially of radiating fibres terminating at the surface in a tuft of 



