391 



ON THE GENERA ECHINAXIA AND RHABDOSIGMA 



[Porifera]. 



By E. F. Hallmann, B.Sc, Linnean Macleay Fellow of the 

 Society in Zoology. 



(Plates xxi.-xxii. ; and two Text-figures.) 



The genera Echinaxia and Rhahdosigma were proposed, with- 

 out definition, in my " Revision of the Genera with microscleres 

 included, or provisionally included, in the Family Axinellidse," 

 for two species wrongly referred to the genera Axinella and 

 Sigmaxinella respectively. I now publish definitions of these 

 genera, together with remarks on their probable relationships, 

 and re-descriptions of their type-species; and for the reception of 

 certain species, apparently related to Echinaxia, I propose two 

 new genera, Axi^iectya and Hetercetya. 



Genus Echinaxia. 



Definition. — Desmacidonidse of erect, lamellar or ramose habit, 

 with a skeleton consisting axially of a reticulation of spiculo- 

 spongin fibres cored by comparatively small, smooth styli and 

 echinated by vestigially spined acanthostyli, and extra-axially of 

 (typically non-connected) fibres radiating outwards to the 

 surface, composed partly of the same two kinds of styli, and 

 partly of obliquely directed {i.e., plumosely disposed) long, smooth 

 styli — the last-mentioned spicules typically occurring only 

 towards the outer extremities of the fibres, and forming terminal 

 tufts which project beyond the dermal membrane; the extra- 

 axial fibres, however, may be so reduced as to be represented by 

 scarcely more than their terminal tufts of long styli. The acan- 

 thostyli are of characteristic form, having their basal moiety free 

 from spines and more or less curved. Microscleres are absent. 



Type, E.frondnla Whitelegge. 



Two species with a spiculation closely analogous to that of 

 Echinaxia frondula have been described by Thiele(5) under the 



