398 ECHINAXIA AND RHABDOSIGMA, 



range from 80 to 1 20/x in length and from 4*5 to S/x in stoutness. 



(iii.) The long smooth styli (Text fig. 1, c, d, e) are, almost with- 

 out exception, more or less curved (though mostly only slightly 

 so, and chiefly in their basal moiety), and are of uniform diameter 

 to about the middle of the length, whence they taper gradually 

 to a sharp point. A distinction should, perhaps, be drawn 

 between those belonging to the axial region of the skeleton and 

 those occurring in association with the extra-axial fibres. The 

 former range from (very rarely less than) 250 to nearly 600/a in 

 length, and from 2 to 1 2/z in diameter, but are seldom less in 

 size than 350 by 4/x. The latter are of about the same dimen- 

 sions, both as regards length and maximum size, in the younger 

 portions of the skeleton (but are uniformly stouter, never less 

 than 6 or 7/x in diameter); whilst in the older regions of the 

 sponge they appear usually to be shorter and stouter, ranging 

 from less than 200 to rarely more than 400/x in length and 

 abnormally attaining to 20/x in diameter. 



Loo. - Shoalhaven Bight, coast of New South Wales. 



Genus Rhabdosigma. 



I)e/inUio7i.~T)e{imsicidonidse in which the skeleton is a reticu- 

 lation of well-developed spiculo-spongin fibres, and the only 

 megascleres are rhabdostyli, typically exhibiting a vestigial 

 spination, and in part projecting from the fibres as echinating 

 spicules. The microscleres are sigmata. 



Type, li. maminillata Whitelegge. 



Though characterised mainly by the possession of megascleres 

 similar in form to those constituting the sole common and dis- 

 tinctive feature of the species comprised in the genus Rhahder- 

 emia, Rhahdosiyma mammillata nevertheless difiers so decidedly 

 from any of these in the structure of its skeleton that the 

 desirability of a separate genus for its reception appears unques- 

 tionable. An adequate description of the skeleton in most of 

 the species of Rhabderemia has not been given; but all of them 

 are of encrusting or semi- encrusting habit, and apparently only 

 in one of them, R. indica, are the megascleres at all aggregated 

 into definite fibres or strands; even in this species, only a pro- 

 portion of the megascleres are so arranged, and, according to 



