SPONGES. 175 



0'02 millim. at the base (including spines). Although they are verticillately spined, 

 the annulation of these spicules is not nearly so distinct as in Agelas mauritiana. 

 R.N. 304 ; 312 (type). (Both from Ceylon seas.) 



Echinodictyum, Ridley. 



Ectyoninse with reticulate main skeleton composed of spicular fibre containing smooth 

 oxea and echinated by spined styli. Smooth styli may also be present. 

 Microscleres usually absent. 



Echinodictyum clathratum, n. sp. Plate XL, fig. 4. 



The single specimen forms a sub-spherical, clathrous mass of rather thin, short, 

 flattened trabecule, echinated on the outer surface by slender conuli. Vents and 

 pores not seen. Colour (in spirit) pale greyish-yellow ; texture soft and resilient, 

 fairly tough. Total diameter about 20 millims. 



The main skeleton is a very irregular network of fairly stout spicular fibre ; the 

 size and shape of the meshes and the thickness of the fibres varying greatly. The 

 fibres contain a very large number of oxeote megascleres closely packed together side 

 by side, while the spongin cement which unites them is inconspicuous on account of 

 its very pale colour. The fibres are echinated more or less abundantly by spined styli 

 which project from them almost or quite at right angles. Numerous loose megascleres 

 (oxea and styli) are scattered between the fibres. There is a dermal skeleton of well 

 developed brushes of very slender styli ; the brushes are well separated from one 

 another, and each exhibits a beautiful radiate arrangement of its component spicules. 

 These brushes appear to be confined to the outer surface of the sponge as a whole, 

 and are absent from the surfaces of the inner trabeculse. 



Spicules. (1.) Oxea (Plate XL, fig. 4, c, d) ; smooth, slender, usually more or less 

 sharply bent at or near the middle, gradually and sharply pointed at each end ; size 

 very variable, commonly about - 25 millim. by - 006 millim. In the fibres and 

 scattered between them, forming the greater part of the skeleton. 



(2.) Smooth styli (Plate XL, fig. 4, a, a) ; very long and fairly stout, tapering 

 gradually from the evenly rounded base (which may be very faintly tylote) to the 

 sharply pointed apex ; nearly straight but generally slightly curved towards the base ; 

 size variable, say about 1'26 millims. by 0'012 millim. These spicules lie parallel to 

 the surface in the thickness of the sponge-lamella, without any definite arrangement. 



(3.) Smooth styli (Plate XL, fig. 4, h) ; very slender, almost hair-like; straight or 

 gently curved ; evenly rounded at the base, very gradually and finely pointed at the 

 apex ; size about - 34 niillim. by 0"002 millim. In the dermal brushes. 



(4.) Spined tylostyli (Plate XL, fig. 4, e, f) ; rather long and slender, straight, 

 tapering gradually from the slightly developed head to the narrow, fairly sharp- 

 pointed apex. Spines small but abundant all over, especially on the head. Size about 

 O'l millim. by 0'006 millim. where the shaft joins the head. 



