SPONGES — WHITELEGGB. 493 



intervals. These often coalesce marginally, and the mesh between 

 the fibres varies from elongate to rhomboidal. Near the surface 

 and in the central regions the fibres are somewhat plexoid and 

 rim parallel to each other, being separated by narrow spaces 

 charged with scattered spicules. The fibres ai-e composed of a 

 central core of spined styli — about six or more spicules in a row 

 - — enclosed in a broad mass of spongin, which is densely echinated 

 by spined styli of two sizes, the smaller being the most abundant. 

 The larger correspond with those of the axial core in general 

 appearance. The summits of the fibres and the valleys between 

 are clothed with radiating tufts or irregularly scattered oxeote 

 spicules, interspersed with an immense number of stoutish 

 isochelfe. The latter in the choanosome are fairly scattered and 

 about their own length or more apart, but in the ectosome they 

 are so densely packed that it is somewhat difficult, under a low 

 power lens, to distinguish them as separate spicules. 



Megascleres : — (1) Spined styli of the spicular core and also 

 sparsely echinating the fibres. These are slightly curved, with 

 the base a little swollen, and very spiny ; the shaft tapers gradu- 

 ally to an acute point, and the spines become smaller and more 

 distinct as the apex is approached ; size 0"15 to 0-2 by 0-01 mm. 

 less the spines. 



(2) Echinating styli, straight, spined and gradually tapering ; 

 size 0-1 by 0-0U8 mm. 



(3) Smooth oxea of the ectosome, straight cylindrical to 

 within about one diameter of the not very acute points ; size 0"18 

 by 0-006 mm. 



Microscleres : — stout, strongly curved, tridentate isochelse ; 

 size 0-02 to 0-024 mm. 



This species is closely allied to Stylosticlwn plumosa, Montagu, 

 but differs in habit and in its spicular characters. 



MICROCIONA, Bowerlanh. 



MICROCIONA CLATHRATA, sp. nov. 



(Plate xlvi., figs. 38-38a.) 



Stations 48, 56. 



Sponge arising from a small basal plate, and having a well 

 defined peduncle, which gives oflf a series of more or less flattened 

 branches ; the latter are distinct at their origin, but rapidly 

 become lost in a mass of stoutish trabeculae. Six out of the seven 

 specimens are fusiform or subclavate in outline, and measure 

 100 mm. in height and about 40 in their greatest diameter. The 



