COLLECTED BY THE SCOTTISH NATIONAL ANTARCTIC EXPEDITION. 443 



Microciona tenuis n. sp. (Plate XL, fig. 5.) 



Station 482. Houtjes Bay, Saldanha Bay, shore. 19th May 1904. 



Sponge forming an encrustation about 0'3 mm. in thickness on the outer and 

 inner surfaces of a large dead Patella shell. 



The surface of the sponge is very finely hispid. 



The colour in spirit is pale yellow. 



The main skeleton consists of short, unbranched, plumose fibres, running vertically 

 from the base of the sponge to the surface. The fibres are about 0'075 mm. in 

 diameter and are set about O'l mm. apart. Between them, rather numerous small 

 styli, spiny along their whole length, are set vertically with their heads based on the 

 substratum. The spicules of the skeletal fibres are styli which vary greatly in 

 length and in amount of spinulation according to their position. The largest styli, 

 spined only on the head, are inserted towards the centre of the fibre. The shorter 

 styli are placed externally to them. They increase in length and decrease in amount 

 of spinulation from the base to the summit of the fibres. 



The dermal skeleton consists of slender styli occurring among the terminal 

 spicules of the fibres and also lying more or less horizontally in the dermal 

 membrane. 



Spicules. — (l) Styli of the main fibres, 0'075-0'55 mm. in length by 0'005- 

 0'018 mm. The longest styli occur at the summit of the fibres. They pierce the 

 dermal membrane and cause the chief hispidation of the surface of the sponge. They 

 are smooth, except at the head, which is thickly covered with short, blunt spines. 

 The shaft is curved and tapers evenly from the base to a sharp point. The smallest 

 styli are spined along their whole length ; the shaft is straight or very slightly 

 curved. These styli occur in greatest numbers at the base of the fibres, and are also 

 placed between them. They are about 0'075 mm. in length by 0'005-0'007 mm. 

 A series of spicules can be found bridging over the differences between the longest 

 and the shortest styli. At the one end, leading from the entirely spined spicules, 

 are styli about 0"1-0'125 mm. long, with spines extending along the shaft for about 

 three-fourths of its length. Rather longer spicules are spined to about half their 

 length, while still longer styli, with only a few spines a little way along their shaft, 

 lead on to the largest styli which are only spined on the head. (2) Dermal styli, 

 slender, exceedingly finely spined on the head. Shaft usually slightly curved. 

 Length 0'14-0'25 mm. by 0'003 mm. These spicules are not very numerous. (3) 

 Isochelse palmatse scattered in abundance through the sponge. Length 0'015 mm. 

 (4) Toxa. — These spicules are strongly curved in the centre. They vary from 

 exceedingly minute to about 0'18 mm. long by 0*0025 mm. Not very numerous. 



Pocillon hyndmani (Bowerbank). 

 Station 483. Entrance to Saldanha Bay, 25 fathoms. 21st May 1904. 



