t'AU'AUKA. 39 



skeleton proper; the gastral cortex is supported by the paired rays of the chiactines 

 a ucl subgastral triradiates (see Fig. 120). The dermal mrti-x is formed of a thick laver 

 of irregularly scattered triradiates (Fig. 124). 



The osculc is shown ill Fig. 121. There is a ring of small quadriradiatcs lying 

 tangentially round the inner edge, with short pointed api'-al rays from which springs 

 tlic diaphragm. There is a thick fringe of hair <>\>-.\, outside which there is an open 

 fringe of large oxea. The oscule is thick and the flagellated chambers reach almost to 

 the edge. Near the oscule they are only in a single layer, but in the middle of the 

 sponge they are ten or twelve layers thick. 



Spicules (Fig. 123). 



. There arc four sorts of ( >xea : 



(") Large projecting oxca, pointed sharply at the inner end. and very bluntly at 

 the outer end, which is thicker. Curved all along, more sharply near the 

 thicker projecting end. Length fairly constant about 700 p., thickness 30 p 

 to 35 p. 



(/') Hair oxea, projecting in dense tufts, quite straight, length over 500 p., 

 thickness about 1 p.. 



(') Minute spined hastate oxea, scattered all through the body-wall. Slightly 

 bent, with the largest spines in a ring round the "set-over" of the spear- 

 head. Usual length GO p., occasionally 150 p., thickness 4 p. to 5 p. 



(d) Small irregular oxea from the body-wall about 350 p, X 20 p., often set-over 

 in the middle of their length. 



'railiiifi;*. There are two sorts of Triradiates : 



(c) Large alate subgastral triradiates. Hasal ray straight, tapering uniformly 

 to a sharp point, about 700 p. long x Mi/x thick. Paired rays equal, nearly 

 straight, 200 p. to 320 /x long X 20 p. thick ; oral angle 160. 



(/") Smaller alate triradiates from the dermal cortex (probably the same as the 

 rare ones in the body-wall). These vary widely in size. Basal ray 

 straight, tapering uniformly to a sharp point, 170^ to 700 p. long x 10/u, 

 to 18 p. thick. Paired rays equal, forming a rounded bend at the centre, 

 but straight for the rest of their length. 12<>// lo 270 p. long x 10 /A to l<\ p. 

 thick. Oral angle very constant, 108 to 112. 



(//) Ckiactiiics. Basal ray straight, sharply pointed, 600 p. to 750 p. long x 14 p. 

 thick. Paired rays bent more or less forwards, 200 p. to 280 p. long X 16 p. to 

 20 p. thick. Oral angle variable, 135 to 160. Apical ray about 80 /* X 12 p.. 



(//) Large oxea like (</), but shorter; ::sO> to 480 p. long X 18 p. thick. 



form an external fringe. The inner fringe is formed of hair oxea of 

 unknown length. 



VOL. IV. - N 



