CALCABEA. 



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

 and suhgastral triradiates (see Pig. 120). The dermal cortex is formed of a thick layer 

 of irregularly scattered triradiates (Fig. 124). 



The osc.ule is shown in Fig. 121. There is a ring of small quadri radiates lying 

 tangcntially round the inner edge, with short pointed apical rays from which springs 

 the diaphragm. There is a thick fringe of hair oxea, outside which there is an open 

 fringe of large oxea. The oscule is thick and the Hagellated 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). 

 Oxen. There are four sorts of Oxea : 



() Large projecting oxea, pointed sharply at the inner end, and very bluntly at 

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

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

 to 35 ft. 



(/<) Hair oxea, projecting in dense tufts, quite straight, length over 500ft, 

 thickness about 1 ft. 



(c) 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 60 ft, occasionally 150ft, thickness 4 ft to 5 p.. 



(</) Small irregular oxea from the body-wall al>out 350 p. X 20 ft, often set-over 



in the middle of their length. 

 Tri radiates. There are two sorts of Triradiates : 



(?) Large alate subgastral triradiates. Basal ray straight, tapering uniformly 

 to a sharp point, about 700 p long x 16 p. thick. Paired rays equal, nearly 

 straight, 200 p, to 320ft long X 20ft 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 p. to 700 ft long x 10 ft 

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

 but straight for the rest of their length, 120 ft to 270ft long x 10 ft to 16ft 

 thick. Oral angle very constant, 108 to 112. 



(y) Chiactines. Basal ray straight, sharply pointed, 600ft to 750 ft long x 14 ft 

 thick. Paired rays bent more or leas forwards, 200 ft to 280 ft long x 1 6 ft to 

 20 ft thick. Oral angle variable, 1 35 to 1 60. Apical ray about 80 ft x 1 2 ft. 



Oscular spiculfs. 



(h) Large oxea like (a), but shorter ; 380 ft to 480 ft long x 18 ft thick. These 

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

 unknown length, 



TOL. IV. 2 N 



