26 C. F. JENKIN. 



The rim of the tube is formed by a ring of small quadriradiates regularly and closely 

 packed, with the unpaired ray downwards and apical ray inwards. The rim is 

 crowned by a fringe of long nearly straight hastate oxea. (See Fig. 78.) The sharply 

 defined line of the small quadriradiates forming the rim of the collar, standing 

 above the widely spaced quadriradiates which form the lower part of the skeleton, 

 produces the effect of a vacant space with no spicules between the two. The space 

 is however no wider than between other rows of the collar skeleton, and occasionally 

 one of the big quadriradiates is found in the rim itself. No diaphragm can be seen. 



Fig. 80 represents a longitudinal section through the junction between the 

 oscular collar and body. The gastral skeleton is continuous and the flagellated 

 chambers grow outside it. The first is very minute, with no skeleton ; the second is 

 larger, with a primitive skeleton. The length of the chambers continues to increase 

 down to the base of the sponge. 



Spicules (Fig. 76). 



Oxea. There are three sorts of oxea : 



(a) Stout projecting hastate oxea, usually straight, but occasionally bent 



sharply through an angle of about 120, varying irregularly in thickness ; 

 300 n to 1,250 /x long x 9 A* to 15 M. 



(b) Thin projecting oxea, quite straight, faintly hastate, maximum size 



1,020 ju, x 6yu. 



(c) Small hastate oxea 140/x x 8 A*. 



Triradiates. There are two sorts of triradiates : 



(d) Large alate triradiates from the gastral layer. Basal rays straight, 



tapering uniformly to a sharp point from 190/u to 300 /x long x 6/u to 8/t 

 thick. The paired rays are nearly equal, nearly straight, from 80/t*tol50jw 

 long X 6 M to 8 /X thick. Oral angle 130 to 140. 



(/) Small alate triradiates from the tubar skeleton. Basal ray straight, 

 100/u x 6M, tapering to a sharp point. Paired rays irregularly bent, 

 70/u x 6/x. Oral angle 120 to 135. Considerably folded. 



Quadriradiates. There are two sorts of quadriradiates : 



(g) Large alate quadriradiates from the gastral layer. Basal ray straight, 

 tapering uniformly to a sharp point, 230 A* to 430 M long x 6/* to 12 /x 

 thick ; the larger sizes occur in the oscular collar. Paired rays bracket- 

 shaped, nearly equal in length, 140/u to 215/x long x 8 M to 10/x thick. 

 Apical ray thin and sharply pointed, bent orally. Apparent size seen 

 facially, 32 M x 4ju. Oral angle varying from 110/u in body to 150 in 

 oscular collar. 



(A) Small chiactines from the tubar skeleton. Basal ray, 140/ to 220 n 

 long x 4 it to 6 tt thick, tapering uniformly to a sharp point, appearing 



