CALCARBA. 9 



The commonest size is 90// long x 4 m to 5 m thick. In some specimens 

 the maximum size is 90 m long. 



Among the ordinary oxea there are a very few T type oxea. It is uncertain 

 whether these are always present. It seems probal)le that in those 

 specimens in wliich the oxea are very scarce there may be none of T type. 



(Ij) Refringent oxea, similar to the smaller and thinner sizes of (a) and usually 

 nearly straight. 



The Triradiates are of one sort : — 



(c) Alate triradiates, with the basal ray longer than the paired rays. Basal ray 



straight, tapering, fairly sharply pointed, 90m to 140m long x 5m to 10m 

 thick. Paired i-ays equal, bent very slightly downwards, tapering slightly 

 for about two-thirds of their length, then fairly sharply pointed, 50 m to 

 90 m long X 5 m to 7 m thick ; oral angle 130° to 140°. 



The Quadriradiates are of one sort : — 



(d) Alate quadriradiates, facial rays the same as the triradiates (c). Apical 



ray sharply pointed. 



Oscidar spicules : — 



{e) Oxea from the fringe, like (a) but shorter, with bluntly pointed lance heads, 



55 M to 65 M long X 5 m to 6 m thick. 

 (/) Quadriradiates from the oscular edge like (d), but of the smallest size, the 



paired rays rather more bent. Oral angle 160°. 



Grade HETEROCOELA Pol. 

 Family SYCETTIDAE Dendy. 



Tenthrenodes. 



A Sycettid in which the radial chambers, with freely projecting distal cones, are 

 " linked " so as to form a reticulated pattern round the large inter-canals. 



This genus contains two species. In both these species the sponge is in the form 

 i)f a tube, usually more or less bent, the cross-section being probably circular when 

 alive, though it is considerably flattened in some of the preserved specimens. The 

 diameter of the tube is greatest near the middle of its length. It tapers to the base, 

 which is rounded off, and also to the top, which terminates in the oscule. The interior 

 of the tube forms the gastral cavity. The inner or gastral layer is supported by a 

 special skeleton of tri- and Cjuadriradiates, the apical rays projecting into the gastral 

 cavity. Outside the gastral layer stand the flagellated chaml)ers, pointing more or 



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