CALCAREA. 15 



Spicules (Fig. 34). 



The Body spicules are of one sort : — 



(rt) Kegular triradiate.s. Rays straight, very slender, parallel, bluntly pointed, 

 140 y« to 200/* long X 4m to 7m thick. Ratio of length to thickness, 

 25 to 40. 



The Oscular spicules are of one sort : — 



{!)) Alate triradiates, strongly folded. Basal ray straight, Jiearly parallel, 

 bluntly pointed, 55 /a to 90 m long x 7 m to 8 m thick. Paired rays nearly 

 straight in facial view, and twice bent when viewed parallel to the basal 

 ray. Tapering, moderately sharply pointed, 90 m to 140 m long x 8 m to 

 10 m thick. Oral angle 105° to 115°. Angle of foM 110°, 



Leucandra frigida. 

 (Plate XXVIL, Fig. G, and Plates XXIX. and XXX., Figs. 35-40.) 



There are eleven specimens of this new species in the collection. They are all fig- 

 shaped, with the oscule at the thick end (see Fig. 6). The surface is smooth, pure white 

 and rather chalky in appearance. They vary in size from 10 mm. x 3 mm. to 

 30 mm. X 10 mm. (see Fig. 35). They are all solid to the touch, though they vary 

 very much in texture wlien cut ojien. All Ijut one of the specimens have the oscule 

 completely closed, and its presence is only indicated externally by a slight 

 protuberance. One specimen, 21 mm. long x 7 mm. diameter, has the oscule open ; it 

 is 2 mm. in diameter, and is surrounded by a short spiculated memliranous collar (see 

 Fig. 39). 



The canal system varies considerably in the different specimens ; in some there is 

 a wide gastral cavity with large branching canals opening into it, while in others there 

 is no gastral cavity, the excurrent canals all converging to the oscule. In cross-section 

 the specimens difler less than might be expected, for the gastral cavity appears to l)e 

 divided by delicate septa, which give the whole section a meshwork appearance even 

 wlien longitudinal sections show a large cavity. 



The excurrent canals are usually surrounded with a fairly distinct skeleton of 

 triradiates, among which are a few quadriradiates. 



The incurrent canal system is made up of a series of very irregular spaces leading 

 from the surface into the rather more regular longitudinal canals ; these run parallel 

 to the excurrent canals, from which they may be distinguished l)y their less 

 pronounced skeleton, which never contains quadriradiates. 



The l)ulk of the skeleton consists of regular triradiates ; the quadriradiates round 

 the gastral cavities and excurrent canals are very constant in size. In some specimens 

 they are so rare that they can only be found with great difficulty. The apical rays, 

 which are slender and crooked, project into the canals. 



VOL. IV. 2 K 



