8 PROF. E. A. MINCHIN ON THE [May 2, 



ray is usually 8 or 9^, but may reach 12/x ; speaking generally, 

 slender triradiate systems, with rays not exceeding lO^u in 

 breadth, can be distinguished from thick ones with rays exceeding 

 lOju (text-fig. 3, 2 (x-2/). In some specimens the triradiate 

 systems are all, or nearly all, of the slender type ; in others, 

 triradiate systems of the thick type are more abundant. 



Some of the triradiate systems develop gastral rays, becoming 

 quadriradiates, and others do not. As a rule the quadriradiates 

 are more abundant than the simple triradiates. 



In some specimens there is a tendency for the simple 

 triradiates to be of rather stouter build than the quadriradiates, 

 but in other specimens this cannot be noticed. 



The gasti^al rays of the quadriradiates are attached at the 

 centres of the triradiate system, and are remarkable for their 

 slenderness and usually also for their length (text-fig. 2, 1 g-1 i). 

 Arising from a slightly expanded base, the gastral i-ay sometimes 

 tapers rapidly to a point, then reaching a length equal to about 

 one-half or one-third of that of the basal rays ; but more usually 

 the gastral ray is prolonged to a considerably greater length than 

 the basal rays, reaching 130^, 140 ju, or even 150yuin length. 

 The gastral ray then becomes excessively slender for the distal 

 half or two-thirds of its length, and ends in a sharp point ; it is 

 not bent oralwards as ITaeckel describes it, but it is either quite 

 straight or irregularly curved. Haeckel's figure of a quadi'i- 

 radiate (Kalkschwamme, iii. pi. 14. fig. 6 c) obviously represents 

 a spicule of L. convplicata (compare his fig. 1 e on pi. 15, I.e.). 

 Quadrii-adiates are also to be found in which, with gastral rays of 

 great length, are found basal rays much shorter than usual 

 text-fig. 2, 1 (7 ; text-fig. 4, 4 e) ; these are probably young forms 

 in which the rapid growth of the gastral ray * has caused it to 

 attain its full length before the basal rays have done so. 



In the thick quadriradiates found in many specimens, I have 

 observed a curious point with regard to the gastral ray, when 

 seen in the facial aspect of the spicule. When the basal system 

 is focussed so that the bases of the rays show sharp contours, the 

 origin of the gastral ray appears as a dark central spot roughly 

 triangvilar in outline, each side of the triangle being transverse 

 to the base of one of the rays of the triradiate system, and the 

 angles of the triangle rounded ofi" (text-fig. 3, 2 a, 2 6). If now 

 the focus is slightly raised, the base of the gastral ray appears as 

 a sharp ring, within the triangle. The dark triangle appears to 

 be the expanded base of the gastral ray, but it is only to be seen 

 in the case of the thickened triradiate systems, not in the slender 

 ones. 



The monaxon spicules of Claihrina contorta vary in the most 

 singular manner, constituting the most remai'kable feature of the 

 species. The variations are best considered, first, from the point 



* As I have described in a former memoir (Quart. Journ. Micr. Sci., n. s. xl. 

 pi. 42. fig. 55), the elongated gastral rays of contorta are covered by a plasmodial 

 mass containing four nuclei, more than I have observed on the gastral rays of any 

 other Ascon. 



