8 PROF, E. A. MINCHIN ON THE [May 2, 
ray is usually 8 or 9 u, but may reach 12; speaking generally, 
slender triradiate systems, with rays not exceeding 10p in 
breadth, can be distinguished from thick ones with rays exceeding 
10 (text-fig. 3,2a-2f). 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. Asarule the quadriradiates 
are more abundant than the simple triradiates. 
Im 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 gastral 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 2). 
Arising from a slightly expanded base, the gastral ray 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, or even 150 » in length. 
The gastral ray then becomes excessively slender for the distal 
half or two-thirds of its length, and ends ina sharp point; it is 
not bent oralwards as Haeckel describes it, but it is either quite 
straight or irregularly curved. Haeckel’s figure of a quadri- 
radiate (Kalkschwamme, iii. pl. 14. fig. 6c) obviously represents 
a spicule of LZ. complicata (compare his fig. 1 e on pl. 15, l.c.). 
Quadriradiates are also to be found in which, with gastral rays of 
great length, are found basal rays much shorter than usual 
text-fig. 2, 1g; text-fig. 4, 4e); 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 
triangular 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 off (text-fig. 3, 2a, 2). 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 Clathrina contorta vary in the most 
singular manner, constituting the most remarkable 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. 
pl. 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. 
