108 LANUGONYCHIA FLABELLUM. 
It has been stated above that some of the fully developed rays are more 
eylindroconie and less sharply pointed than the great majority of rays. Such 
blunt rays have only been observed in the hexactines and pentactines, and it is 
always the distal protruding ray of these spicules which exhibits this peculiarity. 
This differentiation is interesting, since it would, if further developed and associ- 
ated with an increase in the size of the spines, convert these superficial hexactines 
and pentactines into pinules. 
The onychhexasters (Plate 13, figs. 6b, 15b, 27) measure 86-135 y in total 
diameter. Their main-rays, which are regularly arranged and enclose angles 
of 90° with their neighbours, are 5-8 » long, thickened at both ends, and, in the 
middle, where thinnest, 2-3 « in transverse diameter. From the end of each 
main-ray several, most frequently four, branch-rays arise. These are con- 
siderably curved, convex to the centre of the spicule, at the base, but soon 
straighten out, often, however, exhibiting slight bends farther on. They are 
48-60 » long, 1.3-2 » thick at the base, and gradually attenuated to 0.3-0.6 u 
at the end. They bear along their length sparse, minute, backwardly directed 
spines, and on their ends two to four, most frequently three, slender terminal 
spines, 3-5 » long. These usually enclose angles of 90-120° with the end-ray, 
and are curved, concave towards the centre of the spicule, or nearly straight. 
They generally arise from the same point, quite terminally, and form a verticil. 
Sometimes, however, one is situated a little below the end of the end-ray. 
All the discohexasters (Plate 13, figs. 1-4, 5a, 6a, 15a, 17-26) have very 
much the same shape, but they differ quite considerably in regard to their size 
and the number of their end-rays. I measured 22 of them and found that 
QO was under’ 80 
2 were 81-100 
Ose 101-120 
3 en 121-140 
0 was 141-160 
2 were 161-180 
(he alld 181—200 
Slee 201-220 
0 was. over 221 
in total diameter. 
This gives the following frequency-curve (Fig. 3). 
From this remarkably regular double curve I conclude that two kinds of 
discohexasters are to be distinguished, a large kind over 150 » in diameter and a 
small kind under 150 uy. 
