HOLASCELLA EUONYX. 
45 
spines, inclined towards the end, in their distal part. The lateral rays are 215- 
420 n long and often thickened at the end. The proximal ray attains a length 
of 400-530 n. The fragmentary state of the specimen renders it impossible to 
determine which of the superficial hexactines observed are dermal and which 
gastral. 
The tetractine principal spicules (Plate 25, fig. 16) have two long rays extend- 
ing longitudinally and two shorter transverse rays. The four rays do not lie 
in one plane. The rays are 80-140 n and more thick at the base. About their 
length I cannot be definite, since the larger spicules of this kind were invariably 
broken. The longest longitudinal ray-fragment, observed was 19 mm. long. 
The tetractine comital spicules (Plate 25, fig. 18) are similar to the principal 
ones, but have rays usually only 9-17 n thick. 
The large loose hexactines (Plate 25, figs. 19, 20) have straight or curved, 
equal or unequal rays, which arise from a distinct central thickening, 38-50 n 
in diameter. The rays are 0.3-1. 7 mm. long, at the base 10-35 n thick, usually 
10-15 n, and smooth or, more frequently, covered with sparse fairly stout, low 
spines. 
The small hexactines measure 120-150 n in diameter, and have straight, conic 
rays, 6-7 n thick at the base, and densely covered with rather large spines. 
The onychhexactines and hemionychhex asters (Plate 24, figs. 13, 14; Plate 
25, figs. 1, 6-9, 13b) are both derivates of onychhexasters, and there is no differ- 
ence between them, except that in the former (Plate 25, figs. 7, 9) all the main- 
rays bear only one end-ray, while in the latter (Plate 25, fig. 8) one or two of the 
main-rays bear two end-rays. When, as is the rule,' only one end-ray is present, 
this either extends exactly in the continuation of the main-ray (Plate 25, fig. 9), 
or there is a slight, abrupt curvature at the point where the main-ray passes into 
the single end-ray (the upper ray, Plate 25, figs. 7, 8). In any case the main- 
and the single end-ray together form a ray, simple in outer appearance. That 
these apparently simple rays are in truth composed of a main-ray and a (single) 
end-ray is, however, clearly shown by the axial thread, which is only 7-8 n long, 
and present in the basal (main-ray) part of the ray only. These onychhexac- 
tines and hemionychhexasters measure 53-95 n in total diameter. Their simple 
rays are 25-45 n long. The main-rays which bear two end-rays are, like the 
axial threads of the simple rays, 7-8 n long. The simple rays are 2-3 n thick at 
the base and taper distally to 1-1.5 n. They are either smooth throughout, or 
slightly roughened by exceedingly minute spines in their basal and middle-parts. 
Each ray (end-ray) bears at its end a verticil of four or, more rarely, three large 
