CALYCOSILVA CANTHARELLUS. 83 
This absence of intermediate forms, and the fact that the spines are no 
closer together on the reduced than on the long proximal rays, show that the 
reduction of the short ones cannot be due merely to obstacles which impeded 
their longitudinal growth. It is, therefore, probable that we have here to deal 
with two distinct kinds of pinules, one with long, and one with short proximal 
ray, even though the pinules with short proximals are locally aggregated only 
in so far as they are relatively much more numerous on the stalk than on the 
body. 
The scarce microhexactines (Plate 3, fig. 1), which have been found only in 
C. c. vars. simplex and helix, measure 16-19 » in total diameter, and consist of 
six equal, cylindrical, terminally rounded rays, (without centrum) 6-8 u long, 
and 3-8 uw thick, which enclose right angles. The rays bear numerous larger or 
smaller spines on their sides and on their ends. 
At first I took these spicules for central remnants of hexasters which had 
lost their end-rays, like those described by F. E. Schulze! and Ijima? in other 
Hexactinellida. But since I found no indication of these spicules having once 
possessed end-rays, I think this view hardly tenable. 
Of hexasters two main groups can be distinguished:— one represented by 
the regular onychhexasters, the onychhexaster-derivate oxyhexasters, their 
regular onychhexasters, and the helonychhexasters; the other by the plumi- 
comes. 
The regular onychhexasters (Plate 2, fig. 3a; Plate 3, figs. 21-30; Plate 4, 
figs. 1-19) form a series commencing with small ones with stout end-rays and 
recurved terminal spines, and ending with large ones with slender end-rays 
and terminal spines directed obliquely outward. In C.c¢. vars. helix and simplex 
the whole of this series of onychhexasters is met with; in C. c. var. megonychia 
I have observed the large forms with slender end-rays only. The onychhexasters 
of C. c. var. hex are 39-88 uw in total diameter, those of C. c. var. simplex 48- 
106 u, and those of C. c. var. megonychia 80-130 u. They consist of a centrum, 
5-6 » in diameter, from which arise the six concentric and equal main-rays, the 
axes of which enclose angles of 90°, with trumpet-shaped, proximal extensions. 
The main-rays are smooth, 2-4 uv thick, (without the centrum) 1.5-6 » long, and 
thickened in a trumpet-shaped manner and divided into from two to five end- 
rays at the distal end. The end-rays of the same spicule are fairly equal in shape 
1 F. #. Schulze. Amerikanische Hexactinelliden, 1899, p. 31, taf. 5, fig. 8. 
21. Ijima. Studies on the Hexactinellida. I. Journ. Coll. sci. Tokyo, 1901, 15, p. 198, 292, pl. 4, 
fig. 20. 
