CALYCOSILVA CANTHARELLUS. 
87 
have a centrum 4-6 n in diameter, from which six main-rays arise. These are 
very similar to the main-rays of the regular onychhexasters, enclose right angles 
with their neighbours, are smooth, 2-4 n thick, and (without the centrum) 
2-5 fx long. Forms with long and slender end-rays and outward directed termi- 
nal spines, forms with short end-rays and recurved terminal spines, and inter- 
mediate forms, corresponding to the different forms of the regular onychhexasters 
described above, are met with also among the helonychhexasters. 
The twisted end-rays of the same spicule are always curved in the same 
direction and describe evolvent (spiral) curves extending in planes parallel to 
each other and vertical to one of the three axes of the spicule. The two (oppo- 
site) main-rays of the spicule representing this axis, lie in the axis, the four others 
in a plane parallel to the spirals accordingly. Each main-ray bears from one to 
four end-rays. When only one end-ray is present the main-ray usually passes 
into it gradually. The end-rays 10-35 n long arising from the main-rays, which 
lie in the axis of the spiral, often do not participate in the general twisting and 
are usually either irregularly curved throughout, or curved only basally and 
nearly straight distally, like the end-rays of the regular onychhexasters. The 
end-rays arising from the four main-rays parallel to the plane of the spiral twist 
are generally all affected by the torsion. At the base, where they are most 
strongly curved, their radius of curvature is about 7 n. Farther on their curva- 
ture, being a spiral or evolvent one, decreases. Still farther, at a smaller or 
greater distance from the distal end, the curvature is usually reversed, the 
terminal part of the end-ray being fairly straight and arising radially or obliquely 
from the convoluted central mass of the spicule. Depending, as it does, on the 
variable position of the point of recurvature, the length of this end-part is very 
variable. 
The transverse diameters parallel to the plane of spiral twist, which pass 
through the centrum of the spicule, represent the breadth of the spicule, while 
the diameter along the axis of torsion can be considered as its length. Taking 
breadth and length in this sense, we find that the spicule is 33-58 n long, whilst 
its central convoluted mass measures 15-22 n, and the whole spicule 16-67 n 
in breadth. Numerous small, recurved spines, uniformly scattered along the 
length of the ray, and two to five larger terminal spines 1.7-4 n long originate 
from the end-rays arising from the main-rays lying in the torsion-axis and also 
from those of the others in which the straight end-part attains a greater length. 
Accordingly the spinulation of these end-rays is very similar to that of the end- 
rays of the regular onychhexasters. The spinulation of the end-rays spirally 
