CALYCOSILVA C'ANTHARELLUS. 87 



have a ceijtrum 4-6 m 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 neighbom-s, are smooth, 2-4 // thick, and (without the centrum) 

 2-5 Ai 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 yu 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 m. 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 veiy 

 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 m, 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 fi 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 



