66 



CAULOPHACELLA TENUIS. 



current. As a rule (Plate 12, figs. 1-4, 7, 8) their curvature is simple, the spines 

 extending in planes which pass through the axis of the ray. In a few cases, how- 

 ever, the spines (Plate 12, figs. 5, 6) are curved doubly, and spirally twisted round 

 the ray. 



The lateral rays are conic, straight or slightly curved, and rather uniformly 

 and densely covered with small spines. The proximal ray is rudimentary, very 

 considerably shortened, cylindrical, terminally rounded, and also covered with 

 small spines, some of which arise from its apex. The dimensions of the dermal 

 and gastral pinules are tabulated below. 



PINULES. 



The oxyhexasters and hemioxyhexasters (Plate 12, figs. 9-13, 16-18) measure 

 100-125 M in total diameter, rarely 137 n. The main-rays are in the same spi- 

 cule equal, and regularly arranged, each one enclosing right angles with its four 

 neighbours. They are straight, cylindrical, 8-11 ix long, and 2.7-5 m thick, rarely 

 as much as 6 /z. Each main-ray bears from one to three end-rays. The number 

 of end-rays is by no means always the same on the six main-rays of the same 

 spicule. Most frequently oxyhexasters are observed with three end-rays on 

 some main-rays and two end-rays on the others, and with two or three end-rays 

 on all the main-rays. More rarely one or two main-rays bear only one end-ray, 

 which is either clearly distinguished as such or gradually passes into the main- 

 ray. These spicules, which appear as hemioxyh'exasters, are, apart from their 



