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. 
Dermal 
pinules 
Gastral 
pinules 
Distal ray 
length n 
270-373 
115-ISO 
thickness at 
base n 
6-13 
5-7 
maximum trans- 
verse diameter 
(with the spines) 
above n 
14-22 
8-15 
Proximal ray 
length /x 
5-16 
5-10 
thickness 
6-13 
5-7 
Lateral rays 
length /x 
120-232 
85-130 
thickness at 
base yu 
5-12 
5-6 
The oxyhexasters and hemioxyhexasters (Plate 12, figs. 9-13, 16-18) measure 
100-125 m in total diameter, rarely 137 p. 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 m long, and 2.7-5 ^ thick, rarely 
as much as 6 m- 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 hemioxyhexasters, are, apart from their 
