72 THE VOYAGE OF H.M.8. CHALLENGER, 
towards the furrow is very slightly convex. Their armature consists of :—(1.) A furrow 
series of seven or eight moderately elongate, subprismatic spinelets, perfectly rectangular 
in section, slightly compressed laterally, and tapering slightly towards the tip, which is 
more or less pointed. The base is broad, with its greatest dimension transverse to the 
longitudinal axis of the ray; and when viewed in this aspect the tapering of the spine 
is seen to be considerable, but when viewed in the other dimension, parallel to the axis 
of the ray, the thickness of the spine is nearly uniform almost to the tip, and the tapering 
is very slight. The outermost spine at each extremity of the series is much smaller than 
the others, of which the median are the longest (about 2 mm. in length), and the rest 
decrease slightly as they recede on each side. In many cases there are not more than 
five worthy of being called marginal spinelets. The spines stand parallel and touch one 
another, the group thus forming a subtriangular or wedge-like comb, with the apex 
roundly truncate. (2.) On the actinal surface of the plate, behind the marginal series, is 
a more or less irregular row of about five or six small, cylindrical, rather widely spaced, 
subequal, papilliform granules, which in some specimens have a tendency to become more 
spiniform on a few of the plates on the inner part of the ray; and external to these is a 
second row of merely papilliform granules running along the outer margin of the plate, 
The inner eight or ten adambulacral plates, which are broader than the others, have several 
irregularly disposed papilliform granules or spinelets interspersed between the two series, 
and the regularity of the arrangement above noted is somewhat affected thereby. In the 
second lineal series, behind the furrow spines, at least along the inner half of the ray, is 
usually a small pseudo-pedicellaria, formed by two or three slightly modified papilliform 
spinelets, and its position is usually at the aboral extremity of the series, but not invari- 
ably so, neither is it always present. 
The mouth-plates are large and conspicuous, the united pair being elongately oval, and 
prominently convex or subtubercular, rising abruptly from the otherwise level interradial 
area. Their armature consists of a marginal series of true mouth-spines about nine in 
number on each plate, similar in form and character to the furrow series on the adam- 
bulacral plates. The actinal surface of the plates is echinulate, with numerous irregularly 
disposed small papilliform spinelets, which increase slightly in length as they approach the 
inner end of the mouth-plates, where, however, they are less than the marginal or true 
mouth-spines, and can scarcely be said to become definite spinelets. 
The actinal interradial areas are comparatively extensive and well-developed, reaching 
as far as the seventh or eighth adambulacral plate ; they are covered with plates bear- 
ing paxilliform groups, which form series running between the adambulacral and the 
marginal plates, although a definite order is scarcely perceptible on account of the 
crowding of the small papilliform spinelets composing them; these short papillz spring 
from a membrane which covers an apparently subcircular tabulum, and there are about 
nine or ten on each, some being central and some marginal, but with little regularity. 
