328 THE VOYAGE OF H.M.S. CHALLENGER. 
well produced, flat, tapering to a narrow extremity. Interbrachial ares very wide and 
round. Lateral wall or margin angular in the interbrachial are and at the base of 
the rays, but becoming vertical on the outer part of the ray, the section of the ray 
being there quadrangular in consequence. 
The marginal plates are well developed and form a conspicuous border to the 
abactinal surface. The supero-marginal plates are twenty-four in number from the 
median interradial line to the extremity. In the interbrachial are the surface of the 
plates is only slightly curved, thus forming the bevelled slope above noticed, and the 
supero-marginal plates do not there attain the extreme margin in consequence of the 
extension of the infero-marginal plates, which are visible when the starfish is viewed from 
above, sometimes extending a distance nearly equal to one-third of the breadth of the 
supero-marginal plates,—the amount seen varying according to the posture of the rays 
and the relative inflation of the disk. On the outer part of the ray, however, the abacti- 
nal and lateral areas of the supero-marginal plate are at right angles to one another, with the 
junction abrupt and subangular. The length of the supero-marginal plates is slightly 
greater than the breadth throughout the ray, excepting perhaps the innermost two or 
three in which the dimensions are subequal or with the breadth very slightly in excess. 
The height of the supero-marginal plates, where they enter vertically into the lateral wall, 
is rather more than half the length. The surface of the plates is covered with a mode- 
rately thick membranous tissue, which is continuous over the whole abactinal area of the 
disk and rays, and is beset with small, uniform, rather widely spaced granules. No spines 
of any kind are borne on the supero-marginal plates, but towards the extremity of the 
ray there is a tendency towards the formation of a low tubercular elevation on the angular 
rounding of the plate near its aboral end. Frequently on the plates that border the disk 
there is one, or sometimes two or three, small pedicellariz, having a pair of comparatively 
elongate pincer-formed jaws, placed in a small circular cavity. 
The infero-marginal plates correspond in number and length to the superior series, 
and are like them covered with membranous tissue and a similar small granulation. The 
breadth of the innermost four plates on each side of the median interradial line is rather 
greater than the length, but beyond this the length is the greater dimension throughout 
the ray. The bevelled angular edge of the infero-marginal plates which forms the extreme 
margin of the disk, bears a subregular horizontal series of four or five very short, conical 
pointed spinelets, sometimes with one or two additional above the line and sometimes 
with a little irregularity. These marginal dog-tooth-like spines do not extend beyond 
the area of the disk. Along the ray the infero-marginal plates, have a small, poorly 
developed tubercule on the rounding between the actinal and lateral areas and close 
to the aboral end of the plate, which becomes more definitely developed towards the 
extremity of the ray; and is much more distinct throughout than the low incipient 
tubercule noticed on the outermost supero-marginal plates. 
