178 THE VOYAGE OF H.M.S. CHALLENGER. 
ing. The largest paxille occur midway between the centre of the disk and the margin, 
and at the base of the rays. These consist of a comparatively large, convex tabulum, 
covered with rather coarse hemispherical granules, having more or less of a mulberry 
form, with a fringe-like series at the margin of the tabulum of short, equal, skin-covered 
papilliform spinelets, all directed horizontally. On the large paxillee there may be from 
ten to twenty granules on the central area of the tabulum, and from sixteen to twenty in 
the marginal series. In the medium-sized paxille, beyond the base of the ray and in the 
neighbourhood of the margins throughout, there are not more than three or four of the 
central granules, and eight to ten of the marginal series, whilst in the smaller paxille on 
the outer half of the ray there is seldom more than one central granule, and seven or 
eight appear to be the normal number of marginal spinelets; in these the membranous 
investment is even more apparent than on the larger paxille, and is continuous or united 
for a considerable distance between adjacent spinelets. Upon the rays the paxille are 
arranged in remarkably regular, straight, transverse series, which extend uninterruptedly 
from one series of marginal plates to that on the other side of the ray, traversing the 
whole paxillar area of the ray. Although there is no formation of a definite median line, 
the paxillee in the middle of the area on the inner third of the ray are distinctly larger 
than the others in the same transverse series. 
The marginal plates are large and remarkably massive, forming a broad border to the 
abactinal and actinal areas, and are well rounded in the lateral wall. The supero- 
marginal plates, thirty or thirty-one in number from the median interradial line to the 
extremity, have the breadth equal to about twice the length, the proportion diminishing 
slightly towards the extremity. Their height at the summit of the interbrachial arc is 
about twice the length, about midway on the ray it is nearly one and a half, and at the 
extremity subequal. The width of the paxillar area is equal to that of the supero- 
marginal plate at the fifteenth plate from the median interradial line ; midway on the ray 
it is rather greater. The plates are slightly, but rather flatly, convex along their median 
transverse line (¢.e., breadth), and are separated by well-defined channels. Their sur- 
face is covered with rather large, uniform, tolerably well-spaced, hyaline, hemispherical 
granules, which are abnormally deciduous, and around the margin of the plate is a fringe 
of small, uniform, papilliform spinelets, invested with a continuous web-like membrane, 
directed horizontally in relation to the vertical plane traversing the breadth of the plate ; 
the fringe thus covers over the furrow between the supero-marginal plates, and is con- 
tinous round the end of the plate abutting on the paxillar area. There are no spines on 
the supero-marginal plates. 
The infero-marginal plates correspond exactly to the superior series, and their length 
is the same; their height in the lateral view is nearly twice their length at the summit of 
the interbrachial arc, but diminishes along the ray, being subequal or even slightly less 
when midway. Their breadth on the actinal surface is about twice the length midway 
