44 THE VOYAGE OF H.MS. CHALLENGER. 
rays flat and level. Actinal surface of disk very prominent at the mouth-angles, and 
sloping thence to the margin and along the rays. 
The paxille of the abactinal area are moderately large, numerous, and usually well- 
defined, consisting of eight to twelve small, uniform, papillose spinelets, encircling a central, 
robust, more or less elongate, conical spinelet. Smaller paxille of three to five spinelets, 
and without a central conical spine, are interspersed occasionally amongst the larger 
paxillee, and entirely occupy the outer part of the ray. Peculiar pedicellaria-like bodies 
formed of four or five flattened and modified spines are present here and there, most 
frequently alone the margins of the abactinal area of the rays, where they form a more or 
less definite line close up to the marginal plates; and comparatively few are to be found 
upon the disk, excepting in the neighbourhood of the papular areas at the base of the rays. 
The marginal plates are small, and confined to the side of the ray, to which they form 
a nearly vertical wall. The supero-marginal plates are about thirty in number from the 
median interradial line to the extremity; they are longer than high, and little more than 
the thickness of the plate is visible on the abactinal surface. Each supero-marginal plate 
bears on, or near, this upper margin a moderately long conical spine, robust at the base, 
tapering to a sharp point, and directed almost vertically. Two or three spines on each side 
of the median interradial line are very small, then follow the longest spines on the ray, and 
the series diminishes gradually towards the extremity. In consequence of the length of the 
supero-marginal plates the spines are rather widely spaced. The general spinulation of the 
plate consists of minute conical granules, widely spaced. Below the spine the plate is usually 
very sparsely granulated, and not unfrequently a more or less extensive naked area occurs 
at the base of the spine, only a few well-spaced conical granules being present at the sides 
of the plate near the suture, except in the interbrachial arc, where the granules in- 
variably extend over the whole of the plate. One of the four-valved pedicellarize may be 
present on the suture between the supero-marginal plates, and sometimes two or three, or 
more, occur in close succession in the interbrachial are. 
The infero-marginal plates correspond to the superior series, each bearing a similar 
and equal-sized conical spinelet, directed horizontally and placed opposite to the supero- 
marginal spine. On the inner portion of the ray there may be one or two small spines at 
the base of the lateral spine. The superficial spinulation of the infero-marginal plates 
consists of conical or papilliform granules similar to those on the superior series, and some- 
times a similar naked or sparsely granulated area occurs below the spine. On the edge of 
these plates adjacent to the adambulacral plates are a series of pedicellariz of the same 
form as those above described on the abactinal surface, but rather irregular in their 
disposition. 
The adambulacral plates form an angular prominence into the furrow, and bear on 
their inner margin a semicircular comb of about seven short, equal-sized spines, which 
taper slightly, but are rather obtuse. External to these, on the actinal surface of the plate, 
