36 THE VOYAGE OF H.M.S. CHALLENGER. 
disk have a delicate elongate central spinelet, and these are chiefly in the region of the 
papularia ; along the rays, however, the occurrence of the central spinelet is more fre- 
quent. No order is traceable in the arrangement of the paxille. No pedicellarie are 
present on the abactinal surface, nor elsewhere on this species. 
The marginal plates form a broad and slightly raised border to the disk and rays, the 
breadth of which diminishes gradually towards the extremity of the rays. ‘The supero- 
marginal plates are thirty-nine in number (forty-four in the largest example) from the 
median interradial line to the extremity. Their breadth is greater than their length. 
The breadth of the paxillar area midway on the ray is only equal to, or very little greater 
than, the breadth of the supero-marginal plates. The height is greater than the length 
in the innermost plates of the ray, but rapidly diminishes, being subequal along the 
greater part of the ray, and less than the length near the extremity. Hach supero- 
marginal plate, excepting the first on each side of the median interradial line, bears a 
single very small conical-pointed spine, which stands on the middle of the rounded angle 
of the plate. The longest of these spines is not more than 1°75 mm. in length, and 
they diminish in size as they proceed outwards, becoming mere microscopic thornlets 
on the outer part of the ray. The surface of the plates is slightly tumid, emphasising 
the divisional sutures, the direction of which is slightly oblique, trending from within 
outwards towards the base. The surface of the plates is covered with very minute 
subpapilliform spinelets, widely spaced. 
The infero-marginal plates correspond to the superior series, and on the inner part 
of the ray the two series alternate instead of being directly superposed. Each plate bears 
a single short, robust, tapering lateral spine, the longest about 2°5 mm. in length, and 
decreasing in length on the outer part of the ray. The surface of the plate is covered 
with small, short, papilliform but slightly tapering thornlets, well spaced, which become 
more spiniform as they approach the lateral spine, the two or three immediately below 
this being longer than any of the others, but still none long enough to be ranked as a 
companion lateral spine. 
The adambulacral plates have a prominent angular projection towards the furrow. 
Their armature consists of :—(1.) A furrow series of six or seven rather elongate, cylindrical, 
tapering spinelets, the median one longest, and all radiating apart. In consequence of 
the straight sides of the angular projection of the adambulacral plate the furrow series of 
spines have more or less the appearance of being divided into two sets which radiate 
apart. (2.) On the actinal surface of the plate are two robust tapering spines, and occa- 
sionally three on the inner part of the ray, forming an oblique series, the median spine 
being longest when three are present, and this is usually equal to or longer than the longest 
of the furrow series. On the aboral side of this oblique series and on the actinal surface 
of the plate are usually two small delicate spinelets which appear to form with more or 
less regularity a secondary series parallel to the larger one. On the adoral margin of 
