100 THE VOYAGE OF H.M.S. CHALLENGER. 
Rays short, tapering shghtly along the ray, but rapidly at the extremity, and although 
narrow they have a comparatively robust appearance. Interbrachial arcs widely rounded. 
Disk large. Abactinal surface slightly inflated. Actinal surface subplane or slightly pro- 
minent centrally, and sloping thence to the margin. 
The paxille of the abactinal surface are small, compact, and, though very near 
together, are distinctly spaced ; the larger ones are composed of ten to fifteen small, low, 
rounded, papilliform granules, forming a compact group of uniform height, but sometimes 
those in the centre are a little more robust than the others. Smaller paxille are inter- 
spersed, but no order of arrangement is to be observed except near the margin of the disk 
and the base of the rays, where the paxille are disposed in lineal series, the lines of 
which, if produced beyond the margin, would converge to a point in the prolongation of 
the median interradial line. 
The supero-marginal plates, sixteen or seventeen in number from the median inter- 
radial line to the extremity, are small, and form a conspicuous and well-defined border to 
the disk and rays. When viewed from above their breadth on the abactinal surface is 
slightly greater than their length; when viewed laterally the length is slightly greater 
than the height on the outer part of the ray, but the height increases towards the inter- 
brachial arc, and in the innermost plates the height is greater than the lencth. The 
supero-marginal plates bear no spines, but their surface is covered with low, rounded, 
subpapilliform granules, which are well spaced, and those in the median region of the 
plate are slightly larger. 
The infero-marginal plates correspond exactly to the superior series. Their surface 
is covered with well-spaced, conical, subpapilliform granules. The plates in the inter- 
brachial are and at the base of the ray bear at the junction of the actinal and lateral 
regions a single, large, very robust, but conical granule or papilla, which can in no way 
be spoken of as a spine, though it is the only representative they possess of a lateral spine. 
The adambulacral plates are elongate, and have the margin towards the furrow slightly 
curved. ‘Their armature consists of :—(1.) A furrow series of seven very short, cylindrical, 
obtuse spinelets, which are almost subequal, except at each extremity of the series, 
where the spinelets are usually much smaller. (2.) The actinal surface of the plate is 
covered with equal-sized, uniform, obtuse, papilliform granules, which, though not form- 
ing altogether regular lines, have a longitudinal disposition suggestive of two or even 
three irregular series. There is no trace, even at the extremity, of the single, large, conical 
spine, which is usually present there in this genus. 
The mouth-plates are elongate and narrow. The united pair are prominently convex 
along the line of suture. Their armature consists of a marginal series of about ten short 
spinelets, the outer five or six being little more than papilliform granules; the rest are 
short, conically-pointed spinelets, increasing slightly in length as they proceed inwards. 
The actinal surface of the plates bears numerous small, obtuse, papilliform granules, 
