334 THE VOYAGE OF H.M.S. CHALLENGER. 
at the margin, where a faint tendency to develop rudiments of two or three very 
short radiating processes may be noticed. No caleareous union or connection exists 
between individual paxille. Numerous small papulze occur in the interspaces, three to 
five being present in the quadrangle formed by four neighbouring paxille. Their mem- 
brane is very delicate, and they taper somewhat rapidly towards the tip, which is thickened 
into a small knob. Owing to the manner in which the papule taper, a comparatively 
swollen appearance is given to their lower part. 
The marginal plates, which are small and subtubercular in appearance, are arranged in 
superior and inferior series, thirty-seven to thirty-eight plates being present in each 
between the median interradial line and the extremity of the ray. Each plate is rounded 
or boss-like externally, and covered with a great number of small spinelets similar to 
those of the paxille, which gives them a prominent cushion-like appearance. The infero- 
marginal plates are the largest, transversely suboval in form—the length increasing 
towards the summit of the interbrachial are—and bear not less than a hundred spinelets. 
The supero-marginal plates are smaller, usually round, and are placed rather more 
aborally than the companion plate of the lower series, the pairs standing consequently 
slightly oblique. ; 
The actinal interradial areas are well developed, and the intermediate plates extend 
up to the very extremity of the ray. The plates, which are oblong, are arranged in 
regular transverse and slightly oblique lines between the adambulacral plates and the 
marginal plates. Hach series or column thus formed is isolated, being separated from the 
neighbouring column by a narrow space; and each plate in a column overlaps or imbri- 
cates upon the next innermost plate. The number of the columns corresponds exactly to 
that of the adambulacral plates, and is not in relation with that of the marginal plates. 
The whole actinal area is overlaid by a uniform layer of membrane, by which the shape 
of the individual intermediate plates is hidden from superficial observation. Each inter- 
mediate plate bears a single paxilla near its free extremity, which is rather more robust 
than those on the abactinal surface, and carries rather fewer spinelets, which are somewhat 
longer and more widely expanded. The paxille, like those on the abactinal area, are 
naked and not invested with membrane. In consequence of the size and arrangement of 
the intermediate plates, the actinal paxille are more widely spaced than the abactinal 
ones, and are disposed in regular lines which run from the adambulacral plates to the margin, 
the lines or columns being marked off by straight furrows or wrinkles in the membrane. 
As the paxille ave equidistantly spaced in each of these transverse rows, equally regular 
and uniform longitudinal lines are also traceable along the ray. In the interbrachial arc 
nine or ten paxille stand in each transverse series, the same number being maintained 
until about the outer fifth of the furrow. 
The adambulacral plates are broader than long, and appear to stand on the furrow 
margin as the terminal plates of the transverse series of actinal intermediate plates ; 
