378 THE VOYAGE OF H.M.S. CHALLENGER. 
whole thickness of the lateral wall. The superior and inferior series alternate more or 
less distinctly. The plates, which are subequal and similar in size and character, bear a 
group of small equal-sized spinelets about twenty in number. The groups are well-spaced 
apart, the interspace being greater than the breadth of the group (7.e. length in relation to 
the ray), and they appear to have a vertical disposition, the height of the group being 
greater than the length. The spinelets are similar to those on the abactinal plates, and 
their bases are similarly imbedded in membrane. About twenty-five infero-marginal 
plates may be counted between the median interradial line and the extremity. 
The adambulacral plates are small, and their armature consists of two rather short, 
robust, subequal, slightly tapering spinelets placed on the furrow margin of the plate, and 
standing slightly oblique, the adoral spinelet being more inward. On the actinal surface 
of the plates is an oblique series of three obtuse, cylindrical, dumpy spinelets, shorter than 
the furrow series. On the inner half of the ray this series forms an angle of about 45° to 
the line of the furrow. On the outer part of the ray the adambulacral plates are very 
short, and there is only one spinelet on the furrow margin, and the spinelets on the 
actinal surface of the plate—here reduced to little more than papilliform granules—form 
with it a single transverse line. 
The mouth-plates are large, and their armature consists of five robust, subequal spines 
on the free margin of each plate. The actinal surface is plane and covered with mem- 
brane, and the only spines borne on this surface are a group of two or three placed far 
back near the outermost end of each plate. The marginal spinelets have a slight down- 
ward trend, which causes the united pairs of mouth-plates to have rather a scoop-shaped 
appearance. 
The actinal intermediate plates are small and regularly arranged, forming lines parallel 
to the furrow, and series which run obliquely from the adambulacral to the marginal 
plates. Hach plate bears three or four short, cylindrical, obtusely-rounded, equal, erect, 
papilliform spinelets, which are skin-covered and imbedded at the base, forming a 
definitely spaced little group, more or less paxilliform in appearance. Only the series 
adjacent to the adambulacral plates extends to the extremity of the ray. The other 
series terminate gradually along the ray: eight or nine groups may be counted at the 
median interradial line. 
The madreporiform body, which is large, circular, and more or less convex, is situated 
nearer the centre than midway between that point and the margin, and there are several 
larger groups of spines amongst those which surround it. 
The anal aperture is slightly excentric; there is no modification in the spine-groups 
around its periphery. 
The ambulacral tube-feet have well-defined sucker-disks. 
No pedicellarize are present. 
Colour in alcohol, a bleached yellowish white, with a slightly warm brownish shade. 
AS al 
