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 (i.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 fines parallel 

 to the furrow, and series which run obliquely from the adambulacral to the marginal 

 plates. Each 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 pedicellarias are present. 



Colour in alcohol, a bleached yellowish white, with a slightly warm brownish shade. 



