546 THE VOYAGE OF H.M.S. CHALLENGER. 



capable of some inflation, tapering gradually from the base to the extremity, the outer 

 half of the ray being narrow and attenuate, and the tips recurved in the specimen under 

 notice. The disk is comparatively large for the genus. 



The plates of the abactinal surface are small and form a compact network. Amongst 

 them are larger plates, which are slightly more prominent and bevelled into an indistinct 

 ridge ; and these larger plates are so arranged as to form a continuous but still more or 

 less indistinct, large and widely-open network, in the large meshes of which are placed a 

 number of the smaller plates with single isolated papulae interspersed. Upon the larger 

 plates are borne small compact groups of short microscopic spinelets, the groups being 

 distinctly spaced ; on the smaller plates within the meshes there are seldom more than two 

 or three similar spinelets, and their posture is divergent rather than tendiug to form a 

 compact group. All the spinelets are covered with skin, and they are undistinguishable 

 without the aid of a magnifying-glass. 



An indistinct" line of small narrow plates, forming a thin longitudinal series (the 

 posture of the plates being horizontal), may be discerned on the upper part of the lateral 

 wall of the ray, the representatives, perhaps, of a supero-marginal series. About midway 

 between this series and the adambulacral plates is a second longitudinal series of larger 

 plates (the posture of the plates being vertical), probably the representatives of an infero- 

 margiual series. The plates of both these series bear groups of spinelets similar to those 

 above described. The intermediate space between the two series, which diminishes in 

 breadth as it extends along the ray, is occupied by small plates similar to those on the 

 abactinal surface, and these have a tendency to form vertical and equally spaced lines 

 between the two longitudinal series, with irregular plates and papulae in the interspaces. 

 Much irregularity, however, occurs, and the arrangement indicated can only be made out 

 here and there. The space between the lower longitudinal series (the infero-marginal 

 plates 1) and the adambulacral plates is occupied by larger plates, arranged in more or less 

 regular longitudinal lines parallel to the furrow. These plates, which are probably actinal 

 intermediate plates, are much more uniform and bear more definite groups of rather longer 

 spinelets than those on the lateral and abactinal areas. About two series of these inter- 

 mediate plates may be counted midway on the ray, and the number increases gradually 

 towards the disk. Papulae are present between the intermediate plates. 



The armature of the adambulacral plates consists of a single small skin-covered spinelet 

 standing at the apex of the plate and placed high in the furrow, which is followed by about 

 two or three pairs of larger spinelets and a small compact group of irregularly placed 

 spinelets, the whole forming a transversely placed group, the spinelets of which decrease in 

 size as they recede from the furrow. 



The madreporiform body, which is rather large and circular, is situated rather nearer 

 the centre than midway between that point and the margin. Its surface is grooved with 

 deep striae, radiating from the centre to the margin, and the intervening dissepiments 



