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 papulee 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 tending 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- 
marginal 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 papule in the interspaces. 
Much irrecularity, 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 ?) 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. Papule 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 strix, radiating from the centre to the margin, and the intervening dissepiments 
