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



It is directed at a slight angle to the vertical outwards (sometimes inwards on the outer 

 part of the ray), and towards the extremity. 



The mouth-plates are small and elongate, the outline of the united pair being fusi- 

 form, and their surface is not convex or prominent actinally. Their armature consists of 

 a marginal series of five or six small spinelets, which extend from the inner extremity 

 to the junction with the adambulacral plate. Close within this series is a second which 

 quite masks them, consisting of a lineal series of eleven or twelve short, robust, subcorneal 

 and pointed spinelets, which extend from one extremity of the plate to the other, de- 

 creasing slightly in length, but less in robustness, as they recede from the mouth. 



The actinal interradial areas, which are comparatively small and triangular, are occupied 

 by a few very large, regular, intermediate plates, arranged in definite order, mosaic-like and 

 not imbricating. The first or innermost plate on each side of the median interradial line 

 is considerably larger than the mouth-plates, and the pair together have an hexagonal 

 outline ; they occupy fully two-thirds of the distance between the mouth-plates and the 

 marginal plates, and are separated by a median suture corresponding to the median inter- 

 radial line. The space intervening between this pair and the marginal plates is occupied 

 by a single odd oblong plate standing in the median interradial line ; only in one area, in 

 the specimen under description, are there two plates, and these are symmetrical, and 

 the suture marking their line of imion falls in the median interradial line. The other 

 plates extend the whole way from the adambulacral to the marginal plates, and vary in 

 shape according to their position. The number also varies from three to five in each half 

 area, and may vary even in the two halves of one and the same area. The second plate 

 counting from within is in all cases the largest plate in the area. The surface of these 

 plates is covered with small, hemispherical, deciduous granules, similar to those on the 

 marginal plates, and round the margin of each plate is a fringe of small spinelets united 

 by a membranous web, similar to that described on the marginal plates, which is directed 

 horizontally over a channel running between the plates. 



I have been unable to detect the slightest trace of an anal aperture ; indeed, from the 

 small and compact character of the paxillse in the centre of the dorsal area, it might be 

 said, reasoning from the analogy of Astropecten, that no such aperture existed. The 

 region is sometimes slightly protruded in a low cone, sometimes slightly introverted in 

 the centre. 



The madreporiform body is moderately large, subcircular, and situated midway between 

 the centre of the disk and the margin. The central area of the body is abruptly elevated 

 and occupied by one of the mulberry-like masses of hemispherical granules similar to 

 those on the tabulum of the paxillas, and this again is surrounded by the marginal fringe 

 of spiuelets (in fact a central, but sessile, paxilla) ; beneath this the striation-furrows, 

 which are fine, may be seen radiating to the periphery of the body. 



The ambulacral furrows are completely closed in by the adambulacral plates and 



