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



adambulacral plates, widely spaced and standing in a subregular lineal series parallel to 

 the median suture. On the anterior part of the plate are two or three isolated and much 

 smaller spinelets, and there is usually a thornlet or miliary spinelet opposite the middle 

 spine of the three main superficial mouth-spines, or opposite the interspace between the 

 middle and the outermost. The surface of the plates is covered with membrane and no 

 other spinelets are present. 



The actinal interradial areas are very small, and do not extend beyond the third or 

 fourth marginal plate, and probably not more than twelve or fifteen intermediate plates 

 are present in each ; but the exact number is undeterminable on account of the whole area 

 being covered with membrane. Between each of the plates of the inner row is one of the 

 spiracle-like pedicellarian apparatus, similar to those just described, but much larger ; 

 and there are thus five or six in each area. The few remaining intermediate or ventral 

 plates bear one or two short, cylindrical, obtusely tipped spinelets. 



The anal aperture is subcentral, small and very distinct ; it is surrounded by small 

 spinelets somewhat larger than the small spinelets on the spicules generally. 



The madreporiform body which is comparatively large and oval, is situated a little on 

 the outer side of midway between the centre of the disk and the margin. Its surface is 

 sub-plane or very faintly convex, and is grooved with highly convoluted furrows, the 

 general direction of the striations appearing to radiate from a central point to the margin. 



The papulae, which are rather large and distinct, are confined to an area at the base 

 of the rays, which does not extend beyond the fourth supero-marginal plate, but reaches 

 on the disk as far as the spine referred to as marking the primary radial plate. No 

 papulae are present on a band-like area along the median interradial line; and on the 

 outer part of the papularium at the base of the ray, there is likewise a V-shaped area, 

 with the angle passing far downward adoentrally along the median line, which is similarly 

 devoid of papulas. 



Colour in alcohol, a bleached ashy white ; with some traces of a brownish, or dark 

 purple, pigment remaining upon the abactinal surface. 



Individual Variation. — In some cases the small spinelets on the abactinal plates 

 or spicules are very regularly grouped into threes or fours along the ray, excepting just at 

 the sides. The regularity of this arrangement gives at first sight rather a striking feature. 

 In other examples no such general grouping takes place, although here and there a faint 

 approach to it may be noticed. The usual pedicellariee are present in both instances. 

 The second large spine on the infero-marginal plates is more definitely developed in some 

 cases than others ; and in some specimens when this spine is small its character is in a 

 great degree masked by the presence of a companion smaller spinelet standing beside 

 it, giving the appearance of a pair of small spinelets standing side by side below the true 

 lateral spine. 



Young Phase (?). — There is a very small specimen from Station 143 which is probably 



