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



The abactinal area is covered with small plates, the major diameter of which is usually 

 transverse in relation to the ray, showing a more or less distinct tendency to form 

 longitudinal series along the ray. A median radial series is more or less indistinctly indi- 

 cated by a faint ridge, and on the sides of the rays a regular arrangement in longitudinal 

 as well as transverse series occurs. Several small, uniform, papilliform spinelets are borne 

 on each plate, well spaced apart, and several small forcipiform and forficiform pedicellariae 

 which at first sight can hardly be distinguished from the spinelets ; the whole forms a 

 uniform papillose covering to the abactinal surface in which no definite order of arrange- 

 ment can be detected. On the plates that I consider to be the representatives of the 

 supero-marginal plates there are generally one or two spinelets definitely placed, which 

 may stand as an oblique pair,Hhe series forming a regular longitudinal line along the 

 ray. Between the supero-marginal and the infero-marginal plates, there are on the 

 inner part of the ray in large examples one or two series of intermediate plates, separated 

 by papulae, the spinelets on which show a tendency to fall in lineal transverse series. On 

 the abactinal area generally single papulae occur between the plates. 



The infero-marginal plates, which stand at the junction of the lateral and actinal 

 areas, form a regular longitudinal series along the ray. Each plate bears an oblique series 

 of three short, compressed, flaring, truncate, chisel-shaped spinelets, which radiate slightly 

 apart, and form an oblique comb at the margin of the ray. Sometimes the truncate 

 extremity of the spinelet is more or less crenulate or denticulate. 



The adambulacral plates are contingent on the infero-marginal plates. Their armature 

 consists of two moderately robust, equal spinelets, which stand one behind the other and 

 radiate apart, forming two regular longitudinal series on each side of the furrow. The 

 outer spine of the pair is usually more or less compressed and chisel-shaped, resembling 

 the spinelets on the infero-marginal plates, but is not so broad ; the inner spine, on the 

 other hand, is generally subcylindrical, tapering, but rather obtusely pointed, and skin- 

 covered. At the base of the inner series of spines, and rather high in the furrow, is a 

 series of small forficiform pedicellariae. Occasional isolated forficiform pedicellariae are 

 present between the outermost spines on the adambulacral plates and the comb of spines 

 on the infero-marginal plates. And one or even more very large robust forficiform pedi- 

 cellariae may not infrequently be found in the narrow actinal interradiai area behind the 

 mouth-plates. Several large forficiform pedicellariae with broad, curved, denticulated, 

 interlocking extremities, may generally be found on the disk at the summit of the inter- 

 brachial arc. 



The madreporiform body is small, and situated near the margin of the disk. It is 

 grooved with comparatively few, coarse, convoluted striations, and its periphery, which is 

 circular, is surrounded by a circlet of spinelets. 



The ambulacral furrows are wide, and the tube-feet, which have a fleshy terminal disk, 

 are quadriserially arranged. 



