5G TUE VOYAGE OF H.M.S. CHALLENGER. 



midway along the ray they consist of three, or rarely four, very short spiuelets, whilst 

 only one or two are frequent near the margin. On the central part of the disk, larger 

 paxillse occur, with five or sis, or even more, spinelets. When more than five are present, 

 one is usually central, but is uniform in length and size with the rest. In each inter- 

 radial line, midway between the centre of the disk and the margin, is a conspicuous 

 circular plate bearing twenty to thirty spinelets similar in all respects to those forming 

 the paxilla3, of which in fact this may be considered as an enlarged example. These are 

 probably the representatives of the primary basal plates of the embryo. There is also a 

 similar large oval plate, slightly convex, on the inner side of the papularium, which appears 

 to be the representative of the primary radial plate. No definite order is discernible in 

 the arrangement of the paxilltB, and no pedicellariae are present on the abactinal area. 



The supero-marginal plates, eighteen in number from the median interradial line to 

 the extremity, form a moderately broad, definite, and well-rounded border on the abactinal 

 surface ; they are longer than broad, and the suture or line of junction between adjacent 

 plates is more than usually oblique, passing from within outwards adorably. The height 

 and breadth are subequal, the latter dimension being perhaps slightly the greater, except 

 in the innermost part of the series. Each supero-marginal plate bears a single, short, 

 conical spinelet, broad at the base and tapering throughout to a sharply pointed extremity. 

 They are placed upon, or even on the lateral side of, the rounding of the plate. The 

 fourth or fifth from the base of the ray measures about 2 '2 5 mm. in length ; and they 

 decrease in size as they proceed outwards, whilst the innermost pair are very small. The 

 rest of the surface of the supero-marginal plate is covered with minute, uniform, and 

 tolerably closely placed thornlets. 



The infero-marginal plates are rather higher than the superior series, except on the 

 inner part of the ray ; and they show a decided tendency to alternate with the companion 

 series instead of each being placed immediately opposite or under the corresponding plate ; 

 the upper margin of the infero-marginal plates and the lower margin of the supero-marginal 

 plates being angulated so as to appear superficially bifacetted. The breadth of the infero- 

 marginal plates is greater than that of the superior series ; and their breadth on the inner 

 part of the ray is greater than the length, but the latter dimension increases and becomes 

 the greater on the outer part of the ray. Each plate bears a short lateral spine near the 

 upper margin, of the same size and character as those on the supero-marginal plates ; and 

 the rest of the plate is covered with small, uniform, tolerably closely placed thornlets, 

 like those on the superior series of plates, amongst which no larger spinelets whatever 

 occur. 



The adambulacial plates are elongate and narrow, excepting the prominent angular 

 extension into the furrow. Their armature consists of:— (1.) A furrow series of seven 

 short, cylindrical, obtusely pointed spinelets (the median three or more, the longest), arranged 

 on the free margin of the plate which projects into the furrow, and forming a scoop-like 



