REPORT ON THE ASTEROIPEA. 89 



circlet. In the central region of the disk, along the median radial line, and upon the 

 whole of the outer two-thirds or more of the rays, no order of arrangement is discernible. 

 In the abactinal interradial areas, on the region adjacent to the marginal plates, the paxilla? 

 are disposed in regular lineal series, the lines of which, if produced beyond the margin, 

 would meet at a point in the prolongation of the median interradial line. Ei"h.t or nine 

 paxillae may be counted in the series adjacent to the median interradial line, and the 

 paxillse in each series decrease slightly in size as they approach the margin. This arrange- 

 ment extends only a very short distance outward beyond the base of the rays. 



The supero-marginal plates, twenty-three or twenty-four in number from the median 

 interradial line to the extremity, are large, and form a broad and very conspicuous margin 

 to the disk and rays. On the innermost plates in the interbrachial arc the breadth is more 

 than twice the length, but gradually diminishes until these dimensions are subequal, a 

 proportion which is then maintained throughout the ray. The width of the paxillar area 

 midway along the ray is slightly less than the breadth of the supero-marginal plate. The 

 outer surface of the plate is regularly curved or arched, and forms a slightly bevelled 

 rounding to the abactinal area ; and on the inner part of the ray there is also a trace of a 

 median convexity along the breadth of the plate. The supero-marginal plates bear no 

 spines, but their surface is covered with very numerous small granules, uniform through- 

 out, which, though closely crowded, do not touch one another. The suture-lines between 

 successive plates are well defined by a distinct channel; and this in the interbrachial 

 arc is rather deep and emphasised by the convexity of the plates. 



The infero-marginal plates correspond exactly to the supero-marginal series, and their 

 length is the same ; their height in the lateral view is slightly greater than the length 

 in the inner part of the interbrachial arc, but speedily becomes less than the length, the 

 proportion being about two-thirds midway along the ray and outwards. Their breadth 

 on the actinal surface is more than twice the length on the innermost plates in the inter- 

 brachial arc, but gradually diminishes along the ray, until the dimensions become subequal 

 near the extremity. The rounding of the plates externally is rather sharp and abrupt, 

 and the infero-marginal plates are a shade more prominent than the superior series, 

 which causes them to be just visible when the starfish is viewed from above. Each plate 

 bears a single, short, robust, conical spinelet, about a millimetre in length, which is placed 

 on the rounding, centrally between the adoral and aboral margins of the plate in the inter- 

 brachial arc, but gradually travels nearer to the aboral margin as the plates proceed along 

 the ray. The surface of the plate is covered with numerous, very small, uniform granules, 

 similar to those on the supero-marginal plates ; and the suture lines between the successive 

 plates are well defined by channels. 



The adambulacral plates are longer than broad, and have the farrow margin slightlv 

 convex. Their armature consists of : — (1.) A furrow series of seven or eight short, cylin- 

 drical, faintly clavate, spinelets ; the outermost at each extremity of the series smaller 



(ZOOL. CHALL. EXr. — PART LI. — 1887.) 1 2 



