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



Kays elongate, very narrow on the outer portion, moderately broad at the base, and 

 tapering continuously therefrom to the extremity, which is fine and pointed. Inter- 

 brachial arcs acute, but rounded. 



The abactinal paxillar area is very uniform and compact in character, the paxillse 

 diminishing in size towards the centre of the disk and the extremities of the rays. The 

 paxillse consist of three to six central granules, surrounded by about a dozen short papilli- 

 forrn spinelets on the margin of the tabulum. The paxillse are arranged in regular trans- 

 verse lines at the sides of the ray, whilst the median line is narrow and with the paxillas 

 slightly larger and irregular in their arrangement. In some examples a slight prominence 

 occurs in the centre of the disk. 



The supero-marginal plates, about 40 in number from the median interradial line to 

 the extremity, are comparatively flat, and higher than broad, their surface forming an 

 arched bevel to the ray rather than a tumid rounding. Flat squamiform granules are 

 present on the upper part of the plate, but are wanting on the lower part, which is 

 covered with membrane. No spines or tubercles of any description are present on the 

 supero-marginal plates. 



The infero-marginal plates are higher than broad, and form a gentle and weii-rounded 

 curve on the actinal surface. In consequence of the form of the plates, nearly the whole 

 height of the supero-marginal and infero-marginal plates can be seen when the side of the 

 ray is placed in direct line of view. Each infero-marginal plate bears three small, straight, 

 flattened, tapering and sharply-pointed spinelets arranged close together in an oblique line 

 close to the lateral margin and the aboral edge of the plate. The upper spinelet, which is 

 nearest the margin, is the smallest, and the other two are about equal in length. All are 

 directed slightly outward in the direction of the ray, and being closely appressed to the 

 side of the ray are almost invisible when seen from above. On the inner half of the ray a 

 fourth spine is present a little way behind the foregoing on the aboral side of the plate, 

 and on the innermost plates of all a fifth may also occur. The infero-marginal plates have 

 a number of small, closely placed, papilliform squamules on the end adjacent to the adarn- 

 bulacral plates, but the rest of the plate is covered with membrane. 



The armature of the adambulacral plates consists of an inner or furrow series of five or 

 six nearly equal and delicate spinelets, slightly clavate, cylindrical or subcompressed, which 

 form a very slightly radiating fan. The second series usually consists of three spinelets, 

 shorter and more compressed than the inner series, and with truncate tips ; and the third 

 series of three or four similar spines. Irregularity frequently occurs in the arrangement of 

 the second series. 



External to the adambulacral plate is a small intermediate plate, the series of which 

 extends far along the ray ; these bear a compact group of six to eight spinelets, similar in 

 every respect to the outer series of adambulacral spinelets, and from which they are 

 indistinguishable on the outer part of the ray, forming together a common group. The 



