216 THE VOYAGE OF II. M.S. CHALLENGER. 



adambulacral plates is more stumpy in character, and there are usually two unequal, 

 flattened, papilliform spinelets on the actinal surface of the plate, with a smaller one 

 behind them opposite their interspace. 



14. Astropecten monacanthics, Sladen (PI. XXXIII. figs. 7 and 8 ; PI. XXXVII. 



figs. 10-12). 

 Astropecten monacanthus, Sladen, 1883, Journ. Linn. Soc. Lond. (Zool.), vol. xvii. p. 263. 



Rays five. R = 26 mm. ; r = 1 mm. R > 3 - 5 r. Another specimen measures, 

 R = 22 mm. ; r=6 mm. Breadth of a ray at the base, 6 "25 mm. 



Disk moderately large. Rays rather long and narrow, tapering rather rapidly on the 

 outer portion to a pointed extremity. Interbrachial arcs rounded. 



The paxillar area is wide, measuring more than three times the width of the supero- 

 marginal plates near the middle of a ray, and is very regular in composition. The paxillce 

 are large and well-spaced, and have one large granule-like spinelet in the centre of the 

 tabulum, and seven to ten very short clavate spinelets on the circumference radiating out 

 widely, almost horizontally. Occasionally on the disk, paxillse have two to four central 

 granules ; but the single, large-sized, low granule is very characteristic. On the sides of 

 the rays the paxillse are arranged in transverse lines, about three or four in each ; the 

 median radial band is scarcely defined. In the centre of the disk a conical peak is present, 

 in the neighbourhood of which the paxillse become very small and crowded. In some cases 

 the centre of the cone is invas;inated. 



The supero-marginal plates, about twenty-three in number from the median interradial 

 line to the extremity, which are small, higher than broad, and not tumid, form an even and 

 well-rounded margin to the ray ; their extension on the abactinal surface is small in con- 

 sequence of the narrowness of the plates. The surface of the plates is covered with large, 

 fiat-topped, well-spaced granules, which diminish a little in size at the margins ; and the 

 suture or furrow between the neighbouring plates is almost hidden. The usual fine cilia, 

 if present, are entirely concealed. No spinelets or tubercles of any kind are borne on the 

 supero-marginal plates. 



The infero-marginal plates, which are much broader than high, do not extend beyond the 

 superior series, and have a sharp subangular rounding towards the actinal surface. Each 

 plate bears a single lateral spine, and no other spines are present, the whole surface of the 

 plate being covered with moderately spaced, small, flat, subacuminate squamules very little 

 longer than broad. Two of the squamules immediately behind the lateral spines are longer 

 than the rest, and subspiniform. There is no tendency to develop spines on any other part 

 of the plate. The lateral spines are short, delicate, subcylindrical, slightly compressed, 

 tapering from the base to a very finely pointed extremity, and are very faintly curved : 

 they are directed horizontally from the ray at right angles to the axis, and are wide apart ; 



