REPORT ON THE ASTEROIDEA. 153 
2. Styracaster armatus, Sladen (Pl. XXIV. figs. 1-4; Pl. XXVIIL figs. 1-4). 
Styracaster armatus, Sladen, 1883, Journ. Linn. Soc. Lond. (Zool.), vol. xvii. p. 232. 
Rays five: “R=38 mm); 7—1mm, R < 3°57: 
Rays long and slender, subcylindrical, nearly uniform in thickness throughout their 
leneth, the expansion at the base and the attenuation at the tip being very slight. The 
disk is depressed, not inflated, and not higher than the marginal plates ; the minor radius 
is in the proportion of 28 per cent. The interbrachial arcs are very wide, with the curve 
somewhat flattened in conformity with the pentagonal character of the disk. 
The abactinal area is covered with a leathery integument beset with minute imperfect 
pseudo-paxille, and simple spiculate spinelets closely crowded, the general appearance 
being that of spinelets only. Naked spaces occur at the base of the rays. No definite 
epiproctal protuberance is present, but a faintly elevated indication of the centre may 
be discerned. 
The marginal plates are high, curving slightly inward above and below, and forming a 
rounded margin. The supero-marginal plates are nine in number from the median inter- 
radial line to the extremity, exclusive of the terminal, and all are considerably longer than 
high. Along the rays, commencing at the fourth plate from the median interradial line, the 
supero-marginal plates on each side meet in the median radial line and entirely encase the 
upper portion of the ray. The ray is rather compressed laterally, and the abactinal sur- 
face is arched. ach alternate supero-marginal plate along the ray bears a large robust 
conical spine placed in the median line of the ray, the series forming a single line of five 
spinelets, which stand perpendicular to the ray and diminish in size as they proceed out- 
ward. Unfortunately many of the spines have been damaged, but the longest remaining 
one measures about 6 mm., and the tip appears to have been broken. The ‘penultimate 
supero-marginal plate is small, and the ray is slightly bent upwards at the extremity. 
The terminal plate is small and comparatively inconspicuous, not at all swollen or tuber- 
cular, and is less than the pair of ante-penultimate supero-marginal plates. It bears three 
spinelets, one in the median line above the extremity of the ambulacral furrow, and two 
beneath, all close together. 
The infero-marginal plates correspond in number to the superior series, but their 
length is very much greater in relation to their height—fully three times. The four 
outermost plates do not correspond in length to the companion supero-marginal series. 
Three cribtiform organs are present in each interbrachial arc; they are rather broad, 
but well defined, and their structure is papilliform. (See Pl. XXVIII. fig. 4.) 
The ambulacral furrows are very narrow and quite closed in by the overarching adam- 
bulacral plates and spinelets. The adambulacral plates are elongate and vertebra-like, the 
margin towards the furrow being deeply scooped out, whilst the extremities are promi- 
nent and thickened. The armature of the adambulacral plates consists of three spines, 
which are moderately long, sharply tapering, and slightly compressed : two stand near the 
(ZOOL, CHALL. EXP.—PART LI.—1887.) 20 
