40 THE VOYAGE OF H.M.S. CHALLENGER. 
very short. On the actinal surface of each plate are three robust, tapering, secondary 
mouth-spines, two placed so that a line joining them would run parallel to the median 
suture, and this line is continued on the outer part of the plate by one or two smaller 
spinelets. The third large spinelet is placed opposite the interspace between the two large 
spinelets above mentioned, midway between them and the outermost of the marginal 
mouth-spines. 
The actinal interradial areas are very small, not more than eight to ten intermediate 
plates being present in each. The two innermost may bear a small central conical spinelet 
surrounded by a few minute miliary thornlets only. There are three complex pedicellarian 
apparatus in each area, situated in the lateral sutures which separate the two innermost 
intermediate or ventral plates; these organs consist of an oval cavity equally scooped 
out of the margins of the two adjacent plates, each margin beset with about five short, 
compressed, pointed, “ dog-tooth” shaped spinelets, directed over the cavity, and fre- 
quently turned upwards into the same. The major axis of the cavity measures about 
1 mm. There are also structures which I take to be very minute pedicellarize present 
on a number of the adambulacral plates, appearing to protrude through the membrane, 
usually on the outer part of the adoral margin. 
The anal aperture is subcentral and distinct, its margin being surrounded by a close 
circlet of small spinelets longer than the small spinulation of the paxille. At a little 
distance from the aperture is a circlet of the large armed paxille, standing more or less 
regularly in the radial and interradial lines. 
The papulze, though confined to the base of each ray, occupy a much greater area than 
in the other members of the genus, and are probably not comprised in a specially consti- 
tuted papularium. They are small and widely spaced, more than fifty may be counted in 
each area, and isolated ones extend as far as the fourth marginal plate. 
The madreporiform body, which is small, circular, and convex, is situated close to the 
marginal plates, and its surface is striated with rather fine convoluted furrows. One of 
the large powerfully spined paxille stands on its adcentral side. 
Colour in alcohol, a bleached ashy white. 
Locality.— Station 232. South of Yeddo (Japan). May 12,1875. Lat. 35°11'0’N., 
long. 139° 28’ 0” E. Depth 345 fathoms. Green mud. Bottom temperature 41°:1 Fahr. ; 
surface temperature 64°°2 Fahr. 
Remarks.—This is, perhaps, the handsomest species in the genus, at any rate the 
most striking, and is at the same time remarkably well characterised. Without referring 
to minor points of difference, it will suffice to say that the form is at once distinguished 
from all others by the group of large conical spines on the abactinal area of the disk, and 
by the presence of more than one large spine arranged in transverse series on the infero- 
marginal plates. Even without these striking features, Pontaster oxyacanthus would be 
well marked. 
