520 THE VOYAGE OF H.M.S. CHALLENGER. 
sion exactly. Rays well produced, fine and tapering at the extremities. Abactinally the 
centre of the disk is elevated into a sharp conoid, and the rays are prominently arched. 
The supradorsal membrane is very delicate. The spinelets of the paxille, which are 
prominently projecting, very delicate, and tapering towards their extremity, are distributed 
regularly at uniform intervals apart over the whole abactinal area. Numerous very fine 
thread-like fibrous bands pass between the tips of the spinelets, crossing over and under 
one another, but not merging or forming a coherent reticulated structure. The fibres are 
not tightly stretched between the tips of the spinelets, but slope downward at a high 
angle like slackened ropes round a tent-pole; in consequence of this and of their great 
prominence the spinelets appear to superficial examination to stand like well-spaced 
conical prickles upon the abactinal area. The oscular orifice is of moderate size, the outer 
margin (from which the valves take their rise) being marked off by prominent sharp 
spinelets into a pentagon, 9°5 mm. in diameter, the angles opposite to the rays. The 
valves are very regularly subtrianeular, composed of ten to twelve radiating spines, and 
when closed form a pyramidal peak in the centre of the disk. 
The ambulacral furrows are narrow and deeply sunken, constricted near the mouth, 
widest about the outer third, and then sharply tapering to the extremity. The armature 
of the adambulacral plates consists of three short, stout, tapering, compressed spines, placed 
in line oblique to the direction of the furrow, and also to the horizontal plane of the 
ray. The adambulacral spines are quite hidden in the furrow, not webbed together, but 
probably invested with a rather long membrane. The aperture-papille are large and 
squarely oval. 
The mouth-plates are somewhat broad, short, and almost perpendicular in position ; 
the keel is flattened. Hach plate bears two short, thick, secondary or superficial spinelets, 
the aboral ones being the most robust. One mouth-spine stands above the innermost 
secondary, and another, much smaller, is placed isolated on the horizontal lateral margin 
of the plate. 
The actino-lateral spines, which are twenty-seven or perhaps about thirty in number, 
are robust at the extremity of attachment, but very delicate and tapering outwardly, and 
do not meet in the interradium. 
Colour in alcohol, dark purple, with the fibrous bands on the abactinal surface white, 
which gives a very elegant effect. The ambulacral tube-feet are very dark purple, almost 
black, with white tips. 
Locality.—Station 218. Off the north coast of New Guinea, south-west of the 
Admiralty Islands. March 1, 1875. Lat. 2° 33’ 0” S., long. 144° 4/0” E. Depth 1070 
fathoms. Blue mud. Bottom temperature 36°°4 Fahr.; surface temperature 84°-0 Fahr. 
Remarks.—The structure of the supradorsal membrane, the form and armature of the 
mouth-plates, and the presence of cross muscular fibres in the web of the actinal floor, 
serve to distinguish this species from its congeners. 
