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 paxillse, 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 subtriangular, composed of ten to twelve radiating spines, and 

 when closed form a pyramidal peak in the centre of the disk. 



The ambulacra! 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-papillse are large and 

 squarely oval. 



The mouth-plates are somewhat broad, short, and almost perpendicular in position ; 

 the keel is flattened. Each 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 Guiuea, 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 0, 4 Fahr. ; surface temperature 84° - 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. 



