530 THE VOYAGE OF H.M.S. CHALLENGER. 



placed very obliquely, the inner or aboral spine being the smallest ; the outermost spine 

 is probably the representative of the aperture-papilla, of which it occupies the place, 

 although it differs in no way from the other two spinelets ; sometimes a small additional 

 spinelet is present. The spines are long, delicate, and needle-shaped, and there are 

 traces of a fine investing membrane. 



The mouth-plates are of the Hymeaaster-type, and present a prominent peak aborally, 

 sloping adorally, and little prominent in front. Each plate bears two long, clavate, thorny, 

 somewhat curved secondary or superficial spines, nearly equidistant from one another 

 and from the median suture, the posterior spinelets being longest. Two mouth-spines 

 proper are situated on the horizontal margin of each plate, the innermost one being 

 slightly smaller than the anterior secondary (superficial) spine, which it resembles exactly 

 both in form and character ; whilst the outer spinelet is very much smaller, and slightly 

 tapering and smooth, instead of being clavate and thorny. 



The actino-lateral spines are delicate and rather widely spaced ; about fifteen are 

 present on each side of a furrow, the fourth or fifth from the mouth being longest. The 

 spines diminish slowly in size as they proceed outward, and maintain a fair length even 

 at the extremity of the ray. The actinal membrane is perfectly transparent, and com- 

 posed of very fine and widely spaced fibres, reticulated rather rectangularly. No marginal 

 fringe is formed ; and the actinal tissue appears to pass over the margin continuous with 

 the supradorsal tissue. The actino-lateral spines project considerably beyond the margin, 

 and are naked. 



Colour in alcohol, greyish white. 



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. 



Subfamily Pythonasterin^e, Sladen, 1888. 



Genus Pythonaster, Sladen. 



Pythonaster, Sladen in Narr. Chall. Exp., 1885, vol. i. p. 609. 



Bays very elongate and flexible, swollen for a short distance from the disk, then 

 rapidly becoming narrow, compressed laterally and extending to an attenuate extremity. 

 Disk small, with a well-defined channel traversing each interradial line, which causes the 

 starfish to appear to be composed of five united rays only. In the central abactinal 

 region are five triangular fan-like valves, composed of delicate spinelets united by mem- 

 brane, radial in position, which meet together when shut down and cover the dorso- 

 central aperture. 



Abactinal and lateral surfaces beset with delicate plates imbedded in membrane and 



