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 Hymenaster-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 PyTrHonasTeRIN&, Sladen, 1888. 
Genus Pythonaster, Sladen. 
Pythonaster, Sladen in Narr. Chall. Exp., 1885, vol. 1. p. 609. 
Rays 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 
