ASTEEOIDEA OP H.M.S. ' CHALLENGEB ' EXPEDITION. 217 



growth both of spines and tissue in the interhrachial angle, and 

 the tension produced thereby, the majority of the spines at the 

 extremity of the ray are made to radiate inwards towards the 

 angle, and the web appears considerably stretched. 



Colour, in alcohol, yellowish grey. 



Station 325. Lat. 3G° 44' S., long. 46° 16' W. Depth 2650 fms.; 

 bottom temperature — 0°'4 C. ; grey mud. 



Htmenastee sacculatus, n. sp. 



Marginal contour stellato-peutagonoid ; interradial indentation 

 small; rays usually recurved dorsally, making the dorsal area 

 deeply concave, the ventral being convex. Minor radial pro- 

 portion 66"6 per cent.; i2 = 42 millim., r=28 millim. Radii 

 taperiug somew^hat sharply at the extremities ; marginal fringe 

 distinct and well-developed. 



Supradorsal membrane thick and coriaceous in appearance. 

 Papilla; numerous, crowus with rarely more than 4 or 5 spine- 

 lets, which are prominently protrusive of the membrane, — that 

 portion lying between the tips of each individual crown being 

 thick, devoid o£ spiracula, and forming a slightly distended 

 saccular area. Thick bands of tissue, with fibres, radiate between 

 the crowns ; and the narrow interspaces are occupied by numerous 

 small spiracula, generally three or four, or even more, in line 

 together, separated only by very fine, thin dissepiments. Oscular 

 orifice large ; valves 5 in number, regular, and forming, when 

 closed, a compact exactly fitted pyramid, rising as a small cone 

 in the centre of the concave dorsal area. The spinelets of the 

 valves are of moderate length, thickly webbed, and with numerous 

 spiracula in the interspaces. 



Ambulacral furrows moderately wide, very uniform in breadth, 

 except towards the extremity, where they taper rapidly, and near 

 the mouth, where they are also somewhat constricted. Ambu- 

 lacral spines 2, o£ moderate length, but with a very long sac- 

 culate investing membrane ; the pairs standing slightly oblique 

 to the median line of the ray. Aperture-papillae large, thickly 

 invested, subspatulate, slightly constricted near the outer third. 



Mouth-plates elongate, largely keeled, prominent aborally, each 

 plate bearing two short, thick, dumpy secondary surface-spines — 

 one near the adoral extremity, and the other, of similar size and 

 character, standing behind this, about midway on the surface of 

 the plate. Mouth-spines 4, small, short, conical, on the lateral 



15* 



