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



Locality. — Station 150. Between Kerguelen Island and Heard Island. February 2, 

 1874. Lat. 52°4'0"S., long. 71° 22' 0" E. Depth 150 fathoms. Coarse gravel. Bottom 

 temperature 35°"2 Fahr. ; surface temperature 37°'5 Fahr. 



Remarks. — Pteraster rvgatus may be readily recognised by its almost pentagonal form 

 and by the rugose character of the abactinal (supradorsal) area. It also differs from the 

 other members of the genus in structural details, which need not be recapitulated. ■ 



4. Pteraster stellifer, Bladen (PI. LXXIV. figs. 1 and 2 ; PI. LXXVII. figs. 1 and 2). 

 Pteraster stellifer, Sladen, 1882, Journ. Linn. Soc. Lond. (Zool.), vol. xvi. p. 193. 



Marginal contour stellato-pentagonoid, interbrachial arcs slightly indented, the minor 

 radial proportion being 67 "6 per cent. R = 34 mm. ; r= 23 mm. 



Piays very broad at the base, and tapering to a fine extremity, which is slightly re- 

 curved, margins of the rays not curved outward. Abactinal surface depressed and flatly 

 convex. Lateral fringe scarcely extending beyond the margin. Actinal surface flat. 



The supradorsal membrane, which is rather thick, regularly papillose in appearance, 

 and not reticulated, is composed of closely interlacing fibrous tissue. The paxillse are 

 numerous and closely placed, having crowns of usually six spinelets radiatiug round a 

 central one ; the expansion of the spinelets is slight, and all are uniformly protuberant. 

 The tips of the spinelets elevate the membrane into little conical papillse, which, in con- 

 sequence of the regularity of the crowns of the paxillae, have the appearance of forming 

 six-rayed stars with a central papilla, raised slightly in relief above the general superficies. 

 The crowns are closely placed, with the interspaces rather deep ; and the " stars " often 

 appear to overlap. A more or less distinct lineal arrangement of this ornamentation may 

 be observed upon the rays, although here and there irregular paxilla-crowns, with fewer 

 or more minute spinelets, as the case may be, are interspersed. The " stars " diminish in 

 size as they proceed outward on the ray. The spiracula are small and rather widely spaced. 

 The oscular orifice is small, and the spinelets of the valves are short and crowded. 



The ambulacral furrows are narrow, straight, not petaloid, and converge gradually 

 towards the extremity. The tube-feet are arranged in simple pairs. The borders formed 

 by the transverse combs of spinelets on the adambulacral plates are rather broad. The 

 armature of the adambulacral plates consists of a comb of five comparatively short 

 spinelets, the innermost one diminutive, not half the length of the others, and placed 

 aborally to them on the plate, the comb being thus curved round aborally at the margin of 

 the furrow ; the spine next to the outermost is usually the longest. The web, which is 

 moderately thick and semitransparent, is rather deeply incurved between the spinelets, 

 somewhat thickened round them, and slightly sacculate over their extremities ; it is con- 

 tinued from the outermost spine of the comb far out upon the actino-lateral spines. 



The segmental apertures are rather large and conspicuous for this genus. The aperture- 



