ASTEEOIDEA OF H.M.S. ' CHALLEKGEE ' ESPEDITION. 245 



Colour, in alcohol, grey, with traces of a purple shade remain- 

 ing here and there upon the paxillar area and on the rays. 



Station 157. Lat. 53° 55' S., long. 108° 35' E. Depth 1950 

 fms. ; diatom-ooze. 



Thoeacastee, n. gen. 



Rays five, moderately long, cylindrical, and rigid. Disk large. Supero- 

 marginal plates united in the median dorsal line and form a cylindrical 

 encasement to the ray. Marginal plates devoid of spinelets. Abactinal 

 area covered with small, closely crowded paxillse. No central epiproctal 

 protuberance. Actinal interradial areas extensive, paved with plates 

 imbedded in membrane, and carrying numerous, small, uniform, rather 

 closely placed papilliform granules or spinelets. Ambulacral furrows 

 narrow and enclosed. Ambulacral spines short, equal, ranged on the 

 furrow-margin of the plate and forming a lineal series along the ray. 

 Outer portion of the adambulacral plates occupied by small papilliform 

 spinelets more or less definitely arranged. Cribriform organs 14 in number 

 in each interbrachial angle, in the single species known. Terminal plate 

 small, inconspicuous, and unarmed. 



Thoeacastee cylestdeattjs, n. sp. . 



Marginal contour stellate, with large disk and five very narrow 

 cylindrical rays which taper to a point. Interbrachial angle 

 Tcry wide and well rounded. The lesser radius in the propor- 

 tion of 33*8 per cent. ; B=62 millim., r=21 millim. 



Disk slightly inflated, forming a convex surface of low curva- 

 ture. The dorsal area is covered with very small, compact, and 

 closely crowded paxillge, which are, however, confined entirely to 

 the disk, in consequence of the junction of the supero-marginal 

 plates in the median line along the whole of the free portion of 

 the ray. The paxillge are very small and composed of 6-10 small 

 spinelets closely appressed into a fascicule, the whole area 

 appearing to the unaided eye almost like a uniformly granular 

 surface. The paxillae are a sliade smaller in the centre of the 

 disk, which they further define by their arrangement, although 

 no prominent anal peak is produced. The actinal area of the 

 disk is slightly convex and slopes downwards at a small angle to 

 the prominent mouth-plates. 



The marginal plates are high, forming a gently rounded mar- 

 gin to the disk, the plates curving slightly inward towards the 



