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



Each plate bears a few small pointed thorn-like spinelets, rather widely spaced, but at the 

 same time more or less grouped. 



The anal aperture is subcentral and very distinct, and is emphasised by a few of the 

 spinelets of the paxillte that surround it being sensibly more robust than the rest. 



The papulae occupy a limited area at the base of the ray. They appear smaller and 

 perhaps more numerous than in some species, but I am unable to give their number accu- 

 rately ; and no definite order of arrangement is discernible. 



The madreporiform body, which is small, circular, and slightly convex, is situated 

 midway between the centre and the margin of the disk ; the striation furrows with 

 which its surface is grooved are rather coarse, and radiate centrifugally with more 

 than usual regularity. 



Colour in alcohol, a greyish or ashy white. 



Young Phase. — A small example, which measures R = 16 mm., r = 5 mm., and has 

 thirteen or fourteen supero-marginal plates, accords in all respects with the larger specimen, 

 and is perfectly recognisable. The anal aperture is distinct ; there are a few comparatively 

 large papular pores at the base of the rays ; and the large isolated paxillse are entirely 

 characteristic. The adambulacral plates have not more than four or five spines on the 

 furrow margin, though there is a small thornlet at each extremity of the series at the 

 margin of the actinal surface. On the infero-marginal plates the small secondary spinelets 

 below the lateral spine are not yet distinguishable from the miliary spinuhition of the 

 plate. The madreporiforrn body is very simple and placed close to the marginal plates. 



Locality. — Station 164. Off the coast of Australia, east of Sydney. June 12, 1874. 

 Lat. 34° 8' 0" S., long. 152° 0' 0" E. Depth 950 fathoms. Green mud. Bottom tem- 

 perature 36°"5 Fahr. ; surface temperature 69 0, 5 Fahr. 



Remarks. — This species is readily distinguishable by the broad margin of the supero- 

 marginal plates on the abactinal area, by the tubercles borne on these plates, by the 

 absence of pedicellarise, and by the character of the large isolated paxillse on the abactinal 

 area; and further by the short and comparatively obtuse rays. Pontaster subtubercidatus 

 may probably be regarded as the southern representative of Pontaster venustus. 



Subfamily Plutonasterin^;, Sladen, 1886. 



Genus Dytaster, Sladen. 



Dytaster, Sladen in Narr. Chall. Exp., 1885, vol. i. p. 608. 



Disk more or less inflated. Eays very long and attenuate, often subcarinate along 

 the median line abactinally, very slightly flexible. 



Marginal plates rectangular ; the supero-marginal plates thin and lamelliform, con- 

 fined more or less to the lateral wall of the ray, which is usually vertical. The plates of 

 the superior series are directly superposed on the corresponding plate of the inferior series, 



