192 THE VOYAGE OF H.M.S. CHALLENGER 



Colour in alcohol, a dirty ashy or brownish grey. 



Locality. — Station 148. Between Marion Island and Kerguelen Island. January 3, 

 1874. Lat. 46° 47' 0" S., long. 51° 37' 0" E. Depth 210 fathoms. Hard ground (gravel, 

 shells). Surface temperature 41 o, Fahr. 



Remarks. — This form is unquestionably the southern representative of Leptopty- 

 chaster arcticus, Sars, sp., of the North Atlantic, to which it is structurally nearly 

 related. It is distinguished by the comparatively larger disk and shorter rays, the latter 

 being also broader at the base aud more sharply pointed at the extremity. The supero- 

 marginal plates are relatively smaller or more aborted, the paxills? of the abactinal area 

 are smaller and less compact, and the adambulacral armature is usually more compact 

 and grouped in its disposition. Leptopty chaster herguelenensis, Smith, is distinguished 

 by the longer and more cylindrically rounded rays, by the larger and more compact 

 paxillse of the abactinal surface, by the smaller actinal interradial areas, and, above all, 

 by the characteristic adambulacral armature, almost recalling that of Cribrella in its 

 character. 



It is interesting to note that Leptopty chaster antarcticus is more nearly related to 

 the distant Arctic form than to the comparatively neighbouring species Leptopty chaster 

 herguelenensis ; perhaps a more extended series of specimens than we possess at present 

 might lead to Leptopty chaster antarcticus being ranked as a variety only of the northern 

 form. At present I do not feel justified in taking that step. 



Genus Moiraster, n. sen. 



Disk large. Rays rather elongate, broad at the base and tapering to the extremity. 



Marginal plates of both series with well-developed ridges, separated by deep fasciolar 

 channels. Infero-marginal plates with large flattened spatulate spinelets, chisel-shaped or 

 square-cut at the tip. No prominent large spines on either series. 



Abactinal area with paxillae borne on stellate plates, without internal imbricating 

 ridges. Paxillos with long pedicles, and erect compact crowns of short inbending spinelets. 

 No definite medio-radial series. 



Actinal interradial areas large, with numerous intermediate plates arranged in regular 

 transverse columns, each plate imbricating on its neighbour in its own column. The 

 intermediate plates extend along fully two-thirds of the ray, and all bear stout, flattened, 

 spatulate spinelets. 



Armature of the adambulacral plates more or less regularly triserial, simulating that 

 of Astropecten. A series of usually three spines form a triangle on the furrow margin, 

 and are followed by two outer series of two or three stout chisel-shaped spines, similar to 

 those on the actinal intermediate plates. 



Strongly developed superambulacral plates are present. 



