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



series ; the innermost spine on each plate is greatly enlarged, and forms with its companion 

 a robust pair directed horizontally inward at each mouth-angle. On the actinal surface of 

 each plate are two longitudinal series of short, stumpy papillae, the innermost two or three 

 rather more elongate than the rest, and all covered with membrane. 



The actinal intermediate plates are confined to a small area in the interradial region, 

 where they are arranged in regular columns or series parallel to the median interradial 

 line ; and they do not extend along the ray further than the ninth adambulacral plate, or 

 the fifth infero-marginal plate. They bear a number of short skin-covered spinelets, simi- 

 lar to those on the actinal surface of the adambulacral plates, and, as these are more or 

 less grouped together, the separate plates remain distinguishable. 



The madreporiform body is very small, situated about midway between the margin and 

 the centre of the disk. Its surface is grooved by comparatively few coarse striation 

 furrows, and in the central region of its surface there is a tendency towards the develop- 

 ment of a few isolated granules upon the intervening dissepiments. 



Colour in alcohol, a bleached yellowish white. 



Locality. — Off the Cape Verde Islands. (Depth and conditions not recorded.) 



Remarks. — This is a very abnormal Astropectinid, and I feel great doubts as to 

 the correctness of referring it to the genus Psilaster. The form presents several points 

 of affinity to the Archasteridae, but I am unable to include it in any of the genera belong- 

 ing to that family. Under the circumstances I consider it better to refrain from con- 

 stituting a new genus for the reception of this single species until more is known of its 

 structure. 



The species cannot be mistaken for any of the other forms of Psilaster ; the broad and 

 distinctly tumid marginal plates, the presence of the incipient pedicellarise, the character of 

 the paxillas, and the armature of the infero-marginal plates readily distinguish it. 



Genus Phoxaster, Sladen. 

 Phoxaster, Sladen in Narr. Chall. Exp., 1885, voL i. p. 611. 



Disk small. Rays moderately elongate, robust and tapering. Lateral walls high and 

 nearly vertical. 



Marginal plates short and high, confined to the lateral wall. Superior and inferior 

 series correspondent. The surface of both series of plates is covered with short, uniform, 

 fiat-lying squamiform papillae. No large or prominent spines are normally present. 



Abactinal area with small compact paxillse, composed of short skin-covered papillae, 

 which fit together subprismatically. A small but prominent and well-defined conical 

 epiproctal protuberance is present in the centre of the disk. 



Actinal interradial areas small in the interbrachial region, but a series of narrow band- 

 like plates extends along the ray, nearly to the extremity, separating the adambulacral 



