294 THE VOYAGE OF H.M.S. CHALLENGER 



marginal plates. The spinulation of the actinal intermediate plates is well-developed and 

 delicate, the delicacy emphasising the spiniform character. The spines forming the arma- 

 ture of the adambulacral plates are also more delicate and relatively longer than in the 

 adult. 



Malformation of ray. — The smaller specimen above mentioned is interesting from 

 the fact that one of the rays is bifurcate, forming two subequal branches, each having 

 about ten supero-marginal plates on a side. The two branches are formed with great 

 regularity, and there is no imperfection to lead to the suggestion that one has better claim 

 than the other to be ranked as the true tip of the radius. Both have a terminal plate, 

 and the ambulacral furrow passes along each branch regularly and equally. 



Colour in alcohol, a bleached greyish white. 



Locality. — Station 313. Off Cape Virgins, eastern coast of South America, near the 

 Atlantic entrance to the Strait of Magellan. January 20, 1876. Lat. 52° 20' 0" S., 

 long. 67° 39' 0" W. Depth 55 fathoms. Sand. Bottom temperature 47°*8 Fahr. ; surface 

 temperature 48° "2 Fahr. 



Remarks. — Perhaps the nearest ally of this species is Gnathaster meridionalis. The 

 present form may, however, be at once distinguished by the more depressed form of 

 the body, by the less produced rays, which are broader at the base and distinctly tri- 

 angular, by the peculiar capitate tubercle-like paxillae, and by the character of the spinu- 

 lation of the actinal area generally. 



Genus Nymphaster, Sladen. 

 Nymphaster, Sladen in Narr. Chall. Exp., 1885, vol. i. p. 612. 



Disk large and flat. Bays elongate, slender, tapering, and almost square in section. 



Marginal plates forming a broad border to the disk, and either united along the median 

 abactinal line of the ray throughout, or separated only by a single series of medio-radial 

 plates. The marginal plates of both series are granulated and bear no spines. 



Abactinal area of the disk covered with large and regularly arranged plates ; those in 

 the radial areas well separated, usually hexagonal, more or less tabulate and paxilliform, 

 and frequently bearing an excavate or entrenched pedieellaria. 



Actinal interradial areas large, confined to the disk. Actinal intermediate plates well 

 defined, covered with uniform granules and occasionally bearing pedicellarise. 



Armature of the adambulacral plates arranged in longitudinal series. 



Madreporiform body exposed and situated within one third of the distance from the 

 centre to the margin. 



Large entrenched pedicellarise are frequently present on the marginal plates in some 

 species. 



