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



Station 49. South of Halifax, Nova Scotia. May 20, 1873. Lat. 43° 3' 0" N.,long. 

 63°39'0"W. Depth 85 fathoms. Gravel, stones. Bottom temperature 35°-0 Fahr. ; 

 surface temperature 40° "5 Fahr. 



3. Leptoptychaster antarcticus, n. sp. (PI. XXXI. figs. 3 and 4 ; PI. XXXII. figs. 7 

 and 8). 



Pays five. K = 15 mm., r = 6 mm. E = 2"5 r. Breadth of a ray between the fourth 

 and fifth marginal plates, 5 mm. 



Disk large and inflated; rays short, broad at the base and thence tapering gradually 

 to a sharply pointed extremity. Interbrachial arcs wide and subparaboloid in outline. 

 Abactinal surface of the disk convex and subject to more or less inflation ; that of the 

 rays subcarinate, with the character strongly marked at the extremity, but towards the 

 disk gradually merging into the general tumidity, the inflation being sometimes empha- 

 sised in spirit specimens by the presence of a slight depression along the median inter- 

 radial line, probably consequent on the posture of the rays at death. Actiual surface 

 plane. Lateral margin thin and rounded. 



The abactinal surface of the disk and rays is covered with very small and rather widely 

 spaced paxillaB, consisting of twelve to fifteen or more extremely fine, short, delicate 

 spinelets disposed in a little tuft, but radiating more or less apart. No definite order of 

 arrangement is discernible in the paxillse. 



The marginal plates are small and short. The superior series are very small ; and 

 have the appearance of being enlarged paxillse rather than true marginal plates. They 

 are confined entirely to the margin and the abactinal side ; and not infrequently the edge 

 of the infero-marginal plates is also just visible when the animal is viewed from above. 

 They bear a tuft of spinelets similar to, but slightly larger than, those on the true paxillse, 

 and these are arranged on a well-developed eminence. They are devoid of any large 

 spines whatever. 



The infero-marginal plates are twenty-one in number, counting from the median inter- 

 radial line to the extremity, and their breadth on the inner part of the ray is four or five 

 times the length or even more, but diminishes as they proceed along the ray. They are 

 well rounded at the margin and form a broad border to the actinal surface ; their posture 

 being very oblique in relation to the median radial line. Along the median line of each 

 plate, that is to say, traversing its greatest dimension, is a high, narrow keel, which bears 

 a covering of small, delicate, uniform spinelets, slightly larger than those on the super- 

 marginal plates and abactinal paxillse ; these are directed outwards and over the interven- 

 ing channels between the keels. 



The adambulacral plates are small, with the length and breadth nearly equal. They 

 bear an armature closely resembling that found in some species of Astropecten, which con- 



