KEPOET ON THE ASTEKOIDEA. 95 



Station 46. May 6, 1873. Lat. 40° 17' 0" N., long. GG° 48' 0" W. Depth 1350 

 fathoms. Blue mud. Bottom temperature 37°'2 Fahr. ; surface temperature 40°*0 

 Fahr. 



Station 47. May 7, 1873. Lat. 41° 14' 0" N., long. 65° 45' 0" W. Depth 1340 

 fathoms. Blue mud. Surface temperature 42 o, Fahr. 



4. Plutonaster ambigiius, n. sp. (PI. XL figs. 5 and 6 ; PI. XIII. figs. 11 and 12). 



Rays five. R = 25 mm. ; r= 6 - 5 mm. R < 4r. Breadth^ of a ray near the base, 

 6 '5 mm. 



Rays narrow and pointed, tapering throughout from the base. General form thin and 

 subdepressed, with the abactinal surface slightly inflated along the median radial lines, 

 forming a more or less definite keel. Actiual surface subplane, prominent at the mouth- 

 angles ; and sloping thence to the margin and slightly along the ray. Interbrachial arcs 

 widely rounded. 



The paxillse of the abactinal surface are very minute and crowded ; each with a crown 

 of five or six small, equal, papilliform spinelets, almost subclavate in form, which radiate 

 outward. The paxilhe diminish in size as they proceed along the ray, and simpler ones 

 are frequent on the outer half. 



The supero-marginal plates, twenty-eight to thirty in number from the median interradial 

 line to the extremity, are very small and slightly tumid ; they form a well-rounded lateral 

 wall to the disk and rays ; and when viewed abactinally present a narrow but definite 

 border. The length of the plates is greater than their height throughout the series, and their 

 breadth is subequal to, or slightly greater than, their length on the inner part of the ray, 

 but gradually becomes slightly less than the length on the outer part. The surface of the 

 plate is covered with small, well-spaced papilliform granules, and one small tubercle- 

 like granule, larger and more robust than the rest, is placed on the rounding of the plate, 

 and represents a supero-marginal spine. This tubercle-like granule is, however, scarcely 

 distinguishable from the rest of the covering of the plate on the outer part of the ray, and 

 it is doubtful whether it extends to the extremity. 



The infero-marginal plates correspond to the superior series, but their breadth is fully 

 twice as great as their length on the inner part of the ray, and subequal on the outer 

 part. Their surface is covered with minute conical thornlets of about the same general 

 size and distance apart as the rounded granules on the supero-marginal plates. Each plate 

 bears one short, tapering, pointed, spinelet, not more than a millimetre in length, directed 

 horizontally outward. Their length diminishes along the ray, and I am unable to speak 

 of their character or presence at the extremity. 



The adambulacral plates are longer than broad, and of a subrhomboid form, with a 

 slightly convex margin towards the furrow. Their armature consists of: — (1.) A furrow 



