ASTEROIDEA OF H.M.S. ' CHALLEXGElt ' EXPEDITIOJT. 237 



is little more than a tubercular granule, and stands equidistant 

 between the middle spine and the aboral extremity. Occasionally 

 the adoral secondary spinelet is largest. A few irregular rounded 

 granules may occur on the aboral portion of eacb plate. 



The ventral interbrachial area is extensive, covered with a 

 thin transparent membrane and with a compact plating of 

 delicate imbricating scales. The scale-like plates are more or 

 less regularly hexagonal and arranged in columns parallel to the 

 median interradial line. The plates diminish in size and depth 

 towards the margin, where they become narrow elongate strips. 

 Each plate bears 2 or 3 small rounded granules irregularly dis- 

 posed ; the large plates near the interior o£ the interradial area 

 with a few additional granules in proportion to their size. 



Colour, in alcohol, greyish white, with a brownish or slightly 

 orange shade over the dorsal membrane. 



Station 274. Lat. 7° 25' S., long. 152° 15' W. Depth 2750 

 fms. ; bottom temperature 0°'9 C. ; radiolarian ooze. 



Htphalaster diadematus, n. sp. 



Marginal contour stellato-pentagonal. Eays five, well deve- 

 loped, slender, springing from the disk with a gradual taper, 

 which is continued to the extremity; the upper surface of the 

 ray arched rather than rounded. Interbrachial angles well 

 rounded; the lesser radius is in the proportion of 4<V6 per cent. ; 

 i2=24 millim., r=10 millim. Dorsal surface of the disk slightly 

 inflated above the level of the marginal plates, and with a promi- 

 nent conical peak in the centre of the area. 



Dorsal area covered with a thick integument, uniformly beset 

 with well-spaced pseudo-paxillse, which are very small and regular, 

 each carrying 3 or 4 spinelets, those with the latter number 

 being by far the most numerous. The paxillge do not extend 

 along the rays, but are confined to the actual disk-area ; a 

 blank space is thus left at the base of the rays, which has the 

 appearance of being closely plated with small round scales im- 

 bedded in the integument. In the neighbourhood of the conical 

 peak the paxillae become very small and crowded. Around this 

 as a centre and at some little distance away, a number of larger 

 paxillse made up of more spinelets are arranged ; these are con- 

 gregated with more or less regularity into round groups, of which, 

 roughly speaking, there is one opposite the median line of each 

 ray, with a smaller group intermediate between each of the larger 



