ASTEROIDEA. OF H.M.S. ' CHALLENGER' EXPEDITIOX. 225 



edges compressed together to form the keel. The aboral ex- 

 tremity is more elevated than any other part and presents a 

 sharp angular peak, the mouth-plates sloping down therefrom 

 with a graceful inward curve to the level of the interbrachial 

 area. A single short conical mouth-spine is placed at the ex- 

 tremity of tlie adoral peak : and two others, about equal in size to 

 the ambulaeral spines, stand on the lateral margins of each plate, 

 the most adoral of the two being situated nearly midway be- 

 tween the extremities of the margin. 



The actinal interbrachial areas are small and sagittiform in 

 outline, and do not extend beyond the third adambulacral plate. 

 The plates are small, subregular, transversely elongate on the 

 outer portion of the area, and with a tendency to imbricate, this 

 character, however, being so faintly presented that it is difficult 

 to say whether imbrication really exists or not. 



Colour, in alcohol, greyish white, rather darker over the 

 dorsal area of the disk. 



Station 237. Lat. 34° 37' N., long. UO" 32' E. Depth 1875 

 fms. ; bottom temperature 1°'0 C. ; red clay. 



PORCELLAJSTASTER CRASSUS, U. Sp. 



E,ays five, elongate, robust, gradually tapering from the base 

 to the extremity. Disk small. Interbrachial angles well 

 rounded, the lesser radius being in the proportion of 30 per 

 cent.; i2 = 35 millim., r=10'5 millim. Disk not high and only 

 slightly inflated above the level of the marginal plates. 



Dorsal area much contracted in consequence of the inward 

 arching of the marginal plates, these latter forming a broad 

 border enclosing a regular pentagonal area when seen from 

 above. The whole dorsal area, excepting a very small sjoace at 

 the base of the rays, is beset with simple spinelets, unit'crmly 

 distributed over the surface and moderately well spaced, the 

 spinelets being very small, short, cylindrical, and invested with 

 membrane. In the interspaces between the spinelets, small 

 papuliB may, with difficulty, be detected here and there ; in 

 external appearance they resemble the spinelets, but are rather 

 larger and thicker. A broad, tapering, epiproctal tubular pro- 

 longation, about 3 millim. in length, is present in the centre of 

 the disk. 



Marginal plates high, arching inward, and forming a sloping 

 or bevelled edge to the disk in the interbrachial angles ; and with 



17* 



