ASTEEOIDEA OF H.M.S. ' CHALLEJfGER ' EXPEDITION. 223 



beiug rounded, thickened, protruded, and lipped in corre- 

 spondence ; but the two do not join up closely, and a narrow 

 vacant space is left between. Ambulacral spines two, minute, 

 delicate, acicular and sharply taper ins:, the adoral one longest 

 and placed at the extreme adoral end of the margin of the plate, 

 and the companion spine situated at the commencement of the 

 curve along the furrow-margin ; the long spine is consequently 

 directed almost transversely across the furrow, whilst the small 

 spine stands at an angle of about 45° to it. 



Mouth-plates rather broad and suboval, elevated into a mode- 

 rately high and well-rounded keel, a small elliptical space being 

 left between the two adjoining plates near the middle of the 

 median line. Tlie aboral extremity of the plates is gracefully 

 rounded, and the margins of the plates do not meet along the 

 lower portion, but leave a triangular outline of the odontophore 

 visible. Mouth-spines : one short conical spinelet at the adoral 

 peak of the mouth-angle, standing at the junction of the two 

 plates ; and two small spinelets, similar to this, on the lateral 

 margin of each plate. The aboral spinelet is placed near the 

 middle of the margin, and the companion one, which is smaller, 

 nearer the adoral extremity of the plate. All the mouth-spines 

 are smaller than the ambvilacral spinelets. 



Interbrachial areas small, subtriangular, covered with mem- 

 brane; plating irregular and small. 



Colour, in alcohol, greyish white, with a darker shade of bluish 

 grey over the disk. 



Station 191. Lat. 5° 41' S., long. 134° 4' E. Depth 800 fms. ; 

 bottom temperature 3°"9 C. ; mud. 



POKCELLANASTEK TUBEEOSUS, U. Sp. 



Eays five, interbrachial angles well rounded, the minor radial 

 proportion being 82 per cent. ; i2=18-5 miilim., r=6 millim. 

 The rays spring gradually from the angle and taper moderately 

 towards the extremity, maintaining a robust character through- 

 out. Disk not high, and very slightly inflated. Dorsal area 

 covered with a rather fleshy integument beset with simple spine- 

 lets somewhat closely placed ; these are short, cylindrical, obtuse, 

 covered with membrane, and occupy the whole of the surface 

 excepting only the extreme angle at the base of the ray. A well- 

 developed epiproctal tubular prolongation rises from the centre 

 of the dorsal area, and is nearly equal in length to the distance 



LINN. JOUEN. — ZOOLOGY, VOL. XVII. 17 



