REPORT ON THE ASTEROIDEA. 139 
is placed above the termination of the ambulacral furrow in the median line, and one 
on each side a little beneath. Occasionally one or both of these lateral spines may be 
accompanied by a supplementary spine, thus producing the additional number. 
The infero-marginal plates correspond in number and length to the superior series, 
and are, like them, longer than high; they do not curve round upon the actinal surface 
of the ray, which is flat. 
One cribriform organ is present in each interbrachial are; it is very broad, well 
defined, and with a deep depression down the median line. The structure is lamelliform. 
(See Pl. XXVII. fig. 12.) 
The ambulacral furrows are broad, open, and straight. The adambulacral plates are 
small, rather elongate in the direction of the ray, and rather widely separate. The 
margin towards the furrow is incurved, and the adoral extremity is somewhat scooped 
out, and has the margin slightly lipped, the aboral extremity of the next plate being 
rounded, thickened, protruded, and lipped in correspondence ; but the two do not join 
up closely, and a narrow vacant space is left between. The armature of the adambulacral 
plates consists of two minute, delicate, acicular, and sharply-tapering spines; the adoral 
spine, which is the longest, is placed at the extreme adoral end of the margin of the plate, 
and the companion spine is 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. 
The mouth-plates are rather broad and suboval, elevated into a moderately high and 
well-rounded keel, a small elliptical space being left between the two adjoining plates near 
the middle of the median line. ‘The 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. The armature of the mouth-plates consists of 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 spines which constitute the armature of the adam- 
bulacral plates. 
The actinal interradial areas are small, subtriangular, and covered with membrane ; 
the actinal intermediate plates are irrecular and small. 
Colour in alcohol, greyish white, with a darker shade of bluish grey over the disk. 
Locality.—Station 191. In the Arafura Sea, west of the Arrou Islands. September 
23, 1874. Lat. 5° 41’ 0” &., long. 134’ 4’ 30” E. Depth 800 fathoms. Green mud. 
Bottom temperature 39°°5 Fahr.; surface temperature 82°'2 Fahr. 
Remarks.—Porcellanaster caulifer is distinguished by the elongate tapering rays, 
by the long delicate spinelets on each supero-marginal plate, by the small terminal plate 
