KEPOKT 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 arc ; it is very broad, well 

 defined, and with a deep depression down the median Une. The structure is lamelliform. 

 (See PI. 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 irregular 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" S., 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 raj's, 

 by the long delicate spinelets on each supero-marginal plate, by the small terminal plate 



