416 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.40. 



half of ray formed by superomarginals which meet in median line. 

 Superomarginals massive, increasing in size from the first to sixth, 

 which is decidedly larger than the rest and meets its fellow on dorsal 

 median line; next 6 plates decreasing slightly, higher than wide, and 

 bearing on the rounded dorsolateral angle a stubby conical spine; 

 final 3 or 4 plates decreasing rapidly in size and covered by the big, 

 elliptical, very convex spiniferous terminal plate, margined by a 

 fimbriate channel. Inferomarginals lower than superomarginals 

 and beyond the sixth plate not corresponding to them, but near tip 

 of ray alternating, there being one more in the series. Cribriform 

 organs spiniform and in the interbrachial arc, continuous without a 

 break as far as the middle of the sixth or enlarged superomarginals, 

 except for a slight wedge-shaped area in the middle of the lower edge 

 of each inferomarginal. In each mterbrachium 11 fused cribriform 

 organs, the odd one over the median interradial suture. The sixth 

 supero- and inferomarginals have a median vertical bare space 

 about as wide as the adjacent cribriform organs, which from here 

 on rapidly narrow, and from the twelfth plate on may be said to be 

 rudimentary. These separated cribriform organs extend upon the 

 dorsal surface of ray and fuse with those of opposite side so that the 

 whole area. from the limit of paxillae to terminal plate and between 

 the two dorsal rows of spines is a thick continous mat of spinelets, 

 absolutely identical with the lateral cribriform organs, and a fimbri- 

 ate channel leads on either side from this area along the lower edge 

 of the terminal plate. The total number of lateral organs is: Rays 

 9 + 9 + mterbrachium 11=29. This varies to 30, as some rays have 

 an additional small one at tip. The distal organs are of course 

 rudimentary. 



Paxilise large, fairly high, crowded, those on rays largest, decreas- 

 ing in size toward center of disk. The larger paxillas have 15 to 20 

 peripheral and 5 to 15 central spinelets, cylindrical and slightly 

 knobbed at tip. Papula? in radial areas at base of ray and adjacent 

 portion of disk. 



Actinal interradial areas large, covered with spaced short slender 

 bluntly pointed spinelets, which increase in length toward margin. 

 The plates extend in a narrow area nearly to end of ray. Adambu- 

 lacral plates longer than wide with 7 or 8 compressed, basally webbed 

 furrow spines on a curved margin, and on surface of plate 10 to 12 

 much shorter spinelets, similar to the actinal intermediates, in about 

 two series. Furrow very narrow. Mouth plates prominent and 

 with wide suture. Marginal spines 12, the innermost abruptly 

 enlarged into a flattened conspicuous lanceolate tooth, the others 

 subsimilar to adambulacrals. Suborals about 15 to a plate, in two 

 series, small except inner two, which form a series just back of the 

 teeth. Madreporic body a little more than its own diameter from 



