294 BULLETIN OF THE BUREAU OF FISHERIES. 



Rays elongate, stout, fairly slender, abruptly tapering at base, but very gradually on outer three- 

 fourths; interbrachial arcs, wide and well rounded; disk only slightly or not at all inflated; ambulacral 

 furrows very wide; actinostome large; rays more or less reflexed, but not greatly curved. 



Abactinal area slightly sunken below level of inner edge of superomarginal plates; fairly narrow 

 on rays (4 mm. wide at outer edge of lateral cribriform organs, 2 mm. at middle of ray); integument 

 thin but resistant, covered with simple, slender spinelets which are well spaced, sheathed in mem- 

 brane, and slightly longer toward edge of disk than in the center; spinelets absent from rays beyond 

 miter cribriform organ; scattered among the spinelets are numerous papula 1 , especially in the inter- 

 radial areas; externally these papulae appear subglobular, and are much larger than the spinelets; epi- 

 proctal cone varying in thickness, and from 3 to 5 mm. high. 



Marginal plates arching inward, so that contour of body is defined by the inferomarginals when 

 viewed from above, these forming a sloping lateral face to the rays and disk. Superomarginals, 18 or 

 19 in number from the median interradial line to extremity of ray, nearly quadrate and larger than 

 the lower series, each plate bearing 1 robust, tapering, sharp spinule (or occasionally 2) nearly as 

 lung as height of plate, these forming a series at upper edge of plates and decreasing in size toward 

 extremity of ray; terminal plate prominent, notched at inner abactinal edge adjacent to integument, 

 and bearing 5 tubercular spinules, 1 at extreme tip, 1 at either side of end of furrow, actino-lateral in 

 position, and 1 on either side, abaetino-lateral in position, placed farther inward; inferomarginal 

 plates longer than high, corresponding to superomarginals in number, and not extending upon actinal 

 surface at. all, but forming an angle with it. 



Cribriform organs, 3 in each interbrachial arc, placed rather close together, the median largest, 

 having about 20 to 24 lamella', each organ with a slight depression down the center. 



Adambulacral plates narrow and rather long, conspicuously excavated on furrow margin, adoral end 

 most prominent and surmounted by 2 sharp tapering spinelets, one, slightly curved, usually directed 

 into the furrow, the other often a trifle smaller, either reflected back over the plate or turned aborad; 

 midway between extremities of plates a small, thin, scale-like papilla, with the straight base upon 

 which it is articulated running parallel to the furrow, and having the rounded free edge directed 

 outward. The pit covered by the papilla is in a very rudimentary condition on the proximal plates, 

 and beyond the basal fourth of the ray is absent, the papillae themselves becoming changed into small 

 lanceolate spinelets, accompanying the 2 other spinelets, so that on the outer half of the ray each 

 plate appears to have 3 spinelets. 



Mouth plates prominent, the united pair forming a broad keel; median suture prominent, the 

 companion plates touching at inner and outer ends; inner extremity of the combined pair roundel, 

 with a single, robust, short, conical spinelet at the union of the two, at this inner angle; placed higher 

 up, a curved, compressed, smaller spinelet at either side, on each plate, and between the latter and 

 the margin adjacent to first adambulacral plate 2 semicircular papilla?, the adoral occasionally the 

 smaller, though not conspicuously so. 



Actinal interradial areas small and triangular, and covered with a thin skin through which the 

 plates are not discernable until the specimen is partially dried. 



Madreporic body large, adjacent to a median cribriform organ. 



Color in life: General tint whitish, bluish cast on disk due to viscera showing through integument. 



Localities: Type from station 4397, about 200 miles off San Diego, Cal., 2,196-2,228 fms., gray mud. 



This species is nearest Pun, llanastt r crasms, which was taken by the Challenger Expedition in 2,335 

 fathoms in the South Pacific, midway between Sydney ami Valparaiso. From this form tenebrarius 

 differs in having longer and slenderer rays, more numerous marginal plates, longer spinelets on the 

 abactinal membrane, frequently 2 superomarginal spines, 2 adambulacral spinelets, less well-developed 

 pits and papillae, ami broader mouth plates, which have an additional lateral spinelet. 



Two of the specimens regularly have 2 superomarginal spinules, and on a few plates there are 3, 

 forming a linear series. 



