634 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.48. 



a^. Marginal mouth spines 8 to 15 (if the lowest number, or exceptionally less, then 

 rays also very slender tliroughout). 

 6'. Abactinal radial plates conspicuously wider than long (much as in mucronatus) ; 



rays very slender leptodovius. 



b'. Abactinal radial plates roundish or hexagonal, not conspicuously broader than 



long. 



c^ Second superomarginals meeting in median line across ray (4 superomarginals 



in each interbrachium); inferomarginals of ray very narrow and long, the 



length at middle of ray exceeding the height (or thickness) of lateral face 



of ray; rays slender and delicate; oral spines. 10 or 9 atopus. 



<?. Fourth, fifth, and sixth superomarginals meeting in median line across ray 



(sometimes thii-d in young specimens), and therefore 6 to 12 superomarginals 



to each interbrachium); length of inferomarginals at middle of ray equal 



to or less than height of lateral face of ray. 



«F. Ray broader at base, measured as in a)- equaling first A\ superomarginals; 



superomarginals verj^ broad, not tumid; oral spines, 10 to 12; furrow 



spines 10; inferomarginal plates of interbrachia extending laterally 



beyond superomarginals moluccanus. 



d?. Ray narrow at base, measured as in a} equaling first 3 to 4 superomarginals; 

 if approaching d\ then superomarginals tumid; in interbrachia supero- 

 marginal plates extending laterally beyond inferomarginals. 

 e^. Marginal plates individually tumid; noadambulacralpedicellariae; mouth 



spines 9 or 10; fuiTow spines 9 to 11 at middle of ray arthrocnemis , 



e^. Marginal plates not individually tumid; adambulacral pedicellariae; 

 furrow spines at middle of ray more than 11. 

 p. Dorsolateral angle of ray about 90°, square cut; dorsal surface plane; 

 marginal graniilation closer; sixth and sometimes fifth superomarginal 

 longer than width of its dorsal surface; 10 inferomarginals correspond- 

 ing to about 16 adambulacrals; mouth spines 9 to 11 meseres_ 



p. Dorsolateral angle of ray more rounded, the dorsal surface being convex; 

 marginal granules more spaced; ninth or tenth superomarginal longer 

 than width of its dorsal surface; 10 inferomarginals corresponding to 

 13 or 14 adambulacrals; mouth spines 12 to 15 habrotatus. 



NYMPHASTER EURYPLAX, new species. 



General form similar to that of N. diomedex ILudwig and N. ternalis 

 (Perrier), but superomarginals with plane abactinal surface, not 

 tumid; rays broad at base and actinal surface conspicuously wader 

 than abactinal, the edges between the 4 faces of the ray being abruptly 

 angular; disk arcuately pentagonal, gradually merging into rays at 

 corners; extreme width of ray, measured at proximal suture of the 

 first pair of superomarginals, wliich meet medially, equaling length of 

 fu'st 4 or 5 superomarginals, measured on ambitus; inferomarginals 

 broad; rays not sunken along median radial line; inferomarginals 

 broader than superomarginals on disk, but narrower on ray; radial 

 and adradial abactinal plates broader than long, hexagonal, elliptical, 

 and lozenge-shape; adambulacral plates with very strong furrow 

 angle and 9 or 10 furrow spines, the apices of the angles of opposite 

 plates meeting in middle of furrow and segregating consecutive pairs 

 of tube-feet beyond proximal fourth of furrow; mouth plates \vith 

 6 to 8 marginal spines; no pedicellarias except rarely on the first 



