570 



separated by prominent transverse grooves (as wide as 

 the elevated ridge of plate); actinal intermediate series 

 reaching quite or nearly to tip of ray . . leviuscula (Stimpson). 



dd. Papular areas usually larger than pseudopaxillae, much 

 sunken, the latter elongated with fewer than 20 spine- 

 lets arranged on the tabulate elevation in 2 or 3 rows; 

 marginal plates much compressed, the thin spine-be- 

 aring tabula separated by fairly deep grooves ; actinal 

 intermediate plates not distinguishable much beyond 

 middle of ray annectens new subspecies. 



cc. Abactinal pseudopaxillae with numerous slender often 

 glassy spinelets ending in 3 to several sharp awns or 

 points; adambulacral spinelets numerous (25to 50); 

 typically with 2 spinelets in furroAv beyond middle of 

 ray but only 1 proximally .... muUispiiia new subspecies, 

 bbb. Abactinal skeleton open, with large often sunken 

 papular areas containing numerous papulae : spinelets 

 scattered along the ridges surrounding papular areas, 

 or if clustered, never many to a cluster. 



c. Spinelets scattered, often quite small; not in definite 



clusters or pseudopaxillae; adambulacral spinelets in a 

 single, sometimes zigzag, transverse series. 



d. Rays slender, long, and rigid, the skeleton forming an 

 open mesh work with large sunken papular areas; ab- 

 actinal spinelets minute, generally immersed in the 

 integument and arranged along the trabecular ridges 

 in 1 to 3 irregular series; adambulacral spinelets in zig- 

 zag transverse series, few, thick, stubby, and immersed 

 in membrane; marginals regular with large inter- 

 marginal papular spaces aspera Fisher. 



dd. Rays weak; spinelets comparatively large (as long as 

 the height of ridge bearing them) in a single series 

 along the skeletal ridges, well spaced. Adambulacral 

 spinelets slender, long, in a transverse series, webbed 

 basally, but not impeded by thick investment. Mar- 

 ginals not always regular asthenacHs new species. 



cc. Spinelets in definite pseudopaxillae or in fascicular 

 groups, 

 d. Genre la form intermediate between aspera and levius- 

 cula] papular areas usually small; pseudopaxillae ob- 

 long with 2 or 3 rows of upwards to 20 very short 

 spinelets; prominent wide and short (compressed) 



