288 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



marginals). UiSermg from. S. ammophilus (Fisher) a.nd S.hourgeti 

 (Perrier) in having much narrower superomarginals, more restricted 

 papular areas, much longer adambulacral plates, with more numerous 

 furrow spines and larger mouth plates. Form pentagonal, with 

 straight sides, produced at angles into rays, only 2 superomarginals 

 in length. Superomarginals narrow, increasing slightly in size up 

 to the third, the remaining 2 being smaller; surface bare, except 

 for scattered granules, and several rows near margin. Abactinal 

 plates granulate, a comparatively few of the radial and adradial 

 series being low tabulate; plates hexagonal on radial regions, gen- 

 erally 4-sided interradially, and irregularly hexagonal on center of 

 disk. Adambulacral plates longer than wide, or as long as wide, 

 with a straight-edged furrow comb of 9 or 10 flattened, rather narrow 

 truncate spines, and spaced from these 2 or 3 subambulacral series 

 of granules, the inner the larger. Mouth plates large, with 15 to 17 

 furrow spines. Abactinal, marginal, and actinal intermediate spatu- 

 late pedicellariae with " sugar-tongs " jaws. E=32 mm., r=22 mm., 

 R=1.45 r. 



Description. — Abactinal area pentagonal, the plates being flat and 

 only those of the very restricted papular areas slightly tabulate. 

 All are covered with uniform, depressed, subtruncate, hemispherical 

 granules, those in the central part of the plate being spaced one- 

 third to one-half the diameter of a granule ; those on the periphery 

 just touching. Scattered over the radial and interradial regions 

 are numerous small pedicellariae, with 2 narrow jaws abruptly 

 widened and spatulate at the tip, and with a rather narrow base ; 

 length of jaw about width of 2 granules. Sometimes the spatulate 

 part is notched or denticulate, sometimes entire. The papular areas 

 are restricted to the radial and either adradial series of plates. There 

 are 9 or 10 radial plates, but only about 6 of the radial and 5 of 

 the adradial series are tabulate. These plates are hexagonal or (being 

 usually a little longer than w4de) kite-shaped. In the middle of 

 the papular areas the lateral peripheral granules are slightly length- 

 ened, truncate, and have the appearance of acting as opercula to pro- 

 tect the papulae beneath.' The interradial plates are four or five 

 sided, or if six-sided the plates appear to be four-sided with 2 oppo- 

 site corners cut off. 



The plates of the papular areas, seen from the coelomic side, 

 have 6 short, broad lobes, directed slightly downward, by which the 

 plates join. They are most pronounced on the radial plates, and the 

 kite-shaped plates have a strong lateral lobe on either side, the 

 rest being suppressed. The adradial and adjacent series have very 

 short lobes. 



Superomarginal plates narrow. First 2 longer than extreme 

 width ; third much wider at distal transverse suture than at proximal, 



