418 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



Descri'ption. — Abactinal plates crescentic, those of disk not reg- 

 ularly arranged ; along median radial region is an area 6 or T plates 

 wide where the plates are arranged in quincunx with sometimes a 

 small roundish plate in the concavity of the crescent; then on either 

 side are regular longitudinal series of plates, about 10 at the base 

 of ray and 3 to 5 at the tip, which meet the superomarginal series 

 obliquely. Near the margin, forming an area 5 plates wide at base 

 of ray, the plates are in transverse series (between the outermost 

 oblique longitudinal series of crescentric plates and the ambitus), 

 are elliptic or quadrate in form, have no papulae between them, and 

 bear subcircular groups of radiating spinclets. The crescentic plates 

 bear 35 to 45 very delicate sharp spinelets r.nd have a papula on the 

 concave side. 



There is no lateral flange. The superomarginal plates are clearly 

 distinguishable and are about the same size as the small adjacent 

 abactinal plates, while the inferomarginals are considerably larger, 

 are set obliquely, and bear an elliptical group of numerous fine spine- 

 lets. 



On either side of the interradial line 9 actinal intermediate plates 

 can be counted between the adambulacral plates and margin. The 

 series opposite the first and second adambulacrals do not reach the 

 margin, while the third is complete. The plates also form longitu- 

 dinal series, 4 extending to the middle of ray, but only 1 attaining 

 the tip. The proximal plates bear 7 to 9 slender, slightly tapering, 

 pointed spines united for half their width by membrane ; the smaller 

 plates bear 6 or 7 spines. The spines form a group rather than 2 

 series, as it frequently happens that 5 to 8 spines form a circle 

 around a central spine, and all flare apart, more or less, but are 

 nevertheless directed toward the margin. 



Furrow spines 6 or 7, slender, very slightly tapering, blunt, and 

 webbed for nearly their whole length. The adoral spine is quite 

 short; the next is half again as long, the third about twice as long 

 as the first, the fourth and fifth each slightly longer than the pre- 

 ceding; the sixth about equal to the fifth. When there are 7, the last 

 spine about equals the third. Subambulacral spines 8 to 12. There 

 is a semicircular webbed series parallel in general to the furrow 

 series, consisting of about 8 (as many as 10) spines increasing in 

 length from the short adoral to the fifth or sixth, then decreasing, 

 the last spine being longer than the first, unless there are 10, when 

 the series is symmetrical. Often 1 or 2 -ipines stand in the hollow 

 of this series segregated from the others. The subambulacral spines 

 are a trifle stouter and are more acute than the others. 



The oral armature is of the same character as the adambulacral. 

 Marginal spines about 9, slender, untapered, blunt, the inner 3 or 4 

 being the stoutest. Subambulacral spines about 12, sharp, and ar- 



