90 BULLETIN 76, UNITED STATES NATIONAL MUSEUM 



skeleton reduced to small circular plates widely spaced on rays but closer on disk, 

 each bearing a slender needlelike spine heavily wreathed by pedicellariae borne on 

 the expanded top of a retractile sheath; inferomarginal plates spaced, with a single 

 wreathed spine; superomarginal plates and spine above alternate inferomarginals; one 

 rather long adambulacral spine; papulae numerous, slender, vermiform, in groups of 

 2 or 3 to 15, arranged in an intermarginal series, and in four to six, sometimes evident, 

 abactinal series; without arrangement and crowded on disk. 



Description. — Abactinal surface of disk typically covered with very delicate 

 needlelike spines from 2 to 2.5 mm. long, encircled by a conspicuous globose bouquet 

 of small crossed pedicellariae borne upon a heavy sheath. This sheath consists of a 

 circular expansion of membrane, the upper or distal convex surface of which is 

 thickly beset with pedicellariae, while that encircling the spinelet below is naked. 

 These wreaths are a little larger and a little more crowded inside the middle of r, 

 although there is more or less variation. The spines spring from small roundish 

 independent plates imbedded in the integument and spaced about 0.5 to 2 mm. 

 apart, each plate being 0.5 to 1.25 mm. in diameter. They are a trifle convex in 

 the center, and are closer together on the central portion of the disk than near the 

 periphery. On the ray the plates are spaced 1 to 4 mm. apart, and about four 

 irregular longiseries are sometimes evident, although often no serial arrangement is 

 observable. The abactinal plates of the ray also bear each a delicate wreathed 

 spine. These are not nearly so numerous to the square centimeter as on the disk. 

 Scattered between the primary plates are relatively few minute grains. 



Marginal spines longer and stouter than the abactinal, with larger bouquets of 

 pedicellariae. The inferomarginal plates are much larger than the abactinal plates, 

 rudely lozenge-form and attached to the outer face of the adambulacrals, usually 

 one to every four or five adambulacral plates. The inferomarginals are spaced in 

 such a manner that proximally two or three adambulacrals (distally two) can be 

 seen between them. The spine is borne on a ventral boss of the plate, and is about 

 3.5 mm. long in large specimens. 



Just above each alternate inferomarginal is a somewhat larger oblong supero- 

 marginal, the lower end of which overlaps the upper end or side of the inferomarginal, 

 while at the dorsal end upon a boss is borne an acicular wreathed spine subequal to 

 the inferomarginal spine, and standing directly above it. Opposite the other, 

 alternating, inferomarginals, the superomarginals are small and rudimentary, reduced 

 to an ossicle devoid of a spinelet, and wholly invisible until the skin is dried. This plate 

 disappears entirely beyond the middle of R. The first five or six inferomarginals are 

 a little more crowded and each has a spiniform superomarginal adjacent to it. 



The papulae are numerous, long, and vermiform, and are clustered in groups of 

 from 2 or 3 to 10 or 15. There are usually about three, but up to five, and occasion- 

 ally more, papulae to each pore which pierces the integument. For instance, in a 

 group of 15 papulae the coelomic surface of the body wall shows 5 pores, evenly 

 scattered. On the disk, the long papulae are packed in tightly between the spines 

 and their globes of pedicellariae. On the rays the papulae are really in longitudinal 

 series but it is difficult to make them out in most specimens, except in the case of the 

 intermarginal series. There seem to be about six abactinal series indicated. In a 



