262 BULLETIN "U, UNITED STATES NATIONAL MUSEUM. 



contain on the disk of large specimens about fifty to sixty-five conspicuous papulae, 

 these decreasing gradually on the rays to about thirty, then fifteen, then ten; 

 smaller specimens with fewer papulae. No papula; on actinal surface. Skin rather 

 thick, obscuring (lie outlines of plates which form narrow raised ridges, the isolated 

 spines occurring on the larger raised primary plates, usually at a point where three 

 or four ridges join; in other words at corners of papular areas. The spines are 

 borne on a slightly raised boss of plate, boss and spine together being 3 to 6 mm. in 

 length. Spines stout, tapering, usually rather sharp, in small specimens being 

 arnuiged in a mid-railial, superomarginal and uiferomarginal series, with a row of 

 scattered adradials and one of actinal intermediate smaller spines. There is also a 

 large |)rimary basal spine in each interradius and a large central spine. The primary 

 "radials" and "basals" are connected by a ridge so as to form a pentagon, the 

 corners radial. Within this apical area is another more stellate pentagon with the 

 primary basals for corners and the infra-basals for interadii. Connecting the infra- 

 basals with the central plate are five straight ridges, which also form interradial lines 

 to the inner pentagon. The infra-basals have short spines and occasionally one 

 of the ridges radiating from the central plate is missing. These ridges are of course 

 radial with reference to ray, since the points of the inner pentagon are interradial. 

 In mature specimens this regular arrangement is more or less disturbed, although the 

 two pentagons, one within the other, can be readily recognized in the apical region. 

 In large specimens the radial scries of spines is usually irregular. There is some- 

 times an intermediate series of shorter spines between the median radial and adradial, 

 and one between adradial and superomarginal; thus three laterodorsal series, of 

 which the middle (the adradial of young specimens) is more regular and has longer 

 spines; one or two irregular intermargiuai series, shorter than marginal spines; 

 inferomarginal spines slightly grooved along one side at tip, or simply flattened and 

 truncate; occasionally not perceptibly flattened but blunter than upper series. 

 Actinal intermediate spines often entirely wanting, even in adult specimens, and 

 when present are arranged in one to four very irregular and often incomplete series 

 which do not extend beyond middle of ray; sometimes only a few irregularly 

 scattered spines are present. Fine creases or lines in the integument proceed out- 

 ward between the spines, from the adambulacral to marginal plates. Lowest papular 

 areas are the longitudinal intermargiuai series, containing upward to twenty-five 

 papula} to the area. 



Preparation of the body wall shows that the papular areas contain many small 

 scattered calcareous grains, most numerous near central portion of each area. In 

 some areas these are arranged in fines and appear to be embryonic plates, while in 

 other areas a few have enlarged sufficiently to form isolated chains of small plates or 

 have even formed an attachment with the nearest trabecula. 



Adambulacral plates considerably wider than long, rather smaU and crowded. 

 Armature consists of (1) a single truncate or round-tipped untapered or tapering 

 furrow spine, 3.5 to 4.25 mm. long, usually flattened and grooved along the upper 

 (or outer) side; (2) on the actinal surface of plate, a similar but generally longer 

 upright spine, usually very conspicuously scoop-shaped at tip. Both spines are 

 covered with membrane, as is also the surface of plates. Some specimens have 

 outer furrow spines longer and slenderer than others or relatively longer than the 



