1894. PROCEEDINGS OF THE NATIONAL MUSEUM. 259 



parallel to the marginal plates; next the marginal plates they become 

 much smaller than elsewhere and squarish or hexagonal in form, while 

 tlie central column becomes reduced to a slight elevation of the surface. 

 These small plates, without interspaces, also extend along the margins 

 of the rays and fill xx.^ the entire abactinal area of the arms beyond the 

 distal fourth, where there are about five rows. In the central area of 

 the disk the central and ten primary plates are larger and more rounded 

 than those upon the rays ; and the papular pores are smaller and less 

 numerous than upon the rays, so that the areas having pores form a 

 five-rayed star upon the disk and arms, which is conspicuous when the 

 granules are removed. The petal-like groups of papular pores are also 

 often distinctly visible in dry specimens without the removal of the 

 granules. 



Each of the dorsal plates bears a very even and regular fiat or concave 

 group of papilliform granules; each group consists of a central cluster 

 of from twelve to twenty-five rather small rounded granules, shghtly 

 separated from each other, and of a marginal series of fifteen to thirty 

 or more, somewhat longer, very even, flattened, blunt papillae, which 

 are somewhat divergent, so that those of the adjacent groups are nearly 

 or quite in contact, except where the papulae come forth. Owing to the 

 somewhat greater length of the marginal papilhe the central area of 

 the whole group is lower than the margin. Some of the smaller groups, 

 towards the sides of the rays contain but six to ten granules in the 

 central cluster, in the midst of which one, slightly the largest, is cen- 

 tral and the others form a circle around it. Close to the marginal 

 plate, in the interradial areas, where the plates are most crowded, the 

 granules become very uniform in size and elevation, so that the separate 

 groups are scarcely distinguishable and the granulation is nearly iden- 

 tical with that on the marginal plates. 



On several of the largest specimens many of the dorsal plates, both 

 of the disk and rays, bear a single, small, subcentral or marginal 

 bivalved pedicellaria, which is a little higher than the adjacent gran- 

 ules and two or three times as broad ; seen from above the outline is 

 oblong; each one appears to take the jjlace of from two to four gran- 

 ules, Sometimes two such pedicellari.e occur on the same plate, and 

 occasionally they have three valves. Those that occur near the inter- 

 radial margins are smaller than those on the central area. The valves 

 are flat, incurved, and truncate at the end. 



The madreporic plate is small, with few branched gyri, and is sit- 

 uated, much nearer to the center than to the margin; in a specimen 

 having the lesser radius 22 mm. the madreporic plate is 7 mm. from the 

 center. The central or anal pore is usually small and inconspicuous, 

 but in some specimens it is very evident and is surrounded by a con- 

 vergent group of numerous small spinules. In the papular areas at 

 the bases of the arms the pores are large and each has a single papula; 

 usually each plate is surrounded hy six pores. 



