350 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



Albatross specimens appear to be referable. It is especially char- 

 acterized by the very prominent, often sharp dorsal spines, together 

 with siipero- and inferomarginal spines. 



Genus PENTACEROPSIS Sladen. 



Pentaceropsis Sladen, 1889, p. 350. Type, P. obtusata l=Astcrias obtu- 

 sata Bory de Saint Vincent]. 



PENTACEROPSIS TYLODERMA Fisher. 



Plate 94, figs. 8, 8a-b ; plate 97, fig. 1 ; plate 98, fig. 2 ; plate 100, fig. 1. 

 Pentaceropsis tyloderma Fisher, 1913c, p. 209. 



Diagnosis. — Differing from P. ohtusata in having one series of 

 subambulacral spines, in lacking inferomarginal tubercles, except on 

 the first few plates, in having less prominent distal superomarginals 

 without smooth tubercles, and very much smaller granules among 

 the papulae than on the convex plates. R=94: mm., r=49 mm., 

 R=1.9 r; breadth of ray at base, 44 to 54 mm. Disk inflated, rays 

 convex, much lower than disk; actinal surface subplane; inter- 

 brachial arcs well rounded ; rays broad, tapering little until near the 

 end, which is rounded. 



Desc7'iption. — Abactinal surface of disk convex or inflated, about 

 half as high as width of ray at base. No true spines anywhere ex- 

 cept on the adambulacral and mouth plates. Abactinal surface 

 paved with plates of about 3 sizes, but only 2 of these are evident 

 externallj^, because the small ossicles which fill in the spaces between 

 the large plates are covered with granules. First the appearance of 

 the abactinal surface before the removal of granules: There is a not 

 very regular carinal series of about 12 convex, transversely elliptical 

 plates, starting with the primary radial, spaced about one-fourth to 

 one-half their longer diameter, which varies from 4 to 7 mm. Be- 

 tween this and the superomarginal series are 3 others, not at all 

 regular, spaced, convex, decreasing in size toward the margin, the 

 adradial plates being transversely elliptical, the others irregularly 

 roundish. Two dorsolateral series reach the end of the ray, the 

 third extends about two-thirds or three- fourths the length of ray. 

 while in the interbrachial arcs are 2 additional series, the plates 

 being rather small and of secondary size. These primary plates are 

 covered with close-set, flat, or very faintly convex polygonal gran- 

 ules, which increase very rapidly in size from the margin toward 

 the center, where 1 to several are conspicuously larger than the rest 

 and slightly more convex. The plates of second size are widely 

 spaced, unequal, and, except near the ambitus, are conspicuously 

 smaller than the primary plates. They are most numerous on the 

 disk and proximal portion of ray. rather few on the oivter part of 

 ray. They are convex, and usually bear a relatively large hemi- 



