368 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



DISSOGENES STYRACIA Fisher. 



Plate 102, fig. 1 ; plate 103, fig. 1 ; plate 131, figs. 1, la^l&. 

 Dissogenes styracia Fisher, 1913c, p. 212. 



Diagnosis. — Disk large, somewhat inflated; rays moderately long, 

 narrow, tapering at first rapidly then gradually to pointed ex- 

 tremity; interbrachial arcs wide, rounded. R=110 mm., r=28 mm., 

 R=4 r; breadth of ray at base, about 34 mm. Marginal -plates small 

 confined to side of ray, unarmed except for a small central spine on 

 the first 2 or 3, Body overlaid by a close granulation obscuring out- 

 lines of all plates except marginals; abactinal plates irregularly 

 lobed, irregular in arrangement and connected irregularly by smaller 

 secondary plates; primary plates of disk and basal part of ray con- 

 A-ex with a central rigid, short, stout, subtruncate tubercular spine; 

 about 4 chevrons of similar longer spines on actinal interradial areas 

 (not reaching margin) ; furrow spines slender, rather long, 4 or 5 

 proximally, 4 over most of ray; subambulacral spines heavier, sub- 

 truncate, 2 on disk and 1 on ray. Papulae single, all over disk and far 

 along ray, numerous but irregular in arrangement ; no 'pedicellariae. 



Description. — Abactinal plates of disk convex, the convexity 

 diminishing on the ray, the distal plates being nearly flat. 

 The plates are strongly overlapping, without order (even the 

 carinal series being irregular) and are covered with closely 

 placed small, irregularly polygonal to subcircular granules which 

 obscure completely the sutures. Many of the plates of disk 

 and proximal fifth of ray bear a central robust slightly tapering 

 round-tipped tubercular spine 1.5 mm. long. These spines aro ar- 

 ranged in an irregular carinal series and 3 or 4 subparallel series on 

 either side. On some of the spiniferous plates the granules de- 

 crease slightly in size near the base of the spine, Avhile on the edge 

 of the spiniferous area a few plates bear low thimble-form tubercles. 

 Near the end of ray a number of plates have a small central 

 naked area. The papulae extend to within about 25 mm. of the end 

 of ray. They are irregularly distributed and on the outer part of 

 ray tend to form lines of 2 to 4, outlining the larger plates; on the 

 disk and proximal part of ray they are single, spaced, and surround 

 the large and small plates irregularly. Some or all of the granules 

 immediately bordering papular pores are smaller than the others. 



The abactinal plates when denuded of granules are seen to be of 

 2 kinds. Larger irregular plates overlie smaller irregular connecting 

 plates. The 2 kinds intergrade in size. The former are slightly to 

 markedly convex and have 2 to 5 semicircular excavations in the 

 margin bordering papular apertures. The smaller connecting plates 

 as seen from the coelomic side are either oblong, irregularly ellipti- 

 cal, or irregularly triradiate in form. The latter seem to develop 

 into primary plates. 



