270 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



larger madreporic body; narrower inf eromargiiials : coarser, and 

 more tuberculate, sometimes mueronate, unequal, actinal intermediate 

 granules: smaller month plates, with the first adambulacrals nearly 

 or quite meeting behind them ; many of the subambulaeral spines of 

 conspicuous size, and graduated into the tubercular granules of the 

 actinal intermediate plates. Rays broad at base, the width at inner 

 end of the first 2 superomarginals which meet medially equaling 

 first 4 superomarginals measured on ambitus; interbrachia arcuate; 

 inf eromarginals defining contour of ray ; dorsal surface of ray 

 nearly plane ; normal marginal plates not tumid, though inf eromar- 

 ginals with slightly arched ventral surface; adambulacral furrow 

 spines 4 or 5 on first few plates, these gradually increasing to 9 or 10; 

 oral spines 6 or T. R=101 mm., r=30 mm., E=3.4 r; breadth of 

 ray at midinterbrachium, 34 mm. 



Description. — Abactinal plates small, the radial being elliptical 

 and much wider than long; the median radial plates with 1 or some- 

 times 2 transverse rows of subglobular granules (4 to 8 in number) , 

 surrounded by a not very regular peripheral series of about 15 to 18. 

 Most of the granules of these as well as of other abactinal plates 

 have a peculiar form; it is subglobular with often 4 or 5 faces, 

 slightly broader at tip than base, and from the middle arises a 

 slender, sharp spine or mucro, often half as long as the granule, or 

 rarely longer. Many granules do not have the mueronate tip, while 

 in others there is a slight indication of it. Some of the radial gran- 

 ules of N. euryplax have a rudimentary mueronate tip, and the 

 plates are larger and more compactly placed. Papular areas broad, 

 comprising about 13 longitudinal series, the interradial areas, cor- 

 respondingly small and with about 5 chevrons of 4-sided plates. 

 Abactinal area within the marginal plates stellato-pentagonal. Xo 

 abactinal pedicellariae. 



Superomarginals 29, massive, the lateral face visible from above, 

 and the rounded angle between the 2 facets of the plate more than 

 a right angle. The plates encroach conspicuously upon the abactinal 

 area and are slightly beveled in the interbrachia. Fifth or sixth 

 plates the largest and meeting medially; sometimes a fifth meets a 

 sixth of the other side. Length of twenty-second plate equal to 

 chord of width, all the others wider than long; length of seventh 

 plate equal to Avidth of abactinal surface; the fifth and sixth are 

 wider than long and the first to fourth vary from a little wider than 

 long to a little narrower, with regard to the dorsal surface. Granules 

 slightly spaced (more so on arm than disk) similar to abactinal inter- 

 radial granules, but the mueronate tip present onh- on lateral face 

 of ray where the granules resemble miniature acorns. No marginal 

 pedicellariae. Terminal plate ovoid, about as wide as long. 



