146 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



lias definite inferomarginal spines which form transverse series on 

 the proximal plates. Alcock writes (and the figures bear him out) 

 that the marginal plates correspond plate to plate. In nesiotes the 

 tAYO series do not correspond, but even alternate on the outer part of 

 ray. The actinal intermediate plates of nesiotes are not very strongly 

 carinated, but the character is such a comparative one that it would 

 be difficult to apply without direct comparison of specimens. The 

 furrow spines of sladeni are "needlelike," but in nesiotes very con- 

 spicuously compressed and bladelike. The subambulacral spines 

 can scarcely be said to form a " rosettelike or paxillalike group of 

 about 12." There is a very definite longitudinal series, just back of 

 the furrow spines, of 3 to 5 shorter, terete tapering spinules, and 

 back of this 12 to 18 spinules in 2 or 3 irregular series, or more or less 

 scattered. They do not suggest a rosette or a paxilla and are more- 

 over more numerous than in sladeni. The interbrachia of nesiotes are 

 more open and rounded, owing to the peculiar form of the ra3^s. 



DIPSACASTER IMPERIALIS Fisher. 



Plate 32, figs. 1, 2 ; plate 40, figs. 1, la-b ; plate 41, figs. 1, la. 

 Dipsacaster imperialis Fishee, 1917&, p. 89. * 



Diagnosis. — Differing from D. nesiotes Fisher in having broader 

 rays, more delicate, longer, and sharper paxillar spinelets; in 

 averaging 1 or 2 more true furrow spines to the plate, and in 

 having an odd interradial series of actinal intermediate plates 

 which reach only a little more than half the distance between outer 

 end of combined mouth plates and inferomarginals. Differing from 

 D. sladeni Alcock in respect to the inferomarginal spines, which are 

 smaller and do not form a definite transverse series, especially on the 

 proximal plates; in having the distal marginals alternating, instead 

 of opposite, and in having more numerous actinal intermediate plates 

 on the ray, the second longitudinal series extending to the twenty- 

 third or twenty-fourth inferomarginal, and the third extending to 

 the sixteenth. E=160 mm., r=55 mm., K=3 r; breadth of ray 

 at base, 62 mm. Rays broad at base, tapering from arcuate inter- 

 brachia, at first rapidly then more gradually to a subacute extremity. 



Description. — The ray is a little broader at the base than in sladeni, 

 the interbrachia more rounded, and the tip more pointed. The bor- 

 der formed by the marginal plates is wider, so that on the outer part 

 of the ray the paxillar area is no broader than in sladeni. The pax- 

 illae are fairly uniform in size on the disk, though a trifle smaller 

 at the center than midway to margin; from the latter point the}' 

 decrease gradually as the margin is approached. The paxillae have a 

 fairly stout, high, convex pedicel, which is broader at the summit 

 than at the surface of the integument, and is crowned with a brush- 



