KEVISIOX OF PALEOZOIC STELLEROIDEA, 117 



Comparing it with the actinal area of P. longihracMatus ^filler, it 

 is evident that both forms arc identical. In the hitter the rays are 

 complete, very long and slender, and there is nothing to show that 

 they were dissimilar in P. sirinulosus Miller and Dyer. Both types 

 are nearly of the same size and the actinal plates are identical in form 

 and arrangement. The abactinal area in P. longibrachiatus is not 

 known, but since its actinal structure is that of Promo palieaster 

 S'pinulosus it is safe to assume that the abactinal structure is alike 

 in both. 



P. spinulosus actinally is also closely related to P. exculptus (IMiller). 

 The latter appears to have shorter and more rapidly tapering rays 

 and in general seems to be a more robust species. Another character 

 by which these species can be separated is that the interbrachial 

 areas in P. spinulosus have two, vvhile P. exculptus has thi'ee inter- 

 brachial marginal plates. It is possible that the former species 

 also has three interbrachial marginal plates, but as yet the small 

 single piece of each area has not been observed, while in P. exculpius 

 it is distinctly present in each of the five areas. Should P. spiiv- 

 ulosus also prove to have tlirce interbrachial plates, it would be difR- 

 cult to distinguish it actinally from P. exculptus. 



P. dycri and P. magnificus are far larger species and have five 

 interbrachial marginal plates in each area. 



Cat. No. 40S81,^U.S.N.M. 



PROMOPAL^ASTER EXCULPTUS (Miller). 



Plate 18, fig. 7; plate 20, fig. 2. 



Compare wdth Promopalieaster spinulosus (Miller and Dyer). 

 Palxaster exculptus Miller, Journ. Cincinnati Soc. Nat. Hist., vol. 4, 1881, p. 69, 

 pi. 1, fig. 1. 



Original description. — ''Pentagonal; rays a little longer than the 

 diameter of the body; diameter of the body, about 0.93 inch; length 

 of ray measuring to the center of the body or disk, about 1} inches; 

 breadth of a ray at the junction ^vdth the body, about 0.57 inch; rays 

 obtusely pointed. 



"The [infra-] margmal range consists of somewhat quadrangular 

 plates, having a width a little greater than the length; the first 8 

 of these have a length of one-half inch, and there are about; 18 in 

 the length of an inch, and not far from 25 in each range, though the 

 specimen does not permit us to make the count with certainty. The 

 surface is strongly tubercular, and was probably spinous [originally 

 covered with numerous small spines]. 



"The adambulacral range consists of about 28 [25] plates, on each 

 side of a ray; they are narrower than the marginal plates, but have 

 about the same length. Each })late [has a short, ambulacra] exten- 

 sion conforming with the ridge of the ambulacral plates and] bore 



