EEWSION OF PALEOZOIC STELLEROIDEA. 115 



Remarks. — The similarity and difference between P. hellidus and P. 

 speciosus are pointed out above. Anotlicr related species is P. spinu- 

 losus, which has the same kind of abactinal plates and madreporite 

 as P. hellulus. In the former the rays arc far longer and narrower, 

 with fewer ambital plates and columns between the supramarginals. 

 Actinally P. spinulosus is at once distinguished from P. hellulus 

 in the much smaller interbrachial areas, in that it does not have 

 more than two interbrachial marginal plates v/hile P. hellulus has 

 four. In the latter species there are also far more adambulacral 

 plates around the interbrachial pieces. 



It will always be diflicult to distinguish fragments of P. hellulus, 

 P. speciosus, and P. spinulosus from one another, even with good 

 material, smce at least two spechnens of P. hellulus were identified 

 as Palseaster granulosus Hall = Promopalseaster speciosus (Meek) . 



Cat. No. 40879, U.S.N.M. 



PROMOPALiEASTER SPINULOSUS (Miller and Dyer). 



Plate 16, fig. 2; plate 17, figs. 1, 2; plate 18, figs. 1-3. 



Compare with Promopalseaster exculptus (Miller). 



Palxaster spinulosus Miller and Dyer, Journ. Cincinnati Soc. Nat. Hist., vol. 



1, 1878, p. 32, pi. 2, figs. 12-126. 

 Palxaster longibrachiatus Miller, Journ. Cincinnati Soc. Nat. Hist., vol. 1, 1878, 



p. 102, pi. 3, fig. 4. 



Original description (of Palseaster spinulosus). — "Pentagonal; 

 rays longer than the diameter of the body; marginal plates globular 

 near the apices of the rays, but lengthened toward the junction 

 with the body. Six of these plates measure from the body on a ray 

 three-tenths of an inch. Two wedge-shaped plates form the junc- 

 tion of the marginal plates with the body. 



''Adambulacral plates a little smaller [in width] than the margi- 

 nal pieces, and possessed of two or three [four or more] spines to 

 each plate. These spines taper to a fine point, and are longer than 

 the diameter of the plates. The oral pieces are not determined 

 [they are hke those in P. exculptus]. The ambulacral plates have 

 their greatest length across the rays, and are possessed of a sharp 

 ridge in the middle which seems to be [is] connected at one end with 

 the adambulacral pieces. [The entire number of plates in each 

 range can not be given, since the rays are imperfect.]. 



"The dorsal side is covered with plates united by angular exten- 

 sions. They are of unequal size, and strongly tuberculated or spi- 

 nous. 



"The madreporiform tubercle on its upper face is an oblate sphe- 

 roid, much depressed, and marked by fine radiating striae, which 

 become more numerous by intercalation, ^\ithout bifurcation. 

 [This plate is interpolated between the proximal plates of two ad- 



