2,2. NEW YORK STATE MUSEUM 



Remarks. We have before us parts of five specimens, two of 

 which show the abactinal side, the others the actinal side. . This 

 species is most similar to A cant h aster clarki (Clarke & 

 Swartz) from the Jennings formation (Chemung member) of 

 Oakland, Md. The latter species has a much more convex disk, 

 the basal radial and supramarginal plates are of less unequal size 

 and the accessory ambital plates in the interbrachial areas are 

 absent; the radial plates are less elongate and the accessory plates 

 are of very minute size. The supramarginal plates are not so 

 distinctly wedge-shaped but rounded quadrangular, leaving not 

 any or but small depressions between them. The inframarginal 

 plates do not appear as marginal crescent-shaped pieces. All the 

 plates of the rays are much more convex and the rays were 

 narrower and thicker. On the actinal surface the ambulacral 

 grooves are narrower and shallower, the ambulacral plates do not 

 show the pronounced transversal ridges, the inframarginal plates 

 are broader and shorter and no long central spines are seen. As 

 A . clarki is only known in one small specimen, it may appear 

 possible that our species represents but the mature types of A . 

 clarki. We have, however, two specimens of the size of the type 

 of that species which exhibit the adult characters of A. pers- 

 p i n o s u s , both on the actinal and abactinal sides. As it is, A . 

 clarki bears in all its features a more primitive and hence 

 younger character than A. perspinosus, although of approx- 

 imately the same geologic age. Devonaster chemung- 

 e n s i s Schuchert, from the Chemung of Central Pennsylvania, is 

 a larger form which is known only from the actinal side and bears 

 in its general outline a considerable resemblance to A . per- 

 spinosus, but is distinguished by the broad form of the supra- 

 marginal plates, which, however, distally become like those of 

 our species. The inframarginal plates lack in Devonaster 

 chemungensis all indication of the marginal articulated spines 

 so prominent in A. perspinosus. The axillary inter- 

 brachial and the proximal inframarginal plates bear centrally large 

 spines in D. chemungensis; in A. perspinosus 

 only the axillary interbrachial and the first two inframarginals 

 show large central spines in the larger specimen, while in the smaller 

 one no such spines or spine bases are noticeable. The differ- 

 ence in the development of the spines in the two species could there- 

 fore be considered as one of individual age within the same species. 

 From the evidence available we consider it possible that also 

 Devonaster chemungensis belongs in this genus. 



