REVISION OF PALEOZOIC STELLEROIDEA. 69 



Hall writes: " Lower side of arms showing two ranges of plates on 

 each side of the avenue, the outer range composed of strong hex- 

 agonal plates, with an inner range of smaller ones alternating, the latter 

 usually covered by tufts of spines." The type-specimen clearly 

 shows columns of adambulacral and inframarginals bordering the 

 ambulacral grooves and that in each axil there is a single large axillary 

 marginal plate. This matter need not here be followed further than 

 to add that Stenaster originally included two generic types, both of 

 which are widely different from Palseaster. On the other hand, Hall 1 

 is in error in regarding all of Stenaster as synonymous with Uraster- 

 ella McCoy, a name never properly defined and finally abandoned by 

 its author. Billings originally referred to Stenaster, S. salteri, and 

 S. pulcTiellus. The latter is certainly congeneric with the type of 

 Urasterella as illustrated by Salter, but the former is quite different, 

 as is pointed out elsewhere in the remarks on Stenaster, which is a 

 good genus. 



Palseaster in many respects reminds one of Hudsonaster, and the 

 actinal generic characters may be regarded as alike in both. The 

 abactinal area is also similar, but in Hudsonaster there are five columns 

 with decidedly fewer plates, while in Palseaster there are no radial 

 columns. The former genus is the more primitive one and the 

 progression in differentiation toward Palseaster appears to be as fol- 

 lows: In Hudsonaster, the rays throughout are composed of five 

 columns of plates, two inframarginals, two supramarginals, and one 

 radial. In Palseaster, there are but four columns in the outer third 

 of the rays, two infra- and two supramarginals, but in the proximal 

 two-thirds where the radials are also absent, their place is occupied 

 by numerous small, irregular accessory plates. This introduction of 

 numerous supplementary plates also takes place to a far greater 

 extent on the disk, where they are crowded in between the larger 

 central and the five basal radial plates. 



The primitive disk structure of Palseaster is in large part again 

 repeated in Neopalseaster, but otherwise the two genera are different. 



PALSEASTER NIAGARENSIS Hall. 



Plate 7, figs. 1^. 



Palseaster niagarensis HALL, Nat. Hist. N. Y., Pal., vol. 2, 1852, p. 247, pi. 

 51, figs. 21-23 (not p. 352, pi. 85, figs. 8-10, possibly an undescribed 

 species). BILLINGS, Geol. Surv. Canada, Can. Org. Rem., dec. 3, 1858, p. 

 78, fig. 1. HALL, Twentieth Hep. N. Y. State Cab. Nat. Hist., 1868, p. 282; 

 rev. ed., 1868=1870, p. 324. QUENSTEDT, Petrefactenkunde Deutschlands, 

 vol. 4, 1876, p. 73, pi. 92, figs. 32, 33. HUDSON, Bull. N. Y. State Mus., 

 No. 164, 1913, pis. 9, 10, 12, 13. 



Original description. "Body stellate; disk small; arms short, terete 

 with a deep avenue on the lower side, which is margined by strong 

 short spines; centre of plates (in the fossil) nearly smooth, margins 



i Twentieth Rep. N. Y. State Cab. Nat. Hist., rev. ed., 1808=1870, p. 325. 



