REVISION OF PALEOZOIC STELLEROIDEA. 69 



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

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

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

 usually covered by tufts of spines." The tyj)e-specimen clearly 

 shows columns of adambulacral and mframarginals bordermg the 

 ambulacra! grooves and that m each axil there is a single large axiUary 

 margmal plate. Tliis matter need not here be followed further than 

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

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

 is in error m regarding all of Stenaster as synonymous with Vraster- 

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

 its author. BiUings origmally referred to Stenaster, S. salteri, and 

 S. pulclieTlus. The latter is certainly congeneric wdth the iy^e of 

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

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

 good genus. 



Palseaster m many respects reminds one of Hudsonaster, and the 

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

 abactinal area is also similar, but m Hudsonaster there are five colunuis 

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

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

 progression m differentiation toward Palseaster appears to be as fol- 

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

 columns of plates, two uiframai^gmals, two supramai-ginals, and one 

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

 of the rays, two uffra- and two supramargmals, but in the proximal 

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

 by numerous small, irregidar accessory plates. Tliis introduction of 

 numerous supplementary plates also takes place to a far greater 

 extent on the disk, where tliey are crowded in between the laiger 

 central and the five basal radial plates. 



The primitive disk structure of Palseaster is hi large part again 

 repeated in Neo palseaster, but otherwise the two genera are different. 



PALiEASTER 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 Rep. N. Y. State Cab. Nat. Hist., 1868, p. 282; 

 rev. ed., 1868=1870, p. 324.— Quenstedt, Petrefactenkunde Deulschlands, 

 vol. 4, 1876, p. 73, pi. 92, figs. 32, 33.— Hudson. Pull. N. Y. State Miis., 

 No. 161. 1913, pis. 9, 10, 12, 13. 



Original description.— "Body stellate; disk smaU; 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, margms 



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



