PALEOZOIC FOSSILS. 289 



This species differs very remarkably from any of the preceding, and 

 every other described species, in its robust form, its more numerous and 

 proportionally larger marginal plates, and in the large and deep ambulacra 1 

 grooves and poral plates. In the single large tuberculose plate at the base 

 of the marginal range it resembles the Niagara species; and in having 

 more adambulacral than marginal plates it resembles P. granulosa, but 

 differs from the last in the large plates of the dorsal side. 



Geological formation and localities. In rocks of the Hamilton group; near 

 Hamilton, Madison county, and near Summit, Schoharie county; also from 

 near Cooperstown, Otsego county, whence I have received a specimen 

 retaining the impression of the lower side, from Paul F. Cooper, Esq. of 

 Albany. 



GENUS URASTERELLA^^ (M'Coy, 1851). 



STENASTEE (Billings, 1858). 



The Genus Stenaster is described by its author as having slender rays, 

 with only a single range of plates (adambulacral) on each side of the ambu- 

 lacral groove. In this respect it appears to me to correspond with the figures 

 of TJraster ruthveni and TJ. hirudo of Forbes, species which M'CoY pro- 

 posed to include in the Genus Urasterella. The British species are from 

 strata of Silurian age (Ludlow rocks). 



Urasterella (Stenaster; pulchella. 



PLATE 



P al<B a si er pulchella : Billings, Geol. Surv. of Canada, Report for 1856, p. 292. 

 Stenaster pulchellus : Id. Decade iii, pa. 79, pi. x, f. 2. 



The specimen which I have referred to this species has long slender arms, 

 with a narrow ambulacra! groove and a single range of short plates on each 

 side. It preserves two rays nearly entire, and parts of others. The single 

 range of plates on each side (adambulacral) only, would preclude its refe- 

 rence to the Genus Pal^aster as defined by me.t 



Geological formation and locality. In the Trenton limestone, near Cana- 

 joharie, New-York. 



•Proposed as a generic name for Uraster ruthveni and U. hirudo of Forbes. British 

 Palseozoic Fossils, p. 59. 



t Mr. Salter, apparently overlooking my description of Palceastcr niagarensis, 

 has placed both the above cited European species under Pal^aster, as defined by 

 himself ; but as it has been shown that this genus has two ranges of plates on each 

 side of the ambulacral groove, these forms cannot, with propriety, be arranged with 



typical Palaeasters. 



There was the same reason for adopting the generic term Urasterella as for 

 adopting Palasterina ; both of which were proposed by M'Coy at the same time, 



37 [ Published December 1866.] 



9 



