436 Forty-second Report on the State Museum. 



in closest proximity to it. The Cystidians afford perhaps the most 

 positive Silurian feature of the fauna, and we should not underrate 

 its importance. It has already been observed that Kayser's Hercynian 

 contains a Graptolite faunula, affording a still more ancient expression 

 than do the Cystidians in the Lower Helderberg, and we may perhaps 

 safely consider this element in the same light as Kayser has these 

 Graptolites, not as necessarily compromising the Devonian cast of the 

 fauna, but as emphasizing its extreme Devonian age. At the same 

 time the fact must not be overlooked that Cystidians do occur in faunas 

 conceded to be Devonian. 



In matter of species, it is believed that none pass over from the 

 Niagara fauna to that of the Lower Helderberg save the cosmopolitan 

 forms Strophomena rhomboidalis and Atrypa reticularis. Affinities of this 

 character are far more pronounced between the Lower Helderberg 

 and the Oriskany. 



In the typical localities of the Lower Helderberg in Albany county, 

 the Oriskany sandstone has a very meager development. As the Lower 

 Helderberg limestones diminish in thickness, the overlying Oriskany 

 sandstones increase, and the relative development of the faunas cor- 

 responds thereto. This is true wherever the two formations can be 

 traced. In the Southwestern Appalachians at Cumberland, Md., the 

 faunas, are to a large degree commingled, at all events a very 

 considerable per-centage of the New York Lower Helderberg species 

 is embodied in the Oriskany fauna. Though this is to a less 

 degree the case in the New York development of these faunas, there 

 is, in the broader faunal characteristics, a much more intimate 

 homogeneity than will be found between the Lower Helderberg 

 and the Niagara. We may instance the genera Homoerinus, Mariacrinus, 

 Edriocrinus among the crinoids, Anomalocystites among the cystidians; 

 Orthis* of the 0. Vanuxemi group; abundance of large Strophodontas; 

 Eatonias, Gyrtina of the group of G. heteroclita; Spirifers with faintly 

 lineate varices; typical Meristellas; abundant Kensselserias; among 

 the Lamellibranchs, great Actinopterias; of the Gastropods, an 

 immense development of Platyceras and Sir opho stylus; Phacops with 

 duplicate pygidial ribs; Homalonotus of the type of H. Vanuxemi, 

 and the occurrence of Dalmanites pleuroptyx. 



It is not necessary to enter into detailed argument, or to adduce 

 data to demonstrate the Devonian character of the Oriskany fauna. 

 It was assigned to the Devonian by Profs. Hall and De Verneuil in 

 1845 and it will unquestionably maintain its position as such. 



*Prof. Hall observed in Pal. N. Y„ Vol. 3, p. 406, that the similarities in the brachiopods 

 of the two faunas were very close, those of the Oriskany being generally of larger siziQ. 



