H. 8. Williams—Fauna of the Chemung Group. 108 
Strophodonta perplana, var. nervosa, and Strophodonta mucro- 
nata of the Chemung group are much nearer the western Stro- 
phodonta perplana than the eastern variety of the Hamilton 
Steen and the variety called Str. eanace of Iowa, in the higher 
eds, itself appears in the High-point beds of the Chemung. 
The common Str. Cayuta of the upper Chemung, although 
quite distinct from the Str. inequistriata of the Hamilton, is 
apparently only a variety of the western Str. arcuata. A like 
ae may be seen among the Spirifers of the Sp. mucronatus 
ype. 
The Chemung Sp. mesocostalis is easily distinguished from 
any New York varieties of Sp. mucronatus. But the forms 
beds and the Chouteau limestone of Missouri to the Chemung 
eriod., 
re are other reasons, which I cannot here array, for 
regarding the Rockford, Indiana, Goniatite beds as equivalents 
Ocean, the true equivalents will probably be found in the Pilton 
and Marwood beds of Devon. While the Genesee slates, pass- 
108 gradually into the Portage, as they do in Ontario county, 
New York, with its hard concretionary, calcareous layer, fill 
With Goniatites, and its Colcolus aciculum and C. tenwicinctum, 
