20 



NEW YORK STATE MUSEUM 



Orthis impressa Hall 



0. tioga Hall 



O. carinata Hall 



Stropheodonta cayuta Hall 



S. inequistriata Hall 



S. demissa Conrad 



S. perplana var. nervosa Hall 



Athyris polita Hall 



Orthothetes chemungensis Conrad 



Camarotoechia eximia Hall 



C. cf. tethys Hall 



Orbiculoidea sp. 



Ambocoelia umbonata gregaria Hall 



Lingula punctata Hall 



L. spatulata Hall 



L. cf. nuda Hall 



Leptodesma potens Hall 



L. maclurii Hall 



L. billingsi Hall 



L. robustum Hall 



L. lichas Hall 



L. spinigerum Hall 



L. disparile Hall 



L. matheri Hall 



Leptodomus interplicatus Clarke 



Paleoneilo filosa Hall 



P. constricta Conrad 



P. bisulcata Hall 



P. cf. maxima Hall 



Lyriopecten tricostatus Vanuxem 



Pterinopecten imbecilis Hall 



P. strictus Hall 



Macrodon chemungensis Hall 



Aviculopecten cancellatus Hall 



Avicula sp.? 



Modiomorpha subalata Hall 

 Mytilarca carinata Hall 

 M. umbonata Hall 

 Grammysia circularis Hall 

 Nucula sp.? 



Sphenotus clavulus Hall 

 Conocardium sp.? 

 Schizodus chemungensis Hall 

 Spathella sp.? 



Cypricardella bellistriatus Conrad 

 Glossites cf. subtenuis Hall 

 Manticoceras pattersoni Hall 

 Orthoceras bebryx var. cayuga Hall 

 Phacops rana Green 



Chemung sandstones 



The term Chemung has been applied with such a breadth of mean- 

 ing in New York stratigraphy that faunally and stratigraphically it 

 no longer meets the requirements of precise expression. The forma- 

 tion has been, in a general and vague way, regarded as that mass 

 of arenaceous deposits lying above the Portage of western New 

 York and the Ithaca of central New York, from which there is, as 

 is now known, a transition lithologically so gradual as to make a 

 separation a pure convention. In respect to fauna the " Chemung 

 group " has been commonly regarded as well defined by the pres- 

 ence of a notable series of species specially brachiopods, lamelli- 

 branchs and dictyosponges, all of which have been in a way regarded 

 as centered about the species Spirifer disjunctus and the 

 horizon, as a whole, including a thickness of from iooo to 1500 feet 

 of strata, regarded as the horizon of Spirifer disjunctus. 

 This conception, as we have heretofore explained, is misleading, 

 vague and inaccurate. The horizon of Spirifer disjunctus 



