560 Contributions to Invertebrate Palaeontology. 



FOSSILS OF THE ERIE SHALES. 



There appears to be no question regardinj^ the equivalence of the 

 Erie shales of Ohio with the Portage and Chemung groups of New- 

 York ; and the Palaeontological features of these latter formations 

 are so well known, and so marked, that there ought to be no doubt 

 as to their geological position. Their stratigraphical relations also 

 to the Catskill group, the American equivalents of the Old Red 

 Sandstone of England, which is considered as typical Devonian, 

 would apparently leave no doubt as to their place in the geological 

 record, or to the zoological age to which they should be referred. 

 From these considerations I have considered the following fossils 

 from the Erie shales, as of Devonian age, an opinion for Avhich I 

 alone may be held responsible. The group, taken as a whole, are 

 of special interest on account of the Crustaceans; while the other 

 forms associated with them are sufficiently characteristic to show 

 their stratigraphical relations. 



MOLLUSCOIDA. 



Genus DISCllVA Lemarck. 



Discina liuniilis. 



Plate XII, figs. 1 and 2. 



Discina humilis Hall, Pal. N. Y., vol. 4, p. 1(5, pi. 2, fig. 18. 



A crushed and fragmentary .specimen of this species, but quite 

 too imperfect for illustration, has been detected in one of the nodu- 

 les from the Erie shale at Leroy, Lake Co., Ohio. The shell shows 

 it to have been circular, nearly discoid in form, with the surface 

 covered by distant elevated lines or ridges, and corresponds in all 

 respects, as far as can be seen on the specimen, to those from the 

 Marcellus shale and Hamilton beds of New York. 



