CnONETES OP THE HAMILTON GROUP. 130 



portion being distinctly limited, while towards the margin the imprints 

 of striaB are a little more definite than in the others. These slight diffe- 

 rences between specimens occurring in limestone, and those in arenaceous 

 beds, are almost universal in other examples of identical species occur- 

 ring in the different sediments. 



In the yellow sandstone of Licking county, Ohio, there are similar 

 casts of Chonetes ; and I have a piece of sandstone from near Bedford, 

 Ohio, preserving several casts of the same species. These specimens from 

 the several localities show, along the area line, the casts of five or six 

 tubes on each side ; the three inner ones are parallel to the sides of the 

 foramen, while the others are less oblique. The three, nearest the apex 

 are not known to be produced into spines, but probably form minute 

 pustules on the margin of the area. 



In authentic specimens of C. logani from Burlington, there is great 

 variation in the convexity of the ventral valve ; the smaller and younger 

 being moderately convex, while the older ones are ventricose. The num- 

 ber of costaD varies from twenty to forty. There are two spines (and rarely 

 indications of a third) on each side of the beak. The area shows evi- 

 dence of the oblique tubes observed in the casts. 



The interior of the dorsal valve is papillose, with the striae more or 

 less strongly marked. The muscular and vascular impressions are often 

 pretty well preserved. The cardinal process is short, and supported oh 

 each side by an elevated ridge, with or without an obsolete median ridge, 

 giving the appearance presented by the cardinal process in some of the 

 species of Streptorhynchus. 



We have, therefore, a species of Chonetes, so far as we can judge by all visible 

 features, ranging from the Tully limestone to the base of the Burlington lime- 

 stone ; or from the top of the Hamilton group to beds directly in conjunction with 

 the base of the Carboniferous limestones, as known in Iowa and the Mississippi 

 valley. 



I have been indebted, in the first instance, to Ledyard Lincklaen, Esq., of 

 Cazenovia, for species of this fossil from DeRuyter ; and subsequently it waa 

 found by Mr. Whitfield at Tully. 



Geological formations and localities. In the Tully limestone, at Tully, Onondaga 

 county, and at DeRuyter, Madison county, New- York; in Cuyahoga, Licking and 

 Medina counties, Ohio. The typical forms of the species-occur at Burlington, 

 Iowa, and at Quincy, Illinois. 



