ATKYPA OF THE UPPER HELDERBEKG GROUP, &c. 321 



as in fig. 19 of Plate 53. The specimen flg. 16, is a ventral valve of a large individual, from beds 

 at Waverly, Iowa, equivalent to those at Independence. It is less extended on the hinge-line, 

 and has been broken so as to show the spires. 

 Figs. 12 and 13 of Plate 53, are from Lime Creek, near Rockford, Iowa, in beds which are probably 

 of the age of the Chemung group. The specimens are gibbous and finely striated, with strong 

 lamellose lines, and much resemble similar forms from the Chemung group of New York. 



This form of Atrypa becomes a little more robust in the Chemuug group, as 

 compared with those of the Hamilton group of New York, but retains generally 

 the same essential characters. Figure 17 is a dorsal view of a specimen from 

 that formation, and figure 18 is the imprint of the ventral valve in shaly sand- 

 stone, a common condition of the species in these rocks. Figure 19 is a broader 

 and more finely striate form with straighter hinge-line. 



Geological formations and localities. — In the formations under consideration, 

 this species occurs in the Corniferous limestone of New York, Canada West, Ohio, 

 Kentucky, Indiana and Illinois. It is found in the Hamilton group of New York 

 and Canada West ; and undeij an aspect similar to A. zonata of Schnur, in the 

 Hamilton group of Iowa and Illinois. It occurs in the Chemung group of New 

 York, more especially in the eastern or eastern-central portions of the State, and 

 also in rocks of the same age in Iowa. 



Its localities are so numerous that it is scarcely necessary to name them in detail. 

 It is found in nearly every exposure of the Corniferous limestone from Albany county 

 to Black Rock, on the Niagara river. I have received specimens from Mr. Joseph 

 StTLLFVANT, from Columbusj from Dr. Mann and other sources, collected at Milford, 

 Ohio ; from the Falls of the Ohio, by Mr. S. S. Lyon; and very fine specimens from 

 Dr. James S. Knafp, of Louisville. Specimens from Iowa, have been received from 

 Mr. O. H. St. John, besides collections by Mr. Whitfield, myself and others ; I 

 have likewise obtained it at the Bake-oven in Illinois, where the Corniferous lime- 

 stone is intimately connected with calcareous beds of the Hamilton group. 



In the Hamilton group of New York, it is not abundant in the arenaceous shales 

 of the eastern counties, but is common on Cayuga, Seneca and Canandaigua lakes; 

 in several localities in the Genesee valley, and at Darien, Eighteen-mile creek, 

 Hamburg, &c., on Lake Erie shore. It is less common in the Hamilton shales of 

 West Williams, Bosanquet and Widder, in Canada West. It occurs at Rock Islaud 

 in Illinois, at New Buffalo, Independence, and other places in Iowa. 



In the Cherimng group it occurs on Cayuta creek, Ithaca, Elmira, Painted-post, 



Bath, etc., but is rare or unknown in the more western localities of that formation 



within the State of New York. 



[PAL^ONTOLoar IV.] 41 



