Report of the State Geologist. 



385 



any other stratum of the group, or that it is known at any place 

 outside of these quarries in the neighborhood of Delphi. 



The gregarious (and at the same time isolated) habit of the Pen- 

 tameri, in a few of their species, becomes an interesting factwhen we 

 observe the P. oblongm, in its early appearance in the Clinton group 

 of New York, occupying, almost to the exclusion of any other 

 fossil^, a thin stratum on the Genesee river, and which can be 

 traced for many miles along its outcrop in Wayne and Monroe 

 counties, marked by the presence of this fossil in its entire or 

 fragmentary condition. 



The species is scarcely known in Orleans and Niagara counties, 

 but again recurs in moderate numbers in the limestone of the 

 Niagara age in Ontario, becoming more abundant in the western 

 extension of the group. In Springfield, and perhaps elsewhere 

 in Ohio, the species has acquired a remarkable development in 

 size, and sometimes constitutes, almost by itself, an entire stratum 

 of the Magnesian Niagara limestone. In Indiana, Illinois and 

 Wisconsin, this species of Pentamerus acquires a most remarka- 

 ble development in size and in numbers of individuals, often con- 

 stituting beds of considerable thickness. • It is usually elongate- 

 ovoid, but is sometimes found having a length of from four to six 

 inches, with a nearly equal width, while it may be symmetrically 

 rounded or trilobate in form. 



We note the recurrence of similar conditions of abundance 

 attending the occurrence of P. laqueatus (=P. nobilis) which is 

 remarkable in its limited geographical extent while P. galeatus 

 occurs so abundantly in a limestone near the base of the Lower 

 Helderberg that the stratum is known as the Pentamerus lime- 

 stone. So far as known to the writer the Devonian forms of Pen- 

 tamerus are rarely very abundant or especially characteristic of 

 any bed or stratum in the system.* 



At the Delphi quarries I had the volunteer assistance of 

 Prof. Collett, of Indianapolis, and two students of the High 

 School, where we spent two days of delightful work. To Messrs. 

 A. B. and John A. Cortwright, W. 0. McCain and Edward 

 McCain, of the Delphi Lime Company, we were indebted for 

 facilities, and for the providing of barrels and other material for 



* Pentamerus papilio7iensis of the Hamilton group is the most abundant form of 

 Devonian age known to me in New York, while Pentamerus costatus of the same group 

 in Michigan, is comparatively abundant at a single locality. 



49 



