FOSSILS OF THE NIAGARA GROUP. 145 



increase of size in the volutions. It differs from S. mopsus, Hall, from the 

 Niagara group of Wisconsin, in the smaller number of more rapidly en- 

 larging volutions, in the revolving ridges of the surface, and in the more 

 depressed spire. 



Formation and locality : In the upper part of the Niagara group, at Cedarville, Ohio. 

 Collected by Rev. H. Hertzer. 



Genus TREMANOTUS, Hall. 



(20th Rept. State Cab., p. 347.) 



Tremanotus Alpheus, 



Plate 8, fig. 1. 



Tremanotus Alpheus, Hall ; Extr. in Advance of the 20th Rept. State Cab., 18G5, p. 43. 

 Tremanotus Alpheus, Hall; 20th Rept. State Cab., p. 347, pi. 15, figs. 23 and 24. 

 Bucania {Tremanotus) perforatus, Winch, and Marcy; Enumeration of Foss. collected 



in the Niagara Limestones near Chicago, etc., p. 100, pi. 3, fig. 7. 

 Bucania Chicagoensis, McChesney (in part) ; Expl. of pi. 8, fig. 4, Pal. Foss., 1865. 



An example of this species, possessing all the features, as far as the im- 

 perfect condition of the specimen will permit of identification, has been 

 obtained from the limestones of the Niagara group, of Genoa, Ohio. The 

 example shows the shell to have been composed of two or more volutions, 

 which are broad and flattened, their lateral diameter being nearly double 

 that of the dorso-ventral diameter, the outer volution embracing the 

 inner one, as seen on the internal cast, to the extent of a little less than 

 one-half their diameter, leaving a broad, open umbilicus. Volutions 

 broadly rounded on the back, and sharply rounded on the lateral por- 

 tions. The aperture is not preserved on the specimen under considera- 

 tion ; that of the species, however, is broadly expanded. The middle or 

 dorsal i:>ortion of the outer volution is marked by a number of elongated 

 projections, their long diameter corresponding with the plane of the 

 volution, indicating the dorsal perforations characteristic of the genus. 

 Seven of these projections can be counted on a little less than half of the 

 outer volution. 



The surface of the cast is smooth, there being no evidence of the ex- 

 ternal revolving ridges which characterizes the exterior of the shell on 

 the typical specimens. These, however, are frequently not preserved on 

 the internal casts from the original locality. 



Formation and localitij : In the limestones of the Niagara group, at Genoa and 

 Springfield, Ohio. Collections of Columbia College and of Prof. Edward Orton. 



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