FOSSILS OF THE NIAGARA GROUP. 143 



strong revolving lines or ridges, and apparently by transverse lines, and 

 on the lower side by revolving ridges crossed by concentric lines of 

 growth parallel to the margin of the aperture Apertural notch not fully 

 determined. 



The shell differs somewhat from those from the more western localities 

 in Wisconsin and Iowa, especially in the greater flattening of the volu- 

 tions, and in the more strongl}^ carinate and less distinctly banded pe- 

 riphery. But these features may be due in part to the vertical compres- 

 sion to which the specimen has been subjected. The species is closely 

 related to P. labrosa, Hall, from the Lower Helderberg group of New York, 

 but differs in the smaller depth of the volution below the periphery. 



Formation and locality: In the limestones of the Niagara group, at Yellow Springs, 

 Ohio. Collected by Prof. E. Orton. 



Genus TROCIIONEMA, J. W. Salter. 

 Trochonema pauper ?. 



Plate 8, fig. 4. 



Comp. Pleurotomaria patqx'r, Hall; Extr. 20th Rept. State Cab., p. 343, 1865. 

 Comp. Trochonema {Pleurotomaria) -pauper ; 20th Rept. State Cab., Expl. pi. 15, figs. 

 5, 6, and 9. 



Shell of medium size, broadly turbinate, consisting of three or more 

 rounded ventricose and moderately increasing volutions. Suture line 

 deeply marked and distinct, giving to the exposed portion of the volu- 

 tion a full, round, almost inflated character. Form of the inner lip of 

 the aperture and umbilicus unknown from Ohio specimens. 



Surface of the volutions marked by numerous distinct revolving bands, 

 with concave spaces between them ; about twelve of these bands can be 

 counted on the exposed part of the last volution, which extends to near 

 the lowest jDoint as preserved in the rock. Between some of the more 

 distant bands, and near the largest part of the volution, there are faint 

 traces of intermediate bands of smaller size. There a,re also fine, closely 

 crowded concentric stride of growth marking the surface and crossing 

 the volution with a strong backward direction from the suture line 

 toward the base of the shell, which undulate but very slightly as they 

 cross the revolving bands. On the upper volutions the revolving bands 

 are sharper, and the spaces between narrower and more deeply concave. 



There may be some question concerning the specific relations of this 



