146 PALEONTOLOGY OP OHIO. 



Tbemanotus? trigonostoma (n. sp.). 



Plate 8, fig. 5. 



Shell moderately large, consisting of two or more volutions, the last 

 one broadly expanded, forming a broadly sub-triangular lip bordering the 

 aperture, the margins of which extend at right angles to the plane of 

 the shell, on all sides, to a distance equal to the extent of the preceding 

 volution, as seen on the posterior side of the aperture, except on the front 

 or dorsal border, where it is directed upward, corresponding to the car- 

 inate front of the volution, and deeply sinuate, forming a broad, triangu- 

 lar notch. Inner volutions rounded on the back, and somewhat modified 

 on the inner face by those within. Umbilicus apparently broad and 

 deep. Surface smooth, not ribbed or costate, as is shown by the impres- 

 sion of the exterior surface in the rock. 



The specimen used for description is a cast partly of the interior and 

 partly of the exterior. It has a broadly expanded body volution and 

 protruded front, which characterizes the genus Tremanotus, but the speci- 

 men is not perfect enough to show the perforations on the dorsal portion 

 ■of the last volution. The inside of the aperture is sub-triangular, the 

 inner lip forming a straight margin across this side, which is scarcely 

 modified in the center by the preceding volution, the outer margin of the 

 lip on this side overlapping the inner whorl, and extending backward 

 as far as the extent of the whorl. 



It is possible that the spS'cies may prove to belong to the genus Bucania, 

 but the evidence is rather in favor of the other determination. It differs 

 from T. alpheus, Hall, in the smooth surface, that one having strong ribs 

 ■ or costse marking the outer volution; also in the triangular form of the 

 aperture. 



Formation and locality: In the limestones of the Niagara group, at Genoa, Ohio. 

 ;From the collection of Columbia College, New York. 



