Monograph of the Gasteropoda. 319 



Raphistoma lenticularis — (Conrad). 



Shell lenticular ; breadth generally a little more than twice the 

 height ; convexity often nearly equal above and below ; volutions 

 about four and a lialf, flattened or slightly concave, with a moderate 

 slope above, coincident with that of the spire, the outer or last one 

 sharply carinate around the periphery, and convex below, the greatest- 

 convexity being near the umbilicus, into which the slope is abrupt ; 

 suture merely linear, and not very distinctly defined ; umbilicus nearly 

 as wide as the outer volution, as seen in internal casts ; aperture trans- 

 versely rhomboidal, the breadth being about one fourth wider than the 

 height. 



The specimens, which may be very doubtfully referred to this 

 species, are found at different elevations throughout the Cincinnati 

 Group. They are usually mere casts. Prof. Hall referred lenticularis 

 to the genus Pleurotomaria, and if this reference is right, then, I 

 think, that the specimens found here belong to another species. The 

 specimens found here seem to me to have the generic characters of 

 Raphistoma, and an examination of specimens having the shell appar- 

 ently very little worn, discovered none of the striaj marking the sur- 

 face of this species. 



Genus Cyclonema — (Hall). 



fGr. xyxAoc, amhifus, and vs/^a, filum, in allusion to the elevated 

 thread-like striae marking the surface of several species.] 



Shell turbinate, thin ; ^spire short, consisting of few volutions, which 

 increase rapidly from the apex ; aperture large, rounded anteriorly, 

 and somewhat flattened on the columellar side ; umbilicus none ; sur- 

 face strongly marked by spiral, thread-like striae, which are cancellated 

 by finer striae. 



The shell has no slit or indentation in the outer lip, or band upon the 

 volution. The surface is marked by elevated striae, parallel to the 

 direction of the volutions, and the spaces between these are marked 

 by finer striae, crossing the others obliquely ; the latter, however, are 

 often obsolete. 



Cyclonema hilix (Conrad), is the type of the genus. 



Cyclonema hilix — (Conrad). 

 Obliquely conical ; spire short, composed of four or more volutions. 



