Monograph of the Gasteropoda. 317 



Pleurotomaria siibconica — (Hall, 1847). 



Trocliiform ; spire elevated, apex acute ; volutions about five, flat- 

 tened above, with a projecting carina just above the suture; last 

 volution strongly cariuated on the outer edge, and marked with a 

 spiral band, ventricose below ; aperture transverse, subquadrate, an- 

 gular on the outer side and round below; surface marked by fine striae, 

 which bend gently backward from the suture, and more abruptly on 

 the lower part of the whorl ; spiral band a distinct groove, margined 

 by sharp elevated edges, upon wliich the stride bend backward in an 

 abrupt curve ; below this the striae bend gently forward, and thence 

 curving backward, terminate in the umbilicus ; longitudinal striae 

 crossed by transverse, sharp, elevated lines, which are finer than the 

 longitudinal ones. 



The casts referred to this species are found in the upper part of the 

 Cincinnati Group, at Weisburg, Richmond, and other places. 



Pleurotomaria tropidophera — (Meek). 



Shell rather small, obliquely rhombic in general outline, as seen in 

 a side view ; height somewhat greater than the breadth ; spire conical, 

 with an apical angle of about 70 degrees to 90 degrees ; volutions four 

 to four and a half, each flattened, or sometimes slightly concave above, 

 with an outward slope from the suture to a prominent angle, that passes 

 around the middle of the body turn, and below the middle of those of 

 the spire, to which it imparts a somewhat turreted appearance ; suture 

 moderately distinct, but not channeled ; lower side of body volution 

 sloping rapidly inward from the mesial angle, a little below which there 

 usually revolves an obscure, undefined ridge ; aperture rhombic, sub- 

 quadrate. Surface nearly smooth, but sometimes showing under a 

 magnifier very obscure lines of growth, that curve very strongly 

 backward as they approach the angle around the middle of the body 

 volution, both above and below ; thus indicating the presence of a deep 

 sinus in the lip, widening rapidly forward, though there is no defined 

 revolving band at the angle. 



Height, 0.55 inch; breadth, 0.50 inch. 



I found this species at Versailles, Indiana, about fifty miles west of 

 Cincinnati, and 300 feet below the rocks of the Upper Silurian. It is a 

 rare species. 



