Contributions to Invertebrate Paldeontology. 589 



elongate, and cylindrically oval, the cardinal and basal margins parallel and 

 very slightly curved, and the extremities very nearly equally rounded ; beaks 

 small, inrolled, barely projecting above the cardinal line, and situated at 

 about one-fourth of the entire length from the anterior end. Body of the shell 

 very evenly and highly rounded from the cardinal to the basal margins, and 

 almost as convex posteriorly as in front. Umbonal ridge scarcely perceptible, 

 and the umbonal slope convex ; escutcheon and lunule not defined ; anterior 

 slope abruptly rounded. Surface of the shell marked by faint concentric 

 undulations of unequal strength, but most strongly marked on the posterior 

 end and on the umbonal slope. 



The evenly convex and rearularlv evlindrical form of the shell, 

 together with the inconspicuous beaks and the equal-sized anterior 

 and posterior extremities, are distinguishing features of the species. 

 The shell shows evidence in its form and curvature, in a profile 

 view, of having been slightly gaping behind. 



Formation and Locality. — In limestone of the age of the Chester 

 group of Illinois, at Newtonville, Ohio. 



GASTEROPODA. 



Genus STRAPAROLLIJS Montfort. 



Straparollus siiuilis. 



Plate XIV, figs. 9-11. 



Straparollus similis M. and W., Geol. Surv. 111., vol. 3, p. 285, pi. 19, figs. 4 and 5. 



Shell about a medium size, helicoid, with a slightly elevated spire, and a 

 broad open umbilicus in which are exposed portions of several of the volu- 

 tions. Volutions from four to four and a half in number, moderately increas- 

 ing in size, flattened on the upper surface, sharply carinate on the upper 

 peripheral angle, and rounded on the periphery and on the basal and umbilical 

 surfaces. Besides the carination on the upper lateral angle of the volution, 

 the larger one often bears a second ridge, of considerable strength, on the 

 middle portion of the lower surface ; which, on many of the larger specimens, 

 is developed into a sharply elevated ridge ; while on other specimens of similar 

 size it is entirely obsolete. Aperture circular. Surface of the shell marked by 

 fine, closely crowded, transverse lines of growth, presenting a slightly rough- 

 ened surface under a lens. 



A number of the specimens on hand, of both small and large size, 

 are marlied on the centre of the periphery by an irregular fringed 

 expansion of considerable width, presenting an appearance similar 

 to what might result from a vertical crushing of the volution and 

 spreading out of this portion of the shell laterally ; but as many of 

 them do not possess this character to any extent, it can scarcely be 



