476 GEOLOGY OF OHIO. 



The evenly convex and regularly cylindrical 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 hav- 

 ing been slightly gaping behind. 



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

 group of Illinois, at Newtonville, Ohio. 



GASTEROPODA. 



Genus STRAPAROLLUS Montfort. 



STRAPAROLLUS SIMILIS. 



Pi, ate X, 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 volutions. Volu- 

 tions from four to four and a half in number, moderately increasing in size, flat- 

 tened on the upper surface, sharply cariuate on the upper peripheral angle, and 

 rounded on the periphery and on the basal and umbilical surfaces. Besides the ca>- 

 ination on the upper lateral angle of the volution, the larger one often bears a sec- 

 ond 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, pre- 

 senting a slightly roughened surface under a lens. 



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

 are marked on the centre of the periphery by an irregular fringed expan- 

 sion 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 considered as an organic 

 feature of the species. A single individual among them shows this feat- 

 ure existing on all of the volutions, the outer whorls reaching to just 

 below the expansion. 



- The shell, is of a form common to the Lower Carboniferous forma- 

 tions, and also to those referred to the Waverly group and to the Chemung 

 of New York; species occurring both with and without the revolving 

 carinae, E. Hecale Hall (Illust. Dev. Foss., pi. 16, fig. 12), of the Chemung 

 group, is usually destitute of the ridges, as is also .S. cyclostomus, of the 

 Burlington sandstones of Iowa and other States. There are forms in the 

 Lower Carboniferous of Illinois, in the St. Louis and Chester groups, 

 showing the carina?, as does also Euomphalus {Strap.) laxus White, and 

 Euomph. (Strap) Uta/ietisis H. and W., from the Waverly group as repre- 

 sented in the far West. The different species described present slight 

 differences from each other, but are all so closely allied in form as to be 

 not readily distinguishable. 



