46 PROCEEDINGS OF THE ACADEMY OF 



This species is evidently closely allied to E. nodosus, of Sowerby, from the 

 Mountain Limestone of England. It may be distinguished, however, by its 

 much less convex periphery, and by having its carina on the upper side of the 

 outer whorl, nearer the outer side, as well as more rugose from an apparent 

 effort to form irregular nodes. The true nodes around the prominent portion 

 of its under side are more numerous than in E. nodosus (which has ten instead 

 of fourteen to each whorl), and differ in being more irregular and nearly 

 obsolete on the last half of the outer whorl. 



Even if Montfort's name, Straparollus, must be adopted for this genus, we 

 think Sowerby's name, Euomphalus, should be retained in a subgeneric sense 

 for these planorbicular species with angular whorls, such as E. pentangulatw, 

 for which it was at first proposed. 



Locality and position. Alton, 111. Lower Coal-measures. 



Straparollus (Ecomphalus) subquadratus, M. and W. 



Shell attaining nearly a medium size, discoid or subplanorbicular, concave, 

 and showing all the whorls both above and below, though the concavity is 

 deeper below than above. Periphery nearly flat, rather broad, and generally 

 more or less oblique, with a distinct carina at the upper and lower edges, the 

 former of which is more acute than the other, and irregularly crenate, or sub- 

 nodose, and projecting nearly upward, while the lower one is a little rounded 

 and projects outward. Volutions five or six, not embracing, nor coiled ex- 

 actly in the same plane ; on the upper surface, each sloping, with a slight 

 concavity, distinctly inward from the marginal carina to the suture, while the 

 flattened outer side usually has an obscure longitudinal sulcus near the upper 

 and lower angles, the upper one being a little deeper than the other. On the 

 under side the whorls slope gently inward from the marginal angle, so as to 

 form a broad, depressed-subconical umbilicus. Surface marked with rather 

 strongly defined lines of growth, which, at places, become subimbncating, or 

 form little irregular ridges. In crossing the upper side of the whorls, these 

 lines start, at first, nearly at right angles out from the suture, but curve a 

 little backward as they approach the marginal angle ; and immediately after 

 crossing this angle, and passing downward upon the nearly vertically flattened 

 periphery, they are deflected a little forward, but soon after pass straight down 

 to, and over the lower marginal angle to the under side, where they extend 

 obliquely backward and inward, with a rather distinct curve, to the immediate 

 vicinity of the suture, and then curve a little forward. Aperture and sections 

 of interior of whorls subcircular, or transversely oval. 



Greatest breadth of a specimen with apparently about one-third of the outer 

 volution broken away, 1-25 inches ; height, 0-50 inch. When entire, this spe- 

 cimen was probably not less than 1-43 inches in breadth. 



From the foregoing description, it will be seen that this shell is nearly allied 

 to the common western Coal Measure species figured and described by Prof. 

 Hall, in his Jour. Geological Report, under the name Euomphalus rugosus (not 

 E. rugosus, Sowerby*). Indeed, it is so nearly like that species that we atone 

 time suspected that it might be only a gigantic and more ventricose variety of 

 the same. Yet on comparing our shell with an extensive series of good spe- 

 cimens of E. rugosus, Hall, it is found to be greatly larger than any known 

 authentic examples of that shell, its breadth being a little more than twice 

 and a half that of the usual mature examples of E. rugosus. Its umbilicus, 

 and the concavity of its upper side, are also proportionally deeper, particularly 

 the former, while the flattened outer side of its whorls is broader, and gener- 

 ally less oblique. Its lines of growth also differ in being rather distinctly de- 

 flected backward at the marginal angle of the upper side, so as to indicate an 

 obscure sinus of the margin of the lip at the termination of this angle, though 



* If Sowerby's species is really congeneric, the American form called E. rugosus by Prof. 

 Hall might be distinguished by the specific name subrugosus. 



[April, 



