394 LAXD AND FRESH-\yATER SHELLS OF N. A. [PART IV. 



whereas in ours it is formed by an oblique, inward projection of the 

 columella near the base. The external conformation is exceedingly 

 irregular, varying from subconical to globose, sometimes compressed 

 on the back, at others strongly gibbous. The aperture is also fre- 

 quently distorted. Young specimens are of a light olive-green color, 

 while older ones are nearly black, and usually covered with an earthy 

 coating. The lower whorl is invariably marked at its base by a 

 broad, dark brown band, and has frequently one on the middle and 

 one on the superior portion. Some of the varieties of this shell, 

 when undistorted, have so great an external resemblance to some of 

 the varieties of Turbo palliatus, Say, that a figure of one might an- 

 swer very well for both. It was found in abundance on the rocks, at 

 the rapids, about a mile above the falls of the river Potomac, appar- 

 ently delighting in situations where one would imagine it difficult for 

 it to adhere. The only shells found in company with it were Melania 

 Virginica, Say, and Ancidotus nigrescens, Conrad, which latter was in 

 great abundance and variety of form. Some of its less angular vari- 

 eties closely approached A. dentatus in their general appearance, but 

 were easily distinguished by the form of the aperture and the absence 

 of the columellar lacuna. — Couthuoy. 



No. 772 is a copy of the original figure, and Xo. 771 is one 

 selected from a number of Maryland specimens kindly loaned 

 to me for examination by Mr. Anthony. 



The following description of Anculosa dentata was published 

 by Mr. Lea in-the Phil. Proc, but suppressed in Philos. Trans., 

 probably because it was discovered to be a synonyme. 



Anculosa dentata. — Shell subglobose, thick, blackish; spire short, 

 obtuse; sutures impressed; whorls convex; aperture large, subro- 

 tund ; columella thickened, dentate. 



Habitat.— YicinMy of Richmond, Virginia; J. A. Warder, M.D. 



The following is the only description of Anculosa affinis, 

 Fi"- 773. Haldeman. Its claim to specific ranlc was yielded by 

 ^^™ that gentleman, probably, for otherwise he would have 

 F m piit)lished a diagnosis for it. 



Ancxdosa {Mudalia) affinis.— I propose this name for a shell 

 allied to Faludina dissimilis, Say; but which differs from it in having 

 a slight tooth upon the columella. 

 JJabilat.— Ohio; Mrs. Saj. 



