90 THE NAUTILUS. 



rather thin, translucent, pale horn-color, smooth, shining, lines of 

 growth very fine, close and regular ; spire obtuse. Whorls 3^, 

 round, very convex, rapidly increasing toward the aperture, sepa- 

 rated by a deep suture. Aperture large, slightly oblique, scarcely 

 expanded, subcircular, equally rounded above and below, but flat- 

 tened on the columellar side. Columellar lip thin, straight, oblique, 

 adnate to the body-whorl only at the upper extremity, emarginate in 

 the central portion, below which it is expanded, forming a rounded 

 angle at its junction with the basal lip. Lip thin, sharp, not ex- 

 panded nor callously thickened within. Operculum paucispiral, 

 nuclear whorls large and subcircular. Animal black. 



Alt, (apex eroded) 3, diam. 3 mm. 



Types (No. 28434, Coll. Walker), from the Coosa River at 

 Duncan's Riffle, Chilton County, Ala. Cotypes in the collections 

 of T. H. Aldrich, Geo. H. Clapp, John B. Henderson, Jr., and the 

 Philadelphia Academy. Found also at The Bar, Butting Ram 

 Shoals and Higgins' Ferry. 



Deprived of its operculum, this species at first sight, from its gen- 

 eral shape, rounded whorls and deep umbilicus, would be taken for 

 a Valvata allied to V. sincera Say. But the straight columellar lip 

 and the decided projection of the lip at its junction with the peri- 

 treme show its affinity to Somatogyrus. 



The peculiarities of the radula and operculum have been sufficiently 

 stated under the generic description. I am indebted to Dr. Pilsbry 

 for the figure of the dentition. It seems eminently proper that this 

 very distinct addition to the fauna of Alabama should both generi- 

 cally and specifically bear the name of Mr. Geo. H. Clapp, the 

 original promoter of the explorations of Mr. H. H. Smith, which 

 have added so much to our knowledge of the moUusca of that State. 



Explanation of Plate VI. 

 Figures 1, 3, 9 and 10 are on the same scale, x8. 

 Figures 2, 8 and 11 are x6. 



Figs. 1, 4 and 7. Clappia clappi. Duncan's Riffle, Coosa R., Ala. 

 Fig. 2. Somatogyrus hendersoni. Duncan's Riffle, Coosa R., Ala. 

 Fig. 3. Somatogyrus pygmceus. The Bar, Coosa R., Ala. 

 Fig. 5. Somatugyrus depressus. Watertown, Wis. 

 Fig. 6. Somatogyrus subglohosus. Big Muddy R., Blairville, Ills. 

 Fig. 8. Somatogyrus kinhleyi, Coosa R., Weturapka, Ala. 

 Fig. 9. Somatogyrus hinkleyi. Coosa R., The Bar, Ala. 

 Figs. 10 and 11. Somatogyrus decipiens. Coosa R., The Bar, Ala. 



