MARINE MOLLUSCA OP THE UNITED STATES. 85 



of the bod}'- whorl with revolving striae. Aperture nearly orbicu- 

 lar, peristome thin and sharp. 

 Length 2.6, diam. 1.7 mill. 



Maine, northicards. 



11. R. L^vis, De Kay. Fig. 163. 



iCingula.) Moll. New York, 111, t. 6, f. 118. 1843. 

 Shell small, elevated, moderately solid ; whorls five, very con- 

 vex, with deep sutures; surface smooth; body-whorl large; aper- 

 ture small, oval, the coliimellar lip partially everted over the 

 rather large umbilicus. White. 



Length 5 mill. 



Con7iecticut. 

 This is a doubtful species. 



12. R. PATENS, Gould. 



Bost. Proc. viii. 380. 18G3. 



Shell minute, ovate, thin, smooth ; whorls five or six, ventricose, 

 with a subsutural impressed line ; aperture rounded, emarginate 

 posteriorly ; columella but slightly reflexed ; lips somewhat thick- 

 ened, fuscous. 



Length 3, diam. 2 mill. 



Remarkable for its large aperture and subsutural impressed 



line. 



Fort Johnson, Charleston Harbor, S. C. 



13. R. INCOMPTA, Gould. 



Bost. Proc. vii. 280. 1862. 



Shell small, elongated, vitreous, reddish-white ; whorls seven, 

 rounded, with three revolving ribs and longitudinal lines, the body- 

 whorl carinate ; aperture circular, the peristome simple, thickened. 



Length 2, diam. I mill. 



(.Coral Sand) Florida. 



Genus RISSOELLA, Grny. , 



Zool. Proc. 159. 1847. 

 This genus differs from Rissoa in the shells being thin and 

 without thickened lip ; the operculum differs also, in being annular 

 with a central internal process. 



The animals are found adhering to floating sea-weeds, in pools 

 between tide-marks; their eyes are situated so far behind on the 

 head, that the transparency of the shells appears to be essential 

 to the vision of the animal. 



