MARINE MOLLUSCA OF THE UNITED STATES. 85 



of the body whorl with revolving strioe. Aperture nearly orbicu- 

 lar, peristome thin and sharp. 

 Length 2.6, diaua. 1.7 mill. 



Maine, northwards. 



li. R. l.evis, De Kay. Fig. 163. 



(Cingula.) 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 columellar lip partially everted over the 

 rather large umbilicus. White. 



Length 5 mill. 



Connecticut. 



This is a doubtful species. 



12. R. patens, Gould. 



Bost. Proc. viii. 280. 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. 1 mill. 



( Coral Sand) Florida. 



Genus RISSOELLA, Gray. 

 Zool. Proc. 159. 1847. 

 This genus differs from Bissoa 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. 



