MARINE MOLLUSCA OF THE UNITED STATES. 85 
of the body whorl with revolving striae. Aperture nearly orbicu- 
lar, peristome thin and sharp. 
Length 2.6, diam. 1.7 mill. 
Maine, northwards. 
11. R. pavis, De Kay. Fig. 163. 
(Cingula.) Moll. New York, 111, t. 6, f. 118. 1848. 
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. parEns, Gould. 
Bost. Proc. viii. 280. 1862. 
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. rncompra, 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 fzssoa 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. 
