264 INVERTEBRATA OF MASSACHUSETTS. 



Shell small, thin, hemispherical, or obliquely ovate ; whorls 

 three and a half, regularly convex, minutely wnnkled near the su- 

 ture, and with an occasional transverse scratch ; otherwise 

 smooth, and covered with a rough, greenish-yellow epidermis ; 

 the sutural region is depressed and sub-channelled ; the spire is 

 scarcely prominent above the very large lower whorl, and is 

 placed a little to one side ; aperture oblique, semi-circular, angles 

 a little rounded ; outer lip sharp ; inner lip straight, hke a rounded 

 white rib, broadest and twisted behind ; at the side of it is a nar- 

 row, crescentie, white space, bounded externally by the continua- 

 tion of the sharp lip, along which a groove runs, terminating in a 

 deep umbilicus ; operculum horny, sub-spiral. Length | inch, 

 greatest breadth i inch, divergence 95°. 



A few specimens of this shell have been collected at different 

 times on Chelsea Beach. It is probably floated ashore on sea- 

 weed. 



It is sufficiently distinct from specimens of Tiirho paUidulus, sent me 

 from Europe for comparison, by its narrower channelled space, and 

 its smaller umbilicus ; and more especially by the aperture not being 

 at all trumpet-shaped, or angular, as in that shell. They are so near- 

 ly alike, however, that it is very difficult to delineate, either by de- 

 scription or figures, distinctions which are very obvious on inspection. 

 I have received it from Dr. Loven, labelled, doubtfully, L. Montagui, 

 Turton. 



Genus CINGULA, Fleming. 



Shell small, thin, elongated, of several whorls ; aperture small, 

 entire, the lip continuous posteriorly ; operculum horny; sub-spiral. 



A group of small shells here referred to, seems to present 

 characters which entitle it to a generic rank. These shells differ 

 from the short, solid LiTTORi'NiE by their elongated form, and 

 thin, horny structure ; and the animal has a prolonged muzzle, 

 which that of Littori na has not. Fleming divides his genus into 

 two sections ; first, those which have the "outer lip thickened 

 by a rib," and which answer to the genus Ri'ssoa of Fremin- 

 ville, a well-marked genus; second, those with the "outer lip 



