78 AMERICAN MARINE CONCHOLOGY. 



impressed lines ; suture well impressed ; body-whorl with about 

 sixteen costse. 

 Length 13 mill. 



Massachusetts, southwards. 



7. S. BOREALIS, Beck. Fig. 143. 

 Acirsa borealis, Morch. 1841. 

 S. Eschrichtii, M oiler. 1845. 



Shell white or pale flesh-color, elongated, turreted, acute; whorls 

 ten, convex, with numerous revolving striae; the upper whorls 

 with slight transverse undulations or faint costse, which are want- 

 ing on the lower ones; last whorl slightly carinated; aperture 

 roundish, effuse, and slightly angulated in front. 



Length 19, diam. 6.5 mill. 



Dredged, ten to forty fathoms. 



Maine, northwards. 



Family YI. LITTORINID^E. 



Shell spiral, turbiniform or depressed, never pearly ; aperture 

 rounded; peristome entire; operculum horny, paucispiral. 



Animal with a muzzle-shaped head; eyes sessile at the outer 

 bases of the tentacles ; tongue denticulated ; branchial plume 

 single ; foot with a linear duplication in front and a groove along 

 the sole ; mantle with a rudimentary siphonal canal ; operculum 

 lobe appendaged. Littoral, feeding on algae. Distribution uni- 

 versal, inhabiting sea or brackish w r ater. 



Synopsis of Genera. 



Shell turbinated, thick, pointed, few-whorled ; aperture rounded ; outer lip 

 acute ; columella rather flattened, imperforate ; operculum paucispiral. 



LITTORINA, Ferussac. 



Shell obicular, depressed ; umbilicus wide and deep ; aperture rhombic ; 

 peristome thin ;* operculum horny, subspiral. 



ARCHITECTONICA, Bolten. 

 Shell turbinated, thin ; aperture semilunar ; columella flattened, with an 



umbilical fissure ; operculum paucispiral. LACUNA, Turton. 



Shell minute, thick, white or horny ; conical, pointed, many-whorled ; 

 smooth, ribbed or cancellated ; aperture rounded ; peristome entire, con- 

 tinuous ; outer lip slightly expanded and thickened ; operculum subspiral. 



RISSOA, Fremenville. 



Shell minute, thin, subglobose or conical, transparent ; peristome thin, 

 entire ; operculum annular, regular, with an internal process. 



RISSOELLA, Gray. 



