78 AMERICAN MARINE CONCHOLOGY. 
impressed lines ; suture well impressed ; body-whorl with about 
sixteen coste. 
Length 13 mill. 
Massachusetts, southwards. 
7. S. BoREALIS, Beck. Fig. 143. 
Acirsa borealis, Morch. 1841. 
S. Eschrichtit, Moller. 1845. 
Shell white or pale flesh-color, elongated, turreted, acute; whorls 
ten, convex, with numerous revolving strie; the upper whorls 
with slight transverse undulations or faint cost, 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 VI. LITTORINIDA. 
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 alge. Distribution uni- 
versal, inhabiting sea or brackish water. 
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, Frémenville. 
Shell minute, tin, subglobose or conical, transparent; peristome thin, 
entire ; operculum annular, regular, with an internal process. 
RissoEuua, Gray. 
