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130 Aliierican Seash ells
may also appear in eastern Florida. It has been named floridana Reeve 1855,
rotundata von Martens 1865 and sphaera Pilsbry 193 1.
Smaragdia viridis Linne
Genus Smaragdia Issel 1869
Southeast Florida, the West Indies and Bermuda.
Emerald Nerite
Plate 4h
/4 to H inch in length, glossy, smooth, pea-green, often with tiny chalkwhice
bars and rarely with purplish brown, narrow, zigzag bars. True
viridis comes from the Mediterranean. Some workers separate our form as
the subspecies viridemaris Maury 191 7. N. iveyssei Russell 1940 is a synonym.
Order MESOGASTROPODA
Superfamily LITTORINACEA
Family LACUNIDAE
Genus Lacuna Turton 1827
Rather fragile, smooth periwinkles characterized by a shelf-like colu-
mella and a chink-like umbilicus. Periostracum smooth, fairly thin and light-
brown. Operculum paucispiral and corneous. Cold-water inhabitants, usually
dredged in areas of kelp weed.
Figure 36. Northern Lacunas, a, Lacuna carinata Gould, ^ inch (Pacific coast);
b, Lacuna imijasciata Cpr., y^ inch (California); c to e, Lacuna vmcta Turton,
% inch (both coasts); c, operculum showing reinforcing bar (dotted); d, animal
showing the penis on the right side; e, radula (a single row greatly enlarged).
Lacuna vincta Turton Common Northern Lacuna
Arctic Ocean to Rhode Island. Alaska to California.
Plate 22p-, figure }6c-e
^ to % inch in length, 4 to 5 whorls, resembling a Littorina, but charac-
terized by its fairly thin, but strong, translucent shell, its shelf-like columella
along side of which is a long, narrow, deep umbilical chink. Outer lip fragile.