318 LITTORINID^. 



Species of Bisella. 



imbricata, Gray. nana, Lam. 



livida, Phil. plana, Quoy and Oaim. 



lutea, Quoy and Gaim. vittata, Phil. 

 melanostoma, Gmel. 



Genus LACUNA, Tiirton. 



Operculigerous lobe winged at the sides and furnished 

 behind with two filaments. 



Shell turbinated, solid or thin, subglobose or conical ; 

 spire short or somewhat produced ; aperture semilunar ; 

 columellar lip flattened, with a parallel, umbilical fissure ; 

 outer lip acute. 



Syn. Teraana, Leach. 



Ex. L. divaricata, O. Fahricius, pi. 33, fig. 6. Oper- 

 culum, L. pallidula, Da Costa, fig. 6, a, 6, b. Shell, L. 

 pallidula, fig. 6, c. 



The LacuiKB feed upon sea-weed, and Loven observes 

 that when XkiQfucus is of a brown colour, the animals be- 

 come green, but if red, they assume a rosy tint. They 

 principally inhabit the shores of northern countries, and 

 species occur both in England and North America. 



Species of Lacuna. 



pallidula, Da Costa. rufa, Da Costa. 



puteolus, Turt. 



