LITTORINIDvE. 233 



? Genus CYCLOCHEILA, Conrad. 



Pyramidal ; aperture circular ; labrum expanded, columella flat- 

 tened, subangular at the base ; periphery angular. 



A doubtful little tertiary shell from South America; probably 

 fluviatile. 



Genus LACUNA, Turton, 1827. 



Shell turbinated or globular, thin, covered by an epidermis ; 

 aperture semilunar, columella flattened, with a parallel groove be- 

 hind it ending in the umbilicus, lip sharp, arcuated. Operculum 

 paucispiral (fig. 77.) 



Animal (PI. 40, fig. 76.) Proboscis short, tentacles long, thread- 

 like, with eyes nearly sessile at their outer base, foot truncate in 

 front, attenuated behind, operculigerous lobe with a long filament 

 on either side. Dentition (PI. 40, fig. 68.) 



Spawn vermiform, thick, semicircular. Range low water to 50 

 fathoms. The Lacuna) feed upon sea weed, and the animal takes 

 on the color of its food-plant. 



Temana (Leach), Gray, 1847, is a synonym. 



North Atlantic. 



L. PALLIDULA, DaCosta. Fossil, tertiary ; a single Triassic 

 species. 



Section LACUNA (sensu stricto.) 

 L. PUTEOLUS, Turton. 



Section EPHERIA, Leach, fide Gray, 1847. 



Shell thin, usually with spiral colored bands ; spire rather ele- 

 vated ; inner lip thin, sharp, umbilical fissure linear. L. VINCTA, 

 Turton. 



Section MEDORIA, Leach,^c?e, Gray, 1842. 



Conical, solid, with elevated spire, peritreme dilated, anteriorly 

 reflected; inner lip thick, flattened, umbilical fissure obsolete. 

 L. CRASSIOR, Mont. 



Section HERSILIA, Monts, 1872. 



The paper in which this group was published is inaccessible to 

 me ; I am therefore unable to give the diagnosis. 



L. MEDITERRANEA, Monts. Mediterranean. 



