LITTOKINID.I':. 233 



? Genus CYCLOCHEILA, Conrad. 



Pyramidal ; aperture circular; labruni expanded, columella flat- 

 tened, subangular at the base ; periphery angular. 



A doubtful little tertiary shell from South America; prob!il)ly 

 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 sharj), arcuated. Operculum 

 pauci.spiral (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.) 



Sj)awn vermiform, thick, semicircular. Range low water to 50 

 fathoms. The Lacuna feed uj)on 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, ^(?e Gray, 1847. 



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

 vated ; inner lip thin, sharj). umbilical fissure linear. L. vincta, 

 Turton. 



Section Medorta, Leach, /(ie, 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. 



