234 LITTORINID^;. 



Section LACUNARIA, Conrad, 1866. 



Ovate-conoidal or subglobose, thin, with delicate, close spiral 

 lines; aperture entire, angulated posteriorly, margins disunited, 

 columella flattened, with a long groove descending from the umbili- 

 cus. Eocene ; United States and France. L. ALABAMENSIS, Whit- 

 field (Struct. & Syst. Conch., t. 69, f. 34.) 



Section HALOCONCHA, Dall. 1886. 



Depressed, heliciform, few whorled, thin, with a strong epider- 

 mis, lip thin, with narrow reflexed margin in the adult, continuous 

 with the thin, sharp, unreflected arcuate columella ; umbilicated. 



L. REFLEX A, Dall, Alaska. 



It is Lacunella, Dall (not Desh), and Lacunaria, Dall (not 

 Conrad.) 



Section MEGALOMPHALUS, Brusina, 1871. 



Shell naticiform, with short spire, normal apex, and rounded 

 whorls, thin, minute, with a wide, plicate umbilicus. Operculum 

 spiral. 



L. AZONA, Brusina. Mediterranean Sea. 



The species of this group were first described under Fossarw, 

 from which they differ in apex, sculpture and operculum. Fischer 

 considers Megalomphalus a member of the family Adeorbiidae. 



Section STENOTIS, A. Ad., 1863. 



Shell compressed, elongately ovate, auriform ; spire short, acute ; 

 whorls flattened, the last solute ; aperture oblong, narrow behind, 

 margin continuous, acute ; umbilicus patulous, its margin angulate. 



L. LAXATA, A. Ad. Japan. 



Section CITHNA, A. Ad., 1863. 



Shell shaped like Lacuna, but without epidermis (?) ; apex trun- 

 cated or flattened, umbilicus defined by a ridge. 



Tentacles ciliated. L. TENELLA, Jeffreys. Europe, Japan. 



Hela, Jeffreys, 1870, is a synonym. 



Subgenus LACUNELLA, Desh, 1861. 



Shell oval, thin, pellucid, shining, apex obtuse ; aperture large, 

 dilated, with thin, expanded margin ; columella narrow, thin, con- 

 cave, divided by a narrow channel, scarcely perforate at the base. 

 L. DEPRESSA, Desh. (Struct. & Syst. Conch., t. 69, f. 36.) Eocene; 

 Paris basin. 



