234 LITTORINID^L 



Section LACUNAKIA, 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. ALABAMENSTS, 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. REFLEXA, 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 Fos*<tnix, 

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

 considers Megalomphalus a member of the family Adeorbiidse. 



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. LAX ATA, 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. 



