NERITIDiE. O 



Section Odontostoma (Klein, 1753), Morch. 1852, 



Columellar lij^ smooth or nearly smooth, its margin dentate, outer 

 lip scarcely denticulated within. N, polita, Linn. 



Subgenus Lissochilus, Petho. 1882. 



Inner lip smooth, its margin not dentate, outer lip sharp, not 

 thickened or dentate within. Triassic and Jurassic. 



N. SIGARETINA, BuV, 



Subgenus Otostoma, d'Archiac. 1859. 



Shell with longitudinal plications and very fine spiral lines, col- 

 umellar lip thick, with dentate margin. 



Cretaceous of Europe, Algiers and Asia Minor. N. rugosa, 

 Hoeningh. 



These fossils have usually lost the columellar lip and the inner 

 layer of the outer lip, but traces of these destroyed parts are found 

 upon casts. The discovery of a silicified specimen in good preser- 

 vation and intact has proven the identity of Otostoma with Nerita ; 

 its longitudinal plications will serve to distinguish it subgenerically, 



Lyosoma, White. 1882, appears to be synonymous. Its type is 

 L. PowELLi, White, from the Jurassic of Utah. 



Genus DESHAYESIA, Raulin. 1844 



Shell subglobose, thick, umbilicated, spire short ; aperture entire, 

 semicircular, oblique, columella convex, denticulated, outer lip 

 smooth internally. 



Eocene and Miocene ; Paris and Bordeaux basins. 

 D. Neritoides, Grat. Struct, and Syst. Conch, PI. 78, f. 59. 



This genus presents a very remarkable combination of the char- 

 acters of Nerita and Natica, and appears to establish a passage be- 

 tween those genera. 



Genus NERITINA, Lam. 1809. 



Shell imperforate, rather thin, globose, with short spire, usually 

 smooth, columellar lip flattened, smooth, straiglit-raargined, finely 

 denticulated or smooth, outer lip sharp, not callously thickened or 

 toothed within, aperture with a projection on the inner surface near 

 the base of the columella (PI. 1, fig. 16). 



Operculum calcareous, completely closing the aperture ; exteri- 

 orly paucispiral with excentric nucleus, interiorly with an apical 



