NERITID^E. 9 



Subgenus Tomostoma, Desh. 1823. 



Shell oval, apex slightly spiral, iuclined posteriorly, base I'ounded. 

 PiLEOLus NERiTOiDES, Desh. Eocene, Europe. 



Calana, Gray, 1844, is a synonym. 



This group, resembling the recent Navicellie, has been referred 

 by myself and others to Pileolus. 



Genus NERITOMA, Morris. 1849. 



Shell ventricose, thick, apex eroded ; aperture with a notch in 

 the middle of the outer lip, inner lij^ excavated in the middle, 

 without teeth. Jurassic, Europe. N. angulata, Sowb. (Struct, 

 and Syst. Conch., t. 78, fig. 63). 



Casts of this shell are common, and exhibit the interior charac- 

 teristic of the Nerites: — it was probably fluviatile. 



Subgenus Neridomus, Morris and Lycett. 1850. 



Smooth, ovately globose, spire small, oblique ; last whorl very 

 large ; aperture ovate or semilunar, outer lip thick, inner lip con- 

 vex, smooth. Great Oolite, England. N. hemisph.erica, Romer. 

 (Struct, and Syst. Conch., t. 78, f. 64). 



Subgenus Oncochilus, Petho. 1882. 



Shell smooth, columellar area covered by a swollen, thick callos- 

 ity, the margin smooth or with two or three small teeth ; outer lip 

 sharp, smooth within. Triassic, Jurassic. N. globulosus, Klip- 

 stein. 



Genus DEJAXIRA, Stoliczka. 1860. 



Shell subglobose, consisting of a few whorls, the last one large, 

 spirally grooved, often carinated posteriorly ; aperture large, sub- 

 trigonal or oval-elongated, columellar lip callous, having three large 

 plications, outer lip sharp. Operculum calcareous, inner margin 

 sinuous, with groove corresponding with columellar plication, inner 

 face with an obtuse claviform apophysis. 



Lacustrine Cretaceous of Europe. D. bicarinata, Stol. (Struct. 

 and Syst. Conch., t. 78, figs. 57, 58). 



Leymeria, Munier-Chalmas. 1884, is a synonym. 



Genus NAVICELLA, Lamark. 1809. 



Shell imperforate, oblong, smooth, limpet-like with a posterior, 

 submarginal apex, clothed with a corneous epidermis, often eroded 



