38 



Bryant Wai^kek 



on the right side. Radula with a very small central tooth, 2 to 5 lateral teeth 

 of varying size and shape and numerous spatulate marginals. 



Shell imperforate, globose, spire short; internal divisions of the shell 

 absorbed ; aperture semi-ovate, entire, columellar region expanded and flat- 

 tened, usually thickened ; lip acute ; operculum subspiral. 



Key to the genera of Neritidce. 



1. Operculum calcareous, edge with projecting processes 



(apophyses) articulating with the columella Neritina. 



2. Operculum corneous, without apophyses Lepyriiim. 



Genus NERITINA Lamarck, 1809. 



Shell dextral, spiral, thick and solid, subglobose; spire short; surface 

 smooth (in American species) ; aperture semi-circular, columella flattened, 

 straight, smooth or finely denticulate ; lip acute, inner surface smooth ; oper- 

 culum calcareous, semi-circular, paucispiral, nucleus excentric ; with two 

 apophyses, the upper shorter, sometimes dilated and crested ; the lateral in 

 the form of an arched rib. 



Fig- 137 Fig. 138 



Animal as in the family. Radula with the central tooth small, subquad- 

 rangular, cusp smooth; first lateral large, second and third small, fourth 

 very large, prolonged below and with the cusp semicircular and denticulate, 

 laterals numerous, spatulate. 



Type : N. perversa Gmel. 



Example: N. recUrata Say, fig. 137. Radula, fig. 138. 



Genus EEPYRIUM Dall, 1896. 



Shell small, dextral, spiral, corneous, thin, semi-transpar- 

 ent; spire very small and depressed, body-whorl large; aper- 

 ture large, semi-circular ; columella concavely flattened, cal- 

 loused, straight, smooth ; Hp thin, acute operculum thin, corne- 

 ous, paucispiral without apophyses. 



_^. Radula with a wide rachidian tooth with a finely denticu- 



1 1°" 1 30 



^'^ lated cusp ; laterals two, the inner small and oblique, the other 



large with the cusp finely denticulate ; laterals spatulate, numerous. Animal 



otherwise unknown. 



Type: Neritina shozvalteri hea., fig. 139. 



