The species are rather numerous and Deshayes describes 

 eleven fossil species of the environs of Paris. 



In the following descriptions the shells are considered as 

 sinistral. 



VI 54. 



PLANORBIS LENTUS. 



DESCRIPTION. 



Shell dull brownish or yellowish brown, sub-carinate 

 above, particularly in the young shell ; lohirls nearly five, 

 striate across with five, raised, subequidistant lines, form- 

 ing grooves between them ; .s/)?Ve concave ; aperture large, 

 embracing a large portion of the penultimate volution ; 

 labrum more acutely, but not very prominently arquated 

 above, its basal portion horizontally subrectilinear in the 

 adult and not extending below the level of the base. 



OBSERVATIONS. 



1 obtained this species in the canal at New-Orleans and 

 \ am indebted to INlr. Maclure and also to Mr. Barabino 

 for many fine specimens collected in the vicinity of that 

 city. I also found the same species at Ojo de Agua, Mex- 

 ico, when travelling in that countrj' with INIr. Maclure. 

 It differs from the following species in having the labrum 

 less prominent above, and the basal portion of this part 

 being in the adult horizontally subrectilinear so as not to 



Pi 54. 



