MOLLUSCA. HOLOSTOMATA. 297 



HOLOSTOMATA. 



TURBONID^. 



* Marine. 



a. Aperture ovate, inner-lip formed by the body-whorl on Avhich the 

 peristome is spread. 



b. Pillar-lip simple, or without teeth. 



C' Peristome incomplete retrally. 

 Turbo. 

 Phasianella. 

 Turritella. 



cc. Peristome complete retrally. 

 Cingula. 



bb, Pillar-lip with a tooth. 

 Odostomia. 

 Monodonta. 



aa. Aperture circular, peristome entire, and more or less disjoined from 

 the body-whorl. 



b. Whorls with transverse ridges, the last formed one constituting a 

 thickened margin to the mouth. 

 Scalaria. 

 Cyclostrema. 



bb. Whorls destitute of the transverse ridges, forming, in succession, 

 the peristome. 



c. Shell armed with tubercles or processes. 

 Delphinula. 

 Cirus. 



cc. Shell destitute of processes. 

 Skenea. 

 Euomphalus. 



** Fluviatile. 



a. Peristome entire. 

 Paludina. 

 Ampullaria. 



h. Peristome incomplete retrally. 

 Melania, 



