2 PALUDINA. 



external base: the foot is a thin broad lingui- 

 form disk, longer than the shell, much extended 

 anteriorly, and bearing an opercle upon its 

 upper posterior surface: mantle simple. 



SHELL conoid, whirls convex, modifying the 

 spiral cavity: aperture ovate or subrotund, 

 widest anteriorly, the margins united, sharp, 

 and never reflected: aperture closed with a thin 

 corneous opercle, of which the lines of increase 

 are generally concentric. 



EXAMPLE. Paludina decisa.* 



OBSERVATIONS. 



"The name of the genus was adopted by 

 Lamarck, from Bruguiere, but Montfort applied 

 to it the name of Viviparus, which is retained 

 by Blainville in his plate, though in the text he 

 adopts that of Paludina." Say. As Lamarck 

 was the first to perceive and define the natural 

 limits of the genus, as characterized by him, 

 he must be cited as authority for it. 



* This species is chosen as an example of the genus, 

 because the accompanying description of the animal has 

 been drawn principally from it. This mode will be pursued 

 with the subsequent genera, when reference to the entire 

 animals of typical species cannot be made. 



