14 PALUDINA PONDEROSA. 



and occasionally banded with colors a little 

 lighter or darker than that of the general sur- 

 face: opercle thin, oblong ovate, with the lines 

 of growth concentric. 



COLOR of the shell light green (when young) 

 to dark olivaceous externally, and bluish-white 

 within. 



VARIETY A. The shell does not exceed an 

 inch in length; the transverse wavy striae are 

 obsolete; the spire is low, and truncate-eroded, 

 and the labium very much thickened posteriorly. 

 Specimens were given to me by Mr. Conrad, 

 who found them in the Alabama river. 



GEOGRAPHICAL DISTRIBUTION. This, the larg- 

 est of our species, inhabits the Wabash, Ohio, 

 and other western rivers. "Paludina ponderosa 

 seems a common inhabitant of all the rivers of 

 the west, from the northern districts of Indiana 

 and Illinois, to the waters of the Tennessee 

 valley." Conrad, New Fresh Water Shells, 

 p. 12. 



OBSERVATIONS. 



Deshayes thinks this species might as well 

 be placed in the genus Ampullaria, whilst Say 

 believed it to be allied to Melania. "On pour- 



