the branchial cavity," and are altogether internal, a cha- 

 racter which distinguishes them from the animal of Val- 

 vata. 



They inhabit fresh waters and are very common in al- 

 most all our lakes and streams. As they respire water, 

 they do not so uniformly reside near the water's edge as 

 the Lymnese, which respire air only. Like them, many of 

 the species, if not all, have the power to swim at the sur- 

 face in a reversed posture, the foot being applied to the 

 surface, and the shell being downward. 



Lamarck describes seven recent species, and Defrance 

 enumerates five fossil ones. 



PALUDINA DECISA. 



SPECIFIC CHARACTER. 



Aperture more than half the length of the shell, within 

 bluish-white. 



SYNONYMS. 



Cochlea virginiana e plava viridescens, non pasci- 



ATA. Lister Conch, tab. 127, fig. 27. 

 Petiver GAzoPiiYL. tab. 106, tig. 18. 

 Paeudina decisa. Nobis. Nicholson's Encycl. (Amer, 



edition) article Conchology, pi. 2, fig. 6. 



PLATE X. 



