with a revision of the Limnmidai of Authors. 349 



Genus Limncea. Lam. 1801. 



Mantle not exterior to the shell. Shell turrited, usually dex- 

 tral. 



Sub-genus Radix. Mont. 1810. 

 Shell with the last whorl ventricose, aperture expanded, 

 spire less than half the length of the shell. 



Type Radix auricularia, = L. auricularia. Lin. 



Sub-genus Bulimncea. Ilald. 1841. 



Shell ventricose, spire short, aperture not expanded. 

 Type Bulimncea megasoma = Lymnea megasoma. Say. 



Sub-genus Limnophysa. Fitz. 1833. 



Shell ovate-elongate. Spire as long or longer than the 

 aperture, which is not expanded.* 



Type Limnophysa palustr is = Limncea palustris, Linn. 



Sub-genus Acella. Hald. 1841. 



Central tooth trilobed. 



Shell very slender. Aperture without folds, produced anteri- 

 orly, expanded. 



Type, Acella gracilis = Limncea gracilis. Jay. 



Sub-genus Pleurolimncea. Meek. 1866. 



Shell like Acella, with slender, distant, longitudinal costae ; 

 aperture narrowed instead of rounded anteriorly. 



Type Pleurolimncea tenuicostata = Limncea tenuicostata. 

 M. &H. 



Fossil in the Eocene of Dakota. 



* I cannot draw the line between this group and Leptolivi/nm, Swains. Lim- 

 nophysa has priority (1833). The greater proportion of the species which 

 have been referred by various authors to Bidimnaa, also seem to belong to 

 this section. I regard these sub-genera as for convenience only, and really 

 expressing very slight characters. 



