wiih a revision of thè Limnmdoe of Authors. 349 
Genus Lim,noBa. Lam. 1801. 
Mantle not exterioi' to thè sliell. Shell turrited, usually dex. 
trai, 
Sub-genus Hadix. Mont. 1810. 
Shell with thè last whorl ventricose, aperture expauded, 
.spire less than half thè leiigth of thè shell. 
Type Radix aurieidaria, — L. auricidaria. Lin. 
Sub-genus Bulimncea. Hald. 1841. 
Shell ventricose, spire short, aperture not expanded, 
Type Bulimncea megasoma — Lymnea megasoma. Say, 
Sub-genus Limnojphysa. Fitz. 1833. 
Shell ovate-elongate. Spire as long or longer than thè 
aperture, which is not expanded.* 
Type Limnophysa pcdustris = Limncea palustìàs, Linn. 
Sub-genus Acella. Hald. 1841. 
Central tooth trilobed. 
Shell very slender. Aperture without folds, produced anteri- 
orly, expanded. 
Type, Acella gracilis = Limncea gracilis. J ay. 
Sub-genus Bleurolimncea. JVIeek. 1866. 
Shell like Acella, with slender, distant, longitudinal costse ; 
aperture narrowed instead of rounded anteriorly. 
Type Bleurolimncea tenuicostata — Lim,ncea tenuioostata. 
M. & H. 
Fossil in thè Eocene of Dakota. 
* I cannot draw thè line between this group and Le/ptolimnma^ Swains. Lim- 
noptiysa has priority (1833). The greater proportion of thè species which 
have been referred by various authors to BuUmnasa, also seem to belong to 
this section. I regard these sub-genera as for convenience only, and really 
expressing very slight characters. 
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