Ji LIMNEA. 



surmounted by a free, thin, and movable ap- 

 pendage: mantle simple: foot thin, oval, not 

 extended anteriorly, and shorter than the shell: 

 pulmonary orifice opening upon the right side, 

 'and near it the oviduct, whilst the organ of the 

 deferent canal is situated near the right tenta- 

 cle.' The sexes are united in the same indi- 

 vidual. 



Shell thin in texture, oval or elongated, 

 surface smooth; spire exserted, tapering to a 

 point more or less acute: aperture longer than 

 wide, peristome incontinuous, the labrum turn- 

 ing and entering the aperture anteriorly, form- 

 ing a single oblique fold upon the columella. 



Example. Limnea catascopium. 



OBSERVATIONS. 



The shell can be most readily distinguished 

 from Physa by being dextral; from Succinea 

 by the fold upon the columella, which is want- 

 ing in the latter genus; and from Amphipeplea 

 by the solider texture and more elongated form 

 of the shell. The ova resemble those of Physa, 

 except that the latter are deposited in a semi- 

 circular, and those of Limnea, in a linear mass. 

 This distinction I have observed in several 

 species, but it may not be universal. 



