186 
[Am. Con., p. iv., Marcli, 1832.] 
Limneus. — Shell oblong, ovate, oval, conic or turrited, thin, 
smooth } spire prominent, more or less elongated ; aperture more 
or less dilated, longitudinal, entire; columella at its superior part 
or junction with the labium entering the aperture by a very ob- 
lique fold or undulation ; lab rum acutely edged ; operculum none. 
Animal oval, more or less spiral ; margin of the mantle thick- 
ened on the neck ; foot large, oval ; head with two triangular, 
compressed, earshaped tentacula : eyes sessile, at the inner base of 
the tentacula ; mouth with two lateral appendices, and armed with 
a superior tooth ; orifice of the pulmonary cavity on the right, and 
bordered by an appendage which can be folded in gutter ; orifice 
of the reproductive organs distant ; that of the oviduct at the en- 
trance of the pulmonary cavity ; that of the male organ under the 
right tentacula.^^ — (Blainville.) 
Obs. A numerous genus of fresh water shells, inhabiting almost 
every part of the globe. The species known to Linne were placed 
in his great reservoir Helix ; in which he has been followed by 
many of the English Conchologists, even of late years. Bru- 
guieres, eminent for his useful reform in this science, separated it 
from that genus, but did not distinguish it from his Bulimus ; thus 
uniting the dilferently organized animals of land and water in one 
group. It is very true that some species of these two natural 
genera resemble each other in the form of the shell, but they may 
always be distinguished by the fold of the columella in the present 
genus. Lamarck, aware that the animals were quite difierent in 
organization, and that the one has two tentacula and the other 
four, that one lives only in the water and the other altogether on 
land, placed them in difierent families, and formed a separate genus 
(as Muller and others had already done) under the above name, 
which is now almost universally adopted for the present aquatic 
group. The shell resembles Succinea, which, however, is destitute 
of the fold of the columella, and its animal has four tentacula. But 
of all the adopted genera, it is almost intimately related to PJiym ; 
and Sowerby, in his “ Genera, has reunited the two groups. The 
peculiar fold of the columella exists in both, but the animal of 
Physa has the mantle remarkably dilated, so as to extend over 
