186 



[Am. Con., p. iv., March, 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 ; labrum acutely edged ; operculum none. 



" Animal oval, more or less spiral ; margin of the mantle thick- 

 ened on the neck j 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 Melix ; 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 Bulhmis ; thus 

 uniting the differently 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 different 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 different 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 Siiccinca, 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 Physa ; 

 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 



