164 LIMN.EAD.ffi. 



This shell was confounded by Midler with the last, and 

 has been made the type of a distinct genus by Fleming. 

 It is, however, a true Planorbis, and we agree with Mr. 

 Alder in considering the internal partitions of the shell as 

 only of specific import. The animal closely resembles that 

 of nitidus. 



It is common in ditches and ponds in many parts of 

 England, especially about London, but cannot be regarded 

 as of general distribution. It occurs in the south of Scot- 

 land, but has not been noticed in Ireland, except at Cahir, 

 in Tipperary, where Mr. J. D. Humphreys has taken it 

 (Jeffreys). 



LIMN^lUS. Draparnaud. 



Shell, ovate, oblong, or turreted, thin and horny, dex- 

 tral ; aperture ovate, or expanded, with an entire margin 

 and a more or less twisted columella. No operculum. 



Animal with a broad head and snout ; tentacles two, 

 triangular, rather short, broad, the eyes placed at their 

 inner basis ; mantle even-edged, in some species reflected 

 on the shell ; foot broadly lanceolate or sub-ovate. Tongue 

 armed with many transverse rows of numerous stout 

 uncinated teeth, with furcated hooks, flanking a minute 

 simple, hooked, central denticle. 



The species of this genus are found in streams, ponds, 

 and lakes, in all parts of the world ; and, though nume- 

 rous, bear, for the most part, a striking resemblance to 

 each other. Some of them are very widely diffused, pre- 

 senting, like many other fresh- water animals and plants, a 

 great extent of distribution through various climates and 

 distant countries. Limnai have been found in the fossil 

 state in strata dating as far back as the oolitic epoch ; and, 

 as in the case of Physa and Planorbis, the most ancient 



