54 LIMNjEID^. 



attached to the body by a pedicle ; respirato7'y orifice on the 

 right side ; generative orifices also on the right side, apart from 

 each other, that which serves for the male functions being placed 

 behind, and that for those of the female in front, at the base of 

 the neck, near the respiratory orifice ; jaw with three pieces, 

 smooth, upper one usually slighly beaked ; lingual ribbon 

 usually as in L. stagnalis. 



Shell conic-ovate, more or less elongated ; spire dextral. 



The animals which belong to this genus are gre- 

 garious ; they inhabit sluggish waters, and are ex- 

 tremely prolific. The apex of their shell is frequently 

 eroded, and sometimes the upper volutions are alto- 

 gether wanting. This is mainly caused by the animal 

 retiring downwards, as its body increases in size, into 

 the larger portion of the shell, the upper whorls being 

 thus left untenanted, so that after a time, like a 

 deserted house, they crumble away. I cannot help 

 thinking, however, that the process of demolition is 

 often aided by the ravages of individuals of the 

 same, or even of other species, when the water they 

 inhabit chances to be deficient in carbonate of lime. 

 This erosion is by no means the rule, but rather the 

 exception, and it does not occur, to the same extent at 

 least, in all situations, and I have frequently observed 

 these molluscs engaged in what seemed suspiciously 

 like the act of purloining " building materials " from 

 the apex of their neighbours' shells. It would be 

 interesting if conchologists in different parts of the 

 country would take the trouble to analyze the water 

 from those localities where the molluscs are liable to 

 erosion. Gwyn Jeffreys, in his remarks respecting 

 the members of this genus, says : " Their mode of 

 propagation is very singular, three or more individuals 



