24 



LAND AND FRESH- WATEll SHELLS OE N. A. [PART II. 



Subfamily LIMN^^IIs^E. 



Shell spiral, more or less elongated, the last whirl large ; aper- 

 ture obloiiff. 



Fig. 25. 



Animal of Limnma 

 desidiusa. 



Fiff. 26. 



lAWSMA., Lamarck. 



Tentacles flattened and triangular. Mantle with the front 

 edge thickened. Foot short, rounded. Shell dextral, spiral, 

 oblong, translucent, horn-colored ; spire acute, 

 more or less produced, last whirl ventricose ; 

 aperture large, wide, rounded in front ; inner 

 lip with an oblique fold ; outer lip simple. 



Jaws three, smooth ; one upper, large, trans- 

 A'ersely oblong or ovate ; two lateral, rudi- 

 mentary, narrow, convex. 

 Lingual membrane (of L. columella) broad, teeth 

 crowded, numerous ; cen- 

 tral narrow, long, apex 

 attenuated, recurved ; 

 laterals broad, blunt, 

 apex recurved, denticu- 

 l^ated. 

 This genus is found over almost the whole world, but prefers 

 the more temperate portions of it. In North America, likewise, 

 it is found in greater abundance and perfection in the lake region 

 of the United States, and still more so in the British possessions. 

 In the States bordering on the Gulf, and in Mexico, it is hardly 

 represented. 



The geographical distribution of the species is but little known. 

 It seems certain that the boreal regions are inhabited by several 

 species common to similar latitudes in Asia and Europe, such 

 as L. sfagnalis and L. palustris. 



The name Limnaea is now universally adopted for this genus 



Fig. 27. 



"oa 



Lingual membraue of L. columella. 



