Synopsis Fri^sh-Water Moixusca 

 Genus 10 Lea, 183 1. 



Shell large, spiral, dextral, imperforate, fusiform, 

 smooth, tuberculate or spinose; spire elevated, base of 

 aperture prolonged in a long canal; columella round, 

 smooth and concave; lip thin; operculum corneous, sub- 

 spiral. Animal as in the family. 



Type : Fusus fl.uvialis Say. 



Example : /. spinosa Lea, fig. 122. Radula, fig. 123. 



35 



Fig. 123 



Fig. 125 



Genus LITHASIA Haldeman, 1840. 



Shell of medium size, spire dextral, imperforate, glo- 

 bose conic, smooth or tuberculate ; thick and solid, spire ele- 

 vated, obtusely conic ; aperture large, rhomboidal ; columella 

 smooth, callously thickened above and below; base of the 

 aperture shortly channelled below. Animal as in the fam- 

 ily. 



Type: L. geniculata Hald., fig. 124. 

 Operculum, L. ohovata (Say), fig. 125. 



Section ANGITREMA Haldeman, 1841. 



Shell similar to Lithasia but with the basal canal more 

 produced. 



Type: Melama armigcra Say, fig. 126. 



Fig. 126 



