BYTHYNIA. 341 



position of the nucleus. The species are from Ceylon, 

 where they inhabit ponds, mountain-streams, and water- 

 courses. 



Species of Tanalia. 



aculeata, Chem. neritoides, Reeve. 



serens, Reeve. picta, Reeve. 



crinacea, Reeve. rudis, Reeve. 



dilatata, Reeve. sulcata, Reeve. 



fuuiculata, Reeve. Tennautii, Reeve. 



Gardneri, Reeve. undata, Reeve. 

 Layardi, Reeve. 



Genus BITHYNIA, Leach. 



Animal with a small lobe on one side of the neck. 



Operculum shelly on the inner surface, nucleus sub- 

 central. 



Shell turbinate, covered with a horny epidermis ; spire 

 produced, whorls rounded ; peristome continuous, thick- 

 ened internally. 



Si/?i. Desmarestia, Hartm. ? Subulina, Schmidt, not 

 ScJium. 



Ex. B. tentaculata, Linnaeus, pi. 36, fig. 4. Opercu- 

 lum, B. tentaculata, fig. 4, a, 4, h. Shell, B. tentaculata, 

 fig. 4, c. 



The female is oviparous and deposits her eggs in a band, 

 attached to stones or the stems of aquatic plants ; when 

 she desires to deposit the ova, she seeks some smooth 

 place, and clears the surface with her mouth before com- 

 mencing ; the young are hatched in three or four weeks, 

 and attain their full growth in the second year. 



