258 



MANUAL OF THE MOLLUSCA. 



viviparous ; tlie shells of the young are omamented with. f5piral 

 rows of epidermal cirri. 



Distribution, 60 species. Eivers and lakes throughout the 

 northern hemisphere ; Black Sea, Caspian. 



Fossil, 53 species. Wealden — . Britain, &c. 



Svb-genus. Bithynia (Prideaux), Gray. B. tentaculata' 

 (PL IX., Fig. 27). Shell small; operculum shelly. Animal 

 oviparous ; with only one neck-lappet, on the right side. The 

 bithynia oviposit on stones and aquatic plants ; the female lays 

 from 30 to 70 eggs in a band of three rows, cleaning the surface 

 as she proceeds ; the young are hatched in three or four weeks, 

 and attain their full growth in the second year. (Bouchard.) 



Ampttllaeia, Lam. Apple-snail, or idol-sheU. 



Etymology, ampnlla, a globular flask. 



Example, A. globosa (PI. IX., Pig. 30). 



Synonym, Pachylabra, Sw. 



Shell globular, with a small spire, and a large ventricose body- 

 whorl ; peristome thickened and slightly reflected ; operculum 

 shelly. 



Animal with a long incurrent siphon, formed by the left neck- 



Fig. 109* 



lappet; left gill developed, but much smaller than the right ;t 

 muzzle produced into two long tentacular processes ; tentacles 



* Fig. 109. AmpuUaria canaliculata, Lam. (from D'Orb). South America. The 

 branchial siphon (s) is seen projecting from the left side ; o, operculum. 



t The ampuUaria is said to have a pulmonic sac in addition to its gills (Gray, Owen), 

 but we have not met with specimens sufficiently well preserved to exUibit it. It would 

 be very desirable to examine the amp. cornu-arietis, in which, probably, the giUs are 

 BjTmnetrical, a-s in the cephalopods. 



