18 PALUDINID^. 



BiTHiNiA. Gray, 



Shell — More or less spiral, covered with a horny epidermis, of 

 a yellow colour ; mouth ovate, slightly angular above. 



Animal — Muzzle lengthened ; two tentaculce with eyes at the 

 extremities, those of the male equal Foot ohtuse, with 

 thich shelly operculum. Oviparous. 



B. TENTACULATA. Gray. PL IV, fig. 7. 



Oval, spiral, with five modertely convex volutions of a yellowish 

 colour, smooth and semitransparent ; no umbilicus. 



Helix tentaculata, Linn. Paludina impura. Lam., 



Sowh., 8^c. 



Medium size, about five-twefths of an inch in length, 

 and one in breadth, though we have met with indi- 

 vidual specimens much larger. It is seldom covered 

 with an extraneous epidermis, if^ covered, it is readily- 

 removed, and presents a smooth, shining exterior. The 

 shell is moderately thick. Operculum thick and shelly. 



Hab. Common all over England except the extreme 

 north. It is found in ditches, canals, and slowly-run- 

 ning streams. 



B. Leachii. Sheppard. PL IV, fig. 8. 



Somewhat resembles the young of B. tentaculata, but is more coni- 

 cal, the whorls are better defined, and it has a small oblique umbilicus. 



Bithinia ventricosa. Gray. Paludina ventricosa. 

 Brown. 



Besides the above distinguishing characteristics, the 

 final volution is shorter, more ventricose and nearly 

 circular. Ordinary length a quarter of an inch, and 

 breadth two lines. 



Hob. Many localities in the region of the Thames, 

 and the south of England generally ; but also met with 

 occasionally in the north. Streams near York and the 

 south of Durham. It is not so plentiful as the preced- 

 ing species. 



Valvata. Muller. 



Shell — JVith a somewhat elevated or a discoid spire ; mouth 

 circular ; operculum horny, concentrically spiral. 



