159 



Tliey may be distinguished from Ci/chstoma by the simple la- 



brum, as well as by other characters of the shell, as also of the 



animal, from Jlelania by the simple curvature of the labrum at 



ott- base, and from Valvata by the form of the aperture which is 



not angulated above in that genus. 



The animal has two linear-acute tentacula, with the eyes at their 

 exterior base ; anterior part of the body with a small membrana- 

 ceous wing on each side, the right one is " recurved in a small 

 canal, which introduces the water into the respiratory cavity ;" 

 " the branchiae are composed of parcels of filaments, which are 

 attached to the sides of the branchial cavity," and are altogether 

 internal, a character which distinguishes them from the animal of 

 Valvata. 



They inhabit fresh waters and are very common in almost all 

 our lakes and streams. As they respire water, they do not so 

 uniformly reside near the water's edge as the Lymnese, which 

 respire air only. Like them, many of the species, if not all, have 

 the power to swim at the surface in a reversed posture, the foot 

 being applied to the surface, and the shell being downward. 



Lamarck describes seven recent species, and Defrance enumer- 

 ates five fossil ones. 



Paludina decisa. — Specific character. Aperture more than 

 half the length of the shell, within bluish-white. 



Cochlea virginiana e flava viridescens, non faciata, Lister. 

 Conch, tab. V21,fifj. 27. 

 Petivcr gazophyl, tab. 10Q,fig. 18. 



Paludina decisa, nobis. Nicholson's Encycl. {Amer. Edition^) 

 article Conchology, pi. 2, fig. 6. 



Obs. The species is very common in various parts of the Union. 

 Dillwyn informs us that Muller and others have incorrectly quoted 

 Lister's figure for their Helix angularis. PI. 10, the upper and 

 lower figures. 



Paludina vivipara, Lin. — Specific character. With about 

 three reddish-brown revolving lines. 



Cochlea vivipara fasciata. Fluviatilis, Lister. Conch., tab. 

 126, y?^. 26. 



Helix vivipara, Linn., Gmel. and others. 

 Nerita vivipara, Muller, Verm., p. 182. 

 Cychstoma vivipara, Draparn., pi. 1, fig- 16. 



