78 CONCHOLOGIA CESTRICA. 



Animal, rostrum produced; tentacles cylindrical; 

 eyes sessile, at their extreme bases ; mantle simple in 

 front ; gill exposed, plumose, lamina pinnate, twisted, 

 protected by a respiratory lobe ; foot bilobed in front ; 

 operculum corneous, spiral. 



Genus VALVATA, O. F. MULLER, 1774. 



Shell, sub - discoid, or conoid, umbilicated, thin ; 

 whorls cylindrical, or keeled; peristome circular, con- 

 tinuous. 



V. tricarinata, SAY. 



Cyclostoma tricarinata, Say, Jour. Acad. Phila., I., 

 1817. 



v tricarinata. Shell, with three whorls, and three prom- 



[w. G. B.] inent carina, or revolving lines, one of 



which is on the upper edge, one on the 



^5j^\ lower edge of the whorl, and one beneath 



the base; suture canaliculate; umbilicus 



large. W. 5, mill. 



Station, Schuylkill River, and tributaries. Chester 

 County; abundant. 



Operculum of V, Lingual Dentition of V. tricarinata. 



tricarinata. [W G B 1 



OBS. The ova are deposited from May to midsum- 

 mer, in globose, gelatinous masses, of 10 to 30, and of 

 a green color ; these are hatched in fourteen or fifteen 

 days ; like Limnea, and Physa, they possess the power 

 of swimming in an inverted position, along the surface 

 of water. 



