8 PLANORBIS BICARINATUS. 



MONSTROSITY. P. engonatus, Conrad; of 

 which I have seen but the single original spe- 

 cimen in Mr. Mason's collection. 



GEOGRAPHICAL DISTRIBUTION. General from 

 New England to Georgia; and from the North- 

 west Territory to Tennessee, extremes included. 

 Dr. Richardson found it from Lake Superior to 

 Saskatchewan. 



OBSERVATIONS. 



This very common species inhabits quiet 

 waters, along the surface of which it may be 

 frequently seen moving in an inverted position. 

 Its food is mud, impregnated with vegetable 

 matter. The foot is sometimes reddish, and 

 swollen by a blood-like liquid, which is dis- 

 charged if the animal be disturbed. The ova 

 are deposited from March to July, in small, 

 yellow, irregular, and rather solid masses. 



It appears to be easily affected by cold, as 

 it sinks into the mud, when the temperature 

 decreases slightly, and penetrates deeply to 

 hybernate; having the pulmonary cavity filled 

 with air. The form of the anterior portion of 

 the head, is well adapted to enable the animal 

 to force its way through a soft material. 



