PLANORBIS BICARINATUS. 7 



wards from the posterior base of the tentacles; 

 there is a similarly dotted spot upon each side 

 of the head between the tentacles and in front 

 of the eyes; the mouth is reddish. 



Shell with rather more than three complete 

 whirls, which are angulated upon each side 

 near the periphery; the carinae do not extend 

 to the edge of the aperture in old shells; the 

 spire is upon the left side, and is depressed 

 about as deeply as the umbilicated side; the 

 right margin of the labrum is upon the general 

 plane of that side of the shell, whilst the left 

 margin extends beyond the plane of the penul- 

 timate whirl; the carina upon the left side forms 

 a smaller spiral than that on the opposite side. 



Color of the outside brownish; of the inside 

 chesnut, with pale lines in the grooves formed 

 by the carince. 



Variety unicarinatus. Shell small, with the 

 whirls of the right side rounded; the carina (on 

 the left side) revolves closely, so as to form a 

 very narrow umbilic, and the aperture is much 

 extended towards the left. Inhabits the Schuyl- 

 kill. 



Variety angistoma. Shell small, aperture 

 campanulate, with the throat narrowed. 



