212 PLANORBIS. 



28. P. CIRCUMSTRIATUS, Tryon. 

 Plate 7, fig. 14—16. 



Shell small, rugose, generally distorted in 

 adult specimens, (the whorls not proceeding 

 in the same plane, but elevated or depressed 

 from it at times) ; volutions four, convex, 

 increasing very slowly in diameter, with 

 deeply impressed suture, towards the aperture 

 deflected ; below concave, but exhibiting all 

 the volutions, with two or three raised revolv- 

 ing lines ; aperture small, very oblique. Light 

 horn color. 



Diameter 6 mill, height 1'5 mill. 



Artificial pond at Weatogue, Connecticut. 



The remarkable raised revolving lines are 

 visible on the under surface of all the adults I 

 have examined, but on the young shells there 

 are no traces of them. < 



For the remarkable circumstances con- 

 nected with the discovery of this species, ref- 

 erence is made to the description of Limnea 

 Shurtleffii in this work. 

 (59) 



