PLANORBIS. 205 



line with the truncated plane, at the outer 

 edge of which it forms an angle, marked on 

 the inner surface by a slight groove, correspond- 

 ing to the raised line separating the whorls on 

 the outside ; lip thin, slightly thickened by a 

 bluish-white callus, bordered on the inner 

 edge by a purplish band; the longitudinal 

 lines, as well as the transverse lines of growth, 

 are distinctly seen within the aperture. 



In a few specimens the growth of the 

 whorls has not been in the same plane, leav- 

 ing a slightly projecting turreted spire on the 

 left side. 



Diam. 13, alt. 7 mill. 



Saginaw Bay, Mich. 



I have copied above the whole of Dr. Miles' 

 elaborate description of this very curious spe- 

 cies, which has not been found anywhere ex- 

 cept at the original locality. It is not a 

 locally distorted form of any other species, 

 but perfectly distinct, in my estimation. 



(52) 



