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, leay- 
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) 
