ANCYLUS. 225 
ing beyond the edge of the aperture; within 
bluish-white, darker towards the apex. 
Length 7:5, alt. 3 mill. 
Passaic River, near Patterson, N. Jersey. 
“The specimen which furnished the above 
description was one of the largest which I 
have seen. They are more commonly of the 
dimensions of A. rivularis. I separate it from 
the latter chiefly on account of its solid, calca- 
reous structure.” I have not seen this species, 
and can offer no opinion upon it. 
10. ANCYLUS BOREALIS, Morse. 
Plate 2, fig. 7, 8. 
Shell elliptical, solid, light yellow, apex ele- 
vated, rounded, very obtuse, nearer the poste- 
rior margin of the shell; lateral slopes steep, 
anterior slope slightly convex, near the apex ; 
posterior slope straight. Fine regularly inter- 
rupted radiating lines mark the surface of the 
shell from the apex to the borders; incremen- 
tal lines irregular. 
(19) 
