224 ANCYLUS. 
7. ANCYLUS RIVULARIS, Say. 
Hald. Monog. p. 4, t. 1, fig. 1. 
Extensively distributed through the North- 
ern, Middle and Western States. 
8. ANCYLUS TARDUS, Say. 
Hald. Monog. p. 7, t. 1, f. 3. 
Maine, Vermont, New York, District of Co- 
lumbia, Indiana. 
9. ANCYLUS CALCARIUS, DeKay. 
Plate 2, fig. 3, 4. 
Shell conic, calcareous, opaque. Apex not 
central, moderately prominent; aperture oval, 
entire; the curves on the longest sides dis- 
similar. In very minute specimens, the edges 
somewhat everted. Hpidermis rufous, extend- 
(18) 
