THE NAUTILUS. 53 
P. umbilicatellus oceurs in Manitoba and Montana. 
The other species mentioned below are more or less widely dis- 
tributed over the United States, except hirsutus, which is restricted 
to the northern tier of States. 
I think any normal specimen can be identified by the following 
key: 
I, PERIPHERY ACUTELY KEELED. 
a. Shell bi-convex. 
b. umbilicus broad, shallow, deflectus Say. 
bb. umbilicus small, deep. 
c. lip simple, aperture extremely oblique, exacutus Say. 
cc. lip thickened within, aperture less oblique, 
alabamensis Pils. 
aa. Upper surface flat, lower convex. 
b. lip thickened within, spiral sculpture distinct, 
oregonensis N. V. 
bb. lip thin, spiral culture absent, or very indistinct. 
ec. umbilicus broad, shallow, exacutus Say. 
ec. umbilicus small, deep. 
d. shell very small, radially ribbed below, 
cristatus Drap. 
dd. shell rather large, smoothish, operculuris Gld. 
Il, PERIPHERAL KEEL BLUNT OR ABSENT. 
a. Radially ribbed below, cristatus Drap. 
aa. spiral sculpture distinct. 
b. umbilicus broad, shallow; surface with spiral rows of hairs, 
hirsutus Gld. 
bb. umbilicus small and deep. 
ce. shell rather large; aperture oblique, broader than 
high, keel indistinct, callioglyptus. 
cc. aperture small, nearly vertical, of equal width and 
height, periphery more angular, sampsoni Ancey. 
aaa. Surface smooth or nearly so. 
6. umbilicus broad and shallow 
c. aperture oval, whorls rounded, parvus Say. 
ce. aperture broétler than high, whorls angular, 
eflectus Say. 
