114 The American Naturalist. [February, 
the close of the Lafayette epoch and the opening of the Kan- 
san epoch was longer than all the time since. If we do not 
adopt any very large factor of safety, the known evidence will 
imply a length of time for the Ozarkian period twice and, per- 
haps, thrice as great as all subsequent time. Therefore, by 
reason of its length and other features in some respects pecu- 
liar to it, the Ozarkian period, or more properly sub-period, 
may be considered co-ordinate with the Glacial sub-period, the 
two to constitute approximately equal divisions of the Pleisto- 
cene period as in the table on page 113. 
THE POCKET, OR POUCHED GOPHER. 
(Geomys bursarius.) 
By CLEMENT L. WEBSTER.’ 
In passing over the beautiful prairies of the west, especially 
in portions of Iowa and southern Minnesota, the attention of 
the “traveler is arrested by the great number of isolated or 
grouped mounds, which are seen over the surface. 
Fic, 1. Geomys bursarius. 
These mounds are generally circular, and have a rounded 
or flattened top; and a diameter, at the base, of from four to 
twenty feet; and usually rise to a height of from one to three 
feet. 
1 Charles City, Iowa. : i 
