562 THE JOURNAL. OF GEOLOGY. 
folds of enamel; in P. secuviger there are eight or nine distinct 
folds. 
In another important respect P. securiger appears to differ 
from P. destructor and all other described species of the genus. 
The uppermost border of the enamel band stands out boldly 
from the general surface of the crown on both the anterior and 
posterior sides of the tooth. On the posterior side there is thus 
a distinct valley formed above the enamel band. In the section - 
of the tooth figured by Messrs. Newberry and Worthen the lower 
border of the enamel band is represented as standing out from 
the general surface of the tooth on the posterior side of the lat- 
ter, but nowhere else. The arrangement of the enamel band of 
the tooth in hand suggests that the cutting edge of the tooth 
standing in the opposite jaw, and against which our tooth bit, 
fitted, in the closed mouth, into the valley formed by the band 
of enamel. 
The root of the tooth of P. securiger is considerably broader 
than is that of P. destructor. The posterior surface of the root is 
concave in transverse section at the middle of its length, while it 
is convex in longitudinal section. 
On its posterior face the enamel, for a short distance below 
