426 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 
The anterior face of the incisor teeth is marked with broad, shallow, 
longitudinal grooves, about twice as wide as the rather abrupt, narrow, inter- 
vening ridges. The lower incisor, seen in section, is triangular, with the 
anterior face rounded. The first upper molar has a width of 0.75 (in the larger 
specimen), the succeeding ones becoming successively slightly narrower and 
shorter, except the last, which is the longest. In the lower molars, the first 
is the longest and the fourth the shortest ; the second is the widest. The 
first three are somewhat narrowed near the middle, giving the triturating 
surface an hour-glass form. 
