42G MONOGKAPIJS OF NORTH AMERICAN RODENTIA. 



The anterior lace 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 widt h of 0.76 (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. 



