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420 



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 widtli of 0.7.6 (in the larger 

 specimen), the succeeding ones becoming successively slightly narrower and 

 shortt^', except the last, which is the longest. In the lower Tnolars, 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 tritur.tcijig 

 surface an hour-glass form. 



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