6 MONOGRAMS OF NORTH AMERICAN RODENTIA. 



Diagnostic table of some cranial and dental characters of North American tiXTBXDJB— Continued. 



Subfamily MURINE. 



The characters of this subfamily having already been given in sufficient 

 detail for present purposes, we may at once proceed to consider its subdivision 

 into the two tribes or series of genera ; namely, Mures and Sigmodontes. This 

 separation of the Old World (Mures) and New World (Sigmodontes) repre- 

 sentatives of the subfamily seems to us warranted, and not alone upon geo- 

 graphical grounds; for a decided difference in dentition is found, serving for 

 their immediate identification. 



Mures. — Molars of upper jaw, with the tubercles in three series. Palate 

 extending back of the molars. (Palaeogsean.) 



Sigmodontes. — Molars of upper jaw, with the tubercles in two series. 

 Palate ending opposite last molars. (Neogsean.) 



The Mures which occur in North America, — namely, four species 



