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The Wood Rat, N. Jloriddnd', Svy '& Ord., of ''Florida 

 and northward and westward, is of the size of the Black 

 Rat, grayish-brown mixed with rusty above, and the 

 under parts and feet white. 



The Bush Rat, N. mexicana, Baird, of Texas to Cali- 

 fornia ; the Black Wood Rat, N. micropus, Baird, of Texas 

 and Mexico ; the Brown-footed Rat, N. fuscipes, Cooper, 

 of California ; the Hairy-tailed Rat, N. occidentalis, Cooper, 

 of Oregon ; and the Rocky Mountain Rat, N. cinerea, Baird, 

 are additional species of this genus. N. magister, Baird, 

 is found fossil in the caves of Pennsylvania. 



The Genus Sigmodon Cotton Rats is characterized 

 by the shape of the enamel on the two last molars in the 

 lower jaw, which is in the form of the Greek letter sigma. 



The Cotton Rat, 5. hispidus, Say & Ord., of the South- 

 ern States, is about half as large as the Norway Rat ; the 

 color above reddish-brown lined with dark brown. 



The Texas Cotton Rat, 5. Berlandieri, Baird, is of a 

 lighter color, and with a larger tail. 



3. Arvicolinae are characterized by incisors as broad 

 as deep, molars ^, rootless, ears short and hidden, muz- 

 zle broad and rounded, tail very short and mostly clothed 

 thickly with hair, and the whiskers as in Murinae. 



The Genus Arvicola Field Mice is characterized 

 by small size, soles naked anteriorly, tail rather short, 

 cylindrical, and hairy. The posterior upper molar is 

 composed of five or six prisms, and the posterior lower 

 one of three. This genus is represented in the United 

 States by more than twenty species, about half of which 

 belong to the western portions. 



The Red-backed Mouse, A. Gapperi, Vigors, of the 

 Northern States, is about the size of the common house 

 mouse, the back with a broad stripe of bright rufous 

 brown, sides yellowish -gray mixed with brown, and the 

 under parts yellowish-white. 



