144. Tail flattened laterally and very sparsely haired; hind feet very large 



and partly webbed; getting to be one and one-half to two feet in total 

 length; generally distributed 



Ondatra zihethica (Linn.) Muskrat 

 (Fiber zihethica (Linn.) ) 

 Tail either cylindrical or else flattened and bushy; hind feet not webbed 

 nor especially large 145. 



145. Total length of adult nine or more inches; tail more than three times 



as long as the hind foot 146. 



Total length of adult seldom reaching nine inches; tail shorter than 



the above in most, but not all, species 157. 



146. Ears short, with the apertures almost hidden in the fur; tail scaly, sparse- 



ly haired 147. 



Ears large and plainly visible; tail scarcely scaled Wood Rats or Pack 



Rats 149. 



147. With short, soft under fur and longer shining guard hairs; tail blackish; 



in sphagnum bogs in Florida 



7\[eo/iber alleni True Florida Round-tailed Muskrat 

 With rough, loose pelage; tail dark above, lighter below; southern At- 

 lantic and Gulf states and along the Mexican border 148. 



148. Under parts white or grayish-white; southern states 



S-igmodon hispidus Say and Ord Cotton Rat 

 Under parts buff; New Mexico and Arizona 



Sigmodon mmimus Mearns Little Cotton Rat 



149. Tail flattened and bushy; from the Dakotas, Nebraska and Kansas west- 



ward 



7<leotoma cinerea (Ord) Bushy-tailed Wood Rat, Pack Rat 

 Tail cylindrical, not bushy 150. 



150. First upper grinding tooth only about one-third longer than the last, the 



last grinder with four loops; hind feet dark colored; Pacific region 

 J\leotoma fuscipes Baird Dusky-footed Wood Rat 

 First grinder fully twice as long as the last, the last with three loops; hind 

 feet light colored 151. 



151. East of the Mississippi River 152. 

 West of the Mississippi River 153. 



152. Tail white below, well haired; in the Appalachian Mountain region from 



N. Y. to Ala. 



l\leotoma magister Baird Pennsylvania Wood Rat 

 {J\leotoma pennsylvanica Stone) 

 Tail brownish below, sparsely haired; S. C. to Fla. and westward to 

 Colo. ; northward in the Mississippi Valley to 111. 



7\[eotoma fioridana (Ord) Florida Wood Rat 



153. Total length about fifteen inches; in the southern states westward to' 



Texas, and northward to S. D. 



J\leotoma fioridana (Ord) Florida Wood Rat 

 Smaller; in the southwestern states, eastward to Texas 154. 



520 



