148 RODENTS OF IOWA 



Subfamily CRICETIN/E. 

 Genus Peromyscus Gloger. 



Unworn molars with a double series of conical tubercles which 

 become worn by abrasion, resulting in a constantly changing 1 

 pattern; molar series short, narrow, the teeth decreasing in size 

 from front to back; size moderate, face long, nose pointed; ears 

 thin, rounded; feet small, the palms naked, the soles of hind feet 

 with five or six tubercles; tail slender, haired, at least two inches 

 long ; belly white or whitish ; pelage soft, often glossy. 



Dental formula I. 1/1 ; M. 3/3- 16, 

 Key to Species of Peromyscus. 



Tail vertebrae less than 2.75 inches; tail sharply bicolor; gen- 

 eral color brown mixed with black ; total length, 5.50 to 6.50 inches. 



Prairie White-footed Mouse. 

 Peromyscus maniculatus bairdi. p. 73 



Tail vertebras more than 2.75 inches; tail not sharply bicolor; 

 general color brown, darker along middle of back; total length, 

 about 7.00 inches. 



Northern White-footed Mouse. 



Peromyscus leucopus noveboracensis. p. 69 

 Genus Reithrodontomys Giglioli. 



Body slender; size very small; tail long, more than one-third 

 total length, scaly, slender, and sparsely haired; ears prominent; 

 soles of feet with six tubercles; no cheek pouches; upper incisors 

 with a deep longitudinal groove nearly as broad as the face of 

 the tooth ; lower incisors simple ; molars with the tubercles ar- 

 ranged in two longitudinal series; first upper molar with five 

 principal tubercles; posterior border of palate square, terminating 

 opposite posterior border of last molars ; outer wall of anteorbital 

 foramen a broad thin plate. 



Dental formula^-L 1/1 ; M. 3/3--16. 



A single form occurs in Iowa. 



Prairie Harvest Mouse. 

 Reithrodontomys megalotis dychei. p. 76 



Subfamily MICROTIN/E. 



Genus Microtus Schrank. 



Form short, thickset; tail, legs and muzzle short; ears short, 

 buried in the fur; upper incisors not grooved; root of lower in- 



