148 RODENTS OF IOWA 



Subfamily CRICETIN/E. 



Genus Peromyscus Gloger. 



Unworn molars with a double series of conical tubercles which 

 become worn b}^ abrasion, resulting' in a constantly changing' 

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

 from front to back; size moderate, face lonji, 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. 



Denial formula.— I. Vl ; M. 3/3^16. 

 Key to Species of Peromyscus. 



Tail vertebra 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 maniculattus hairdi. p. 73 



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



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



about 7.00 inches. 



Northern White-footed Mouse. 



Peromyscus leucopus noveljoracensis. p. 69 

 Genus EeWirodontomys 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. 

 ReWirodontomys megaJotis dychei. p. 76 



Subfamily MICROTIN/E. 



Genus Microtus Schrank. 



Form short, thickset ; tail, le^s and muzzle short ; ears short, 

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



