150 RODENTS OF IOWA 



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

 Key to Subspecies of Fiber. 



Size large; hind foot averaging over 80 mm.; color dark brown. 



Common Muskrat. 

 Filter zibethicus zibethicus. p. 96 



Size smaller ; hind foot less than 80 mm. ; color reddish or pale 

 brown. :j ||fj ] 



Great Plains Muskrat. 

 Fiber zibethicus cinnamominus. p. 105 



Genus Synaptomys Baird. 



Front of upper incisors with a distinct longitudinal groove near 

 outer edges; root of lower incisor ending abruptly opposite last 

 lower molar ; crowns of molars with transverse loops ; teeth of 

 molar series strongly convergent anteriorly, the individual teeth 

 large ; ears equal to or longer than the fur ; tail equal to or longer 

 than hind foot ; pelage dense and soft. 



Dental formula^-!. 1/1 ; M. 3/3=16. 



A single form occurs in Iowa. 



Goss ' Lemming Mouse. 

 Synaptomys cooperi gossii. p. 106 



Family GEOMYID. 

 POCKET GOPHERS. 



Form short, heavy; large, external, fur-lined cheek pouches 

 opening outside the mouth; feet fossorial, the front pair being 

 particularly well developed; eyes and ears minute; tail thick, 

 fleshy, usually hairless; molars rootless. 



Genus Geomys Rafinesque. 



Upper incisors furnished with two longitudinal grooves, a broad, 

 deep one along the middle, and a smaller and narrower one along 

 the inner edge; crowns of teeth of molar series with transverse 

 enamel loops, a single loop on each molar, two loops on the pre- 

 molar ; infraorbital foramen confined to lower portion of maxilla ; 

 auditory meatus tubular, elongated. 



Dental formula^-I. 1/1 ; Pm. 1/1 ; M. 3/3=20. 



A single form occurs in Iowa. 



Pocket Gopher. 

 Geomys bursarius bursarius. p. 108 



