150 RODENTS OF IOWA 



Denial formula— \. 1/1; M. 3/3=16. 



Key to Subspecies of Fiber. 



Size larye ; liiiid foot averaging over 80 mm. ; color dark brown. 



Common Muskrat. 

 Fiber zibethiens zibethieus. p. 96 



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



^ro^^'"- i| ! 'li.i 



Great Plains Muskrat. 



Fiber zibethieus einnaynommus. p. 105 



Genus Synapiomys Baird. 



Front of upper incisors with a distinct longitudinal g-roove 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. 1/1; M. 3/3=16. 



A single form occurs in Iowa. 



Goss' Lemming Mouse. 

 Synapiomys cooperi gossii. p. 106 



Family GEOMYID/E. 



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— 1. 1/1 ; Pm. 1/1 ; M. 3/3=20. 



A single form occurs in Iowa. 



Pocket Gopher. 

 Geomys hursanus bursarius. p. 108 



