FEB., 1912. MAMMALS OF ILLINOIS AND WISCONSIN CORY. 233 



Genus SYNAPTOMYS Baird. 



Synaptomys Baird, Mammals N. Amer., 1857, p. 558. Type Synap- 

 tomys cooperi Baird. 

 Front of upper incisors (front teeth) with distinct groove near 



outer edge; molars without pronged roots; tail short; face of incisors 

 orange brown in color; crowns of molars with transverse 

 loops. A North American genus comprising two subgenera, 

 Synaptomys and Mictomys, but only the former is represented 

 within our limits. The subgenus Synaptomys has the 

 crowns of the lower cheek teeth (molars) with closed enamel 



triangles, a loop on the outer edge, and the mammas are 6. 



Dental formula: I. , C. , Pm. , M. ^= 16. 

 i-i o-o o-o 3-3 



Subgenus SYNAPTOMYS Baird. 



Synaptomys cooperi gossii (MERRIAM). 



Goss's LEMMING MOUSE. 



Synaptomys helaletes gossii MERRIAM, Proc. Biol. Soc. Wash., X, 1896, p. 60. 

 Synaptomys gossi HOWELL, Proc. Biol. Soc. Wash., XXIII, 1910, p. 30 (Missouri 



and southern Illinois). 

 Synaptomys cooperi COUES, Monog. N. Amer. Rodentia, 1877, p. 235-236 (part) 



(southern Illinois). OSBORN, Proc. Iowa Acad. Sci., I, 1887-89 (1890), p. 43 



(Iowa). WOOD, 111. State Lab. Nal. Hist., VIII, 1910, p. 559 (Champaign Co., 



111.). 



Type locality Neosho Falls, Woodson Co., Kansas. 



Distribution Kansas, Missouri and southern Illinois, northward 

 through at least a considerable portion of Illinois, Iowa and Nebras- 

 ka to South Dakota ; range not satisfactorily determined. 



Description Adult in summer: General color of upper parts dark 

 rusty brown or reddish brown mixed with black tipped hairs; under 

 parts plumbeous gray, the hairs with white tips but the plumbeous 

 under fur showing through; a dusky mark at base of the whiskers; 

 tail brownish above, paler beneath; skull larger and heavier and 

 brain case actually and relatively longer than in cooperi. 



Adult in winter: Grayer and decidedly less reddish brown. Im- 

 mature specimens are quite different, the general color of the upper 

 parts being dusky slate or grayish brown according to age. 



Measurements Total length, about 5 in. (128 mm.); tail vertebrae, 

 .70 in. (17. 5 mm.); hind foot, .75 in. (19 mm.). 



