176 Field Museum of Natural History — Zoology, Vol. XL 



Part 2. Front of upper incisors (front teeth) without distinct groove near 

 outer edge. 

 Upper parts nearly uniform brown in color; tail not exceeding i inch in 

 length and usually less. Greater Pine Mouse. 



Microtus pinetorum scalopsoides, p. 222. 

 Upper parts with wide chestnut dorsal stripe (down middle of back) in 

 decided contrast to gray brown of sides; tail more than i inch long. 



Red-backed Mouse. 

 Evotomys gapperi, p. 208. 



Subfamily MURIN^E. 



An Old World subfamily of which several species have been in- 

 troduced into America. The characters as given for the following genera 

 will answer our purpose here. 



Genus MUS Linn. 



Mus Linnaeus, Syst. Nat., X ed., I, 1758, p. 59. Type Mus musculus 

 Linn. 



Front teeth (incisors) two in each jaw; no premolars; three molars 

 or grinding teeth in upper jaw having tubercles on crowns arranged in 



three longitudinal rows ; incisors narrow and without groove ; 



crown of anterior molar larger than both the others combined; 



third molar very small ; edges of anteorbital foramen forming 

 Upper Molars, a nearly perpendicular slit in front of zygoma; tail long and 

 usually nearly naked and scaly; hind feet with five developed toes; fore 

 feet with four developed toes and a rudimentary pollex with short nail. 

 Originally this genus included the Old World Rats and Mice, which have 

 been introduced in the United States, but is now restricted to a single 

 species, the House Mouse, the Rats having been separated and placed 

 in the genus Epimys. 



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

 i-i 0-0 0-0 3-3 



Mus musculus Linn. 

 House Mouse. 

 {Mus\ musculus Linnaeus, Syst. Nat., X ed., I, 1758, p. 62. 



Type locality — Sweden. 



Distribution — Old World species, now generally distributed through- 

 out the settled portions of the United States, about buildings and 

 in cultivated fields and occasionally in unsettled districts. 



