364 



BULLETIN 5(3, UNITED STATES NATIONAL MUSEUM, 



Hind foot (fig. 59) 6-tuberculate ; tubercles paired. Pollex with a 

 short nail in phice of a claw. No cheek-pouches. Tail long, nearly 

 naked, with rings of overlapping scales. Vertebrffi: C 7, D 13, L 6, 

 S 4, C 26-32. {Flower and Lydeller.) 



This genus is represented l)y four very distinct species on the Mexi- 

 can Boundary Line. 



KEY TO THE SPECIES OP MUS FOUND ON THE BOUNDARY LINE. 



a. Sizo large. Length more than 300 mm. 



h. Tail ixhoui as long as head and Ixxly, dnsk}^ above and pale below; color of body gray- 



isli-brown above, soiled grayish-white below. Mns nonrfficiis (p. 364). 



/)/). Tail eonsideiably longer than head and body, and dii.sky all round. 



c. Color reddish-brown above, and wliite l>elow; pelage mixed with spines. 



Mils alexandrinus (p. 360). 



cc. Color blue-black, darker on the back, mor(> slaty on the belly. .Mus rattus (p. 365). 



aa. Size small. Length less than 200 mm Mus musculus (p. 366). 



Fig. 50.— Mus musculus. a, Forefoot; h, TTindfoot; r, Far; d, Tail. 



MUS NORVEGICUS Erxleben. 



NORWAY RAT; BROWN RAT; WHARF RAT. 



[Mus] norvegicus Erxleben, Syst. Regni Anim., I, 1777, p. 318 (original description). — 



Elliot, Field Col. Mus., Zool. Ser., IV, 1904, p. 164 (Mam. Mid. Am.). 

 Mus norvegicus, Rehn, Proc. Biol. See. Washington, XIII, p. 167, Oct. 31, 1900. — 



Miller and Rehn, Proc. Best, Soc. Nat. Hist., XXX, No. 1, Dec. 27, 1901, p, 



65 (Sj'st. Results Study N. Am. Mam. to close of 1900). 

 Mus decumanus Pallas, Glires, 1778, p. 91, No. 40. 

 [Mus] decumanus, Elliot, Field Col. Mus., Zool. Ser., II, 1901, p. 117 (Synop. Mam. 



N.Am.). 



Type-locality. — Norway. 



Geographical range. — Cities and larger settlements. 



Description. — Normal coloration grayish-brown above, dirty gray- 

 ish-white below; upper surface more or less lined with l^lack hairs, 

 especially in the vertebral area, wliich is also grayest. Feet soiled 

 grayish-white. Tail dusky above and whitish below, though not dis- 

 tinctly bicolored. Tail usually shorter than head and body, and so 

 sparsely short-haired as to show the annuli plainly. 



RemarTcs. — This cosmopolitan species is found sparingly in the 

 cities of the Southwest. In Arizona and New Mexico the white 

 domestic variety is most common, though brown ones were occa- 



