364 



BULLETIN 56, UNITED STATES NATIONAL MUSEUM. 



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

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

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

 S 4, C 26-32. ( Flower and Lyd( hlcer. I 



This genus is represented by four very distinct species on the Mexi- 

 can Boundary Line. 



KEY TO Till". SPECIES OF MIS POUND <>\ THE BOUNDARY LINE. 



a. Size large. Length more than 300 nun. 



b. Tail about as long as head and body, dusky above and pale below; color of body gray- 

 ish-brown above, soiled grayish-white below Musnorvt gicus (p. 364). 



bh. Tail considerably longer than head and body, and dusky all round. 



r. Color reddish-brown above, and while below; pelage mixed with spines. 



M us alexandrinus (p. 366). 



cc. Color blue-black, darker on the back, more slaty on the belly. .MusrcMus (p. 365). 



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



Pig. 59. Mrs musculus. a, Forefoot; b, Hindfoot; c, Ear; (/.Tail. 



MUS NORVEGICUS Erxleben. 



NORWAY RAT; BROWN RAT; WHARF RAT. 



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



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

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



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



65 (Syst. Results Study X. 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. 



X. 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 black hairs. 

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

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

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

 sparsely short-haired as to show the annuli plainly. 



Remarks. — 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- 



