438 
U. S. P. R. R. EXP. AND SURVEYS-ZOOLOGY-GENERAL EEPORT. 
MUS DECUMANUS, Pallas. 
Norway Rat — Browu Rat. 
Mus decumanus, Pallas, Glires, 1778, 91. 
Schreber, Saugt. IV, 645 ; tab. clxxviii. 
Keyserling und Blasius, Eur. Wirb. I, 1842, 36. 
DeKay, N. Y. Zool. I, 1842, 80. 
Wagner, Suppl. Scbreb. Ill, 1843,1. 
Burmeister, Thiere Brasiliens, I, 1854, 152. 
Aud. and Bach, N. Am. Quad. II, 1851, 22 ; pi. liv. 
Mus nvrvegicus Erxleben, Syst. An. I, 1776, 381. 
Norway Rat, Pennant, “ British Zoology.” 
Brawn Rat, Pennant, “ Synopsis Quadrup.” 
Sp. Ch. —Tail about three-quarters of an inch shorter than head and body. Tail sparsely hairy, with about two hundred 
annuli. Above, grayish brown, mixed with rusty; grayer on the sides ; beneath, ashy white. Upper surface of the feet 
dirty white. Body, 8 to 10 inches. 
The general peculiarities of head, feet, and tail, are as in M. tectorum. The tail is, however, 
much shorter, being considerably less than the head and body. 
The upper parts are grayish brown, mixed with faint rusty, and darkened by black tipped 
hairs ; the sides are grayer ; the belly and feet a light whitish ash, not so pure as in Neotoma 
or Mus tectorum. The under surface of the tail is a little paler than the upper, which is dusky. 
In the dried skin the annuli of the tail are much less distinct than in M. rattus and tectorum, 
owing to the rather longer hairs. 
Specimens from Oregon appear to have the tail slightly longer than those from the east side 
of the mountains. 
Measurements of a fresh specimen. 
Inches. 
Lines. 
Nose to occiput - _____ 
1 
9 
eve _, _ _________ 
8* 
4 
'-v ^------------- 
ear „ _ r __ __------------ 
root of tail. . _..... _ 
6 
5 
end. of ontstretolled liind loirs „ __ 
7 
Tail from root to en d of vertebrae____ 
5 
9 
6 
9 
naked portion - -- -- --_ 
4 
11 
Ear height posteriorly - - ___ 
9 
anteriorly _____ _ __ 
n 
6 
internally above skull___-_ 
above noteb __ 
8 
width in natural position_-_ 
6* 
8 
Arm from elbow to end of claws _----- 
1 
forefoot to end of e.laws - _-------- 
9 
longest claw _ ^ __ _ _ _ 
1 
Lieg from knee joint to end of claws_ 
2 
6 
1 
4 
bind foot from heel to end of claws ---------- 
1 
6 
longest claws - __ 
2 
Annuli of tail 190 to 200. 
