442 U. Ss. P. R. R. EXP. AND SURVEYS—ZOOLOGY—GENERAL REPORT. 
The tail is rounded, and tapers gently to a truncate tip; it is nearly two inches longer than 
the head and body, and has 237 annulations of scales. 
The fur of this species is composed of two kinds of hairs, one external, coarse and rigid, the 
other shorter, finer, and intermediate. 
The color of this species above is much like that of the Norway rat, being of a yellowish 
brown, slightly tinged with reddish on the sides of the back, and grayer on the sides. A 
predominance of black hairs on the back imparts here a dusky appearance. The entire under 
parts, with the upper surfaces of the feet, are quite pure yellowish white, to the very roots of 
the hairs. The ears and entire tail all round are dusky. 
The only specimens of this species I have seen from America are those entered below, of 
which one in alcohol (2811) has served as the basis of the present description. A specimen 
received from Niirnberg, and probably caught there, has the long tail, but is not so white 
beneath. It has 240 annuli on the tail. 
This species is smaller than the common rat, and the tail, instead of being shorter than the 
head and body, is much longer. The under parts and feet are nearly pure yellowish white. 
The ears are larger. 
The Mus leucogaster of Pictet, has the tail not quite so long, and the hairs soft, of equal 
length, and without any intermixture of long stiff bristly ones. 
The roof rat, so called from its fondness for inhabiting the thatched roofs of houses, is origi- 
nally from Egypt and Nubia, from which it was taken to Italy and Spain. It is quite probable 
that the early Spanish discoverers and conquerors carried it to America in their vessels, and 
thus introduced it on the continent long before the brown or even the black rat. It is now very 
common in Brazil and some parts of Mexico; and if, as I have little doubt, the ‘‘ light-colored 
variety of the black rat’’ of Audubon and Bachman be this species, it is abundant in Georgia 
and South Carolina, (according to Major Leconte, more so formerly than now,) and doubtless 
also in Florida. It is said by Mr. Bridger to be very common about Tarboro’, North Carolina ; 
further north I have no knowledge of it. 
I have myself verified very few of the quotations at the head of this article, and am unable to 
say why authors have retained the name of J/. ¢tectorum in preference to the apparently older 
one of Geoffroy. The Mus americanus of some authors is, in every probability, this same species, 
which, after its very early introduction into America, (probably in the fifteenth century,) became 
naturalized, and, at an early date, was described by Seba as Mus americanus, probably from 
South American specimens. The roof rat was not formally separated or distinguished as a 
European species for nearly a hundred years after, and it is not difficult to understand that an 
animal so conspicuously different from the Old World rats known at that time, and brought 
from America, should have been described as new. The name of americanus has really priority 
over either tectorum or alexandrinus, but is objectionable as conveying an erroneous idea of native 
locality. 
