440 U. S. P. R. R. EXP. AND SURVEYS—ZOOLOGY—GENERAL REPORT. 
reflection ; this passes very insensibly on the lower parts into a dark plumbeous ; the tail of the 
same plumbeous cast ; the feet tinged with brown. 
In a specimen from Sweden, on the other hand, the upper parts are not quite so sooty ; the 
plumbeous of the belly is of a grayer shade; the line of separation on the sides quite distinct. 
This coloration is seen also in specimens from San Diego. 
This rat, once better known than the brown rat, is rapidly diminishing since the introduction 
into its haunts of the latter species. Its original locality is not well known, as from time 
immemorial it has been the ‘“‘house rat’’ of Europe, and of the warmer parts of the world 
generally. According to Erxleben, it was brought to the New World about the year 1544, and 
spread to such a degree as to have been apparently more abundant there than in the Old World. 
Indeed, many authors have insisted that the species came originally from America, but there is 
no foundation for such a supposition zoologically ; and it is spoken of familiarly by such authors 
as Gesner,-Aldrovandus, Seba, and others, at as early a date as 1550. ‘ 
The black rat is not mentioned by Burmeister among the animals of Brazil, where the Mus 
decumanus, leucogaster, and tectorum, are abundant. 
In their article on the black rat, Audubon and Bachman refer to a white bellied variety of 
the black rat, from the Edisto river, in South Carolina. This is most probably the Mus tectorum, 
described in the next article. 
I have satisfied myself, from actual examination of the skin and skull of the original Mus 
americanus of DeKay, that it is really a Mus, and of the present species. 
List of specimens. 
Catalogue | Corresponding | Sex & Locality. When collected. Whence obtained. Nature of 
number. | No. of skull. | age. specimen. 
390, 4|nsnccwe eo oeeel een e ss Sweden =-2 See ae ooo 1843 Swedish Academy ---------.- Skin.--.- 
VATA. | eoeecbensan ate |ersesu Halifax t Nis ten o2 ae a] See eee DriJe BGilpise. 222s == CG Ears 
Sf ioe (shee ee es a Se ee Montreal) | Caneaects == a= a6 aoe aan T. Broome....22.-ssanesaece =-dos-2 st 
839 UGE = Skeets Tamaqua, (Pe one nome oleae eee Wis Patten s2se-s=>Sece- =e 2s008—-c— 
12 O21 2 2 Saas Koxburg,, «Panes sovoewas ae ee oe Bere 6. HS Baird: 222 seen sesee= =-d0- cance 
16032 | See oe oe Q | San Diego, Cal.---.-....- Jan. 22, 1856 | Dr. J. F. Hammond, U. 8. A--|--do_..... 
UCI Ce) Ee a aoe oe Ree dossseees sees Seu: a) Se ceee doucessdlsenascs-5en~ G0... 5. cocci] eee 
1605 suilesee oe Gal aes 0-2 a ie ae ay ae dott 5. hae ee nS eon 
514 1649 Q Humboldt Bay, Cale. --|-os2cte-2---- Lt. Trowbridge, U. S. A.....- | sd Oscnmere 
1 Body, 7; tail, 7}. 
? Body, 8}; tail, 6%. 
