60 ZOOLOGY. 



MUS DECUMANUS, Pallas. 



Brown Rat; Norway Rat. 



BAIRD, Gen Report Mammals, 1857, 438. 



Introduced by the ships touching at San Diego, Monterey, San Francisco, and the ports on 

 the Columbia river, the Norway rat has probably been for many years a resident of California 

 and Oregon. It is now, at least, unpleasantly abundant at all these places, and seems to have 

 been ready to sanction by its presence every step of progress made by the Anglo-American in 

 the occupation of the interior. 



At San Francisco, California, and Portland, Oregon, the brown rat swarms about the wharves 

 and cellars in apparently as great numbers as in the Atlantic cities. 



The old residents of San Francisco, that is to say, those who have been there five years, say, 

 that formerly that port of entry was occupied by a colony of white rats, of which no specimens 

 have, to my knowledge, been preserved. It was probably nothing more than a white variety of 

 the brown rat which is now so common there. As most persons are aware, the house mouse (Hus 

 musculus) and Norway rat are both prone to exhibit this variation of color, which is hereditary, 

 and if the white stock can be isolated, forms a permanent variety. 



I could not learn that the black rat (Mus rattus} has ever been a resident of the Pacific coast. 

 The testimony in this case is, however, purely negative. 



MUS. MUSCULUS, Linn. 



TheHouse Mouse. 



BAIRD, Gen. Rep. 



The little house mouse, like most other luxuries of civilization, is now enjoyed in all the 

 habitations of whites on the Pacific coast. In the mansions of the Digger Indians probably few 

 could be found, for the double reason that this fastidious animal would hardly find such quarters 

 agreeable, and that the omnivorous habits of the Indians would imperil their existence. The 

 mouse seems to have arrived with the first ships touching at the western ports, as the colonists 

 say they have &quot; always&quot; been abundant. 



HESPEROMYS GAMBELII, B a i r d . 



California Mouse. 



BAIRD, Gen. Rep. Mammals, 1857, 464. 



SP. CH. Very similar to H. leucopus in size and proportions. Feet perhaps shorter. Ears larger. Tail generally less than 

 head and body, sometimes a very little longer. Above, yellowish brown, much mixed with dusky, but without a distinct 

 broad wash of darker on the back. The entire outside of the fore leg below the shoulder white ? 



One specimen of this species was collected on Klamath lake, 0. T. 



ARVICOLA TOWNSENDII, Bachman. 



Oregon Ground Mouse. 



Arvicola toumtendii, BACHMAN, J. A. N. Sc. Phila. VIII, 1839, 60. 



AUD. & BACH., N. Am. Quad. Ill, 1853, 209 ; pi. cxliv. fig. 1. 

 BAIRD, Gen. Rep. Mammals, 1857, 527. 



SP. CH. Very large, (head and body 5 J inches.) Ears large; two-thirds as long as hind foot; well furred. Tail, in 

 cluding the hairs, rather less than half the head and body ; the tail vertebra twice the length of hind foot. Thumb claw 

 conspicuous. Toes long ; one-third the whole foot. Fur measuring a little over one-third of an inch, with a slight gloss. 



