38 



MAMMALOGY. 



and apparently maintains its specific characters in such a variety of 

 climates and under such various circumstances, as to present quite 

 appreciable difficulties to the theories of some of the earlier naturalists 

 in relation to climatal influence. 

 Mr. Peale remarks : 



" The common brown or Norway Eat was observed at the Hawaiian 

 and some other islands in the Pacific Ocean, where it has been intro- 

 duced by commercial intercourse with Europe and America. It was 

 observed to retain its partiality for the habitations of mankind, with 

 all its burrowing and destructive habits, but does not seem to multiply 

 so rapidly as it does in countries where the cereal grains are grown or 

 dealt with as matters of commerce. We did not find it on islands 

 uninhabited by mankind." 



The collection of specimens of this common animal, especially in 

 unusual or little visited localities, ought, by no means, to be neglected 

 when opportunities are presented to voyagers and naturalists. Such 

 collections furnish materials for investigations involving very impor- 

 tant zoological principles and doctrines, and are the most reliable 

 sources of information and demonstration. 



2. Mtjs exulans, Peale. 



31us exulans, Peale, Zool. Exp. Exp. Mamm. p. 47 (1st ed. 1848). 



Mus penicillatus, Gould, Proc. Zool. Soc. London, 1842, p. 12? 



Mas jacohiai vel dccumanoidcs, Waterh. Voy. Beagle, Mamm. p. 34 (1810) ? 



Atlas, Mammalogy, Plate IV, Fig. 1. Adult. 



This is a species of Rat, named by Mr. Peale as above, and so much 

 resembling the common Mus decwnanus in all characters, except size, 

 that we have not thought a detailed or technical description necessary, 

 especially as our figure correctly represents it. It is mentioned by the 

 naturalists of the Expedition as inhabiting the Coral Islands and others 

 of the Pacific Ocean, and in addition to its smaller size, is represented 

 as possessing quite different habits from the common Rat. No techni- 

 cal description is given by Mr. Peale, but his observations on this 

 animal are of much interest, and are as follows : 



" Nearly all the Coral Islands visited by the Expedition, were found 

 to be inhabited by Rats, so like the common brown or Norway Rat 



