FAMILY MURIDA, 719 
is also erected, and by a very sudden movement he is enabled to strike, leaving the loosened 
spines in the body of his opponent. From their peculiar structure, they penetrate at every 
movement until they reach a vital part. Hence it is rarely attacked, although the hunters 
easily kill it by a blow on its nose. The Indians esteem its flesh, which resembles young 
pork very highly. It dwells in hollow trees, or in caves under rocks, and is said to bring forth 
two at a litter in April or May. The spines are employed extensively by the Indians, after 
having been dyed of various colors, to form ornaments for their dresses. 
The Porcupine is found as far north as 67°. It is found in all the Northern States; in 
New-York, Pennsylvania, the northern parts of Virginia, Kentucky, and through the western 
regions to the Rocky Mountains. In this State, more particularly in the northern and western 
counties, they are quite numerous. The first name given in accordance with the binary sys- 
tem, is that proposed by Brisson, and by the law of priority it must be restored. 
FAMILY VI. MURIDAZ. 
Clavicles robust, and fully developed. Fur not uniformly soft, but without spines or rigid 
hairs. Molars usually six above and six beneath, but various. Some of the genera are 
provided with cheek pouches. Tail cylindrical, usually naked or sparsely haired, of 
various lengths. Mostly composed of small burrowing animals. 
This family comprises numerous species, which are confessedly difficult to group together 
by common characters. They may, however, be divided into two great sections, characterised 
by the presence or absence of cheek pouches. Under those with cheek pouches, we arrange 
the genera Geomys and Diplostoma. 'The other division embraces the genera Mus, Arvicola, 
Sigmodon, Neotoma, Georychus, and Aplodontia. The field for discovery in this family is still 
far from being exhausted. The representatives of only three genera are found in this State. 
GENUS MUS. Linneus. 
Molars six above and six beneath, with tuberculous summits. Tail scaly, nearly naked, 
longer or nearly as long as the body. Ears usually naked or slightly furred. 
Oss. Three of the species have been introduced. 
THE BROWN RAT.—(Introduced.) 
Mus DECUMANUS. 
Mus decumanus. PAttas. 
Brown Rat. Penn. Arct. Zool. Vol. 1, p. 130. 
Common Brown or Norway Rat. Gopman, Am. Nat. Hist. Vol. 2, p. 78. a 
Brown Rat. Ricuarpson, F. B. A. Vol. 1, p. 141. Emmons, Mass. Report, 1840, p. 63 
Characteristics. Grayish brown above, tinged with yellow; beneath whitish. Tail not 
quite as long as the body, and with 180 rings. _ Length 19 - 20 inches. 
