MURIDA—GENERAL CONSIDERATIONS. 3 
be added. The elaboration of the genera which is to follow renders this, 
however, in a measure superfluous. We may here only allude, then, to the 
broad general distinctions—the Murine being animals which include, and, in 
all their members, recall, the familiar house-rat and house-mouse, of lithe and 
supple form, quick in movement, having large bright eyes, pointed mobile 
snout, prominent ears, and lengthened limbs and tail; all of which points are 
contrasted with the squat and heavy shape, the slower action, very small eyes, 
blunt snout, inconspicuous ears, and shortened members of the Arvicoline. 
There is also a striking difference in the ensemble of the dentition of the two 
groups—the compressed and comparatively small incisors of Murine as 
against the large broad fore teeth of the Arvicoline—the small, tubercular, and 
rooted molars of the former, in contrast with the great, flat-topped, prismatic, 
and continually-growing grinders of the latter, in which it would seem that 
the perfection of rodent dentition is attained. 
In their geographical distribution in America, moreover, the two groups, 
though associated to some extent, differ decidedly. The Arvicoline occupy 
the northern half of the hemisphere; they are not known to occur farther 
south than Mexico; they are most numerously represented by individuals in 
high latitudes, while some of them are among the most arctic of mammals. 
The northern limit of the Murine is, perhaps, not exactly known; but they 
do not reach the arctic seas, while they are most abundant in temperate and 
warm climates, and spread over Central and South as well as most parts 
of North America. ; 
In the following table, prepared with much care, the cranial and dental 
characters of Muride, as represented in North America, are exhibited. The 
points brought out, it will be observed, are of varying grade, from those that 
run through both subfamilies down to those that particularize the subgenera, 
and serve to indicate the several degrees of relationship which subsist between 
the respective groups. 
