Zoologically, there is no distinction between mice and rats; these names being employed respectively for most or all of the smaller and larger "mouselike" and "rat-like" representatives of the Muridae, whether they belong to the genus Mus or not.
Of the Muridae there are several genera and a large number of species, some of them evidently importations from the Old World.
HAMSTER, a European mammal of the order Rodentia, scientifically known as Cricetus frumentarius (or C. cicetus), and belonging to the mouse tribe, Muridae, in which it typifies the sub-family Cricetinae.
On account of certain structural peculiarities, the rats of Madagascar, which have a dentition like that of the cricetine Muridae, are separated as a distinct family, Nesomyidae.
The characteristics of the Muridae are those of the Myoidea generally, as given above under the heading of the Spalacidae.