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.
The last representatives of the Muridae are confined to Australasia and the Philippines, and constitute the sub-family Hydromyinae, characterized by the very general presence of only two pairs of molars in each jaw.
The Upper Oligocene Cricetodon in Europe and Eumys in America are the earliest known forerunners of the cricetine Muridae; while at the same time primitive beavers appear in the form of Steneofiber, to be succeeded in the European Pleistocene by the gigantic Trogontherium.
Lemmus), belonging to the mouse tribe, or Muridae, and nearly related, especially in the structure of its cheek-teeth, to the voles.
For the distinctive characteristics of the family Muridae and the genus Mus, to which true rats and true mice alike belong, see Rodentia.
Although the British representatives of this group should undoubtedly retain their vernacular designations of water-rat and short-tailed field-mouse, the term "vole" is one of great convenience in zoology as a general one for all the members of the group. Systematically voles are classed in the mammalian order Rodentia, in which they constitute the typical section of the subfamily Microtinae in the Muridae, or mouse-group. As a group, voles are characterized by being more heavily built than rats and mice, and by their less brisk movements.
The Rodentia have a wider geographical range than any other order of terrestrial mammals, being, as already mentioned, represented by numerous members of the mouse-tribe (Muridae) even in Australasia.