All the dormice are small rodents (although many of them are double the size of the British species), of arboreal habits, and for the most part of squirrel-like appearance; some of their most distinctive features being internal.
The beavers (Castoridae) are restricted to the northern hemisphere, whereas the dormice (Gliridae) and the mole-rats (Spalacidae) are exclusively Old World forms, the latter only entering the north of Africa, in which continent the former are largely developed.
Other allied African genera are Steatomys and Lophuromys, which include several species of small mouse-like rodents, with the habits of dormice generally, though some burrow in cornfields.
In their arboreal life, and the habit of sitting up on their hind-legs with their food grasped in the fore-paws, dormice are like squirrels, from which they differ in being completely nocturnal.
Squirrels and dormice are very destructive to the nut crop, as they not only take for present consumption but for a store for future supply.
The Nannosciurinae, or second sub-family of Sciuridae, are represented only by the pigmy squirrels (Nannosciurus), characterized by their very short-crowned molars (which approximate to those of dormice in structure) and small premolars, of which the first upper pair is often deciduous, while the upper molars have only three oblique ridges.
The intestine (except in the dormice or Gliridae) has a large caecum.