Source : Webster's Revised Unabridged Dictionary (1913)

Flying squirrel \Fly"ing squir"rel\ (? or ?). (Zo["o]l.)
   One of a group of squirrels, of the genera {Pteromus} and
   {Sciuropterus}, having parachute-like folds of skin extending
   from the fore to the hind legs, which enable them to make
   very long leaps.

   Note: The species of Pteromys are large, with bushy tails,
         and inhabit southern Asia and the East Indies; those of
         Sciuropterus are smaller, with flat tails, and inhabit
         the northern parts of Europe, Asia, and America. The
         American species {(Sciuropterus volucella)} is also
         called Assapan. The Australian flying squrrels, or
         flying phalangers, are marsupials. See {Flying
         phalanger} (above).