Which animal has flaps of featherless skin between their front and back legs?

There are actually 60 species of gliding mammals which have flaps of skin that extend between their forelegs and hind legs.

Flying squirrels (43 species), colugos (also known as flying lemurs), scaly-tailed flying squirrels (which are African rodents, and not related to actual squirrels - 7 species but only 6 have membranes), and the ten species of Australian or New Guinean marsupial flying possums and gliders all have this feature.