GERBIL, or GERBILLE  , the name of a group of small, elegant, large-eyed, jumping rodents typified by the North African Gerbillus aegyptiacus (or gerbillus), and forming a special sub-family, Gerbillinae, of the rat tribe or Muridae . They are found over the desert districts of both Asia and Africa, and are classed in the genera Gerbillus (or Patera), Pachyuromys, Meriones, Psammomys and Rhombomys, with further divisions into sub-genera . They have elongated hind-limbs and long hairy tails; and progress by leaps, in the same manner as jerboas, from which they differ in having five hind-toes . The cheek-teeth have trans-verse plates of enamel on the crowns; the number of such plates diminishing from three in the first tooth to one or one and a half in the third . The upper incisor teeth are generally marked by grooves . Gerbils are inhabitants of open sandy plains, where they dwell in burrows furnished with numerous exits, and containing large grass-lined chambers . The Indian G. indicus produces at least a dozen young at a birth . All are more or less completely nocturnal .