Amphisbaena

Webster's Dictionary

(1): (n.) A fabled serpent with a head at each end, moving either way.

(2): (n.) A genus of harmless lizards, serpentlike in form, without legs, and with both ends so much alike that they appear to have a head at each, and ability to move either way. See Illustration in Appendix.

The Nuttall Encyclopedia

A genus of limbless lizards; a serpent fabled to have two heads and to be able to move backward or forward.