masticophis flagelliformis

from The Collaborative International Dictionary of English v.0.48

Coachwhip snake \Coach"whip` snake"\ (Zool.)
   A large, slender, harmless snake of the southern United
   States ({Masticophis flagelliformis}).
   [1913 Webster]

   Note: Its long and tapering tail has the scales so arranged
         and colored as to give it a braided appearance, whence
         the name.
         [1913 Webster]