Source : Webster's Revised Unabridged Dictionary (1913)

Dextral \Dex"tral\, a. [From {Dexter}.]
   Right, as opposed to sinistral, or left.

   {Dextral shell} (Zo["o]l.), a spiral shell the whorls of
      which turn from left right, or like the hands of a watch
      when the apex of the spire is toward the eye of the
      observer.