Source : Webster's Revised Unabridged Dictionary (1913)

Turtlehead \Tur"tle*head`\, n. (Bot.)
   An American perennial herb ({Chelone glabra}) having white
   flowers shaped like the head of a turtle. Called also
   {snakehead}, {shell flower}, and {balmony}.

Source : WordNet®

Chelone glabra
     n : showy perennial of marshlands of eastern and central North
         America having waxy lanceolate leaves and flower with
         lower part creamy white and upper parts pale pink to deep
         purple [syn: {shellflower}, {shell-flower}, {turtlehead},
          {snakehead}, {snake-head}]