The Collaborative International Dictionary of English v.0.48:

Turtlehead \Tur"tle*head`\ (t[^u]r"t'l-h[e^]d`), 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.
   [1913 Webster]