spongia dura

from The Collaborative International Dictionary of English v.0.48

Hardhead \Hard"head`\ (-h[e^]d`), n.
   1. Clash or collision of heads in contest. --Dryden.
      [1913 Webster]

   2. (Zool.)
      (a) The menhaden. See {Menhaden}. [Local, U. S.]
      (b) Block's gurnard ({Trigla gurnardus}) of Europe.
      (c) A California salmon; the steelhead.
      (d) The gray whale. See {Gray whale}, under {Gray}.
      (e) A coarse American commercial sponge ({Spongia dura}).
          [1913 Webster] hardheaded