The Collaborative International Dictionary of English v.0.48:

Shovelhead \Shov"el*head`\, n. (Zool.)
   A shark (Sphryna tiburio) allied to the hammerhead, and
   native of the warmer parts of the Atlantic and Pacific
   oceans; -- called also bonnet shark.
   [1913 Webster]

WordNet (r) 3.0 (2006):

shovelhead
    n 1: small harmless hammerhead having a spade-shaped head;
         abundant in bays and estuaries [syn: shovelhead,
         bonnethead, bonnet shark, Sphyrna tiburo]