The Collaborative International Dictionary of English v.0.48:

Megacephalic \Meg`a*ce*phal"ic\
   (m[e^]g`[.a]*s[-e]*f[a^]l"[i^]k), Megacephalous
\Meg`a*ceph"a*lous\ (m[e^]g`[.a]*s[e^]f"[.a]*l[u^]s), a. [Mega-
   + Gr. kefalh` head.] (Biol.)
   Large headed; -- applied to animals, and to plants when they
   have large flower heads.
   [1913 Webster]