Source : Webster's Revised Unabridged Dictionary (1913)

Lissencephala \Lis`sen*ceph"a*la\
   (l[i^]s`s[e^]n*s[e^]f"[.a]*l[.a]), n. pl. [NL., fr. Gr.
   lisso`s smooth + 'egke`falos the brain.] (Zo["o]l.)
   A general name for all those placental mammals that have a
   brain with few or no cerebral convolutions, as Rodentia,
   Insectivora, etc.