glabellum

from The Collaborative International Dictionary of English v.0.48

Glabellum \Gla*bel"lum\, n.; pl. {Glabella}. [NL. See
   {Glabella}.] (Zool.)
   The median, convex lobe of the head of a trilobite. See
   {Trilobite}.
   [1913 Webster]