The Collaborative International Dictionary
Glabellum
Glabellum \Gla*bel"lum\, n.; pl. Glabella. [NL. See Glabella.] (Zo["o]l.) The median, convex lobe of the head of a trilobite. See Trilobite.
Wiktionary
glabellum
n. (context zoology English) The median, convex lobe of the head of a trilobite.