Proostracum

Pro*["o]s"tra*cum\, n.; pl. Pro["o]straca. [NL., fr. Gr. ? before + ? shell of a testacean.] (Zo["o]l.) The anterior prolongation of the guard of the phragmocone of belemnites and allied fossil cephalopods, whether horny or calcareous. See Illust. of Phragmocone.