Pro*os"tra*cum (?), n.; pl. Proostraca (#). [NL., fr. Gr. before + shell of a testacean.] Zool.
The anterior prolongation of the guard of the phragmocone of belemnites and allied fossil cephalopods, whether horny or calcareous. See Illust. of Phragmocone.
© Webster 1913.