Proostracum \Pro*["o]s"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}.
[1913 Webster]