资料来源 : Webster's Revised Unabridged Dictionary (1913)

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}.