What is the anterior prolongation of the guard of the phragmocone of belemnites and allied fossil cephalopods, whether horny or calcareous. See Illust. of Phragmocone called?
proostracum — The anterior prolongation of the guard of the phragmocone of belemnites and allied fossil cephalopods, whether horny or calcareous. See Illust. of Phragmocone. (Webster's 1913.)
Sources
- Webster's Unabridged Dictionary, 1913 edition (public domain, via GCIDE / Project Gutenberg).
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- Published: 2026-07-17T00:00:00-07:00 · Modified: 2026-07-17T00:00:00-07:00