What is a shelly plate found in the terminal chambers of ammonite shells. Some authors consider them to be jaws; others, opercula called?
aptychus — A shelly plate found in the terminal chambers of ammonite shells. Some authors consider them to be jaws; others, opercula. (Webster's 1913.)
Sources
- Webster's Unabridged Dictionary, 1913 edition (public domain, via GCIDE / Project Gutenberg).
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