AptychusAp"ty*chus\, n. [NL., fr. Gr. 'a priv. + ?, ?, fold.] (Zo["o]l.) A shelly plate found in the terminal chambers of ammonite shells. Some authors consider them to be jaws; others, opercula.
Dictionary.com presents 366 FAQs, incorporating some of the frequently asked questions from the past with newer queries.