The Collaborative International Dictionary
Anaptychus
Anaptychus \An*ap"ty*chus\, n.; pl. Anaptichi. [NL., fr. Gr. ? unfolding; ? back + ? to fold.] (Paleon.) One of a pair of shelly plates found in some cephalopods, as the ammonites.
Wiktionary
anaptychus
n. (context paleontology English) One of a pair of shelly plates found in some cephalopods, such as the ammonites.