Definify.com

Webster 1913 Edition

‖

Noun.

[NL., fr. Gr.

ἀ

priv. + [GREEK], [GREEK], fold.]

(Zool.)

A shelly plate found in the terminal chambers of ammonite shells. Some authors consider them to be jaws; others, opercula.

aptychus ‎(plural aptychi)

A marine fossil consisting of a hard anatomical structure like a curved shelly plate, once part of the body of an ammonite.