Am'mon-ite, n.

n. [Lat. cornu Ammonis, horn of Ammon; Lat. Ammon, Gr. Ἄμμων, an appellation of Jupiter, as represented with the horns of a ram. It was originally the name of an Egyptian god, Amoun, i. e., the unknown.] (Geol.) A fossil shell related to the nautilus, and belonging to the tribe of cephalopods, or cuttle-fish. There are many species, and all are extinct, having existed only in the secondary period, or age of reptiles, in geology, when they were exceedingly numerous. They differ from the nautilus in having the margins of the septa very much plaited, and the siphuncle dorsal. Also called serpent-stone and cornu-Ammonis. Dana.

Ammonites obtusus.