Placenticeras planum Hyatt 1903
Late Cretaceous
Eagle Sandstone
Billings MT USA.

67mm ammonite with colorful mother of pearly shell.

Ammonite. Cephalopod.

Placenticeras is a genus of ammonite that lived across the Late Cretaceous and right up to the end.  It has been found at numerous localities in the North America as well as Europe, India, Iran, and Papua, New Guinea.

Here’s a fine ammonite with refractor-effect mother-of-pearl showing on one side and nice sutures showing on the other. It’s even better-looking in person.