Anthracoceras
Ammonite
Late Mississippian
Bear Gulch Limestone
Fergus County, Montana, USA

15mm goniatite showing evidence of soft anatomy on 37mm matrix. Rare.

Cephalopod.

Anthracoceras is a goniatite ammonite genus that lived during the Carboniferous Period.  It’s known from sites in North America and Europe.  The preservation allowed by the Bear Gulch Limestone sometimes reveals parts of the soft anatomy while other sites would leave you looking at just a broken shell.

An interesting alternative preservation of a goniatite you might want represented in your collection.