Your ammonite probably is...
Bactrites
Suture: Nautiloid
Bactrites is one of the most primitive ammonites, as it did not even have any coiling whatsoever. It was so primitive it often is actually listed as a nautiloid. It lived from the Devonian to the Permian.
Image by Ghedoghedo, CC-BY SA 3.0, https://commons.wikimedia.org/wiki/File:Bactrites_gracilis_Naturalis.JPG
