Your ammonite probably is...

Imitoceras

The shell of Imitoceras was almost spherical, with a rounded venter and a deep, hidden umbilicus. Imitoceras had a goniatitic suture and lived from the Upper Devonian to Lower Carboniferous.

Image by James St. John, CC BY 2.0, https://commons.wikimedia.org/wiki/File:Imitoceras_rotatorium_fossil_ammonoid_(Mississippian;_Seymour,_Indiana,_USA)_(17184552397).jpg