Your ammonite probably is...

Amaltheus

Amaltheus is identified by its involute shell and rope-like keel along its venter. It had S-shaped radial ribs. Amaltheus would have been a good swimmer. It lived in the Lower Jurassic and is found worldwide.

CC0, https://commons.wikimedia.org/wiki/File:Amaltheus_margaritatus_-_Naturhistorisches_Museum,_Braunschweig,_Germany_-_DSC05124.JPG