Your ammonite probably is...
Oxynoticeras
Suture: Ammonitic
Oxynoticeras had a very narrow, involute shell and a sharp keel. Its siphuncle ran close to its venter. It had no radial ribs. Oxynoticeras lived in the Lower Jurassic.
Image by Kevin Walsh from Bicester, England; CC BY 2.0; https://commons.wikimedia.org/wiki/File:Ammonite_Oxynoticeras_oxynotum.jpg
