Your ammonite probably is...
Placenticeras
Suture: Ammonitic
Placenticeras was a very narrow ammonite with a very involute shell. It had a very small umbilicus that was shallow. Most (if not all) of the shell was completely smooth. It had one of the most complex sutures of an cephalopod. The venter was flat but very narrow. Placenticeras lived in the Upper Cretaceous.
