Your ammonite probably is...

Hoploscaphites

Hoploscaphites was similar in morphology to Scaphites, as it had broad, tightly coiled whorls, with the living chamber going out and then hooking back (which probably killed the animal). Hoploscaphites had a much more complex suture than the related Scaphites, which is the only obvious defining feature. Hoploscaphites sometimes had tubercles on its radial ribs and/or a flat venter. It lived in the Upper Cretaceous.