Your ammonite probably is...
Quenstedtoceras
Quenstedtoceras had many sickle-shaped radial ribs, some of which began only halfway across the shell wall. Its early camerae were narrow, but then it grew considerably wider. There was no ventral keel, but there were chevron-shaped patterns on the venter. Quenstedtoceras lived from the Middle to Upper Jurassic and was sexually dimorphic.
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