I found this in a newly ploughed field near Cheltenham in Gloucestershire. I have no idea if it is of any interest or not but looks quite odd. The coin next to it is £1 for size comparison.
It is part of an ammonite.
With most of these, the way they spiral round means that the ribbed outside of one part leaves a ribbed impression on the next-outer spiral.
The particular genus...
The specimen doesn't really include enough to say, or for me to speculate.
But there are folks on NaturePlus with better day-to-day knowledge who might have an idea.
Good find, quite a large piece of the outer section of an ammonite.
Looks like a fresh break at the end of the specimen so there could be more in the area.
It's hard to put a name to a partial specimen but it look very similar to a Stephanoceras humphriesianum?