Unknown from Penn Dixie

[Misha]

I found this on a plate of trilobites and pelycopods, it is around 8mm in diameter and I have no Idea about what it could be.

Any help is appreciated,

Thank you.

[Greg.Wood]

I see an E. rana pygidium next to the cross section of a coral

[Misha]

39 minutes ago, Greg.Wood said:

I see an E. rana pygidium next to the cross section of a coral

Yes there is an Eldredgeops pygidium but the thing it is on is like shell and not very similar to coral, it even has some clear

 growth rings on it.

[Jeffrey P]

Orbiculoidea brachiopod?

[Misha]

18 minutes ago, Jeffrey P said:

Orbiculoidea brachiopod?

This was my first thought, but then what could that small bump at the top be?

[Greg.Wood]

If it’s more oval than circular it could be Lingula

[TqB]

8 hours ago, Misha said:

This was my first thought, but then what could that small bump at the top be?

Looks like Orbiculoidea, they have bumps. Yours looks as if it might be broken to show the inside of the ventral valve, like this one of mine from the Mississippian where the dorsal valve has conveniently come away.

 

Interior ventral:

 

With dorsal in place over it: