Brachiopod or Horn Coral

[Nate c]

A friend of mine found an interesting fossil a Keifer Creek in St.Louis Missouri. He was unsure of what it was but I assumed that it was a horn coral or perhaps a vertically split brachiopod. I am not the best at identifying fossils so I was hoping someone on the forum with more experience could take a look at it. The fossil being referred to is in the middle of the stone.

[Fossildude19]

Cropped and brightened:

 

    

[Nate c]

Thanks for editing the photo @Fossildude19

[Peat Burns]

I'm inclined to think rugose (horn) coral in cross section, even though it's more oval than most.  Might be some form of deformation.

[Rockwood]

Looks like a tabulate colony to me. It would be sort of a side view of the corallites.

[Tidgy's Dad]

Flattened / squashed rugose 'horn' coral for me.