This is a weird looking brachiopod called Pugnax sp. from the Junkerberg Formation (Devonian, Eifelian stage) near Rommersheim, Germany. To me it's odd because it has a very wide sulcus that has it's own plications. Overall the shell is kind of boxy but has a triangular shape in profile.
This genera is first found in the Devonian and survived up until the end Permian extinction. I have specimens of this genera from the Pennsylvanian of Texas but I've not had the chance to blog about it yet.
Thanks go out to Nils for sending me the specimen.