unknown

[Gen. et sp. indet.]

Ordovician or Silurian. Pleistocene erratic boulder. Central Poland. Black, shelly object + nicely ornamented mould, which may or may not belong to the same fossil.

As always - sorry for the unpreped state + poor photos.

So far, I considered: Leptaena fragment, trilobite sclerite, or Catenipora in side view. Any ideas?