I've blogged about Pleurodictyum fossils from the Mahantango Formation before, in this post, but this specimen that I recently found is kind of neat. It's a pair of Pleuordictyum styloporum colonies where there is some detail preserved of the external surface as well as molds of the internal surface.
Here is the anterior view where you can see the rounded, golf ball like mounds. There is a bit of shale still covering the surface of the coral that obscures some of the detail.
This is the posterior view where you can see the internal mold details.
This specimen was collected near Seven Stars, PA from the Mahantango Formation (Devonian, Givetian stage).