I think this might be Dryad's saddle. I've included a picture of the gills.
ID of fungus is only a guess
On hardwood, probably Ulmus.
Polyporus squamosus is a basidiomycete bracket fungus, with common names including dryad's saddle and pheasant's back mushroom. It has a widespread distribution, being found in North America, Australia, Asia, and Europe, where it causes a white rot in the heartwood of living and dead hardwood trees. The name "dryad's saddle" refers to creatures in Greek mythology called dryads who could conceivably fit and ride on this mushroom, whereas the pheasant's back analogy derives from the pattern...