Mycologist alert

My long-suffering friends are all too familiar with my habit of spotting a bit of foliage (which they probably didn't even notice) and then stopping abruptly to examine, photograph, and discuss it at length. The latest example: I spotted this mushroom growing on a decaying willow stump along one of my favorite one-lane roads. Can anyone identify it? It's 2.5 inches across and 3.5 inches high. The gills are separate from the stem, which doesn't have a collar. I'm making a spore print.