Wildlife Spotting

This is a fungus that I found on a fallen dead log. The mushroom cap was white, getting darker in color towards the center. The very center was a quite dark brown. It looked as if there were rings of color around the center, gradually getting whiter and whiter. There were many mushrooms in the same place, as shown in the first picture. There is an indent in the center of the mushroom cap. The mushroom cap is circular so there is no longest/widest point. The cap is about 5 cm long/wide on average. For all of the mushrooms, the sizes vary. The underside is smooth.