White/offwhite mushroomy fungus.
I'm not certain the small ones are smaller versions of the large ones, but it's possible. The upper large one was very flat on top, the lower one somewhat domed. The ribs are the underside of the upper large one. The small ones were very spherical. It's been very rainy here lately, which is likely why these sprouted in my back yard. Appeared dry, not slimy or moist, though I did not touch them. The small ones were very textured, but the large ones appeared smooth.