These white mushrooms cam up after days of rain. The white rounded cap (photo 1), covers pale pink gills (photos 2 & 3). Photo 4 provides context. It is growing on nutrient poor, white sand. These may be specimens of the same Sp as at Sighting 017 which was also growing in this vicinity.
One of the photos shows a clear ring of tissue around one stem – which would be the remnant of the membrane that covered the gills before the cap expanded. That and the pink gills point to the genus Agaricus. It must be one of the species in which the spores turn dark brown late in the development of the mushroom.