On August 3, Pieter did make these great pictures of some edible Agaricus campestris in our garden. They are also called field or meadow mushroom. They are closely related to the cultivated white button mushrooms or Agaricus bisporus. You CAN eat them, no problem whatsoever. They eventually will open up as they grow older, just as the white button mushrooms will do. Or any brown variety of course.
Modern Mushroom Growing by P.J.C. Vedder (my husband Pieter...)