They are Clitocybe nuda. You, like so many others, you are fooled into thinking the gills are free, but if you look closely, yes the ends of the gills dip down into a trench, but looking with a hand lens, or if you have good eyes, you can still see a bit of the gill as a tag remnant attached to the stipe. This is quite common in many of these mushrooms when the cap expands out flat, or even turn up a bit at the edges. That is because some of these genera grow new cells from the center of the cap above the stipe instead of growing along the outer edge.
If you have any doubts at all, one way to tell if the gills are “free” from the stem or attached, try pulling the stem off the cap - turn the cap upside down in one hand and do a pull up with a slight twist of the stipe. If it has “free” gills, the entire stipe will come loose, leaving a relatively smooth “ball & socket” joint in the cap and one the stem with the gills nearly undisturbed. If the gills were attached, then the top of the stem will break, shred, or come loose with very ragged edges and often the fibers of the stipe will peel back or come off too. It is all how the mushroom developed from a primordia (tiny growth bump) on the underground hypha, and is one developmental character that helps taxonomists categorize and separate the various groups of genera from each other.