Now that we picked the mushroom we can see easier under the cap, don't need to make us comfortable down in the dirt just to take a look. Hey maybe a mirror could be used, gonna make a note.
Hymenium could take a couple of forms, gills, sponge, teeth, internal (of the puffballs), gel, and some species' cap forms a cup and grow the spores on the inner surface of it.
Gills come in wide variety. Not just their spacing is important, but how they join to the stem, if at all. Sometimes they have to be cut in half to see exactly how they attach.
Quite curiously the delicious Chanterelles have false gills, ridged on the lower side of the cup and running on the stipe. A type of mushroom looks very similar to these species, it has true gills however.