latin names: Parasola leiocephala, Parasola plicatilis
These are parasola species mushrooms, and they're some of the most underrated mushrooms in my opinion. They're awesome; tiny, transparent, ghostly little things. Two parasola species are pictued in this post, and they're ones that i've gotten severely mixed up in the past, though i think i've got it figured out now.
The larger one is Parasola plicatilis, a.k.a. the "Pleated Inkcap". It grows in wet grass and leaf litter, and can grow barely up to your ankles. It sprouts overnight when it rains, and disintegrates by late afternoon the next day.
The smaller one (seriously it is SO small) is something i've always enjoyed finding when walking through wet grass. I previously believed it to be the Pleated Inkcap but new research suggests that its wayyy too small for that. I think it's parasola leiocephala, and i've affectionately nicknamed it the Umbrella Mushroom. So called because it grows overnight when it rains and is just about the same size as a blade of grass. It's like a blade of grass is growing itself an umbrella. Similar to plicatilis, it also disintegrates under the weight of its cap by late afternoon.
Some much better pictures of these can be found online, and once you know what they look like I implore you to begin scanning the ground when you walk through wet grass, because you're likely to see a little transparent, ghostly mushroom peeking through the grass.