Lepiota naucinoides

This is a key to gilled mushrooms, that is, mushrooms having a definite cap with a fertile surface consisting of gills. The fruiting body usually also has a stem, although that may be lateral or absent (usually, then, the mushroom is growing from wood). You can use this key to identify mushrooms that you find.

Fruiting body containing fibers (usually in the stalk)

Spore print "light-colored": white or buff, sometimes tinged with pink or tan. Greenish and (except for the Russulales) yellow spore prints also go here
Stalk fibrous, not fracturing like a piece of chalk

Gills free
Annulus usually present (on some small species, the partial veil may remain instead as scraps of tissue on the edge of the cap)
Cap often umbonate, often with a concentric design of scales that are an intrinsic part of the cap (not easily peeled off without taking part of the cap with it)
The cap is also usually egg-shaped or completely round (like a globe) at first - - it doesn't start to open until the stem is almost fully grown

Cap can reach more than 2-3" across at maturity
Flesh sometimes changing color if cut or bruised
Ring often thick-edged and can be slid up and down the stalk
If the size of your collection is borderline, try this choice first

Lepiota naucinoides     Peck