Mycena corticola

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

None of the special features distinguishing the other white-spored genera:
Gills not free, as in the Lepiotas and Amanitas
Basidia not extra-long, as in the Hygrophoraceae
Spores smooth, except for Lentinellus

Growing on trees or dead wood, leaves, or sticks, or organic debris, often in moss

Shaped like a “normal mushroom”
Small and fragile to medium-sized, except for one large, grey-capped species

Fruiting body small: cap up to 1 1/4" across (and most clearly smaller than that)

Cap bell-shaped, conical, or either of those with an umbo; margin never incurved; usually some shade of grey or brown, but purplish in one unusually large species.
Stem thin; either very fragile or very tough
Some species have a colored juice that can be squeezed out of the end of the stem
No rhizomorphs

Cap some shade(s) of brown, grey, black and white, with no other colors

Mycena corticola     (Fries) S. F. Gray