Omphalina ectypoides

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)

Mature fruiting body with an omphalos, never bell-shaped or conical. Never even flat except when very young.
Usually more colorful than the other choices
Often growing in or among a lichen

Omphalina     Genus Fruiting body grey, brown, or lighter shades of those two colors, sometimes ochre or pale orange Stem fleshy; concolorous with cap, and of the same texture Gills decurrent

Links from Look-alikes Chrysomphalina     Genus Fruiting body with yellowish or orange coloration, especially on the gills Stem fleshy; concolorous with cap, and of the same texture Gills decurrent

Omphalina ectypoides     (Peck) H. E. Bigelow