Panaeolus semiovatus

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 black, very dark brown, purplish black, or dark purplish brown, but not fitting the Gomphidiaceae
Gills usually light grey, becoming black from spores only when very mature

Panaeolus     Genus Gills with a mottled appearance, since the spores mature (and hence darken the gills) in clumps, not evenly Cap usually rounded, like half of an egg, and colored some shade(s) of gray and/or brown Growing on manure or compost

Links from Look-alikes Psathyrella     Genus Cap up to 2" across; glabrous; often very fragile; some shade (or shades) of brown or gray; usually hygrophanous; sometimes wrinkled (as in the photo) Spore print usually dark purplish brown With a universal veil that usually persists as a few small, white fragments on the stem, cap, and hanging from the cap margin On very well-decayed wood or enriched soil, sometimes in lawns, sometimes in large troops Cap usually almost flat at maturity

Panaeolus semiovatus     (Sowerby: Fries) S. Lundell & Nannfeldt