A small grassland fungus, hemispherical or umbonate, dingy grey-brown in colour, lighter in centre; gills greyish and broadly attached; stipe grey. 

other Mycena in grassland

microscope

This is a difficult species to identify with certainty unless it has been microscopically examined from a specimen.  Expert verification prior to submssion to NatureSpot is recommended.  Also photograph from top down, in side view and from underneath to show gills and full length of stipe.  Note habitat and substrate.

In short grass.

Summer and autumn.

Widespread and fairly frequent in Britain.

Fairly frequent in Leicestershire and Rutland.

https://www.first-nature.com/fungi/mycena-aetites.php