A delicate inkcap with very thin cap that becomes translucent as it matures. Initially, the caps are ovoid and covered in a furry white veil.  The cap changes to convex and flat, and finally turns upwards with an inrolled margin. The white veil fragments are shed.  Gills whitish, then blackening and deliquescing; stem whitish, floccose.

There are several similar species

Photograph from top down, in side view and from underneath to show gills and full length of stipe.  Note habitat and substrate.

Woodchips, compost heaps, vegetable refuse, horse dung, etc.

Early autumn to mid winter.

Widespread and fairly frequent in Britain.

Fairly frequent in Leicestershire and Rutland.

https://www.first-nature.com/fungi/coprinopsis-lagopus.php