Psathyrella are also known as "brittlestems", which is very apt as this mushroom literally fell apart on being handled if not careful. Both cap and stipe broke very easily.
Nichol genus key
Spores very dk brown/purple/black
Cap scaly? n
Cap pleated? n
Gills decurrent? n
Stipe ring? n
Cap ylw-brwn? n
Small, conical? n
Brittle stalk, stipe silver/white? Yes!
Cap 2-6cm, bell-shaped becoming flattened, pale ochreous-brown drying near white
Stem 40-80x4-8mm, white, fragile, hollow
Flesh: white. thin
Smell: not distinctive
Gills: adnate, crowded, greyish lilcac darkening to dark brown
Spores: 6-8x3.5-4um, elliptical/ovate, print dark brown/purple