Pileus up to 17 x 9 mm when still closed, up to 25 mm when expanded, subglobose to oblong, densely covered with mealy to hairy floccose veil, first greyish white, then pale grey to mouse grey. Lamellae free, white to black. Stipe 15-50(-60) x 1-3 mm, whitish; base somewhat clavate. Smell strong, >narcotic=.
  Spores 6.3-9.1 x 4.5-5.6 µm, Q = 1.25-1.80, av. Q = 1.40-1.60, av. L = 7.1-7.8 µm, av. B = 4.9-5.0 µm, ellipsoid or ovoid, with rounded base and apex, dark red-brown; germ pore central, 1.2-1.4 µm wide; episporium weakly developed, smooth, up to 1 µm wide in places. Basidia 10-24 x 6-9 µm, 3-spored, sometimes partly 2- or 4-spored, surrounded by 3-5(-6) pseudoparaphyses. Pleurocystidia 50-100 x 22-50 µm, utriform, oblong or subcylindric. Cheilocystidia 30-70 x 15-45 µm, (sub)globose, ellipsoid, oblong, utriform or subcylindric. Pileipellis made up hyphoid elements. Elements of veil up to 75 µm wide, made up of globose, warty cells connected with narrow, diverticulate hyphae. Clamp-connections not found.

Habitat & distribution

  Very rare, on dung of horse and cow. Known from England and The Netherlands.

Remarks

  The 3-spored basidia is the most important character to recognize Coprinus trisporus.