Closed pileus up to 5 x 4 mm, sometimes up to 7 mm high, date-brown, umbra-brown (Mu. 7.5 YR 3/6, K. & W. 5E5), paler towards margin, up to c. 7 (-10) mm in diam. when expanded. Lamellae free, narrow, white to blackish; L= 8-13. l= 0-1. Stipe 15-50 x 0.25-0.75 mm, whitish, vitreous, sparsely pubescent.
  Spores [60,3,3] 8.0-11.0 x 5.0-6.4 µm, av. L= 9.1-9.7, av. B= 5.5-5.8 µm, Q= 1.50-1.80, av. Q= 1.65-1.70, ellipsoid to ovoid; germ pore eccentric, c. 1.6 µm wide. Basidia 16-32 x 8.5-10 µm, 4-spored. Pseudoparaphyses 4-6 per basidium. Cheilocystidia 13-25 x 12-18 µm, (sub)globose to ovoid. Pleurocystidia absent. Pileocystidia 30-95 x 8-21 µm, lageniform with tapering neck, 2-5 µm wide at apex. Sclerocystidia present. Clamp-connections present.

Habitat

  Solitary or subgregarious on horse dung. Common.

Remarks

  Coprinus heterosetulosus is easily recognizable because of its usually numerous sclerocystidia, its habitat on dung and its spores with an eccentric germ pore. It has very small fruit-bodies, like C. pellucidus, but that species has no sclerocystidia and has spores with a central germ pore. The colour of C. heterosetulosus is a rather dark brown in fresh, young specimens.