Closed pileus up to 6 x 4 mm, cream coloured, at centre with yellow-brown to ochre-brown granular-flocculose veil; expanded pileus up to 10 (-15) mm wide. Lamellae almost free to free, whitish, grey to blackish; L = c. 20, l = 0-1. Stipe 30-60 x 0.5-1 mm, whitish, vitreous, sparsely pubescent from setulae.
Spores [40,1,1] 9.7-13.8 x 6.7-8.8 x 5.8-8.2 µm, av. L = 11.0-12.0, av. B = 7.3-8.0 µm, Q = 1.35-1.70, av. Q = 1.50-1.55, ellipsoid to ovoid in front view; germ pore strongly eccentric, c. 2 µm wide. Basidia 11-28 x 8-12 µm, 4-spored. Pseudoparaphyses 5-7 per basidium. Cheilocystidia globose, up to 35 µm in diam. to subglobose, the latter up to 40 x 35 µm. Pleurocystidia absent. Pileocystidia 40-90 (-110) x 10-20 µm, lageniform to nettle hair-shaped with cylindrical to slightly tapering, 3-7 µm wide neck and subcapitate to capitate, up to 12 (-15) µm wide apex. Sclerocystidia absent. Velar spherocysts on pileipellis up to 40 µm in diam., rather strong incrusted, often brown. Clamp-connections not seen.
Coprinus curtus is the only species, which has both spherocysts and (sub)capitate pileocystidia. Other species with velar spherocysts on the pileus (except C. marculentus) have pileocystidia with tapering or cylindrical neck without enlarged apex. Coprinus marculentus has differently shaped (hexagonal) spores.
Romagnesi (1941: 126) described C. curtus Kalchbr. f. macrosporus which has somewhat larger spores (10.7-14.7 x 6.5-8.5 µm). M. Lange & A.H. Smith raised this taxon to the rank of species, naming it C. heptemerus (see under that name).