Closed pileus up to 8 x 6 mm, pale brown, at centre somewhat darker, up to 15 mm in diam. when expanded. Lamellae narrowly adnate, white to blackish; L = 16-24, l= 0-1. Stipe 20-40 x 0.5-1 mm, whitish, vitreous, sparsely pubescent.
Spores [60,2,2] 9.2-13.3 x 5.3-6.7 µm, av. L= 10.8-11.7, av. B= 5.8-6.3 µm, Q= 1.70-2.05, av. Q= 1.85-1.95, oblong to elongate ellipsoid or ovoid; germ pore eccentric, c. 1.5 µm wide. Basidia 18-36 x 8.5-11 µm, 4-spored. Pseudoparaphyses not noted. Cheilocystidia ellipsoid to oblong, some of them (sub)cylindrical or slightly utriform, 30-55 x 15-23 µm, but also pileocystidia-like cheilocystidia sparsely present on the edge of the lamellae. Pleurocystidia absent. Pileocystidia 60-90 (-120) x 10-22 µm, lageniform with (sub)cylindrical neck and equal, sometimes somewhat broadened, 8-14 µm wide apex. Sclerocystidia absent. Clamp-connections probably present.
The main character of this species is the rather broad, cylindrical neck of the pileocystidia. They resemble the pileocystidia of C. disseminatus very much, but are distinctly shorter.
Coprinus subdisseminatus has been found only twice in the Netherlands, both times on sticks. According to the original description the species also grows on wet, black mull and other vegetable matter in wet places.