Closed pileus ellipsoid, cylindrical-ellipsoid or subglobose, up to 25 mm high and 15 mm wide, completely covered with white, powdery veil, centre of pileus often cream-coloured to pale ochraceous; veil at margin, particularly in early stages, somewhat more hairy-floccose; expanded pileus up to 40 mm wide, conical or convex, finally applanate with slightly deflexed margin. Lamellae, L = 24-38, l = 1-3(-5), free, white at first, then grey to black. Stipe up to 100 x 4 mm, attenuate upwards, white, towards base up to 6 mm wide, and often brownish with white velar flocks. Smell absent. Spore print very dark chocolate brown, almost black.
Spores [180,9,7] 12.2-19.0 x 10.8-15.6 x 7.5-9 µm, Q = 1.05-1.40, av. Q = 1.10-1.30, av. L = 14.5-17.3, av. B = 11.9-13.9 µm, lentiform, limoniform in frontal view, ellipsoid in side view, dark red-brown, with central to slightly eccentric germ pore. Basidia 25-40 x 12-16 µm, 4-spored, surrounded by 5-7(-8) pseudoparaphyses. Pleurocystidia 50-150 x 25-60 µm, vesiculose, ellipsoid, or subcylindric. Cheilocystidia 30-80 x 15-50 µm, similar to pleurocystidia. Veil made up of up to 100 µm wide, (sub)globose elements. Clamp-connections present.
Coprinus niveus can be easily recognized by the very large spores which are limoniform in frontal view and ellipsoid in side-view, borne on 4-spored basidia. Generally, Coprinus niveus has medium-sized basidiocarps, but in collection Uljé 1183 they are only a few mm. In this collection the spores are also somewhat smaller than in normal C. niveus, viz. 12.2-16.0 x 10.8-13.0 µm, Q = 1.15-1.40, av. Q = 1.25, av. L = 14.6, av. B = 12.0 µm. In the description given above, these measurements are included.
Coprinus latisporus was characterized by Orton (1972: 160) in the original description as follows: 'It could be mistaken for a small C. niveus, but differs from that species in its differently shaped spores, which are less elongate in side-view and more rounded and less regular in face-view, and the smaller fruitbody with less copious veil.' He also depicted a small specimen. The type material consists of one, small, probably still very young basidiocarp with spores 13.0-15.4 x 11.2-14.5 µm, which appear for the greater part immature and very pale to dark brown; truly ripe, i.e. black, spores have not been found. The difference in shape, as noted by Orton, was not found (fig. 1b) but only a slight difference in length, which can be explained by the still immature state. Furthermore, small specimens of Coprinus niveus may occur, as pointed out above, and the difference in veil covering does not appear to be a significant difference to us. It is likely that Orton described a small, still immature specimen of C. niveus.