Pileus up to 25 x 20 mm and ellipsoid to cylindric-ellipsoid when still closed, up to c. 35 mm wide when expanded, white to isabelline or pale ochraceous, becoming grey-brown with isabelline to ochre centre, radially sulcate up to centre; finally plano-concave with revolute margin, with veil in primordia smooth, mat, pure white to greyish, covering pileus entirely, but soon breaking up into scattered small, flocculose, fibrillose squamules with tips sometimes recurving and brownish. Lamellae, L = c. 45-60, l = 3-7, free, narrow, rather crowded, first white, soon greyish brown to blackish. Stipe 50-100 x 2-5 mm, whitish, somewhat tapering towards apex, up to 8 mm wide at clavate to bulbous base, hollow, hairy flocculose, and more densely so towards lower part, becoming glabrous with age. Context rather firm and somewhat tough.
  Spores [100,5,5] 7.8-11.7 x 6.4-8.2 x 5.3-7.2 µm; Q = 1.20-1.50, av. Q = 1.35-1.40; av. L = 9.2-10.4, av. B = 6.5-7.6, av. W = 5.7-6.9 µm, very broadly fusiform or rhomboid-ellipsoid, sometimes somewhat amygdaliform, with (sub)conical or rounded base and slightly truncate apex, and central, c. 1.5-1.8 µm wide germ pore, dark red-brown. Basidia 18-38 x 8-10 µm, 4-spored, surrounded by 3-6 pseudoparaphyses. Pleurocystidia 70-150 x 25-60 µm, subglobose, ellipsoid to oblong, utriform or subcylindric. Cheilocystidia 50-140 x 25-50 µm, utriform, oblong or subcylindric. Pileipellis a cutis, made up of more or less parallel, repent hyphae, consisting of cylindrical to fusiform elements, 40-100 x 3-25 µm. Veil made up of elongate, sausage-like elements, 25-150 x 10-40 µm, often inflated, constricted at septa; terminal elements ellipsoid, oblong or fusiform. Clamp-connections present.

Habitat & distribution

  Growing solitary or subfasciculate on wood, often in wounds of living, deciduous trees. Very rare, in the Netherlands only known from a few localities in the western and central parts of the country. In Europe under the name C. extinctorius furthermore recorded from England, France, Germany, Spain, Italy, and Turkey.

Remarks

  Macroscopically Coprinus spelaiophilus is a C. domesticus-like fungus, but it belongs to subsection Lanatuli on account of the structure of the veil, which consists of chains of inflated, thin-walled hyphoid elements. It can be recognized by the C. domesticus-like appearance, the initially white to isabelline colours of the pileus, the fairly firm context, the 'Lanatuli'-like structure of the veil, the very broad, fusiform, 8-11 µm long spores and the habitat, viz. often growing in cavities of the trunk of living, deciduous trees (Populus, Ulmus, Aesculus, and Fagus).
  It is difficult to understand that the name Coprinus extinctorius (Bull.) Fr. has been attached to the present species as Bulliard (1790: pl. 437, 1792/93: 408) described Agaricus extinctorius as very fugacious and growing on dung ('sur les fumiers'). Therefore C. extinctorius sensu auct. europ. p.p. maj. is described here as a new species.