On the type of Coprinus arachnoideus VanDeBogart
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Original description
Coprinus arachnoideus Van De Bogart in Mycotaxon 4: 238. 1976 (The genus Coprinus in Western North America, part 1: sect. Coprinus).
Holotype: North America: state Washington, Seattle, Mar. 1950, F. Van De Bogart 2161 (WTU).

Pileus at first long glandiform, then conic, then campanulate. Prior to expansion 1.8 cm in length and after expansion 3.0 cm in breadth. Pale creamy white at first, soon becoming pale grey-tan to pale creamy grey-tan. Small shallow plicate striations developing as pileus becomes mature. Surface covered at first with a thin wispy fibrillar universal veil that soon breaks up into small scattered irregular patches. Flesh thin and membranous. Stipe hollow, slender, nearly equal but with a slight swelling at the base and slightly narrowed towards the apex, 4.0-6.5 cm x 2.2-3.6 mm. White, opaque, glabrous except for a few small bits of loosely interwoven fibrillose tomentum scattered around the stipe base. Flesh thin and fragile. Lamellae linear, some short lamellae present, 0.6-1.6 cm x 5.0 mm, broadly adnate, crowded, with no appreciable spreading by the limited amount of plicate striation, white, then soot black. Autolyses complete. Odor and taste not observed.
Spores ovate in dorsal view and ellipsoidal in lateral view, flattened, 11.2-13.8 x 7.5-8.8 x 6.2-7.3 µm, suprahilar depression present on most, apiculus small, visible only in lateral view, germ pore eccentric, 1.3-1.8 µm in diameter. Color en masse black, microscopically deep purple-brown in 3% KOH. Wall smooth. Basidia dimorphic, short clavate and 22.0-25.0 x 12.0 µm, long clavate and 30.2-35.2 x 13.0-15.0 µm, all four-spored. Cheilocystidia globose to ellipsoidal, 12.5 µm in diameter to 50.0 x 39.0 µm, mostly with a short pedicel 3.0-6.0 µm long, hyaline, smooth. Pleurocystidia ellipsoidal, 77.0-98.2 x 42.5-58.0 um, pedicellate, pedicels 1.0-12.0 µm long, hyaline, smooth. No other cystidia present. Pileal surface a cutis of more or less radially oriented hyphae, the surface cells two or three times as long in the radial orientation as in any other direction. Universal veil of fibrillar nature, interwoven. Individual elements occurring in long chains of more or less cylindrical cells, hyaline, thin walled, some swollen and somewhat constricted at the septations, others not swollen. Some cells irregular, the chains composed of cells of varied sizes all along its length, some of them branched or anastomosed. The same types of chains of cells found on both the pileal surface and at the stipe base. Universal veil cell size 16.2-12.5 x 2.5-33.8 µm. Clamp-connections absent.
Habitat. Terrestrial, on prepared soil mixes in a greenhouse, solitary.

This species differs from most of the other species of section Coprinus in its lack of any web or thread of hyphae inside the lumen of the stipe, its lack of refractive plugs in the sterigmata, its adnate lamellae and its lack of clamp-connections. C. arachnoideus differs from C. alnivorus microscopically. It resembles some of the species of section Lanatuli in its ubiversal veil characters and in the possession of pleurocystidia.

Observations
Spores [20,1,1] 10.6-15.0 x 6.7-9.1 µm, ellipsoid or ovoid with rounded base and apex, and strongly eccentric, c. 1.6 µm wide germ pore, dark red-brown; Q = 1.45-1.65, av. Q = 1.60; av. L = 13.3, av. B = 8.3 µm. Basidia 20-30 x 11-13 µm, 4-spored, surrounded by 5-7 pseudoparaphyses. Pleurocystidia 90-125 x 30-50(-60) µm, obovoid, ellipsoid or subcylindric. Cheilocystidia 40-100 x 25-40 µm, (sub)globose to ellipsoid or subcylindric. Veil made up of hyphoid, thin-walled elements, 40-60 x 14-25 µm, usually somewhat inflated and constricted at septa; terminal cells ellipsoid or clavate. Clamp-connections sparse, not distinct.

Notes: The material in this collection is fairly good, existing of 4 basidiocarps and a part. Clamp-connections were described by Van De Bogart as being absent but we found some in the veil.
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