Holotype (PDD 27069); Isotype (Herb. HK. ZT 68/381): 'Track to St. Arnaud Range., Lake Rotoiti, Prov. Nelson, N.Z.; leg. Horak, 5.V.1968'. - Herb. HK. ZT 67/118: 'Kowai Bush, Mt. Grey, Prov. Canterbury, N.Z.; leg. Horak, 20.IX.1967'. - Herb. HK. ZT 68/276: Near Base Camp N.Z.F.S., Cave Stream, Craigieburn Range., Prov. Canterbury, N.Z.; leg. Horak, 19.IV.1968'. - Herb. HK. ZT 68/671: 'Maruia, Prov. Nelson, N.Z'; leg. McNabb, 6.V.1968'. - PDD 8393: 'Secotium leucocephalum Massee; near Summit of Haast Pass, Prov. Otago, N.Z.; leg. Moore, det. Cunningham, I.1938'. - PDD 26300: 'Secotium; Lake Rotoiti, Prov. Nelson, N.Z.; leg. Brook, 25.IV.1965'.

Gastrocarp 20-50 x 10-35 mm, globose or depressed globose, margin broadly enrolled and dehiscent from the stipe, (date) brown or yellow-brown, densely covered with small ochraceous patches from the veil, veil remnants becoming larger towards the margin, viscid when wet, otherwise dry, innate-fibrillose, slightly hygrophanous. Peridium 1-4 mm thick, cartilaginous. Gleba loculate or sublamelliform, cells 1-5 mm diam., rust brown, tramal plates well developed, whitish, branching from the inner layer of the peridium into the gleba, dehiscent from upper parts of the stipe, never exposed but covered with whitish-yellow, fibrillose hyphae of the 'cortina'. Stipe 15-60 x 6-15(-20) mm, cylindric, attenuated towards the apex or equal, turbinate-bulbous or marginate at the base, margin of base dentate because of conspicuous, ochraceous or ferruginous remnants of the veil, remnants occasionally even forming a membranous volva, dry, fibrillose, yellowish-ochraceous. Context yellowish-brownish, watery. Odor and taste not distinctive. Chemical reaction on peridium: KOH or HCl - negative.
Spores 10-12 x 6-8 µm, ovate or broadly elliptic, minutely verrucose, warts coarser around the apex, without distinct perisporium, mostly bilaterally symmetric. Basidia 25-35 x 6-8 µm, 4-spored. Cystidia absent. Epicutis consisting of cylindric, repent, slightly gelatinised hyphae forming a cutis, membranes thin-walled, encrusted with brown pigment. Septae with clamp connections.

On ground under Nothofagus fusca, N. menziesii and N. cliffortioides. New Zealand.

Gastrocarpio 20-50 x 10-35 mm, hemisphaerico vel ovoideo, depresso-globoso, marginem versus incurbato, e brunneo luteobrunneo, squamis aurantiacis ferrugineisve e velo obtecto, viscido vel sicco, innato-fibrilloso. Gleba lacunosa vel sublamelliformi, stipite dehiscente, velo alboluteo obtecto numquam exposito, ferruginea. Stipite 15-60 x 6-15(-20) mm, cylindraceo vel apicem versus attenuato, ad basim distincte marginato-bulboso, dense squamis aurantiacis vel volva membranacea concolorique instructis, luteobrunneo, sicco, fibrilloso, pleno. Odore saporeque nullo. Sporis 10-12 x 6-8 µm, ovatis vel ellipticis, minute verrucosis, ferrugineis. Basidiis 4-sporigeris. Cystidiis nullis. Epicute ex hyphis cylindraceis, vix gelatinosis cutem formantibus, pigmento brunneo incrustatis, septis fibulatis. Ad terram in silvis nothofagineis. Novazelandia.

Microscopically this species resembles Th. epiphaeum Hk.; both taxa possess small, minute, verrucose and elliptic spores but they are easily separated by their macroscopical characters. Th. napivelatum Hk. represents one of the most common species of that genus in New Zealand. - There is no doubt that Th. napivelatum Hk. from New Zealand is related to Th. mustella Moser and Th. carneoroseum Hk., hitherto known only from beech forests in South America. The three species have in common the marginate stipe, the colour of the gastrocarp and the minutely warted, ovate spores.

Holotypus (PDD 27069): 'Lake Rotoiti, N.Z.; leg. Horak, 5.V.1968'.