Summary:
Features include minute, yellowish to brownish fruitbodies on dung usually containing only one ascus with more than 1000 spores.

Microscopic:
spores 5-9 x 3-3.5 microns, elliptic, colorless, a large number of spores in each ascus hard to estimate but exceeding 100; asci reaching a length of 200-260 microns and a width of 150-175 microns, usually one ascus per fruitbody, occasionally 2 or 3, "ellipsoid to ovoid, often slightly constricted near the upper end and with a faint suggestion of a ring"; paraphyses slender, septate, (Seaver), spores 5-7 x 3-4 microns, elliptic; asci up to 230 x 140 microns, ellipsoid, containing about 1000 spores, wall 5-10 microns thick below the annular zone, (Dennis), spores 6-7 x 3-4 microns, 1000-2500 spores per ascus, one ascus per fruitbody; asci clavate, rupturing in upper part when mature, (Hansen), spores 5.0-7.0 x 3.0-4.5 microns, walls about 0.8 microns thick when mature, contents granular and homogeneous, number of spores per ascus variable but with 1-ascus forms may approach 2500; asci 140-260 x 80-175 microns, usually one per fruitbody but sometimes 2 or 3, thick-walled; paraphyses 2 microns wide, very delicate, filiform [thread-like], colorless, sometimes branched, closely surrounding the ascus in a mucilaginous sheath when young, but disappearing when mature; wall of fruitbody made up of several layers of cells, but when mature the innermost layers are crushed and indistinct, the outermost cells, usually in 3-5 layers, "are polygonal, 6-14 microns wide, thick-walled, and contain a dark olive-brown pigment", (Kimbrough)

Notes:
Thelebolus stercoreus is found in BC, CA, and WY, (Larsen, but occurrence not confirmed by either author) and not included in the PezWeb preliminary checklist of North American Pezizales (which emphasizes western species). Collections were examined from BC, AB, ON, PQ, SK, CA, NY, and WY, (Kimbrough for Thelebolus stercoreus group), NY (Seaver), Denmark, Finland, Norway, and Sweden, (Hansen), and the United Kingdom (Dennis).

Synonyms and Alternate Names:
Polyporus volvatus Peck
Ryparobius monascus Mouton
Thelebolus nanus Heimerl.