 The holotypes of Archaeomarasmius consist of mushrooms and associated basidiospores . Specimen AMNH NJ @-@ 90Y is a nearly complete mushroom , broken off near the base of the stipe ( stem ) . The pileus ( cap ) is up to 6 mm ( 0 @.@ 24 in ) in diameter and has a convex shape sporting an umbo ( a broad raised central region ) . The mushroom is a medium @-@ dark brown color with thin , minutely textured flesh and an incurved margin . The lamellae or gills are distantly spaced , with 12 gills extending fully from the cap edge to the stipe , and lack lamellulae ( short gills which do not reach the stipe from the edge of the pileus ) . The pileus is centered on the stipe , which is 0 @.@ 5 by 2 @.@ 2 mm ( 0 @.@ 020 by 0 @.@ 087 in ) long and is broken off above the base . The stipe lacks a veil and is smooth and cylindrical . The top of the pileus is exposed on a fracture plain , and to prevent oxidation , the area was coated in a fine layer of synthetic resin , which also resulted in slightly improved visibility of the mushroom . 
