The holotype of Protomycena is a single fruit body without any associated structures , preserved in a piece of clear light yellow polished amber approximately 4 @.@ 5 – 2 @.@ 5 cm ( 1 @.@ 77 – 0 @.@ 98 in ) wide . The pileus is 5 mm ( 0 @.@ 2 in ) in diameter and have a convex shape , sporting a raised central region ( an umbo ) . The pale flesh appear yellowish in the amber , and is smooth and glossy , changing to striate and slightly translucent towards the margin . The pileus margin is striated and slightly flared . The gills on the underside of the pileus are broadly attached ( adnate ) to the top of the stipe , and distantly spaced — between six and eight gills extend completely from the pileus margin to the stipe . These full @-@ length gills are anastomosed with lamellulae ( short gills which do not reach the edge of the stipe from the pileus margin ) of varying lengths . The pileus is centered on the curved stipe , which is smooth and cylindrical , measuring 0 @.@ 75 mm ( 0 @.@ 030 in ) thick by 10 mm ( 0 @.@ 39 in ) long . The stipe lack a ring and rhizoids . The mushroom is preserved with a small liquid and gas @-@ filled bubble , possibly originating from the mushroom itself , which indicate the amber to be very solid and well @-@ sealed .