Generic short diagnoses:
Immersed discomycetes in twigs or leaves of deciduous trees or shrubs, opening by teeth to expose greyish to buffish or yellowish discs; with clavate, filiform or sigmoid spores.
The picture originates from the MycoKey 2.0 DVD. Here you will also find a larger picture along with a detailed generic description, references and an interactive, synoptical key to genera.