The most natural of the genera of Agaricini, but not easily defined by artificial characters. The veil and the gills present the chief marks of distinction. The gills generally become cinnamon-coloured. Very rare or altogether wanting in hot countries, but generally abundant in northern woods. All autumnal. They present a very different appearance in different stages of growth, and in the various stages according as they are moist or dry. It is necessary, therefore, to examine species both in their earlier and later stages. Some Flammula' resemble them, but can scarcely be confounded with them.