SUMMARYBased upon data obtained from a study of the type as well as from Heim's and Singer and Smith's descriptions and from several fresh specimens collected by the author,Psilocybe aztecorumis here emended. This fungus is reported for the first time from four new localities in the states of Mexico and Tlaxcala.Psilocybe bonetiiis reduced to varietal status ofP. aztecorum.Relationships withP. baeocystis, P. quebecensisandP. cyanescensare discussed and a possible evolutionary pathway of these species is proposed. The description ofP. baeocystisis emended.