tion of the Oligocène genus Sieblosia, A detailed descripadapted from Hagen’s description of the type specimen, is given because no material of this remarkable enigmatic genus is available. Possible mistakes in the drawings given by Hagen are discussed and figured. The nearest relative known is the genus Oligolestes Schm., also of Oligocene deposits. Similarities and differences between both genera are pointed out. Oligolestes is ranked among the Sieblosiidae, which family is removed from the Anisozygoptera and included in the Lestinoidea (sensu Fraser). Hypotheses about functional adaptations in the wings of this group and other dragonflies are developed. Illustrations show the complete possible wing venation of Sieblosia (schematized) and the true wing nervation of Oligolestes.