EN
Two new mayfly species, Cheirolgisca ningchengensis gen. and sp. nov. and Olgisca angusticubitis sp. nov. from the Middle Jurassic Jiulongshan Formation of Ningcheng County, Inner Mongolia, NE China are described herein, both attributed to the extant family, Siphlonuridae. The Mesozoic mayfly imagoes have been rarely reported, thus the new material with well-preserved gonostyles provides valuable evolutionary evidence on this family.