A new species and new generic synonymy in the family Vietnamellidae (Insecta: Ephemeroptera) from mid-Cretaceous Burmese amber with notes on ancient dispersal across East Gondwana

The monophyletic mayfly family Vietnamellidae has been introduced for a few extant species from the Indomalayan Realm. All these species belong to the genus <i>Vietnamella</i> and have been described in adult and larval stages. Recently, the fossil genus <i>Burmella</i> was established for male and female imagines of two new species from mid-Cretaceous Burmese amber and assigned to the family Vietnamellidae. In this contribution, we describe another species in the genus <i>Burmella</i>, namely <i>B. inconspicua</i> <b>sp. nov.</b> based on a female imago. It clearly differs from the previously described female of <i>B. clypeata</i> by the absence of an extension of the clypeus and by a different venation in fore and hind wings. Furthermore, we discuss here in detail the systematic position of the monotypic species <i>Burmaheptagenia zhouchangfai</i> originally assigned to the family Heptageniidae and provide arguments for the synonymy of the genus <i>Burmaheptagenia</i> syn. nov. with <i>Burmella</i>. We propose the new combination <i>Burmella zhouchangfai</i> <b>comb. nov.</b>, together with a modified generic diagnosis for the genus <i>Burmella</i> and discuss the adult characters of Vietnamellidae. Systematic placement of the genus <i>Burmella</i> in Vietnamellidae and the phylogenetic position of this family within Ephemerelloidea are discussed. We also consider the geographic origin of the family and the role of the Cretaceous Burma Terrane migration as a key event that facilitated the transfer of Gondwanan fauna to Asia.