Two New Species and First Stage Associations for Two Other Species of the Cincticostella nigra (Uéno, 1928) Complex (Ephemeroptera, Ephemerellidae) from Yunnan, China, with Discussion About Cincticostella Allen, 1971 Species Complexes Based on Winged

Four species of the <i>Cincticostella nigra</i> (Uéno, 1928) complex (Ephemeroptera, Ephemerellidae) from Yunnan, China are described based on egg chorionic structure and nymph and winged stages, including <i>C. wangi</i> Selvakumar Martynov & Subramanian, 2021, <i>C. funki</i> Martynov, Selvakumar, Palatov & Vasanth, 2021, and two new species, viz., <i>Cincticostella xiazhi</i> Zi, Li & Jacobus, <b>sp. nov.</b> and <i>Cincticostella yushui</i> Zi, Li & Jacobus, <b>sp. nov.</b> The egg and winged stages of <i>C. wangi</i> and <i>C. funki</i> are described for the first time. Eggs of all four species have macroreliefs generally similar to one another and to other species in the genus. Male imagoes have preliminary species-level differences in the median convex lobes of the styliger plate and the shapes of the penis lobes themselves. The current delimitation of four complexes of <i>Cincticostella</i> is briefly discussed based on the nymph and winged stages. A partial phylogenetic reconstruction of <i>Cincticostella</i> based on the COI gene illustrates relations of representatives of the four complexes on the one hand and distinct delimitation of <i>C. wangi</i>, <i>C. funki</i>, <i>C. xiazhi</i>, <b>sp. nov.</b>, and <i>C. yushui</i>, <b>sp. nov.</b> on the other. An updated list of species of <i>Cincticostella</i> is provided, along with a new key for the identification of nymphs of the <i>C. nigra</i> complex, which are distinguished primarily based on features of the abdominal terga, mesothoracic projections, tarsal claws, labrum emargination, setation of femora, and body color.