Abundant Emsian （Lower Devonian） cono- donts are yielded in Bahe section, Tiandeng coun- ty, Guangxi. Eleven Polygnathus taxa are identi- fied, from which one is unnamed and two are inde- terminate, including Polygnathus inversus , Pol. gilberti, Pol. laticostatus, Pol. lingui formis bul- tyncki , Pol. nothoperbonus, Pol. perbonus, Pol. serotinus, Pol. vigierei, and can be assigned asthe nothoperbonus, inversus and serotinus zones in ascending order. According to the oral and aboral characters and stratigraphic distributions, it is suggested in Bahe section that Pol. serotinus de-rives from Pol. vigierei by the elevation of the outer platform margin, deepening and broadening of the outer adcarinal trough, and by becoming more and more parallel to the anterior platform margins. What＇s more, the inversion of basal cav- ity in Polygnathus firstly commences during the evolutionary stage of Pol. nothoperbonus.
