Abstract: The Cuifengshan Group is generally subdivided into four formations in ascending order: the Xishancun, Xitun, Guijiatun and Xujiachong formations. The rocks of the group are depositionally continuous between the formations and with the underlying Yulongsi Formation. Previously, this lower part of the Cuifengshan Group (the Xishancun and Xitun formations) was placed in the Lower Devonian by many workers based mainly on the age of the underlying and overlying strata. The new thelodont genus Pdrathelodus including four new and one old species must be a transitional type between Thelodus and Turinia. As it is known, Thelodus ranges generaly from Middle Wenlockian to Middle Pridolian, but Turinia is confined to Early and Middle Devonian (Gross, 1967; Turner, 1973, 1991; Talimaa, 1978; Märss, 1986). According to the transitional feature of the new genus, Parathelodus ranges probably from Middle Pridolian to Early Lochkovian. The age of Parathelodus—bearing strata in the lower part of the Cuifengshan Group of Qujing could be Middle and Late Pridolian, because a more important argument is that Parathelodus scitulus WI. et sp. nov. discovered in lower part of the Cuifengshan Group, associated with Devonian thelodont Turinia sp. and Canonia sp. and conodont zone Icriodus woschmidti was also found in the marine Lower Putonggou Formation of Early Lochkovian age in the West Qinling Mountains, Gansu Province, North China (Wang N Z, 1995a). The new thelodont materials were recovered from 14 horizons in the lower part of the Cuifengshan Group. Based on the new thelodont and other fossil findings, the Siluro — Devonian boundary in Qujing area could be drawn at the middle part of the Xitun Formation of the Cuifengshan Group. Three new vertebrate assemblages from Ludlovian to early Emsian strata of Qujing can be established in ascending order: the Hanilepis—Naxilepis Assemblage from the Guandi, Miaogao to Yulongsi (except for the upper black shale) formations; the Parathelodus—Polybranchiaspis Assemblage from the upper black shale of the Yulongsi Formation to the middle part of the Xitun Formation and the Sanchaspis— Gantarostrataspis Assemblage from the Xujiachong Formation.