The Guadalupian Series (with Roadian, Wordian and Capitanian stages in ascending order) is very suitable for world-wide application as the Middle Permian standard. The conodont faunas of the Delaware Basin and its slope are dominated by pelagic forms represented by ribbed Mesogondolella restricted to the Middle Permian of intraplatform basins and to near-shore slopes of tropical open seas. The first appearance of the serrated Mesogondolella nankingensis (CHING) is important for the definition of the base of the Middle Permian (base of the Guadalupian Series = base of the Roadian Stage). Mesogondolella nankingensis evolved in a phylomorphogenetic cline from the unserrated M. idahoensis (YOUNGQUIST, HAWLEY & MILLER) through transition forms closely related to M. phosphoriensis (YOUNGQUIST, HAWLEY & MILLER). The appearance of serrated Mesogondolella is a very characteristic event in Permian conodont evolution, which can be traced in southwestern and western North America, Arctic Canada and in China. This event is very suitable for the world-wide correlation of the base of the Middle Permian Guadalupian Series. At the upper boundary of the Guadalupian, the serrated Mesogondolella shannoni WARDLAW changed in a phylomorphogenetic cline into the smooth Clarkina altudaensis KOZUR. This cline was also found in intraplatform basins of the eastern Tethys (China). For this reason, the top of the Guadalupian can be well correlated with the Tethyan scale, in which the Late Permian Lopingian Series is defined. The first appearance of Clarkina crofti KOZUR & LUCAS in the uppermost Lamar Limestone and in the uppermost Altuda Formation is very important as it is penecontemporaneously with the first appearance of C. altudaensis. This species is restricted to greater water depths. Two new conodont species, Hindeodus gulloides n. sp., and H. altudaensis n.sp. are described. Additionally, Clarkina crofti KOZUR & LUCAS n.sp. is described to avoid the use of nomina nuda, because the paper of KOZUR & LUCAS (in press) has not yet been printed.