A collection of 57,877 conodont elements that includes 39 species representing 30 genera was made from the upper part of the Phragmodus undatus Zone and the lower part of the Plectodina tenuis Zone (late Turinian–early Chatfieldian). Conodont samples were collected from 30 sections in eastern North America and Baltoscandia, where the P. undatus–P. tenuis Zone boundary projects into B. alobatus Subzone based on K-bentonite bed correlation. Elements previously assigned to form-species of Oistodus are shown to be apparatus associates in coniform apparatuses of Besselodus. Pseudobelodina manitoulinensis new species is described and the apparatus-based taxonomy of Scyphiodus primus and Staufferella polonica are proposed.