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The Middle/Late Devonian boundary is investigated based on twenty-four conodont species and subspecies from the Anarak and Sar-Ashk sections in the northwest and southeast of Central East Iran Microplate. The earliest Frasnian strata are defined by the first appearance of Ancyrodella rotundiloba pristina and can be correlated with the global stratotype in the Montagne Noir, South of France. The Late Givetian - Early Frasnian carbonates of the Bahram Formation in the Sar-Ashk section transgressively overlie the sandstones of the Padeha Formation, whereas the coeval interval in the Anarak section composes the middle part of the Bahram Formation. Conodont biostratigraphy of Late Givetian - Early Frasnian strata in both sections revealed the presence of the Lower hermanni to Lower hassi zones. A new polygnathid species, Polygnathus anarakensis, is also proposed. [ABSTRACT FROM AUTHOR]