Résumé
The terminal zone of the Frasnian standard conodont zonation, the linguiformis Zone has been subdivided into a lower part defined by the total range of Palmatolepis linguiformis and an upper part defined by the absence of the nominal species together with the rare occurrences of Pa. ultima (= Pa. praetriangularis) and Ancyrognathus (= Ancyroides) ubiquitus. This subdivision has proved to be effective in sections on different continental blocks. Furthermore, the two subdivisions correlate exactly with subdivisions formally recognized herein of Montagne Noire Zone 13 (13b and 13c). The lower boundary of the linguiformis Zone lies closely below the base of the Upper Kellwasser event bed, the top of which coincides with the end-Frasnian extinction. Nonetheless, prominent gaps in the geographic distribution of Pa. linguiformis have led to some difficulty in the identification of the zone. These gaps have been partially closed by discoveries of the species in areas where it was unknown until now, notably the central Moroccan Meseta and especially the Frasnian/Famennian boundary-stratotype section at Coumiac Upper Quarry in the Montagne Noire, southern France. Nevertheless, anomalous areas of absence, such as the Anti-Atlas Mts. of southern Morocco and western Canada still exist. The trilobite Palpebralia brecciae is widespread in Europe, North Africa, and Australia, providing evidence for correlation of the lower part of the linguiformis Zone in sections where the nominal conodont species has not been found. Analysis of variation in the relative abundance of the principal conodont genera leads to the conclusion that no substantial difference exists in the conodont associations among representative sections in four of the continental blocks.