A new survey and re-sampling of Rhenish sections showed that there is only one succession with a well-exposed, easily accessible, sufficiently thick, and fossiliferous Pr. kockeli Zone (Lower Stockum Limestone), the Borkewehr near Wocklum. Current data suggest that the phylogenetic change from ancestral Pr. collinsoni to Pr. kockeli is recognizable in the first few transgressive limestones immediately after the siliciclastics of the glacioeustatic Hangenberg Regression. Therefore, it conforms to the recently decided criteria for the future Devonian/Carboniferous GSSP level.