The best definition for the base of the terminal Cambrian (Stage 10) is the conodont Eoconodontus notchpeakensis FAD \textpm onset of the HERB carbon isotope excursion. These horizons allow precise intercontinental correlations in deep marine to peritidal facies. The agnostoid Lotagnostus americanus (Billings, 1860) FAD has been suggested as a Stage 10 base, but restudy of types and typotypes shows that the species occurs only in Late Cambrian (Sunwaptan) debris flow boulders in Quebec (Westrop et al., this volume). Non-Quebec reports of "L. americanus" are an amalgum of small samples of often poorly documented specimens with effaced–highly furrowed cephala and pygidia and with or without a highly trisected pygidial posteroaxis. Many of these occurrences have local species names, but no evidence suggests that they record intraspecific variation of a globally distributed taxon. They are not synonyms of L. americanus. Lotagnostus, largely a dysoxic form, does not allow precise correlation into oxygenated platform facies. Another proposal used the conodont Cordylodus andresi FAD as a Stage 10 base, but other work shows this FAD is diachronous. An unrealistic approach to L. americanus’ systematics and the correlation uncertainty of C. andresi are overcome by defining a Stage 10 base at the globally recognizable E. notchpeakensis FAD, with the C. andresi FAD a useful proxy on cool-water continents. The "Lawsonian Stage", named for Lawson Cove in western Utah, has a basal GSSP at the E. notchpeakensis FAD and replaces informal Stage 10. The Lawsonian, ~150 m-thick in western Utah, underlies the basal Ordovician Iapetognathus Zone.