Ten newly recovered Dunbarites specimens significantly extend the known stratigraphic range of Dunbarites. These include the first documented Midcontinent Basin records of the Missourian type species Dunbarites rectilateralis (Miller, 1930) from north-central Oklahoma. Additional species of Dunbarites from south-central Oklahoma and north-central and West Texas are described as Dunbarites wewokensis n. sp. and Dunbarites boardmani n. sp. Although Dunbarites is an extremely rare component (∼0.025 percent) of Middle and Upper Pennsylvanian ammonoid assemblages, Ruzhencev and Bogoslovskaya (1971, 1978) suggested that Dunbarites and Parashumardites Ruzhencev, 1939 be used as genozone markers for the Kasimovian [Zhigulevian] Stage (Missourian in North America). As demonstrated by this report, the range of Dunbarites is not confined to the Kasimovian, thereby precluding its use as a Kasimovian Stage indicator.