| Summary: | The pliomerid trilobite genus Hintzeia Harrington, 1957, includes only species from the early Tulean (upper Tremadocian) of the Great Basin, USA, and from the Northwest Territories, Canada. Previously assigned species reported from Scandinavia, China, South Korea, and Australia do not appear to be closely related to the western Laurentian species and are excluded from the genus. The monophyly of the group needs to be tested in the context of a broader phylogenetic analysis, but Hintzeia is rediagnosed with potential synapomorphies including a long, wide anterior border with a large, semicircular median arcuate anterior curve in the posterior margin. Hintzeia celsaora (Ross, 1951) and H. firmimarginis (Hintze, 1953) are redescribed based on large new collections from Utah and Idaho. Ontogenetic material of H. celsaora includes an articulated silicified M13 meraspid. Hintzeia parafirmimarginis n. sp. is described on the basis of both abundant disarticulated sclerites and a large articulated individual. Large topotype collections indicate that Hintzeia celsaora (Ross, 1951) is a senior synonym of Protopliomerops aemulus Hintze, 1953; previously claimed differences appear to reflect small original sample sizes, ontogenetic change, and differing photographic orientation.
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