A revision of the Ordovician agnostid trilobite Leiagnostus Jaekel 1909

The holotype and only known specimen of Leiagnostus erraticus Jaekel 1909 is redescribed. It is a well-preserved, enrolled, and highly effaced specimen from a glacial erratic found in Berlin, probably originating from the upper Lower Ordovician (upper Arenig-lower Llanvirn) of Baltoscandia, and not from the Middle Ordovician as previously suggested. A closely comparable form, Leiagnostus sp., is described from the upper Arenig of Västergötland, south-central Sweden. L. erraticus is the type species of Leiagnostus Jaekel 1909, a widespread genus of agnostid trilobites in the Lower Ordovician. The generic concept of Leiagnostus is revised. Phoidagnostoides Capera, Courtessole & Pillet 1978, from the Tremadoc of Montagne Noire, France, is considered to be a junior synonym of Leiagnostus.