Abstract

New collections rich in agnostoid trilobites were recovered from Lower Ordovician strata of the southern Montagne Noire, France. The faunas occur in the La Gardie/Val d'Homs, Saint–Chinian, La Maurerie, and Landeyran formations, coinciding with deposition in muddy outer-platform settings. Many previously described species are revised and their stratigraphic ranges emended. The studied agnostoids include Geragnostus cf. sidenbladhi (Linnarsson), G. aff. sidenbladhi, G. crassus Tjernvik, G. splendens (Holub), G. cf. explanatus Tjernvik, G. boutouryensis Howell, G. occitanus Howell, Geragnostus sp., Trinodus corpulentus Howell, Homagnostoides ferralsensis (Munier-Chalmas and Bergeron), Corrugatagnostus coulobresensis n. sp., Corrugatagnostus sp., Leiagnostus miqueli Sdzuy, and Leiagnostus sp. The record from the upper part of the Saint–Chinian Formation suggests a late Tremadocian age, whereas an early Arenigian age is indicated for the upper part of the La Maurerie Formation. Although the agnostoid record generally reinforces the peri-Gondwanan character of the Lower Ordovician shelly faunas from the Montagne Noire, some agnostoid species are independent of specific paleogeographic boundaries.

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