Background and aims – Aulacoseira sphaerica (Hérib.) Simonsen is described from samples of a boring made in a Late Pliocene freshwater maar sediments in Nogaret (Escandorgue volcanic massif, France). This species is described and compared with works of other authors. Methods – The morphology of this species is examined using light microscopy (LM) and scanning electron microscope (SEM). Key results – Our observations correspond with Héribaud's (1903) description of Melosira sphaerica. It is an initial cell of an unknown Aulacoseira that is either extinct or does not form auxospores in recent waters. But we do not agree with Loseva's (1980) identification of this species found in the upper Pliocene deposits from the locality Omara (Russia) in the Kama river (Volga's tributary) basin. Conclusion – A. sphaerica remains considered as a Late Pliocene fossil, endemic in the south of France (Massif Central, Escandorgue).

AULACOSEIRA; AUXOSPORE; DIATOM; ESCANDORGUE; FRANCE; FRESHWATER; INITIAL CELL; LATE PLIOCENE; MASSIF CENTRAL