A new diatom genus, Labellicula, is described from soil samples taken from the subantarctic island Ile de la Possession (Crozet Archipelago). While this naviculoid genus shows some affinities with Brachysira, Diadesmis, Fistulifera, Neidium and Luticola, it presents a combination of characters that is unique: i.e. the presence of a stigma, large, elongated open alveoli and a relatively simple raphe structure. Thus far only one species, Labellicula subantarctica sp. nov., is placed in the genus. The ecology of this species is described and its valve structure compared to that of similar genera.