A new genus of Palaeozoic herbaceous lycophyte Thomasites, a new species T. serratus and a new combination T. elongatus (formerly Selaginellites elongatus) are proposed. Specimens of the new species Thomasites serratus are from a late Duckmantian tuff in the Ovčín Mine, Radnice Basin, in the Czech Republic. Bisporangiate strobili have megasporangia in the basal part and microsporangia in the apical portion. The leaves and sporophylls are of the same type, with a tetrastichous arrangement. Ligulae are not observed. The new miospore genus Thomasospora and the new combination T. gigantea (formerly Lycospora gigantea and Lundbladispora gigantea) are proposed for the miospores produced by the new species Thomasites serratus. The spores of Palaeozoic herbaceous lycophytes are discussed, and five groups are proposed based on purely palynological criteria, i.e., different kinds of in situ spores. Palaeozoic herbaceous lycophytes probably preferred an environment transitional between wet coal-forming swamps with high water table levels and drier swamps with surfaces above water with poor nutrient supplies.