The status of 23 species-group names used by Charles De Geer, for beetles classified in Pyrochroa Geoffroy, 1762, and Tenebrio Linnaeus, 1758, is assessed. Thirteen of these species-group names are unavailable (ten were published in synonymy, three are subsequent usages of available names): Pyrochroa rubra De Geer, 1775 = Pyrochroa coccinea (Linnaeus, 1760); Pyrochroa bimaculata De Geer, 1775 = Apalus bimaculatus (Linnaeus, 1760); Tenebrio acuminatus De Geer, 1775 = Blaps mortisaga (Linnaeus, 1758); Tenebrio variolosus De Geer, 1775 = Upis ceramboides (Linnaeus, 1758); Tenebrio molitor De Geer, 1775 = Tenebio molitor Linnaeus, 1758; Tenebrio rugosus De Geer, 1775 = Opatrum sabulosum (Linnaeus, 1760); Tenebrio villosus De Geer, 1775 = Lagria hirta (Linnaeus, 1758); Tenebrio hirticornis De Geer, 1775 = Orthocerus clavicornis (Linnaeus, 1758); Tenebrio boleti De Geer, 1775 = Diaperis boleti (Linnaeus, 1758); Tenebrio gibbus De Geer, 1775 = Psammodes gibbus (Linnaeus, 1761); Tenebrio maurus De Geer, 1775 = Tenebrioides mauritanicus (Linnaeus, 1758); Tenebrio aeneus De Geer, 1775 = Tenebrio chalybeus Linnaeus, 1767, a misidentification of Xylopinus saperdiodes (Olivier, 1775); and Tenebrio surinamensis De Geer, 1775 = Oryzaephilius surinamensis (Linnaeus, 1758). The holotype of Pyrochroa tomentosa De Geer, 1775, and specimens described under the name Tenebrio maurus, De Geer, 1775, from the De Geer Collection were rediscovered within the Paykull Collection, Swedish Natural History Museum. Pyrochroa nigra De Geer, 1775, is a junior synonym of Prionychus ater (Fabricius, 1775); a recently reported synonymy with Schizotus pectinicornis (Linnaeus, 1758), is an error. The holotypes of Pyrochroa nitida De Geer, 1775, and Tenebrio lardarius De Geer, 1775, are considered lost. Tenebrio gibbus De Geer, 1778, a junior primary homonym of Tenebrio gibbus Linnaeus, 1760, has the replacement name Tenebrio striatus Retzius, 1783, and is a synonym of Zophosis reticulatus Say, 1824, syn. nov., making the valid combination of this North American species Discodemus striatus (