Abstract Genus-group names for animals established after 1930 must, according to the International Code of Zoological Nomenclature, be accompanied by the designation of a valid type species. We have found several genus-group names of Arachnida described after 1930 that were not validly formed and, while the type species were subsequently designated in mainstream taxonomic literature, including taxonomic revisions and catalogues, others were found to have been designated in the Zoological Record. The following names are determined to have a change of authorship: GlobochthoniusFinnegan, 1932(notBeier, 1931), HeoblothrusBrowning, 1965(notBeier, 1963), HesperochthoniusBrowning, 1970(notMuchmore, 1968), TetrafeaellaMurthy & Ananthakrishnan, 1977(notBeier, 1955) and ToxochernesFinnegan, 1934(not Beier, 1932) (Pseudoscorpiones), RhinokarschiaHarvey, 2003(not Birula, 1935) (Solifugae) and GinosigmaWhittick, 1937(notSpeijer, 1933) (Uropygi). Argentochernes (Pseudoscorpiones), Arenotherus, and Daesiella (Solifugae) are deemed to be nomina nuda. In addition, the type species of the following genus-group names are found to be different from conventional treatments: Chthonius (Globochthonius) histricusBeier, 1931for Globochthonius; Chthonius (Hesperochthonius) oregonicusMuchmore, 1968for Hesperochthonius; Feaella indica Chamberlin, 1931 for Tetrafeaella; and Allochernes (Toxochernes) similis Beier, 1932 for Toxochernes. The change in type species for Toxochernes results in its synonymy with Chernes (new synonymy), rather than with Allochernes.