Generic and familial concepts of the Ascidae Voigts and Oudemans (= Blattisociidae Garman, Aceosejidae Baker and Wharton) are reviewed and modified from a world standpoint. The postembryonic developments of chaetotactic and external morphological features of the body and appendages are discussed. Twenty-two genera in three subfamilies are recognized, keyed, and defined: Arctoseius Thor, Iphidozercon Berlese, Xenoseius nov., and Zerconopsis Hull in the Arctoseiinae Evans; Cheiroseius Berlese and Platyseius Berlese in the Platyseiinae Evans; Aceodromus Muma, Antennoseius Berlese, Arctoseiodes Willmann, Asca Heyden, Blattisocius Keegan, Diseius nov., Gamasellodes Athias-Henriot, Hoploseius Berlese, Lasioseius Berlese, Leioseius Berlese, Melichares Hering, Neojordensia Evans, Proctolaelaps Berlese, Protogamasellus Karg, Rhinoseius Baker and Yunker, and Zercoseius Berlese in the Ascinae Voigts and Oudemans.Newly synonymized genera are Hyattella Krantz under Lasioseius, Mucroseius Lindquist and Orolaelaps DeLeon under Melichares, Garmaniella Westerboer under Proctolaelaps, and Tropicoseius Baker and Yunker under Rhinoseius. Genera removed from the Ascidae include Africoseius Krantz, Digamasellus Berlese, Laelaptoseius Womersley, and Zygoseius Berlese.
Modified systems of nomenclature based on holotrichous Gamasina are introduced and applied to setae on the dorsum of the idiosoma and on the venter of the opisthosoma.