81 pages : illustrations (some color), maps ; 26 cm.Four genera formed a monophyletic group, referred to as the Kochius clade, in the phylogeny of the North American vaejovid scorpion subfamily Syntropinae Kraepelin, 1905: Balsateres González-Santillán and Prendini, 2013; Kochius Soleglad and Fet, 2008; Kuarapu Francke and Ponce-Saavedra, 2010; and Thorellius Soleglad and Fet, 2008. In the present contribution, all except Kochius, treated elsewhere, are revised. The monotypic Balsateres and Kuarapu are redescribed. Thorellius cristimanus (Pocock, 1898) and Thorellius intrepidus (Thorell, 1876) are redescribed and their type localities discussed and clarified. Three new species of Thorellius are described: Thorellius tekuani; Thorellius wixarika; and Thorellius yuyuawi. Vaejovis intrepidus atrox Hoffmann, 1931, is newly synonymized with T. cristimanus based on examination of the type material. A key to identification of the species of Thorellius is presented, and new locality records and updated distribution maps provided for all species covered
