The Corydiidae (Polyphagidae, sensu lato) is a family of extremo-phile cockroaches that have received little taxonomic attention. Their cryptic subterranean way of life in some of the most in-hospitable parts of the planet makes the study of this group particularly difficult. Arenivaga (Rehn) is a genus of Corydiid cock-roach endemic to the American Southwest, Florida, and Mexico. This unusual group of insects, not examined in nearly a century, is revised in this volume. This work includes redescriptions of the genus and its nine known species, descriptions of 39 new species, a key to the adult males, and distribution maps for each species. A photographic series of the habitus and detailed drawing of the genitalia of each species are also provided, and novel morphological characters are described. In addition, the locality data of more than 5000 specimens used in this study is now available to researchers. Even though this research increases the number of species in Arenivaga five-fold, there is little doubt that there are many more species to be found in Mexico, which is poorly surveyed in comparison to the US terrain.