A new monobasic family of endeostigmatic mites, Proterorhagiidae, based on Proterorhagia oztotloica gen. nov., sp. nov., is described from a single adult female from the state of Colima, Mexico. This mite may be mistaken for a rhagidiid because of superficial resemblances in the robustly chelate chelicerae and general form of the palpi and body. The unique mixture of primitive and derivative characteristics of this taxon is discussed, with evidence presented for its placement in the paraphyletic assemblage Endeostigmata, in distinction to Prostigmata. The taxon is hypothesized to represent an ancient lineage of mites, even among the Endeostigmata, and as such, a ’living fossil’. Some predictive characteristics for its placement in Endeostigmata, based on ontogenetic characteristics of the larval and nymphal instars known for other families of this assemblage, are offered as tests of hypotheses on its antiquity and position in this lineage when the immature instars of this taxon are discovered and studied.