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Thamnocephalus is endemic to the American continents, being recorded in the USA, Mexico, Venezuela, Aruba, and Argentina with four recognized species: T. venezuelensis Belk and Pereira, 1982 and T. salinarum Cohen, 2002 from South America, and T. mexicanus Linder, 1941 and T. platyurus Packard, 1877 from North America. A systematic review of Mexican populations of T. mexicanus and T. platyurus is presented that includes a revision of their diagnostic morphological characteristics, a molecular characterization using fragments of the mitochondrial genes 16S and COI to assess their haplotypic identity and genetic differentiation, and an update of their geographical distribution. Molecular and morphological data confirm that T. mexicanus and T. platyurus represent two biological lineages at the species level. Distance range in 16S inter-species haplotypes was 9.6 to 10.0%, whilst in COI it was 17.0 to 18.3%. The Mexican sites where the species co-occurred are updated to 11, three of them in the Sonoran Desert, and eight in the Chihuahuan Desert.