A new species of the helminthoglyptid genus Cahuillus Roth, 1996 from the Mojave Desert of southeastern California, is described as Cahuillus fultoni n.sp. It lacks the dart sac and associated mucus glands of the female system found in all other members of Cahuillus including Eremarionta rowelli unifasciata (Willett, 1930), which is herein reassigned to this genus and elevated to species status as Cahuillus unifasciata. Sequence comparisons support the new species as distinct from other available taxa, based on combined analysis of 16S and COI mitochondrial gene regions for Cahuillus fultoni and four of the nominal taxa of Cahuillus or Eremarionta Pilsbry, 1913 within the Mojave. Although a relevant species, Cahuillus greggi (Miller, 1981), remains unsampled, the estimated phylogeny supports a sister species relationship between C. unifasciata and C. fultoni.