Calliopsis obscurellus Cresson, 1879:201, ♂♀. 6 ♂♀, California (leg. H. Edwards). - Cresson, 1879Cresson, E.T. 1879. Descriptions of new North American Hymenoptera in the collection of the American Entomological Society. Family Apidae (Continued from page 136.). Transactions of the American Entomological Society and Proceedings of the Entomological Section of the Academy of Natural Sciences 7:201-214. (distribution); Cockerell, 1898Cockerell, T.D.A. 1898. On some Panurginae and other bees. Transactions of the American Entomological Society 25:185-198. (distribution); Cockerell, 1903Cockerell, T.D.A. 1903. A catalogue of the bees of California. Psyche 10:74-78. (distribution); Viereck, 1905Viereck, H.L. 1905. Synopsis of bees of Oregon, Washington, British Columbia and Vancouver.—IV. The Canadian Entomologist 37:277-287. (distribution). - As Calliopsis obscurella: - Dalla Torre, 1896Dalla Torre, C.G. 1896. Catalogus Hymenopterorum hucusque descriptorum systematicus et synonymicus, X. Apidae (Anthophila). Sumptibus Guilelmi Engelmann, 1-643. (distribution); Esperanza de Pedro, 2021Esperanza de Pedro, D. 2021. . :. (distribution); Nava-Bolaños & Osorio-Olvera, 2022Nava-Bolaños, A. & L. Osorio-Olvera 2022. Estado del arte del conocimiento de biodiversidad de los polinizadores de México. Revista Mexicana de Biodiversidad 93:1-77. (distribution). - As Nomadopsis obscurella: - Krombein et al., 1979Krombein, K.V., P.D. Hurd, D.R. Smith & B.D. Burks 1979. Catalog of Hymenoptera in America North of Mexico. Volume 2. Apocrita (Aculeata). Smithsonian Institution Press, Washington D.C. 1199-2209. (distribution).