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A diverse assemblage of Late Quaternary continental ostracodes (Class Crustacea) belonging to at least 15 genera and 40 species (including 11 new species and one new genus, Plicocandona, described here) was found in sediments of former groundwater discharge deposits located in valleys of southern Nevada, U.S.A. The fossiliferous deposits are located in Las Vegas, Coyote Springs, Indian Springs, Sandy, and Pahrump Valleys. The ostracodes include species that were probably living in wetmeadow, seep, flowing-spring, stream, and wetland environments, and include aquifer species. Those environments indicate a higher level of effective moisture than occurs today during several episodes of the Late Pleistocene to Early Holocene, from similar to 140 to similar to 9 ka. The ostracode assemblages are significant to our understanding of regional paleohydrology and also contribute to the growing knowledge of aquifer taxa diversity and biogeography.