Limited understanding of the morphological variation and genetics of the genus Lepidurus have caused confusion for workers attempting to determine North American species of this genus. In addition, preliminary culturing data suggests that food quality affects the form of structures previously used as specific characters. Morphological comparisons between Lepidurus packardi Simon, 1886, and the type material of L. couesii Packard, 1877, demonstrate that populations of Lepidurus occurring in the Sierra Nevada, the Cascade Mountains, and the Great Basin regions of northeastern California and south central Oregon, previously reported as L. couesii, “L. couesii-1”, or as the “Modoc Plateau Tadpole Shrimp”, conform to the L. packardi morphotype. The results of my work and King and Hanner's (1998) genetic data demonstrate the presence of a cryptic species within the L. packardi morphotype, described here as Lepidurus cryptus n. sp. Specific diagnoses and a key to North American Lepidurus are presented.