SUMMARY
We describe Dinacoma sanfelipe sp. nov. from southern California, the first new species belonging to the melolonthine scarab beetle genus Dinacoma Casey, 1889 (Scarabaeidae: Melolonthinae: Melolonthini) to be described in 90 years, based upon examination of 141 specimens of that genus. Diagnostic comments, a dichotomous key, photographs of all species of Dinacoma, and a distribution map are presented to facilitate the identification of adult male specimens. One species in the genus is federally listed under the United States Endangered Species act, and all known species may be of conservation concern. Key words: Scarabaeoidea, Melolonthini, scarab beetle, insect conservation, cryptic species