Polyphylla aeolus La Rue, new species, is described from the Kelso Sand Dunes, Mojave Desert, San Bernardino County, California, U.S.A. Illustrations of dorsal habitus, significant morphological details, and adult genitalic forms are provided. A description of the type locality including geographical and ecological parameters is presented. Taxonomic problems within the genus and limitations of recently proposed methods of species identification are discussed. A modified key is provided to distinguish the new species. The heretofore undescribed females of Polyphylla anteronivea Hardy, P. rnescalerensis Young, P. nubila Van Dyke, and P. pottsorum Hardy, are described. The larval host of P. erratica Hardy is reported, and the adult female is redescribed from pristine specimens. A dorsal habitus illustration of each female is provided. Bionomic and distributional data are presented for Polyphylla avittata Hardy, P. cavifrons LeConte, P. hirsuta Van Dyke, P. monahansensis Hardy, P. petiti Guerin, P. stellata Young, and P. squamiventris Cazier
