Greya is a genus of particular biological interest, in that it is among the genera closest related to the yucca moths, which are widely quoted in discussions of coevolution. Both Greya and the new genus Tetragma share some morphological and behavioral traits with the yucca moths. In this paper, the general morphology, classification, distribution, and biology of the western North American genera Greya and Tetragma new genus, are reviewed, and a phylogeny is proposed. Sixteen species of Greya are recognized, including seven new species: G. mitellae, G. obscura, G. enchrysa, G. variabilis, G. pectinifera, G. suffusca, and G. powelli. Greya piperella is resurrected as a valid species. The new genus Tetragma is described, with the single, new species T. gei. Keys are provided for all species, and diagnostic characters of all taxa are illustrated by line drawings and photographs.
