The text treats 169 species in 17 genera of North American moths of the geometrid tribes Abraxini, Cassymini, and Macariini. One genus, 22 species, and three subspecies are newly described. Adults of all species are illustrated in color by 532 specimens and larvae of 81 species by 105 images. Diagnostic characters of all the genera and species are detailed and illustrated.
Specimens of this large group of often closely similar and variable species have proved difficult to identify. Dr. Ferguson's extensive field work in the United States and Canada and large number of rearings has enabled him to resolve many problems of recognition and to discuss the means to accomplish it. Identification keys for all genera and many species based on characters of adults together with illustrations of wings and genitalia and notes on variable characters will be extremely helpful to enable recognition of specimens. The immature stages of 81 species are characterized and illustrated. A synonymic check list of the described species updates the Check List of the Lepidoptera of America north of Mexico.