 A careful and methodical worker, he used venation and mouthparts to determine the relationships of fossil taxa, and was author of the "Treatise" volume on Insects.He reduced the number of extinct insect orders then described from about fifty to nine.Entomologists David Grimaldi and Michael S. Engel consider him "the most influential paleoentomologist of his generation" (Grimaldi and Engel 2005 p. 143).