taxonomy
Needham, J.G. and M.J. Westfall, Jr. 1954. A Manual of the Dragonflies of North America (Anisoptera). University of California Press, Berkeley, California. 615 pp.
Hitchcock, A.S. 1951. Manual of the grasses of the United States. 2nd edition revised by Agnes Chase. [Reprinted, 1971, in 2 vols., by Dover Publications, Incorporated, New York.]
Heil, K.D., and J.M. Porter. 1994. Sclerocactus (Cactaceae): A revision. Haseltonia 2:20-46.
Opler, P., Research associate, and A.D. Warrren. 2002. Butterflies of North America 2. Scientific names list for butterfly species of North America, north of Mexico. . 79 p.
Waithman, J. and A. Roest. 1997. A taxonomic study of the kit fox, Vulpes macrotis. Journal of Mammalogy. 58:157-164.
Rickett, H. W. 1973. Wild flowers of the United States: Vol. 6 (3 parts). The central mountains and plains. McGraw-Hill Book Company, New York. 784 pp. + plates.
Flora of North America Editorial Committee. 1997. Flora of North America north of Mexico. Vol. 3. Magnoliophyta: Magnoliidae and Hamamelidae. Oxford Univ. Press, New York. xxiii + 590 pp.
Hobbs, H.H., Jr. 1989. An illustrated checklist of the American crayfishes (Decapoda: Astacidae, Cambaridae, and Parastacidae). Smithsonian Contributions to Zoology 480:1-236.
Pyle, R. M. 1981. The Audubon Society Field Guide to North American Butterflies. Alfred A. Knopf, New York, New York. 916 pp. + color plates.
Miller, L. D. and F. M. Brown. 1981. A Catalogue/Checklist of the Butterflies of America North of Mexico. The Lepidopterists' Society Memoir No. 2, Sarasota, Florida. 280 pp.