APA (7th ed.) Citation

Ehrlich, P. R., & Ehrlich, A. H. (1961). How to know the butterflies. WM C. Brown.

Chicago Style (17th ed.) Citation

Ehrlich, Paul R., and Anne H. Ehrlich. How to Know the Butterflies. Dubuque, IA: WM C. Brown, 1961.

MLA (9th ed.) Citation

Ehrlich, Paul R., and Anne H. Ehrlich. How to Know the Butterflies. WM C. Brown, 1961.