APA

Ehrlich P. R., . (1961). How to know the butterflies: illustrated keys for determining to species all butterflies found in North America, north of Mexico, with notes on their distribution, habits, and larval food, and suggestions for collecting and studying them. Dubuque, Iowa: W. C. Brown Co.

Chicago

Ehrlich Paul R, . 1961. How to know the butterflies: illustrated keys for determining to species all butterflies found in North America, north of Mexico, with notes on their distribution, habits, and larval food, and suggestions for collecting and studying them. Dubuque, Iowa: W. C. Brown Co.

Harvard

Ehrlich P. R., . (1961). How to know the butterflies: illustrated keys for determining to species all butterflies found in North America, north of Mexico, with notes on their distribution, habits, and larval food, and suggestions for collecting and studying them. Dubuque, Iowa: W. C. Brown Co.

MLA

Ehrlich Paul R, . How to know the butterflies: illustrated keys for determining to species all butterflies found in North America, north of Mexico, with notes on their distribution, habits, and larval food, and suggestions for collecting and studying them. Dubuque, Iowa: W. C. Brown Co. 1961.