APA (7th ed.) Citation

Siringo, C. A. (2011). History of 'Billy the Kid'. Project Gutenberg.

Chicago Style (17th ed.) Citation

Siringo, Chas. A. History of 'Billy the Kid'. Project Gutenberg, 2011.

MLA (9th ed.) Citation

Siringo, Chas. A. History of 'Billy the Kid'. Project Gutenberg, 2011.

Warning: These citations may not always be 100% accurate.