APA (7th ed.) Citation

Twain, M. (2004). Those Extraordinary Twins. Project Gutenberg.

Chicago Style (17th ed.) Citation

Twain, Mark. Those Extraordinary Twins. Project Gutenberg, 2004.

MLA (9th ed.) Citation

Twain, Mark. Those Extraordinary Twins. Project Gutenberg, 2004.

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