APA (7th ed.) Citation

Castle, E., Castle, A., & Speed, L. (2013). If Youth but Knew! Project Gutenberg.

Chicago Style (17th ed.) Citation

Castle, Egerton, Agnes Castle, and Lancelot Speed. If Youth but Knew! Project Gutenberg, 2013.

MLA (9th ed.) Citation

Castle, Egerton, et al. If Youth but Knew! Project Gutenberg, 2013.

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