APA (7th ed.) Citation

Langelaan, S., & Langelaan, D. (1900). The blue dog. Sylvan Press.

Chicago Style (17th ed.) Citation

Langelaan, Simonne, and Donald Langelaan. The Blue Dog. [England?]: Sylvan Press, 1900.

MLA (9th ed.) Citation

Langelaan, Simonne, and Donald Langelaan. The Blue Dog. Sylvan Press, 1900.