MLA

Barrie, J. M. (James Matthew), 1860-1937. Kensington Gardens gate key. Box 74. 1903. https://collections.library.yale.edu/catalog/2014293.

APA, 6th edition

Barrie, J. M. (James Matthew), 1860-1937. (["Box 74"])(1903)[Kensington Gardens gate key]. https://collections.library.yale.edu/catalog/2014293.