MLA

Barrie, J. M. (James Matthew), 1860-1937. Ansell, Mary. Box 1, folder 16. 1917 March 5. https://collections.library.yale.edu/catalog/2008273.

APA, 6th edition

Barrie, J. M. (James Matthew), 1860-1937. (["Box 1, folder 16"])(1917 March 5)[Ansell, Mary]. https://collections.library.yale.edu/catalog/2008273.