MLA

Barrie, J. M. (James Matthew), 1860-1937. Dickens, Ethel. Box 6, folder 149. 1928. https://collections.library.yale.edu/catalog/32312214.

APA, 6th edition

Barrie, J. M. (James Matthew), 1860-1937. (["Box 6, folder 149"])(1928)[Dickens, Ethel]. https://collections.library.yale.edu/catalog/32312214.