MLA

Barrie, J. M. (James Matthew), 1860-1937. Autograph manuscript, signed and dated. Box 44, folder 939. 1926 April 9. https://collections.library.yale.edu/catalog/32314603.

APA, 6th edition

Barrie, J. M. (James Matthew), 1860-1937. (["Box 44, folder 939"])(1926 April 9)[Autograph manuscript, signed and dated]. https://collections.library.yale.edu/catalog/32314603.