MLA

Stieglitz, Alfred, 1864-1946. Letters. Box 91, folder 1803. 1939 Nov. https://collections.library.yale.edu/catalog/2042816.

APA, 6th edition

Stieglitz, Alfred, 1864-1946. (["Box 91, folder 1803"])(1939 Nov)[Letters]. https://collections.library.yale.edu/catalog/2042816.