MLA

Stieglitz, Alfred, 1864-1946. Letters. Box 63, folder 1446-1447. 1928 May. https://collections.library.yale.edu/catalog/2039851.

APA, 6th edition

Stieglitz, Alfred, 1864-1946. (["Box 63, folder 1446-1447"])(1928 May)[Letters]. https://collections.library.yale.edu/catalog/2039851.