MLA

Stieglitz, Alfred, 1864-1946. Letters. Box 87, folder 1750-1751. 1933 Mar-May. https://collections.library.yale.edu/catalog/2040500.

APA, 6th edition

Stieglitz, Alfred, 1864-1946. (["Box 87, folder 1750-1751"])(1933 Mar-May)[Letters]. https://collections.library.yale.edu/catalog/2040500.