MLA

Stieglitz, Alfred, 1864-1946. Letters. Box 67, folder 1480-1491. 1931 Mar-Aug. https://collections.library.yale.edu/catalog/2040950.

APA, 6th edition

Stieglitz, Alfred, 1864-1946. (["Box 67, folder 1480-1491"])(1931 Mar-Aug)[Letters]. https://collections.library.yale.edu/catalog/2040950.