MLA

Stieglitz, Alfred, 1864-1946. Letters. Box 76, folder 1601-1606. 1941 May-Aug. https://collections.library.yale.edu/catalog/2043564.

APA, 6th edition

Stieglitz, Alfred, 1864-1946. (["Box 76, folder 1601-1606"])(1941 May-Aug)[Letters]. https://collections.library.yale.edu/catalog/2043564.