MLA

Stieglitz, Alfred, 1864-1946. Letters. Box 94, folder 1848-1849. 1945 May. https://collections.library.yale.edu/catalog/2044265.

APA, 6th edition

Stieglitz, Alfred, 1864-1946. (["Box 94, folder 1848-1849"])(1945 May)[Letters]. https://collections.library.yale.edu/catalog/2044265.