MLA

Stieglitz, Alfred, 1864-1946. "Mary Steichen". Box 130, folder 2507. ca. 1915. https://collections.library.yale.edu/catalog/2002546.

APA, 6th edition

Stieglitz, Alfred, 1864-1946. (["Box 130, folder 2507"])(ca. 1915)["Mary Steichen"]. https://collections.library.yale.edu/catalog/2002546.