MLA

Benét, William Rose, 1886-1950. Schneider, Isidor. Box 38, folder 1519. undated. https://collections.library.yale.edu/catalog/17204715.

APA, 6th edition

Benét, William Rose, 1886-1950. (["Box 38, folder 1519"])(undated)[Schneider, Isidor]. https://collections.library.yale.edu/catalog/17204715.