MLA

Eberhart, Richard, 1904-2005. Eberhart, Richard. Box 1 | Folder 10. 1940-1941, undated. https://collections.library.yale.edu/catalog/17104140.

APA, 6th edition

Eberhart, Richard, 1904-2005. (["Box 1 | Folder 10"])(1940-1941, undated)[Eberhart, Richard]. https://collections.library.yale.edu/catalog/17104140.