MLA

Sergeant, Elizabeth Shepley, 1881-1965. Ely, Gertrude. Box 2, folder 46. 1920-54, n.d.. https://collections.library.yale.edu/catalog/17054223.

APA, 6th edition

Sergeant, Elizabeth Shepley, 1881-1965. (["Box 2, folder 46"])(1920-54, n.d.)[Ely, Gertrude]. https://collections.library.yale.edu/catalog/17054223.