MLA

Thayer, Scofield, 1889-1982. Mortimer, Raymond. Box 57, folder 1526. n.d.. https://collections.library.yale.edu/catalog/10034093.

APA, 6th edition

Thayer, Scofield, 1889-1982. (["Box 57, folder 1526"])(n.d.)[Mortimer, Raymond]. https://collections.library.yale.edu/catalog/10034093.