MLA

Pratt, Richard Henry, 1840-1924. Miscellaneous. Box 30, folder 818. n.d.. https://collections.library.yale.edu/catalog/2010759.

APA, 6th edition

Pratt, Richard Henry, 1840-1924. (["Box 30, folder 818"])(n.d.)[Miscellaneous]. https://collections.library.yale.edu/catalog/2010759.