MLA

Kilpatrick, Jack Frederick (1915-1967). Recto: Envelope addressed to Henry Watt (Henila Wadi); Verso: Unidentified note. Box 11, folder 986. 1907 May 8. https://collections.library.yale.edu/catalog/15493791.

APA, 6th edition

Kilpatrick, Jack Frederick (1915-1967). (["Box 11, folder 986"])(1907 May 8)[Recto: Envelope addressed to Henry Watt (Henila Wadi); Verso: Unidentified note]. https://collections.library.yale.edu/catalog/15493791.