MLA

Nicholls, Norton, 1741?-1809. Charles de Bonstetten to Norton Nicholls. Bern. Concerns Thomas Gray. Box 1, folder 109. 1771 May 28. https://collections.library.yale.edu/catalog/17439906.

APA, 6th edition

Nicholls, Norton, 1741?-1809. (["Box 1, folder 109"])(1771 May 28)[Charles de Bonstetten to Norton Nicholls. Bern. Concerns Thomas Gray]. https://collections.library.yale.edu/catalog/17439906.