MLA

Audubon, John James, 1785-1851. Martin, Maria to JJA. Box 5, folder 251. 1832 Jul 12. https://collections.library.yale.edu/catalog/10190051.

APA, 6th edition

Audubon, John James, 1785-1851. (["Box 5, folder 251"])(1832 Jul 12)[Martin, Maria to JJA]. https://collections.library.yale.edu/catalog/10190051.