MLA

Pettigrew, Thomas Joseph, 1791-1865. Oldfield, John, 1789-1863. 6 ALS and 1 AL to T. J. Pettigrew. Box 9, folder 408. 1837-38. https://collections.library.yale.edu/catalog/16684173.

APA, 6th edition

Pettigrew, Thomas Joseph, 1791-1865. (["Box 9, folder 408"])(1837-38)[Oldfield, John, 1789-1863. 6 ALS and 1 AL to T. J. Pettigrew]. https://collections.library.yale.edu/catalog/16684173.