MLA

Yale Peruvian Expedition ($d: 1911). Circular letters. Box 2, folder 29. 1915 January-March. https://collections.library.yale.edu/catalog/33346210.

APA, 6th edition

Yale Peruvian Expedition ($d: 1911). (["Box 2, folder 29"])(1915 January-March)[Circular letters]. https://collections.library.yale.edu/catalog/33346210.