MLA

Plowden, David (1932). Entrance to Writing Room, Steamer Assiniboia, Canadian Pacific Railway Great Lakes Steamer (964-888). Box 70. 1964 September. https://collections.library.yale.edu/catalog/2041644.

APA, 6th edition

Plowden, David (1932). (["Box 70"])(1964 September)[Entrance to Writing Room, Steamer Assiniboia, Canadian Pacific Railway Great Lakes Steamer (964-888)]. https://collections.library.yale.edu/catalog/2041644.