MLA
Depot, New-York Union Envelope. Union Patriotic Envelopes - "A Southern GORILLA, (Guerilla)" Published by New-York Union Envelope Depot. 1861. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 21, Folder 9. https://digital.library.emory.edu/purl/634sj3tzgf-cor.
APA, 6th edition
Depot, N.-Y. U. E. (1861). Union patriotic envelopes - "A Southern GORILLA, (Guerilla)" Published by New-York Union Envelope Depot (Box 21, Folder 9) [Envelopes]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/634sj3tzgf-cor.
Chicago
Depot, New-York Union Envelope. “Union Patriotic Envelopes - ‘A Southern GORILLA, (Guerilla)" Published by New-York Union Envelope Depot.” Envelopes. Civil War Collection. New York City, New York, 1861. Box 21, Folder 9. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/634sj3tzgf-cor.