MLA
Magee, John L. Union Patriotic Envelope with Winfield Scott Cartoon - "Governor Banks, Just Chain up That Dog Baltimore, until He Behaves Himself.", Published by John L. Magee, Philadelphia, Pennsylvania. J. Magee, 1861. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 21, Folder 6. https://digital.library.emory.edu/purl/7547pvmf1d-cor.
APA, 6th edition
Magee, J. L. (1861). Union patriotic envelope with Winfield Scott cartoon - "Governor Banks, just chain up that dog Baltimore, until he behaves himself.", published by John L. Magee, Philadelphia, Pennsylvania (Box 21, Folder 6) [Envelopes]. J. Magee; Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/7547pvmf1d-cor.
Chicago
Magee, John L. “Union Patriotic Envelope with Winfield Scott Cartoon - ‘Governor Banks, Just Chain up That Dog Baltimore, until He Behaves Himself.", Published by John L. Magee, Philadelphia, Pennsylvania.” Envelopes. Civil War Collection. Philadelphia, PA: J. Magee, 1861. Box 21, Folder 6. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/7547pvmf1d-cor.