This list features e-books containing information about specialized collections.
The Stamped Envelopes, Wrappers and Sheets of the United States by John Kerr Tiffany (1892) This book gives a summary of stamped envelopes issued by the Post Office Department and lists of varieties by producer printer. https://archive.org/stream/stampedenvelopes00tiff#page/n1/mode/2up
The U.S. 3c Green 1870-1887 By H. L. Wiley (1915) This 34-page booklet details the numerous varieties of 3¢ Green stamps issued. It includes information about printing companies, papers used, grills, shades, perforations, and cancels. books.google.com/books?id=P6I_AQAAMAAJ
Essays for United States Postage Stamps Edward H. Mason (1911) This 90-page book lists all the essays produced from 1850 to 1902. Each one is described with varieties listed below. books.google.com/books?id=mGoNAAAAYAAJ
The Canada Stamp Sheet: Volumes 1-6 (1900-1905) This monthly newsletter was written for collectors of British North American postage and revenue stamps. http://books.google.com/books?id=1pY6AQAAMAAJ&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false
Cancellations and Killers of the Banknote Era 1870-1894 By James M. Cole. This book includes lots of illustrations of cancels used during the banknote era. The cancels are categorized by shape. It’s fun to look through even if you’re not a cancel collector. https://archive.org/stream/CancellationsAndKillersOfTheBanknoteEra18701894/CancellationsAndKillersOfTheBanknoteEra1870-1894150dpi#page/n1/mode/2up
Sterling’s Standard Descriptive and Price Catalogue of the Adhesive Postage and Stamped Envelopes of the United States Only. This book, published in 1887, describes over 1,000 varieties of “adhesives, envelopes, wrappers, letter sheets, postals, postal and metallic currency, telegraph stamps, issues of the Southern Confederacy, and private local postage stamps” according to the title page. books.google.com/books?id=vTHZAAAAMAAJ