This flyer advertises various Boys’ and Girls’ Series books. Interestingly the latest book is the shown is the Pony Riders Boys with the Texas Rangers which is a 1920 book. Other series do not show books that were published in the late teens. For instance, the College Girls Series (#9) lists 4 books the latest of which was published in 1914 but does not list the 1915 book.
Usually Altemus advertising would show all the series up to a certain date and there would not be this disparity in the books listed and not listed. Nonetheless this flyer must date from 1920 based on the book listed.
The flyer has 4 panels per side and is 13 x 6.25.