Henry Altemus published numerous series, mostly with beautifully decorated covers, which were completely composed of reprints of religious stories, essays, poetry, moralistic tales, adventures and fiction novels. Authors like Nathaniel Hawthorne, Thoreau, Edgar Allan Poe, Emerson, Drummond and the like were well represented." this from the henryaltemus.com site. The examples shown here are all from 1907. They are all small, about the size of a modern paperback. These do not seem to have originally been a set since some are noticably more worn and must have had a different history from the others.
Each title was re-issued year after year with a different cover. Each cover had a set format for a given year but the cover color had six variations and the paste-on on the cover had forty-one variations. So each of these books is probably unique in its particular combination of year, title, cover color and picture. On the other hand, there are many essentially similar examples available so they are not really rare.
$16 for the set if you come here or $16+$7.09 online.