From Grey Sprite, The Silver Knight, His Adventures in the Old, Old Forest by Francis E. Park and illustrated by Elizabeth B. Warren, 1926.

It may be true that one can't judge a book by its cover, because the contents of this one are mind-numbingly mundane.  From 1930.

Perhaps your eye caught those three (or more) indentations, like footprints from some other sort of creature.  From St. Joseph's 1961 yearbook.

From Christmas Candles, Plays for Boys and Girls by Elsie Hobart Carter, 1915.

From Star People by Katharine Fay Dewey, 1910. 

The Best Halloween Book by Lenore Dolan, 1931.

Fairy in the Spider's Web by A.L.O.E., 1887.

The Mind Reader by Lundern M. Phillips, 1898.

Who Lifted the Lid Off of Hell? by Elbert Hubbard, 1914.

From The Foolish Almanak, 1906.

We, too, believe in the ellipsis.  From I Believe In ... by Norman Snaith, 1949.  See Annotated Ellipses.

If you could use a hand, here's one.  From Here's a Hand by Wallace Bruce, 1892.

Composed by one of them: Fallen Angels, A Disquisition Upon Human Existence, an Attempt to Elucidate Some of Its Mysteries Especially Those of Evil and of Suffering by One of Them, 1894.

The Olympians, A Tribute to 'Tall Sun-Crowned Men' by Elbert Hubbard, 1921.

Damaged by seawater: To Lovers and Others by Harry C. Morse, 1918.

Here's a precursor to the Jackson family of musical fame.  Janet, One of Many (1962).

Is Hell Eternal Or Will God's Plan Fail? by Charles Hamilton Pridgeon, 1920.

From Taylor University's Gem yearbook of 1957.

It wasn't merely a prop in that old Bewitched episode in which Darrin had to be fluent in Spanish within five minutes.  It's actually a book: Fluency in 5 Minutes.

Not only is this a precursor to How to Be Your Own Cat, but check out that word "metamorphosiological"!  This is the only instance of that word in print that we've found.

From The Woman That Was a Cat, A Metamorphosiological Sketch in One Act by Eugene Scribe, originally presented in 1827.