The cover from this Strange Tales of Mystery and Terror magazine from back in 1932 sums up what in my mind is perfect Horror. Here you have a gentleman just browsing through a book in a library or bookstore and then from behind the door out steps a being from your nightmares.
The painting is for the Clark Ashton Smith tale, “The Hunters From Beyond”. You can find the story online if you have the time to give it a read but here is brief excerpt from it:
“What I saw was a forward-slouching, vermin-gray figure, wholly devoid of hair or down or bristles, but marked with faint, etiolated rings like those of a serpent that has lived in darkness. It possessed the head and brow of an anthropoid ape, a semi-canine mouth and jaw, and arms ending in twisted hands whose black hyena talons nearly scraped the floor. The thing was infinitely bestial, and, at the same time, macabre; for its parchment skin was shriveled, corpselike, mummified, in a manner impossible to convey; and from eye sockets well-nigh deep as those of a skull, there glimmered evil slits of yellowish phosphorescence, like burning sulphur. Fangs that were stained as if with poison or gangrene, issued from the slavering, half-open mouth; and the whole attitude of the creature was that of some maleficent monster in readiness to spring.”
A big thanks to the Monster Crazy Tumblr for the cover pic.