"De Vermis Mysteriis" is a fictional grimoire created by author Robert E. Howard in his story "The Black Stone." The title translates to "The Mysteries of the Worm," and it is said to contain dark knowledge and forbidden rituals related to ancient deities and cosmic horrors. The book is often associated with the Cthulhu Mythos, a shared fictional universe created by H.P. Lovecraft and expanded by other writers. In the context of the mythos, "De Vermis Mysteriis" serves as a source of arcane wisdom, often leading its readers to madness or perilous encounters with otherworldly beings.