If you're a fan of H.P. Lovecraft's work, specifically of his story At the Mountains of Madness, you're going to love this this photo of the original notes and sketch he did, showing the beasts from the story including descriptions. As you can see, the struggling writer used an envelope to help him in his efforts to shape his story. This gives us an idea of what exactly Lovecraft envisioned for his monsters.
The story was written in 1931 and was published in the pulp magazine Astounding Stories in 1936. The image above comes from Slate, which points out the following,
The sketch on the right side of this page of notes, with its annotations (“body dark grey”; “all appendages not in use customarily folded down to body”; “leathery or rubbery”) represents Lovecraft working out the specifics of an Elder Thing’s anatomy. As Lovecraft’s narrator was a scientist, the description of the Things in the novella is dense and layered; here we can see the beginnings of that detail.
The story is written in first-person perspective by the geologist William Dyer, a professor from Miskatonic University. He writes to disclose closely kept secrets in the hope that he can deter a planned and much publicized scientific expedition to Antarctica. On a previous expedition there, a party of scholars from Miskatonic University, led by Dyer, discovered fantastic and horrific ruins and a dangerous secret beyond a range of mountains taller than the Himalayas. There he discovers that ancient beings lurk below the surface of the world, several species of forgotten, intelligent beings, including the “Elder Things.”