“The Face in the Abyss” by Virgil Finlay, 1940.
Wiki says:
Virgil Finlay (July 23, 1914 – January 18, 1971) was an American pulp fantasy, science fiction and horror illustrator. He has been called “part of the pulp magazine history … one of the foremost contributors of original and imaginative art work for the most memorable science fiction and fantasy publications of our time.”[1]
Source: virgilfinlay.tumblr.com