Clifford Simak Collection of Sci Fi; Hellhounds of the Cosmos, Project Mastodon, the World That Couldn't Be, the Street That Wasn't There

Hellhounds of the Cosmos appeared in the June 1932 issue of Astounding Stories. Weird are the conditions of the interdimensional struggle faced by Dr. White's ninety-nine men. Project Mastodon appeared in the March 1955 issue of Galaxy.