The Shadow on the Doorstep / Trilobyte(1987)
An omnibus of novels by James P Blaylock and Edward Bryant
James P. Blaylock's story "The Shadow on the Doorstep" (introduction by Lewis Shiner) is bound back-to-back (like the old Ace Double paperbacks) with Edward Bryant's story "Trilobyte" (introduction by Tim Powers).
Used availability for Edward Bryant's The Shadow on the Doorstep / Trilobyte
1987 : USA Paperback