This is a compilation of Brazilian-created X-Men comics, created as backups strips for the (very) old Brazilian editions of the Marvel superhero comic, trying to bulk up the limited US product. These were not authorized by Marvel, but no one seemed to care very much.
Never republished since original publication in 1968, the ten back up strips by the late Gedeone Malagola and Walter Silva Gomes have been sourced from Malagola's own archives.
The strips also featured other characters from Marvel comics guest-starring, hence the Avengers and Ka-Zar on the cover…
Here's how some of the pages looked.