What is this hole in my basement floor and how do I repair it?
Lots of homebrew construction was still going on back then. I wouldn't be surprised if it's just a makeshift floor drain for occasional use, say in the case of plumbing problems or heavy rain. 

It's also possible that it's just a sinkhole from poorly mixed concrete and inadequate substrate compaction. 

If the basement has been dry for a number of years, just patch it up with masonry of some sort (whatever's on hand). If you're not sure, consider installing a proper drain grate to clean it up aesthetically but leave it functional.