It's called a scratcher chain.
Like Mark said, this is a Reed-Prentice/Craftsman 1200b chainsaw (103cc engine). I have one. Mine is a one-man version, I have a shorter bar without the buddy handle. They were manufactured around 1946-1949 and were about $500 brand new (closer to $4,000 in today's money). Parts are very hard to find, mine is missing the muffler, cylinder shroud and a few other small things. I working on rebuilding mine, it's a process and luckily I came across the service manual on e-Bay and it has an IPL in it so I know for sure what I am missing.
Here is a pic of mine before tearing it down, it sat outside as a lawn ornament for 20+ years:
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Edit: There was a trashy one on eBay that was going for $300 + $250 shipping - totally not worth it in my opinion.