That call was named "Super Hen",...as you can barely read on the call. Ben Lee made them back in the early to mid-1970's as I recall. I have two of them signed by him that I bought that were part of his original batch made, I believe. However, the ones I own have an aluminum calling surface rather than slate. They came with a corn cob striker.
I was never all that impressed with the sounds I could make with the call, so the ones I have were hardy used and are still in pretty good condition. That one you have looks like it was put through the ringer based on the pics.
I'm not sure if Lee made the slate version first as a prototype and then went to the aluminum version, or maybe there were versions with both surfaces,....don't remember. From its appearance, the one you have may be one of the prototype calls Lee made,...and might be worth some money to a collector. I don't really know.