january1may is absolutely correct. A Brazilian 40 reis counterstamp on an 80 reis coin. The problem is which coin?
80 reis coins which were counterstamped with 40 during that period are:
#366.1
#376
#379
#382
#308
#342.1
You'll need to do it by a process of elimination. You need to try and figure out as much detail on your original 80 reis coin. Try and discern a date and and any mint marks to narrow it down.
I wish I had your coin in hand it's the sort of detective work I love.
Best of luck rooneydog.