Hello Jon: Having both Cornish and Welsh ancestors myself, I was pondering the possibility that your man's surname might have been COCK when he lived in Cornwall. You may know that this is a very common surname there. In addition, the Welsh had only recently emerged from a patronymic naming system and many surnames acquired a final 'S'. The purpose would be to change a patronymic like Evan (ap) ROBERT into a surname to be passed on - Evan ROBERTS. I can quite believe that COCK could morph into COX given the right circumstances. Just a thought... Best wishes, Irene