Hi Philip,
Thank you for your reply. That would explain a lot. I have had trouble finding Onesiphorus's birth. I didn't know he signed the register Oney Sephres, I assume for his marriage.
I am just trying to tie up a loose end. My ancestor James Luxon had Onesiphorus and his wife Sally as witnesses at his wedding in 1840. James' mother was called Jane Luxon (Luxton) and doesn't appear to have been married although James does put his father's name down as James - a joiner. I have a feeling Onesiphorus is his uncle.
James himself was born in Bristol in 1819 and moved (back?) to Devon at some point after that.