Ooohh, interesting. My wife is a Trevathan, and apparently its been traced back to Cornwall. I wonder if there's a relation? Could these be spelling variations of the surname? (I'm actually still quite new at this, so I'm afraid I won't be much help, really)
The notes I have from other relatives have show our line with a William Trevathan born about 1690 in Cornwall and coming to the Americas before 1711. Then William Trevethan (with an 'e') born 1662 in Penzance (died in Virgina 1703) -> John 1636 -> William 1609 -> Nicholas 1577 -> Walter 1554, all of Cornwall (Madron, Penzance, Helston, Pydar, and Newlyn).