Hi eac61,
I just googled and found this rootschat and a few of your comments on Treharne Evans. I am descended from him in Australia. I have a lot of info on him and brother William who came togther to Aust on the same ship (I found his birth is illegitmate, so he's a half brother).
I have already found his parents Thomas and Elizabeth John. Also the previous marriage to Margaret. I also used Aviathir as the key to track them in the Censuses, but also couldnt find his birth until this rootchat thread. Spelt wrong it seems.
Ancestry.com trees have Thomas's parents wrongly as James and Jane?, but the Census shows them as Richard, and his grand mother Hannah.
I couldn't find Treharne's birth registered anywhere in the UK. I had a person trawl the Eglwysilan, Glamorgan churches for a christening but to no avail, any luck there?
Also Thomas's nephew (by sister Mary) Richard Ungoed was in Lambton, Newcastle , Aust as well.
So first contact here, hope we can help each other. Scott in Aust.