For those who are new to Bartrum's work online, I thought I would add a few notes to help anyone contemplating following Stewart Baldwin's suggestions, since I found it very confusing to work with the online version of Bartrum's work at first. (It is still somewhat confusing to me. Disclaimer: I have no particular expertise in Welsh genealogy.)
First, the home page is here:
http://cadair.aber.ac.uk/dspace/handle/2160/4026
You want to use the lower search bar.
Next, you look up the person in the indexes. The indexes are organized by male/female; date; and first letter of name. So for Angharad ferch Llywelyn ap Iorwerth Drwyndwn, first I would enter "Index" and "women" in the lower search bar. On the third page of hits, I find the section I am looking for: "Index of Women born c. 985-1215 A-E". If you click on that, you get this:
http://cadair.aber.ac.uk/dspace/handle/2160/6568
It's in alphabetical order, so I open pages systematically until I find the one I am looking for. Angharad turns up on page 179:
http://cadair.aber.ac.uk/dspace/bitstream/handle/2160/6568/179.png
In the column to the right, it gives an abbreviation of the title of the chart on which Angharad appears. In this case, "Gr. ap C. 4", which is Gruffudd ap Cynan 4. If you go back to the home page and search for "Gruffudd ap Cynan", you will find that page ("Gruffudd ap Cynan 04"):
http://cadair.aber.ac.uk/dspace/bitstream/handle/2160/5112/gruffudd%20ap%20cynan%204.png
Going back to the index page for Angharad, the abbreviations below Angharad's name are the sources that Bartrum is citing. He explains these abbreviations in his introduction, starting at page 10:
http://cadair.aber.ac.uk/dspace/handle/2160/6513
If you look up the abbreviations for the sources he cites under Angharad's name, you will find that they are these:
PAR3d = section 3d of "Plant yr Arglwydd Rhys" ed. P.C. Bartrum in NLW Journal XIV. 97-104.
(Available online here:)
http://welshjournals.llgc.org.uk/browse/viewobject/llgc-id:1282484/article/000038164
C119, 182 = pages 119 and 182 of Peniarth 131 pp. 71-138, 177-188 by Gutun Owain, c. 1480.
F30, 76/7 = pages 30, 76/7 of Peniarth 129 pp.4-134 (c. 1500). Copied from John Ryland's Welsh MS. 1 by Gutun Owain, 1497. Photostat copy in NLW 11, 114.1
G32, 79 = page 32 and page 79 of Peniarth 127 by 'Syr' Thomas ap Ieuan ap Deicws, c. 1510 - 1523.
And if you check the sources that Bartrum later pencilled in beside Angharad's name on the chart, you will find they are these:
RV = Peniarth 287 by Robert Vaughan of Hengwrt (d. 1667).
F79 = page 79 of Peniarth 129 pp.4-134 (c. 1500). Copied from John Rylands Welsh MS. 1 by Gutun Owain, 1497. Photostat copy in NLW 11, 114.1
G9, G79 = page 9 and page 79 of Peniarth 127 by 'Syr' Thomas ap Ieuan ap Deicws, c. 1510 - 1523.
C119, 183 = pages 119 and 183 of Peniarth 131 pp. 71-138, 177-188 by Gutun Owain, c. 1480.
Q124 = page 124 of Peniarth 135 by Gruffudd Hiraethog (d. 1564).
Roderick Ward