Llyfyr Gwyn o Rhydderch: HLEE-fir GWIN oh R-HE-ðurX*
ð=th in "leather"
X=ch in "loch"
The White Book of Rhydderch
or, The White Book Mabinogion.
Peniarth MS 4
Transcribed at Strata Florida, Wales ca. 1325, the White Book is an earlier, incomplete copy of the tales now known as The Mabinogion, which are usually translated using the Red Book of Hergest, and a large number of the Welsh triads, which contain the skeltons of tales now lost to us. Interestingly, the book, which contains an early version of the Grail Quest, was transcribed by the Cistercian Order, which has ties to the Knights Templar. But that's another story.
The order of the tales in the White Book differ with that of the current standard order:
Historia Peredur--The History of Peredur
Breuddwyd Macsen--The Dream of Macsen
Cyfranc Lludd a Llefelys: The Adventur of Lludd and Llefelys
Owein; Chwedyl Iarlles y Ffynnawn--Owain, or, the Lady of the Fountain
Gereint ac Enid--Gereint and Enid
Culhwch ac Olwen--Culhwch and Olwen
While "Breudwyt Rhonabwy" ("The Dream of Rhonabwy") is missing from the White Book, it is assumed that it was originally placed between "Lludd" and "Owein," and later inserted into its place in the Red Book, at least according to J. G. Evans, editor of the diplomatic edition.
Evans makes two interesting notes: first, that "Historia Peredur" is not given the title usually reserved for Romances like "Owein" or "Gereint," but is instead called a "historia," meaning it was taken as more true than these two. Whether this is true, I don't know. Either way, all three are related to the romances of Chretien de Troyes, but "Peredur" in particular is full of very primitive material, more in line with the "Four Branches."
Second, the text of "Gereint" is in the same hand as that of the Book of Taliesin.
I wish to thank
Gone Jackal for sending me a copy of the White Book Mabinogion; I hope to soon start translating.