The word ‘map’ in the Welsh genealogies

E. W. B. Nicholson explained the origin of the use of the word ‘ap’ in the Welsh genealogies, see The Dynasty of Cunedag and the ‘Harleian Genealogies’. Take HG 1. Notice the repetition in the names: Cein, Guorcein, Doli, Guordoli, Dumn and Gurdumn. In the manuscript the names are listed in columns preceded by the word ‘map’ as indicated by Phillimore, see The Annales Cambriae and Old-Welsh Genealogies from Harleian MS 3859. These six names appear thus:

map. Cein.
map. Guorcein.
map. doli.
map. Guordoli.
map. dumn.
map. Gurdumn.

Nicholson explains (p. 65) that the manuscript we have is a copy of an original which was of a different form. He writes:

My next point is that in their original form these were not all of them certainly ‘genealogies’ in the modern sense of the word-that, in fact, No. 1 is not a genealogy but a table of succession. Part, at least, of the original table had no map’s, but the preposition guor, ‘over’, in their place.

He then presents how the original table would have shown these names:

guor cein doli
guor doli dumn
guor dumn Amgueryt

In the later versions of the manuscript, the word ‘guor’ was replaced by the word ‘map’ at the start of each line presumably because it involved less repetition, there being no need to restate the last name in one line as the first name in the next. However, accidently the ‘guor’ in just the above three lines of the text were left in, thus generating three fictitious names: Guorcein, Guordoli and Gurdumn. Nicholson goes on to state:

In other words, we have before us what may not be a table of direct blood-descent at all, but only of succession

The above three lines of the text would thus read:

Before Cein, Doli
Before Doli, Dumn
Before Dumn, Amgueryt

showing no assertion of a son-to-father relationship.