The Barddas of Iolo Morganwg, Vol. I., ed. by J. Williams Ab Ithel, , at sacred-texts.com
The years of the sun and moon are as follows:--The year of the sun, 366 days. The year of the moon, 354 days.
p. 424 p. 425
The year of memorial and computation, 364 days.
Twenty-nine years of the sun are thirty years of the moon.
In another place, thus:--
Thirty-one years of the moon make thirty years of the sun.
From the Book of Brith y Coed.