Ynys Seiriol (a.k.a. Puffin Island, Ynys Glannauc, Priestholm and Ynys Lannog)

This island lying off Penmon Point (Trwyn Du) of Anglesey (Ynys Môn) was once known as Priestholm by the Vikings and Ynys Lannog by the Welsh. A charter from 1238AD refers to the canons of the Isle of Glannauch, another name for the island.