The Roman Map of Britain Dumnosa? Dumno<sa>?

Linnonsa (R&C 289) next

Dumnam (Pliny NH iv 104)
doumna nhsoV  Dumna insula (Ptolemy II 3 14)

See Watson CPNS p 40-42 for further on Dumna. McBain identifies Dumna with the Long Island, i.e. the Outer Hebrides, but this is not correct.

This is the last island listed before the Cosmographer's  Item ad aliam partem dicitur insula which seems to jump to the west coast of Ireland. It would be reasonable to expect that this entry is in the vicinity of its predecessor, the island of Skye Scetis

The island of Rum ?