EIDUMANNIA in Britain, mentioned by Ptolemy (Ptol. 2.3.6) as a river between the prominence to the south of the Garrienus ( Yare) and Orford Ness, and the Ἰάμισσα εἴσχυσις (sicin the current editions). Whatever may be the reading, this Ἰάμισσαmeans the Thames. Hence, the Stour, Orwell, Blackwater, or any of the Essex rivers may be the Eidumannia. The Black-wateris the best; in which case the du==the Welsh du,Gaelic dubh==black.
[R.G.L]