Oak, held sacred by the Druids, 33. Oberon, 7, 392. “Ocean”, a black-maned heifer called, 80, 240. Ochall Ochne, king of the Sídhe of Connaught, 164. Ochren, battle of, 305; Caer, 320; see Achren. Octriallach, son of Indech, 110; the “Cairn of Octriallach”, 110. O’Curry, Eugene, 37, 56, 63, 72, 78, 89, 93, 111, 113, 137, 138, 146, 151, 152, 155, 188, 201, 204. Odin, 260. O’Donaghue, the, 247. O’Donovan, 238. Oeth and Anoeth, the Bone-prison of, 270, 271, 317, 373. O’Flynn, Eochaid, an old Irish poet, 231. Ogam, writings in, 58, 93, 151, 189. Ogma, Gaelic god of Literature and Eloquence, 57-60, 79, 80, 82, 84, 85, 112, 116, 117, 122, 136, 139, 157, 276; his wife and children, 57; his epithets of “Cermait” and “Grianainech”, 57, 59; his great strength, 59; kills Indech in the battle of Moytura, 112; inventor of the ogam alphabet, 58. Ogmios, a Gaulish god, 276. O’Grady, Standish Hayes, Mr., 28, 159, 201, 203, 205, 207, 213, 215, 222. Ogyrvran, a British god of the Under World, father of Gwynhwyvar, 329-331, 357, 366. O’Herlebys, wooden idol of the, 413. Old Plain, the, 66. Old Sarum, 29, 386. Olwen, 340, 341, 343, 345, 353. Onagh, queen of the Irish fairies, 243, 244. _Origins of English History_, Mr. Elton’s, 6, 8, 25, 26, 70, 228, 327, 413. Orkneys, 386; King Lot of Orkney, 359. Oscar, son of Ossian, 208, 212, 217, 222, 246, 315. Osla Big-Knife, 352, 353. _Ossian_, MacPherson’s, 203. Ossian, son of Finn mac Coul, 11, 208, 212, 214, 215, 217, 220, 223-227, 246, 318, 337. “Ossianic ballads”, 205, 208, 213; Ossianic Society, see _Transactions_. Other World, the Celtic, 65, 68, 71, 98, 119, 121, 133-136, 150, 151, 175, 176, 201, 202, 203, 224, 252, 255, 270, 271, 272, 273, 278, 279, 281, 305, 307, 316, 317, 318-322, 329, 334, 336, 366, 387, 389, 395; different names of, 133, 318-320; descriptions of, 136, 150-151, 224; variously imagined as upon the sea, 202, 224, 272, 394; under the sea, 305; under the earth, 135-136; upon earth, 271, 272, 273, 278, 279; original abode of men, 119; visited by Cuchulainn, 175-176, 186; Conn, 201; Connla, 202; Ossian, 224; Pwyll, 281; Gwydion, 305; Arthur, 317-320. See also Annwn, Avilion, Happy Plain, Mag Mell, Mag Mon, Land of Happiness, of the Living, of Promise, of Summer, of the Young. Ousel of Cilgwri, 349. Ovid’s _Metamorphoses_, 393. Owain, son of Urien, 328, 330; Sir Owain, 363. Owl, of Cwm Cawlwyd, 349; Blodeuwedd changed into an, 268. Ox, the brindled, 320, 321; oxen, magic, 345. Oxford, 379.