Ballantine Adult Fantasy Series

"The Road Goes Ever On" was not a mass market paperback

In "Imaginary Worlds: The Art of Fantasy", Lin Carter numbered the books in the series that had been published so far from 1 to 57.

X J. R. R. Tolkien The Hobbit
X J. R. R. Tolkien The Fellowship of the Ring
X J. R. R. Tolkien The Two Towers
X J. R. R. Tolkien The Return of the King
X J. R. R. Tolkien The Tolkien Reader
X E. R. Eddison The Worm Ouroboros
X E. R. Eddison Mistress of Mistresses
X E. R. Eddison A Fish Dinner in Memison
J. R. R. Tolkien and Donald Swann The Road Goes Ever On
X Mervyn Peake Titus Groan
X Mervyn Peake Gormenghast
X Mervyn Peake Titus Alone
X David Lindsay A Voyage to Arcturus
X Peter S. Beagle The Last Unicorn
X Peter S. Beagle A Fine and Private Place
X J. R. R. Tolkien Smith of Wootton Major and Farmer Giles of Ham
X Lin Carter Tolkien: A Look Behind "The Lord of the Rings"
X E. R. Eddison The Mezentian Gate
X 1 Fletcher Pratt The Blue Star
X 2 Lord Dunsany The King of Elfland's Daughter
X 3 William Morris The Wood Beyond the World
X 4 James Branch Cabell The Silver Stallion
X 5 George MacDonald Lilith
X 6 Lin Carter Dragons, Elves, and Heroes
X 7 Lin Carter The Young Magicians
X 8 James Branch Cabell Figures of Earth
X 9 Hannes Bok The Sorcerer's Ship
X 10 Fletcher Pratt and L. Sprague de Camp Land of Unreason
X 11 James Branch Cabell The High Place
X 12 Hope Mirrlees Lud-in-the-Mist
X 13 Lord Dunsany At the Edge of the World
X 14 George MacDonald Phantastes
X 15 H. P. Lovecraft The Dream-Quest of Unknown Kadath
X 16 Clark Ashton Smith Zothique
X 17 George Meredith The Shaving of Shagpat
X 18 Evangeline Walton The Island of the Mighty
X 19 Katherine Kurtz Deryni Rising
X 20 William Morris The Well at the World's End, Vol 1
X 21 William Morris The Well at the World's End, Vol. 2
X 22 Lin Carter Golden Cities, Far
X 23 Hannes Bok Beyond the Golden Stair
X 24 Poul Anderson The Broken Sword
X 25 William Hope Hodgson The Boats of the "Glen Carrig"
X 26 H. P. Lovecraft The Doom that Came to Sarnath and Other Stories
X 27 James Branch Cabell Something About Eve
X 28 Joy Chant Red Moon and Black Mountain
X 29 Clark Ashton Smith Hyperborea
X 30 Lord Dunsany Don Rodriguez: Chronicles of Shadow Valley
X 31 William Beckford Vathek
X 32 G. K. Chesterton The Man Who Was Thursday
X 33 Evangeline Walton The Children of Llyr
X 34 James Branch Cabell The Cream of the Jest
X 35 Lin Carter New Worlds for Old
X 36 Lin Carter The Spawn of Cthulhu
X 37 Edmund Cooper and Roger Lancelyn Green Double Phoenix
X 38 William Morris The Water of the Wondrous Isles
X 39 F. Marion Crawford Khaled
X 40 H. Rider Haggard and Andrew Lang The World's Desire
X 41 Clark Ashton Smith Xiccarph
X 42 C. J. Cutcliffe Hyne The Lost Continent
X 43 Lin Carter Discoveries in Fantasy
X 44 James Branch Cabell Domnei: A Comedy of Woman-Worship
X 45 Ernest Bramah Kai Lung's Golden Hours
X 46 Katherine Kurtz Deryni Checkmate
X 47 Lord Dunsany Beyond the Fields We Know
X 48 Arthur Machen The Three Impostors
X 49 William Hope Hodgson The Night Land, Vol. 1
X 50 William Hope Hodgson The Night Land, Vol. 2
X 51 Evangeline Walton The Song of Rhiannon
X 52 Lin Carter Great Short Novels of Adult Fantasy I
X 53 George MacDonald Evenor
X 54 Ludovico Ariosto Orlando Furioso: The Ring of Angelica, Vol. 1
X 55 Lord Dunsany The Charwoman's Shadow
X 56 Lin Carter Great Short Novels of Adult Fantasy Vol. II
X 57 William Morris The Sundering Flood
X (58) Lin Carter Imaginary Worlds: the Art of Fantasy
X (59) Clark Ashton Smith Poseidonis
X (60) Sanders Anne Laubenthal Excalibur
X (61) Katherine Kurtz High Deryni
X (62) Poul Anderson Hrolf Kraki's Saga
X (63) H. Rider Haggard The People of the Mist
X (64) Ernest Bramah Kai Lung Unrolls His Mat
X (65) Lord Dunsany Over the Hills and Far Away
X H. Warner Munn Merlin's Ring
X Evangeline Walton Prince of Annwn