“The Nauglafring” is the name of the fourth chapter of The Book of Lost Tales Part Two, which is the second volume of The History of Middle-earth. It tells of the earliest version of the tale of the Necklace of the Dwarves, a necklace first called the Nauglafring (and later named the Nauglamir), and much of the story does not appear in the Quenta Silmarillion. It is not stated by Christopher Tolkien when his father first had written the tale.
The chapter that follows is "The Tale of Earendel".
At the Cottage of Lost Play, Ilfiniol suggests that Gilfanon tell to the folk gathered the tale of the Nauglafring, and Gilfanon does so. He recounts the dispute over the gold Húrin had brought to King Tinwelint (Thingol) between Tinwelint, Gwendelin his wife, and Ufedhin, one in league with the Nauglath - and the deal made between Tinwelint and the Dwarves that goes awry and results in a slaughter by the Nauglath over possession of the Necklace. In this version of the story, Tinwelint dies outside of Artanor in a later battle with the Nauglath (who are under Naugladur), alongside Mablung, his hunter.
Beren and Tinúvuel enter this tale when Huan, Tinwelint’s hound, goes wandering after the skirmish and brings them the dreadful tidings of the fall of Tinwelint’s land by the Orcs and the ransacking by the Dwarves. In grief and anger, Beren summons his fellowship of neighboring elves and set out to find the Nauglath. Ufedhin murders Bodruith, the Lord of Belegost who was in hiding with Naugladur, and flees. Near Sarnathrod on a following day, the battle between the Nauglath and Beren’s company takes place, at the end of which Naugladur relinquishes the Necklace to him in turn for his life, but is later is slain by Beren after attempting to turn back and kill him. Gwendelin returns to the land of Lórien, and after many years, the Necklace is stolen away from the reach of the sons of Fëanor by Evranin, Elwing’s nurse, and Gereth, a Gnome. The sons of Fëanor’s fates thereafter are narrated, and in conclusion, Gilfanon tells that these events where what gradually weaved together the great tale of Eärendel, who, within the story, would soon be born of Elwing.
Following Gilfanon's narration of this tale of the Necklace, Christopher Tolkien gives his annotated notes and commentaries on the many alterations by his father of character names, places, and circumstances throughout the versions of the tale.