This type of cup is known as a palm cup because of the rounded base that made it suitable for holding in the palm of the hand—and that prevented it from being set down until empty.
Found in Niederbreisig, western Germany.; Friedrich Queckenberg, Niederbreisig, Germany; Joseph Queckenberg, Niederbreisig, Germany; J. Pierpont Morgan, London and New York (until 1917)
Brown, Katharine R., Dafydd Kidd, and Charles T. Little, ed. From Attila to Charlemagne: Arts of the Early Medieval Period in the Metropolitan Museum of Art. New York and New Haven: The Metropolitan Museum of Art, 2000. p. 275, 280, fig. 22.17.