The fourth radiation of Camelidae in North America produced both living tribes of Camelidae: the Camelini of the Old World and the Lamini of South America. This paper focuses on the origin of Lamini. It places on record a new genus and species, Pleiolama mckennai, from the middle Miocene of Nebraska and Texas, and assigns to that genus the species P. vera (Matthew, 1909) from the late Miocene of the High Plains. Pleiolama is distinguished from four other extinct genera of Lamini recognized in North America. The nominal genus and species, Pliauchenia humphresiana Cope(1875), traditionally thought to be an early representative of Lamini, is shown to be a nomen vanum.