The conquest of the River Plate. 1535-1555. I, Voyage of Ulrich Schmidt to the rivers La Plata and Paraguai. From the original german edition, 1567. II, The commentaries of Alvar Núñez Cabeza de Vaca.From the original spanish edition, 1555. Translated for the Hakluyt Society with notes and an Introduction by Luis L. Domínguez