In D’Anville’s manuscripts, which his heirs have kindly permitted me to examine, I find that the surgeon Hortsmann, of Hildesheim, who described these countries with great care, saw a second Alpine lake, which he places two days’ journey above the confluence of the Mahu with the Rio Parime (Tacutu?). It is a lake of black water on the top of a mountain. He distinguishes it clearly from the Lake of Amucu, which he describes as “covered with reeds.” The narratives of Hortsmann and Santos are as far as the Portuguese manuscript maps of the Bureau de la Marine at Rio Janeiro from indicating or admitting a constant connection between the Rupunuri and the Lake of Amucu. In D’Anville’s maps the rivers are better drawn in the first edition of his South America, published in 1748, than in the more widely circulated edition of 1760. Schomburgk’s travels have completely established this general independence of the basins of the Rupunuri and the Essequibo; but he remarks that during the rainy season the Rio Waa-Ekuru, a tributary of the Rupunuri, is in connection with the Caño Pirara. Such is the state of these river basins, which are, as it were, still imperfectly developed, and are almost entirely without separating ridges. The Rupunuri and the village of Anai (lat. 3° 56′, long. 58° 34′), are at present recognised as the political boundary between the British and the Brazilian territories in these uncultivated regions. Sir Robert Schomburgk makes his chronologically determined longitude of the Lake of Amucu depend on the mean of several lunar distances (East and West) measured by him during his stay at Anai, where he was detained some time by severe illness. His longitudes for these points of the Parime are in general a degree more easterly than the longitudes of my map of Columbia. I am far from throwing any doubt on the observations of lunar distances taken at Anai, and would only remark that their calculation is important if it is desired to carry the comparison from the Lake of Amucu to Esmeralda, which I found in long. 68° 23′ 19″ W. from Paris (66° 21′ 19″ Gr.)