In D’Anville’s manuscripts, which his heirs kindly allowed me to examine, I find that Hortsmann of Hildesheim, who described these districts with great care, saw a second Alpine lake, which he places two day’s journey above the confluence of the Mahu with the Rio Parime (Tacutu?). It is a black water lake, situated on the summit of a mountain. He explicitly distinguishes it from the lake of Amucu, which he describes as “covered with rushes.” The descriptions given by Hortsmann and Santos coincide with the Portuguese manuscript maps of the Marine Bureau at Rio Janeiro, in not indicating the existence of an uninterrupted connection between the Rupunuri and the lake of Amucu. In D’Anville’s maps of South America, the rivers are better drawn in the first edition published in 1748, than in the more extensively circulated one of 1760. Schomburgk’s travels fully confirm the independence of the basin of the Rupunuri and Essequibo; but he draws attention to the fact that, during the rainy season, the Rio Waa-Ekuru, a tributary of the Rupunuri, is in connection with the Caño Pirara. Such is the condition of these river-channels, which are still but little developed, and almost entirely without separating ridges. The Rupunuri and the village of Anai, 3° 56′ north latitude, 58° 34′ west longitude, are at present recognised as the political boundaries between the British and Brazilian domains in these desert regions. Sir Robert Schomburgk was compelled by severe illness to make a protracted stay at Anai. He bases his chronometrical determinations of the position of the lake of Amucu on the mean of many lunar distances, east and west, which he measured during his sojourn at Anai. His determinations of longitude for these points of the Parime are in general one degree more east than those in my map of Colombia. While I am far from calling in question the result of these lunar observations taken at Anai, I may be allowed to observe that the calculation of these distances is of importance, when it is desired to carry the comparison from the lake of Amucu to Esmeralda, which I found in 66° 19′ west longitude.