Mus canescens. ST. JULIAN. Reithrodon cuniculoïdes. —— xanthopygus. Reithrodon cuniculoïdes. SANTA CRUZ. Mus canescens. —— micropus. —— xanthopygus. Reithrodon cuniculoïdes. FALKLAND ISLANDS. Mus _decumanus_. —— _Musculus_. STRAITS OF MAGELLAN. Mus xanthorhinus. —— Magellanicus. Reithrodon chinchilloïdes. SECTION—HYSTRICINA. FAMILY— ——? MYOPOTAMUS COYPUS. Myopotamus Coypus, _Auct._ “This animal, in Chile, is known by the name of “Coypu;” at Buenos Ayres, where an extensive trade is carried on with their skins, they are improperly called ‘nutrias,’ or otters. In Paraguay, according to Azara, their Indian name is ‘guiya.’ On the east side of the continent they range from Lat. 24° (Azara) to the Rio Chupat in 43° 20′;—distance of 1160 miles. This latter river is 170 miles south of the Rio Negro, and the intervening space consists of level, extremely arid, and almost desert plains, with no water, or at most one or two small wells. As the Coypu is supposed never to leave the banks of the rivers, and being, from its web-feet and general form of body, badly adapted for travelling on land, its occurrence in this river is a case, like so many others in the geographical distribution of animals, of very difficult explanation. The same remark is indeed applicable, but with less force, to its existence in the Rio Negro. On the west coast, it is found from the valleys of central Chile (Lat. 33) to 48° S., or perhaps even somewhat farther, but not in Tierra del Fuego. So that, on the Atlantic side of the continent, the plains of Patagonia check its range southward, as, on the Pacific side, the deserts of Chile do to the north. Its range, including both sides, is from 24° to 48°, or 1440 miles. In the Chonos Archipelago these animals, instead of inhabiting fresh water, live exclusively in the bays and channels which extend between the innumerable small islets of that group. They make their burrows within the forest, a little way above the rocky beaches. I believe it is far from being a common occurrence, that the same species of any animal should haunt indifferently fresh water, and that of the open sea. We shall see that the Capybara is sometimes found on the islands near the mouth of the Plata; but these cannot be considered as their habitual station in the same manner as the channels in the Chonos Archipelago are to the Coypu. The inhabitants of Chiloe, who sometimes visit this Archipelago for the purpose of fishing, state that these animals do not