I was especially interested in seeing living Gymnotini. I do not here allude to the electric Gymnotus, already so fully described by Humboldt that nothing remains to be said about it; but to the smaller representatives of that curious family, known as Carapus, Sternopygus, Sternarchus and Rhamphichthys. The Carapus, called Sarapos throughout Brazil, are very numerous, and the most lively of the whole group. Their motions are winding and rapid like those of the Eel, but yet different, inasmuch as they do not glide quickly forward, but, like Cobitis and Petromyzon, turn frequent somersets and change their direction constantly. This is also the case with the Sternopygus and Sternarchus, and even the larger and more slender Rhamphichthys have a kind of rolling motion. Though I had expected to find many Cyprinodonts, yet their great variety astonished me, and still more was I struck by their resemblance to Melanura, Umbra, and the Erythrinoids. The presence of Belone and allied forms also surprised me. Our stay on the shores of José Assú and Lago Maximo was particularly instructive on account of the numerous specimens of each species daily brought in by Laudigári and Maia. It afforded me a welcome opportunity for studying the differences exhibited by these fishes at different periods of life. No type passes, in that respect, through greater changes than the Chromides, and among them the genus Cychla is perhaps the most variable. I am sure that no ichthyologist could at first sight believe that their young are really the early stage of the forms known in our ichthyological works as Cychla monocolus, Cychla temensis, and Cychla saxatilis. The males and females also vary greatly during the spawning season, and the hump on the top of the head described as a specific character in Cychla nigro-maculata is a protuberance only found in the male, swelling during the period of spawning and soon disappearing. Once familiar with the young brood of some species of Chromides, it became easy for me to distinguish a great variety of small types, no doubt hitherto overlooked by naturalists travelling in this region, simply under the impression that they must be the young of larger species. A similar investigation of the young of Serrasalmo, Myletes, Tetragonopterus, Cynodon, Anodus, &c. led me to the discovery of an equally large number of diminutive types of Characines, many of which, when full grown, do not exceed one inch in length; among them are some of the most beautiful fishes I have ever seen, so far as the brilliancy and variety of their colors are concerned. Thus everything contributed to swell the collections,—the localities selected as well as the mode of investigating. I should add here, that, several years before my own journey on the Amazons, I had been indebted to the Rev. Mr. Fletcher for a valuable collection of fishes from this and other Amazonian localities.