scattered among the Labroides and the Sciænoids, really constitute a natural group recognized nearly at the same time and in an independent manner by Heckel and J. Müller. But, beside these, there are the genera Enoplosus, Pomotis, Centrarchus, and some other neighboring genera, classed among the Percoids by all Ichthyologists, which seem to me, from this distance and without means of direct comparison, so near the Chromides that I do not see how they can be separated, especially now that I know the lower pharyngials not to be invariably soldered in the Chromides. And then the embryology and metamorphoses of the Chromides, which I have just been studying, have convinced me that the fishes with labyrinthic branchiæ, separated from all other fishes by Cuvier, as a family entirely isolated on account of the strange structure of its respiratory organs, are closely related to the Chromides. Thus this group becomes, by its various affinities, one of the most interesting of the class of fishes, and the basin of the Amazons seems to be the true home of this family. I will not fatigue you with my ichthyological researches; let me only add, that the fishes are not uniformly spread over this great basin. I have already acquired the certainty that we must distinguish several ichthyological faunæ very clearly characterized. Thus the species inhabiting the river of Pará, from the borders of the sea to the mouth of the Tocantins, differ from those which are met in the network of anastomoses uniting the river of Pará with the Amazons proper. The species of the Amazons below the Xingu differ from those which occur higher up; those of the lower course of the Xingu differ from those of the lower course of the Tapajoz. Those of the numerous igarapés and lakes of Manaos differ as much from those of the principal course of the great river and of its great affluents. It remains now to study the changes which may take place in this distribution in the course of the year, according to the height of the waters, and perhaps also according to the epoch at which the different species lay their eggs. Thus far I have met but a small number of species having a very extensive area of distribution. One of those is the Sudis gigas, found almost everywhere. It is the most important fish of the river, that which, as food, corresponds to cattle for the population along the banks. Another problem to be solved is, how far this phenomenon of the local distribution of fishes is repeated in the great affluents of the Amazons. I shall try to solve it in ascending the Rio Negro and Rio Madeira, and as I return to Manaos I shall be able to compare my first observations in this locality with those of another season of the year. Adieu, my dear friend. Remember me to M. Elie de Beaumont and to those of my colleagues of the Academy who are interested in my present studies. My kind remembrance also to your son.