MY DEAR FRIEND:—Yesterday was a most instructive day,—above all, in the “forest fishes.” We have obtained fifteen species in all. Out of this number ten are new, four are found also in Pará, and one has been already described by me in the voyage of Spix and Martius; but what is most interesting is the proof furnished by these species, taken in their totality, that the fishes inhabiting the waters west of the group of islands called Marajó, when considered as a whole, differ from those of the Pará river. The list of names which we have asked from the Indians shows, further, that the number of species found in these localities exceeds greatly that which we have been able to procure; for this reason we have left cans at Breves and at Tajapurú in order to complete the collection. I add some remarks which will help you to appreciate these differences, if you wish to compare them with the catalogue of the Pará species which I left with you. Considering all, it seems to me already apparent that our voyage will make a revolution in Ichthyology. In the first place, the Jacundá of Tajapurú is different from those of Pará; so is the Acará; then we have a new species of Sarapó, and also one of Jeju; a new species of Rabeca, a new species of Anojá, a new genus of Candiru, a new genus of Bagre, a new genus of Acary, and a new species of Acary belonging to the same genus as that of Pará; also a new species of Matupirim. Add to this a species of Aracú, already described, but which is not found at Pará, and you will have at Tajapurú eleven species which do not exist at Pará, to which must be added four species which are found at Tajapurú as well as at Pará, and one which occurs at Pará, Breves, and Tajapurú. In all twenty species, of which fifteen are new, in two days. Unhappily, the Indians have misunderstood our directions, and have brought us but one specimen of each species. There remains, then, much to do in these localities, judging from the catalogue of names collected by Major Coutinho, which includes twenty-six species from the forest and forty-six from the river. We are still lacking at least fifty-two species from Tajapurú, even supposing that this locality contains also the five species from Breves. You see that we shall yet leave a large share of the work to our successors. Adieu for to-day, your affectionate L. AGASSIZ. Footnote 53: