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.
[53]. The opportunity of watching these fishes in their natural element, and keeping many of them alive for hours or days in our glass tanks, was very instructive, and suggested comparisons not dreamed of before. Our arrangements were very convenient; and as the commander of the steamer allowed me to encumber the deck with all sorts of scientific apparatus, I had a number of large glass dishes and wooden tubs in which I kept such specimens as I wished to investigate with special care and to have drawn from life. One of the most striking changes made by J. Müller, in the classification of the spiny fishes, was the separation into a distinct order, under the name of Pharyngognathi, of all those in which the pharyngeal bones are soldered together. With these the illustrious German anatomist has associated a number of soft-rayed types, formerly united with the Pickerels and Herrings, and characterized by the same structure. It would thus seem that there is here a definite anatomical character easily traceable, by the aid of which a vast number of fishes might be correctly classified. But the question at once arises, Are these fishes truly related to one another, and so combined in this new order of Pharyngognathi as to include all which properly belong with them, and none others? I think not. I believe that Müller has always placed too much value upon isolated anatomical characters; and, while he was undoubtedly one of the greatest anatomists and physiologists of our age, he lacked zoölogical tact. This is especially evident with reference to the order of Pharyngognathi, for though the Scomberesoces have fixed pharyngeals like Chromides, Pomacentrides, Labroids, Holconotes, and Gerrides, they have no real affinities with these families. Again, the character assigned to this order is not constant even in the typical Pharyngognathi. I have found Chromides and Gerrides with movable pharyngeals; in the genus Cychla they are normally so. It is therefore not out of place to state here that the Chromides of South America are in reality closely related to a group of fishes very generally found in the United States, known as Pomotis, Bryttus, Centrarchus, etc., and usually referred to the family of Perches, from which they have, however, been separated by Dr. Holbrook under the name of Helichthyoids. They not only resemble the Chromides in their form, but even in their habits, mode of reproduction, peculiar movements, and even in their coloration. Cuvier has already shown that Enoplosus is not a member of the family of Chætodonts, and I may now add that it is a near relative of the Chromides, and should stand by the side of Pterophyllum in a natural system. Monocirrus of Heckel, which I consider as the type of a small family under the name of Folhidæ, is also closely allied to these, though provided with a barbel, and should be placed with Polycentrus side by side with the Chromides and Helichthyoids. The manner in which Pterophyllum moves is quite peculiar. The profile of the head and the extended anterior margin of the high dorsal are brought on a level, parallel to the surface of the water, when the long ventrals and high anal hang down vertically, and the fish progresses slowly by the lateral beating of the tail.—L. A.
[54].
On the Xingu, August 23d, 1865.
My dear Friend:—I am worn out with fatigue, but I will not go to rest before writing you a word. Yesterday evening we obtained twenty-seven species of fish at Gurupá and this morning fifty-seven at Porto do Moz,—eighty-four species in all, in less than twelve hours, and of this number fifty-one are new. It is wonderful. I can no longer put in order what is brought to me as fast as it arrives, and as to obtaining colored drawings of all, it is no longer possible, unless we pass a whole week here on our return.
Wholly yours,
L. Agassiz.
[55]. Representations of these hills may be found in the Atlas of Martius and in Bates’s “Naturalist on the Amazons.”