Note 74 — Chapter VII · LIFE IN TEFFÉ.

When I attempted to record my impression of the basin of the Amazons, and characterized it as a fresh-water ocean with an archipelago of islands, I did not mean to limit the comparison to the wide expanse of water and the large number of islands. The resemblance extends much further, and the whole basin may be said to be oceanic also, in the character of its fauna. It is true, we are accustomed to consider the Chromides, the Characines, the Siluroids, and the Goniodonts, which constitute the chief population of this network of rivers, as fresh-water fishes; but in so doing we shut our eyes to their natural affinities, and remember only the medium in which they live. Let any one enter upon a more searching comparison, and he will not fail to perceive that, under the name of Chromides, fishes are united which in their form and general appearance recall several families of the class, only known as inhabitants of the sea. The genus Pterophyllum, for instance, might be placed side by side with the Chætodonts, without apparently violating its natural affinities, since even Cuvier considered it as a Platax. The genera Symphysodon and Uaru would not seem very much out of place, by the side of Brama. The genus Geophagus and allied forms recall at once the Sparoids, with which some of them were associated by earlier ichthyologists; while the genus Crenicichla forms a striking counterpart to the genus Malacanthus. Finally, the genus Acara and their kindred closely resemble the Pomacentroids. Indeed, had not the fresh-water genera Pomotis, Centrarchus, and the like, been erroneously associated with the Percoids, the intimate relations which bind them to the Chromides, and these again to the marine types mentioned above, would long ago have been acknowledged. The genus Monocirrus is a miniature Toxotes, with a barbel. Polycentrus, which is also found in the Amazons, stands nearest to Acara and Heros; it has only a larger number of anal spines. In this connection it ought not to be overlooked that these fishes are not pelagic, like the Scomberoids, but rather archipelagic, if I may use this word to designate fishes dwelling among low islands. If we discard the long-prevailing idea of a close relationship between the Characines and Salmonides, based solely upon the presence of an adipose fin, we may at once perceive how manifold are the affinities between the Characines on one hand, and on the other the Scopelines and Clupeoids, all of which are essentially marine. These relations may be traced to the details of the genera; Gasteropelecus, from the family of Characines, is the pendant of Pristigaster among the Clupeoids, as Chalcinus recalls Pellona. In the same way may Stomias and Chauliodus be compared to Cynodon and the like; or Sudis and Osteoglossum to Megalops, and Erythrinus to Ophicephalus, &c., &c. The Goniodonts may at first sight hardly seem to have any kindred among marine fishes; but if we take into account the affinity which unquestionably links the genus Loricaria and its allies with Pegasus, and further remember that to this day all the ichthyologists, with the sole exception of C. Duméril, have united Pegasus in one order with the Pipe-fishes, it will no longer be doubted that the Goniodonts have at least a remarkable analogy with the Lophobranches, if they should not be considered as bearing a close structural relation to them. But this relation truly exists. The extraordinary mode of rearing their young, which characterizes the various representatives of the old genus Syngnathus, is only matched by the equally curious incubation of the eggs in Loricaria. And as to the other families represented in the basin of the Amazons, such as the Skates, the Sharks, the Tetraodonts, the Flat-fishes (Pleuronectides), the Bill-fishes (Scomberesoces), the Anchovis, Herrings, and other forms of the family of Clupeoids, the Murænoids, the genuine Sciænoids, the Gobioids, &c., &c., they are chiefly known as marine types; while the Cyprinodonts occur elsewhere both in salt and fresh water. The Gymnotines are thus far only known as fresh-water fishes, nor do I see any ground for comparing them to any marine type. They cannot be compared to the Murænoids, with which they have thus far been associated. The only real affinity I can trace in them is with the Mormyri of the Nile and Senegal, and with the Notopteri of the Sunda Islands. Eel-shaped fishes are by no means all related to one another, and their elongated form, with a variety of patterns, is no indication of their relationship. It may, nevertheless, be inferred from what precedes, that the fishes of the Amazons have, as a whole, a marine character peculiarly their own, and not at all to be met with among the inhabitants of the other great rivers of the world.

These peculiarities extend to other classes besides fishes. Among the Bivalve shells, it has long been known that the Amazons nourishes genera of Naiades peculiar to its waters, or only found besides in the other great rivers of South America; such as Hyria, Castalia, and Mycetopus, to which I would add another genus, founded upon slender, sickle-shaped Unios, common to North and South America. But what seems to have escaped the attention of conchologists is the striking resemblance of Hyria and Avicula, of Castalia and Arca, of Mycetopus and Solen, &c. Thus exhibiting another repetition of marine types in a family exclusively limited to fresh waters, and having structural characters of its own, entirely distinct from the marine genera, the appearance of which they so closely ape. In this connection I cannot suppress the remark, that it would be puerile to consider such mimicry as indicative of a community of origin. Some of the land shells even recall marine forms; such are some of the Bulimus tribe, which resemble the genus Phasianella and Littorina far more than their own relatives. The similarity of the fringes of the anterior margin of the foot is particularly striking. The Ampullariæ remind one also, in a measure, of the marine genera Struthiolaria, Natica, &c., and many fossils of the latter family have been confounded with fresh-water Ampullariæ.

The most noticeable feature of the Amazonian fauna, considered with reference to its oceanic character, is, however, the abundance of Cetaceans through its whole extent. Wherever I have navigated these waters, from Pará, where the tides still send the salt brine up the river, to Tabatinga on the borders of Peru, in all the larger and smaller tributaries of the great stream as well as in the many lakes connected with their ever-changing course, I have seen and heard them, gamboling at the surface and snoring rhythmically, when undisturbed in their breathing. At night, especially, when quietly at anchor in the river, you hardly ever fail to be startled by the noise they make, when reaching the surface to exhale forcibly the air they have long retained in their lungs while under water. I have noticed five different species of this order of animals in the waters of the Amazons, four of which belong to the family of Porpoises and one to that of Manatees. Mr. Burkhardt has drawn three of them from fresh specimens for me, and I hope before long to secure equally faithful representations of the others, when I shall describe them all comparatively. One of the Porpoises belongs to the genus Inia, and may be traced on the upper tributaries of the Amazons to Bolivia, another resembles more our common Porpoise, while still another recalls the Dolphin of the sea-coast; but I have been unable to ascertain whether any one of them is identical with the marine species. At all events, the black Porpoise of the bay of Marajo, frequently seen in the vicinity of Pará, is totally different from the gray species seen higher up the stream.—L. A.