Aristotle mentions six amphibious animals, of which only three are known to us, namely, the seal, the beaver, and the otter; the three others, the _latax_, the _satherion_, and the _satyrion_, still remain unknown, because their names are only mentioned without any description of them. In this case, as in all those where we cannot draw any direct induction from a knowledge of the object, we must have recourse to the mode of exclusion: but we cannot make use of that mode with any success, unless we are nearly acquainted with every thing; when that is the case, we can conclude a negative from the positive, and this negative hence becomes a positive fact. For example, I believe that by long study, I have attained a knowledge of almost every quadruped. I know that Aristotle could not have had any knowledge of those peculiar to the continent of America. I also know those which are amphibious, and among these I separate those that belong to America, as the tapir, the cabiai, the ondatra, &c. and then there remains only the amphibious animals of our own continent, namely, the hippopotamus, the walrus, or sea-cow, the sea-wolf of Belon, the beaver, the otter, the sable, the water-rat, the Muscovy musk-rat, the water shrew-mouse, and we may include the ichneumon, which some have looked upon as an amphibious animal, and styled it the Egyptian otter. I retrench from this number the walrus, or sea-cow, the seal, or sea-cow, which being only met with in the northern seas, was not known to Aristotle; I also retrench the hippopotamus, the water-rat, and the ichneumon, because he speaks of them in another part of his work by their proper names; and I likewise retrench the seal, the beaver, and the otter, which are well known, and the water shrew-mouse, because it is too much like the land one to have received a different name. There then remains the sea-wolf of Belon, the sable, and the Muscovy musk-rat, for the _latax_, the _satherion_, and the _satyrion_. Of these three animals, the sea-wolf of Belon is the only one that is larger than the otter, therefore it alone can represent the latax; consequently the sable and the Muscovy musk-rat, must represent the _satherion_ and the _satyrion_. It must, however, be perceived that these conjectures, which I believe to be well founded, are not among the number which time can elucidate, unless some Greek manuscripts shall be discovered which are unknown at present, where these names are made use of, and explained by new indications. THE SEAL, THE WALRUS, AND THE MANATI.