Many small rodent animals—squirrels, rats, etc.—complete the terrestrial mammalia of the Amazon district.

The waters of the Amazon, up even to the base of the Andes, are inhabited by several species of true Cetacea, of which, however, we have as yet but very scanty information.

Two, if not more, species of Dolphins are common in every part of the Amazon, and in almost all of its tributaries. They are found above the falls of the Rio Negro, and in the Cassiquiare and Upper Orinooko. They vary in size and colour, and two of them have distinct Indian names.—Piraiowára (Fish-dog), and Tucuxí.

D'Orbigny mentions their being killed by the inhabitants of Bolivia to make oil. In the Lower Amazon and Rio Negro they are scarcely ever caught, and I was unable to obtain a specimen. The species described by D'Orbigny is probably distinct, as he mentions their being twenty feet long, whereas, none I have seen could have exceeded six or seven.

Herbivorous Cetacea are also found in the Amazon; they are called by the Brazilians, Peixe boi, or cow-fish, and by the Indians, Juarouá.

It has not yet been ascertained, whether the cow-fish of the Amazon is the same as the Manatus of the West Indies and the coasts of Guiana, or a distinct species. All the accounts of the Manatus Americanus mention it as being twelve or fifteen feet long on the average, and sometimes reaching twenty. Those of the Amazon appear to average seven or eight feet only; of five or six specimens I have myself seen, none have exceeded this; Lieutenant Smyth saw one on the Upper Uaycáli, of the same size; and Condamine describes the one he saw as not being larger.

The inhabitants of the Amazon give accounts of three kinds, which they seem to consider distinct, one smaller, and one larger than the common kind, and differing also in the shape of the tail and fins, and in the colour.

The West Indian species is always described as having external nails on the edge of the fin, or fore-arm. This I never observed in the Amazon species; though in cutting the edge of the fin to take out the bones entire, I must have noticed them, had they been as prominent as they are usually described; neither does Lieutenant Smyth mention them, though he could hardly have overlooked so singular an external character.

I am therefore inclined to think that the Amazon possesses one or two distinct species. Having carefully prepared a skin and skeleton of a fine male (which, with the rest of my collections, was lost on the voyage home), I did not describe it so minutely as I otherwise should have done, but have some notes, referring to male and female specimens, which I will now give:—