DISTRIBUTION OF THE FISHES 63 
few scattered pioneer types from the lowland. The fourth zone presents, appar- 
ently, the limitless waters of the tropical lowlands, with its opportunities for an 
ageressive or resourceful species. To this zone belong the greater part of the 
characin and catfish faunas, which have responded to the opportunity in an un- 
paralleled way. Events have transpired in such a way as to permit not a few 
marine or estuarine fishes to become readjusted to the fresh waters of the new habi- 
tats, so that the uppermost Amazon remote from the sea has its stingrays, its 
flatfishes, puffers, anchovies, ete., as well as its otter, porpoises, and manatees. 
At Cayumba rapids, 8000 miles from the ocean, even a crab was found, elevation 
1800. feet. 
Table II shows at least qualitatively the degrees of relationship between our 
area and other major systems. Unique species are not given, not being of value 
for comparison. As should be expected most, 201, of the lowland fishes given in 
the table belong to the Brazilian Amazon also. The entire Amazon isa unit from its 
mouth to the point where it was an inland sea washing the foothills of the Andes. 
One-hundred ten, less than half the 246 lowland Peruvian species, have also sur- 
mounted the low barriers of the upper Madeira to the Beni, Mamoré, and Paraguay. 
Pearson, 1937b, in a total of 485 species from Bolivia (including also mountain 
species and uniques) finds 316 common to the Paraguay, 229 found in the Amazon. 
The Guiana fauna has no less than 97 species reaching the lowlands of Peru, indi- 
cating a not very remote separation biologically. There is little doubt that the 
68 species mutual to lowland Peru and Venezuela or westward show only the lack 
of exploration of the farther reaches of the Orinoco. 
The streams of the Atlantic seaboard are short and disconnected, and he on 
the farther slopes of the Brazilian plateau, and our table lists only some 26 of their 
species in the lowlands of Peru. 
The fishes of the highlands are almost wholly distinct from those of other 
regions. The intent of Table III is, therefore, not to make comparisons with 
outside areas, but to analyze the distribution within the region itself. Uniques 
are included. 
The Maranon and Santiago boast the largest number of known species, 34, in 
elevations mostly 3000-4000 feet. It will be noted that most of them are either 
lowland species or closely allied to them, obviously derived from the Amazon fauna, 
which has met with considerable success in passing barriers formerly considered 
impassible. The greatest obstacle to passage upstream is to be met at the point 
of emergence from the intercordilleran valley upon the Amazonian plain, the water- 
gap known as the Pongo de Manseriche. When I visited it, I was informed that a 
number of steam launches had succeeded in ascending the rapids, while the books 
tell of numbers of canoe-parties making their way through the pongo safely. It 
has therefore not constituted a very formidable barrier to lowland fishes. The 
larger Pimelodus-types, flying-fishes, piraruci, and fishes of great size, quiet waters, 
marshy habitats, etc., have not made the ascent. The smaller, intrusive or suck- 
ing-mouthed types, and mountain types of Characin, such as Hemibrycon, have 
done better, including two Gymnotids. 
The Pichis river is a good example of a lowland stream deeply invading the 
