64 FISHES OF WESTERN SOUTH AMERICA 
highlands, and certain other lowland fishes have readily made their way there, such 
as Bario or Tetragonopterus argenteus. Ease of access has made it equally desirable 
to fishes and to the canoes and launches of the Via Central. 
The Tarma-Chanchomayo-Perené drainage is one with numerous rapids and 
much difficulty of ascent; thirteen species were taken, nine of them lowland forms. 
The middle Huallaga has been represented by such small and casual collec- 
tions that we might be misled into believing that few aggressive lowland forms 
have populated it from below; probably many more will be found than the ten 
listed from R. Huambo and R. de Totora. Juan Mesa, a riverman, was able to 
name for me offhand more than twenty which he had known at Tingo Maria at 
the mouth of the Monzon. My collecting in the troubled waters of the Upper 
Huallaga (from Cayumba rapids at 2000 feet to 14000 feet) and Dr. Eigenmann’s 
collections in the sources of its tributary, the R. Yanahuana produced a total of 
thirteen species. The Cascada de Cayumba I found to be a much more precipitous 
hazard than the Pongo de Manseriche, and, I believe, satisfactorily accounts for 
our total of only thirteen species above it, as against 34 of the Alto Maranon. 
The middle Urubamba is guarded from the invasion of lowland fishes by the 
formidable Pongo de Mainique, which I did not visit. (Bowman, 1916.) Yet it is 
far from being fish-proof, since 22 species have been recovered from the river above 
this point, 15 of which should be classed as lowland forms, seven from the upper 
reaches of the river and its tributaries. From the number of lowland forms it 
should be rated between the Maranon and the Huallaga as to ease of invasion. It 
must also be remembered that the headwaters of the Urubamba and those of the 
Maranon are at about the same elevation, but that the former has about twice the 
distance in which to climb a stair of equal height. Except for extreme barriers, 
the longer streams should have the more abundant fauna. Unfortunately the 
records from the Apurimac, which should give light on this point, are very scanty. 
Our collections show that only the genera Orestias, Pygidium, Astroblepus, 
with some Chaetostoma, belong to the fauna of the high Andes. The center of 
dispersal of Astroblepus appears to be in the lower elevations of the Andes of South- 
ern Ecuador, diminishing in species southward. Pygidium centers farther south, 
some 26 species having been collected north of our area, some 39 southward, most 
of them following the crests of the ranges. 
Aside from the climbers mentioned above, we have the same types of Characins 
recurring in the Urubamba as in the North, such as the Astyanax-Hemibrycon- 
Bryconamericus group, and the same Apteronotus and Sternopygus. Most of the 
remainder are uniques. 
The Titicaca basin has produced most of the Orestias. Except for the two 
which have arisen in central Peru (Province E) and three in the upper Urubamba 
valley, the genus is still limited to that basin. 
Orestias is the only clear-cut endemic genus of the upland pampas of the 
Andes; Astroblepus is probably so, but has representatives well down toward sea- 
level. There is more doubt about the widely dispersed Pygidium. While Othono- 
cheirodus, our Hemibrycon, Ceratobranchia, Bryconamericus, and Creagrutus are 
