376 - PROCEEDINGS OF THE NATIONAL MUSEUM VOL. 97 
1931 
Feb. 19 Caiio Pamoni, Brazo Casiquiare. 
Feb. 20 Cafio Mabinagui, Brazo Casiquiare. 
Feb. 21 Buenos Aires, Brazo Casiquiare. 
Feb. 22 Brazo Casiquiare, below Cafio Caripo. 
Feb. 23 Upper Orinoco, Tamatama. 
Feb. 24 Upper Orinoco, near Cerro Cariche. 
Feb. 25 Upper Orinoco, near Isla Temblador. 
Feb. 28—Mar. 9 Upper Orinoco, San Antonio. 
Mar. 12-16 Upper Orinoco, right bank opposite Corocoro Island. 
Mar. 17-23 Upper Orinoco, base camp, Cerro Yapacana. 
Mar. 23-Apr. 29 Upper Orinoco, Cerro Yapacana, 
May 8-23 Rio Orinoco, Puerto Ayacucho. 
June 8-11 Rio Orinoco, Ciudad Bolfvar. 
June 11-12 Rio Orinoco, Soledad, Anzodtegui. 
Just as Holt has written a descriptive account of the first trip, he 
also published a similar paper on the second, under the title “‘A 
Journey by Jungle Rivers to the Home of the Cock-of-the-Rock” 
(Nat. Geogr. Mag., vol. 64, Nov. 1933, pp. 585-630). To these 
two articles the interested reader is referred for descriptions of parts 
of the areas traversed. For the present report the map and the 
photographs, kindly furnished by the National Geographic Society, 
will serve in lieu of description. 
Aside from adding to our knowledge of the variations, plumages, 
and distribution of many of the nearly 500 kinds of birds collected, 
the present material has been studied in the hope that it might 
throw some light on the general problem of the variational and dis- 
tributional behavior of species and subspecies at the meeting place 
of two faunal areas, the Amazonian and the Orinocoan. As the study 
progressed and species after species was examined it became apparent 
that there is no marked distinction between the bird life of the Upper 
Amazon and the Rio Negro on the one hand and that of the Casiquiare 
and Upper Orinoco on the other. The two river systems are appar- 
ently so much older than the birds that dwell in their drainage basins 
and the watershed between them became practically nonexistent at 
such an early time geologically that the distribution of the bird 
species today reflects nothing of what may have been an originally 
quite different topographic picture. The statement that the water- 
shed between them became nonexistent is intended to apply pri- 
marily to the routes of the main streams—the Upper Orinoco and 
the Upper Rio Negro, which are, in fact, connected by tbe Casi- 
quiare, a true canallike stream which drains Orinoco water southward 
into the Amazonian system. There is still something of a real water- 
shed along the more eastern part of the Brazilian-Venezuelan and 
the Brazilian-Guianan borders. The great age of the present un- 
interrupted terrain of low forested country from the Upper Rio 
