x8 93 . THE DISTRIBUTION OF BIRDS. 103 



which forms part of Mr. Allen's Sonoran Sub-Province. On the 

 northern boundaries of the Mexican Province, Mr. Salvin's remarks 

 (" Ibis," 1889, p. 242) must be consulted. On the eastern side it seems 

 to follow the forests as they cling to the mountains almost to the Rio 

 Grande, and the presence of Tinamous, Motmots, and Toucans mark 

 the limit of the Neotropical Region. On the northern side the 

 limits of the Mexican fauna are somewhat more extended and reach 

 to about Alamos in Sonora. 



2. The Isthmian Province, extending from Costa Rica to Panama. 



For the rest of the Neotropical Region, I find that nothing can 

 be proposed in modification of the four sub-regions proposed by 

 Mr. Salvin, and published by Professor Newton in his article on 

 Birds, in the " Encyclopaedia Britannica." They are delineated in the 

 accompanying map. 



III. The Patagonian Sub-Region. This includes the southern 

 portion of South America up to Bahia Blanca on the east coast, "thence 

 in a north-easterly direction, passing to the eastward of Mendoza, and 

 then northward along the eastern and higher slopes of the Andes, 

 until it crosses the Equator, and after trifurcating on either side of the 

 valleys of the Magdalena and its confluent the Cauca, returns along 

 the western slopes of the lofty Cordillera, until it trends seaward and 

 reaches the Pacific Coast of South America somewhere about 

 Truxillo, in lat. 7 S." (C/. Newton, t.c, p. 744.) Mr. Salvin 

 tells me that he considers that, besides the trifurcation of this region 

 in Colombia above referred to, there are outlying portions of the same 

 sub-region in the mountains of Santa Marta and Merida. 



IV. The Brazilian Sub-Region. This " marches with the fore- 

 going until somewhere near Potosi in Bolivia, whence it turns to the 

 north-east, and, avoiding the water-shed of the Amazons, strikes, 

 perhaps, the Paranahyba, through or along which it makes its way 

 to the Atlantic." (C/. Newton, t.c, p. 744.) 



V. The Amazonian Sub- Region limited to the southward 

 by the Brazilian boundary, the western frontier of the Amazonian sub- 

 region seems to turn off before the eastern confines of the Pata- 

 gonian sub-region are reached, and, leaving a space intervening, it 

 pursues a generally northward course, at a lower level, on the western 

 bank of the Huallaga, and crossing the great stream, whence it derives 

 its name, in somewhere about long. 77 W., lat. 5 S., it pursues its 

 way towards the mouth of the Orinoco." (Cf. Newton, t.c, p. 744-) 



VI. The Sub- Andean Sub-Region. "This begins in the south 

 with a narrow strip of land, before mentioned as intervening between 

 the comparatively low-lying Amazonian sub-region and that portion 

 of the Patagonian which runs along the lofty Peruvian Andes, and 

 is believed to extend from the frontiers of Bolivia to the table-land 

 of Ecuador, rounding, on the one hand, the forked extremity of the 

 Patagonian sub-region to the westwards until it meets the Pacific 

 at Truxillo, stretching over five hundred miles of sea to the Gala- 



