INDEX 209 LIST OF PLATES IN VOL. I. Plate Page I. MIMUS TRIURUS 8 II. CINCLUS SCHULZI 11 III. Fig. 1. CYCLORHIS OCHROCEPHALA 23 Fig. 2. CYCLORHIS ALTIROSTRIS 24 IV. STEPHANOPHORUS LEUCOCEPHALUS 38 V. SALTATRICULA MULTICOLOR 61 VI. Fig. 1. MOLOTHRUS BADIUS, ad. 95 Fig. 2. MOLOTHRUS RUFOAXILLARIS, pull. 86 VII. TÆNIOPTERA RUBETRA 120 VIII. PHYTOTOMA RUTILA, ♂ et ♀ 164 IX. HOMORUS LOPHOTES 195 X. DRYMORNIS BRIDGESI 199 INTRODUCTION. As regards its Bird-life the Neotropical Region, which, according to the arrangement usually adopted, consists of America south of the Isthmus of Tehuantepec together with the West Indies[1], may be most conveniently divided into six Subregions. These are:-- [1] _Cf._ Sclater, Journ. Linn. Soc., Zool. ii. p. 143 (1857). 1. The _Transpanamic Subregion_, embracing the great Central-American Isthmus from Tehuantepec down to Panama. 2. The _Antillean Subregion_, containing the West-India Islands. 3. The _Colombian Subregion_, containing the South-American littoral and the adjacent Andean ranges in Venezuela, Colombia, Ecuador, Peru, and Bolivia. 4. The _Amazonian Subregion_, containing Guiana and the valleys of the Orinoco and Amazons and their confluents. 5. The _Brazilian Subregion_, containing the great wooded and campos districts of Southern Brazil and Paraguay. 6. The _Patagonian Subregion_, consisting of Antarctic America up to the Brazilian wood-districts and the highlands of Bolivia on the eastern side of the Andes, and apparently extending as far as the Gulf of Guayaquil on the west. It is, of course, impossible to draw a precise line between these six Subregions, and any boundaries assigned to them can only be regarded as approximative; but it is obvious that nearly, if not quite, the whole of the Argentine Republic, the Avifauna of which we are now considering, comes within the limits of the Patagonian Subregion. It is possible that the birds of the Territory of Misiones and of some parts of Northern Corrientes may be more nearly akin to those of Brazil, but we may say generally that the Argentine Republic belongs to the Patagonian Subregion. As shown in the succeeding pages, the number of species of Birds as yet ascertained to be found within the Argentine Republic[2] is about 430. We will now take the leading groups of the Neotropical Ornis, one after another, and consider the _rôle_ they play in the Argentine Avifauna, so as to get some general ideas as to its peculiarities.