1876.] 403 [Garman. 



Sarkady, Seeva, Steindachner, the Thayer and Hassler Expeditions, 

 and others, which contain representatives of local faunas from many 

 points between Mexico and Patagonia inclusive. 



In the greater portion of tropical America the diversity of surface 

 is not excessive, and since in the torrid zone the conditions of light 

 and heat are least variable, we are naturally led to expect to find the 

 species, compared with those of other latitudes, more widely dis- 

 tributed and at the same time less affected by variations in color or 

 covering. The specimens before me accord well with this idea. In 

 a comprehensive view of the South American Reptilia and Batrachia 

 the species seem to fall naturally into four groups, representing as 

 many more or less distinct faunal areas. As indicated by these 

 groups we have a northern section, comprising all of northern South 

 America, including Ecuador and Brazil — except the southeastern 

 part — and extending over the Isthmus to the table land of Mexico; 

 an eastern, containing that portion of Brazil included in Pernambuco 

 and the provinces to the southward; a southern, made up of the 

 pampas of the Argentine Confederation and Patagonia; and a west- 

 ern, which includes the plateaus and western slopes of the Andes in 

 Chili, Bolivia and Peru. For convenience they may be designated 

 as the torrid, eastern, pampan and andean sections. 



Physical features that arc hardly noticed in the movements of the 

 species of one class of animals, assume very imposing proportions in 

 connection with those of species of another. An elevation or an 

 arid region over which the majority of species of the first passes 

 freely offers an insurmountable obstacle to those of the second. 



In a general way, speaking of Reptiles and Batrachians, the geo- 

 graphical conformations present little or no hindrance to the spread 

 of a species between the Amazon- Orinoco basin and the Isthmus or 

 western Ecuador, while the existence of a tolerably effective separa- 

 tion between the Amazon basin and the eastern section, needs no 

 plainer demonstration than that afforded by the difference of their 

 respective faunas. As for the Surinam region, I know of no really 

 distinct form belonging there. Pipa, or as it is commonly called, the 

 Surinam Toad, is represented in the Museum from the Madeira, and 

 Spix is authority for the statement that it occurs in the waters near 

 Bahia. Southward from the Isthmus, on the west coast, a limit is 

 reached in the sterility of northwest Peru. The separation of the 

 North American species from those of the south is effected by the 

 table land of Mexico; it is not absolute, however, a few species 

 being common to both sides. 



