318 Annals of the Carnegie Museum. 



side of the Gulf, while south of that come the Grande de Pirris and 

 lastly the Diquis or Rio Grande de Terraba, which drains a very large 

 area, and is the only Costa Rican River with a delta, having five 

 mouths opening directly into the Pacific Ocean. 



The Life-Zones. 



In attempting a study and definition of the life-zones of this region 

 and their proper correlation with those of North and South America, 

 almost insurmountable obstacles are encountered in the beginning, 

 because of our exceedingly fragmentary knowledge of the local distri- 

 bution of life in Costa Rica. It is quite true that we have fairly com- 

 plete lists of the birds, mammals, and plants of most of the Central 

 American countries, but so little importance has been attached by col- 

 lectors in general to the significance of altitude and humidity, that 

 very little has been recorded which tends to throw light on some of 

 the more obscure points. Carelessness in labelling has tended to ren- 

 der matters more confusing. 



There is no question that Dr. Merriam has solved the fundamental 

 problems of the distribution of life and the life-zones in North 

 America, and his scheme is certainly the most satisfactory and feasible 

 yet advanced. It is also quite certain that the distribution of a por- 

 tion of the bird-life of Central America, with respect to altitude, has 

 a direct correlation with the life-zones of North America. In Central 

 America, however, we have a much more complicated state of affairs 

 than in North America. Here are to be found representatives of 

 the three great primal groups, which constitute the fauna of the 

 northern half of the western hemisphere, the Boreal, the Sonoran, and 

 the Tropical, the first two coming down from the north and the last 

 coming up from the south, and all overlapping in Costa Rica. Some 

 zones or belts of the Tropical occupy exactly the same ground as some 

 of the Sonoran, so that it is only by studying the affinities of the 

 various species and determining whether they are modified Tropical 

 or Sonoran forms, that we are able to account for their presence in 

 certain regions and give a reasonable explanation of the finding of two 

 widely different types in apparently the same zone. 



It is therefore with the hope of stimulating investigation along these 

 lines that the present tentative outline of the different life-areas, their 

 origin and affinities, is attempted. The present uncertainty in regard 

 to the real position of some of the neotropical species only adds to the 



