762 Mr. W. P. Pycraft on the 



The features to be explained are, briefiv, the presence in 

 (central America — which lies within the Tropics — of species 

 belonging; to the temperate regions to the north, and 

 the absence of corresponding elements from the south 

 Temperate Region ; the selective factors which have limited 

 the number of tropical South American species within its 

 borders ; the charac'^er of its autochthonous types ; and 

 the relation of the fauna, as a whole, to that of the Old 

 World and to past geologic times. 



In the fulness of time these several aspects of the 

 problem will doubtless be more or less satisfactorily com- 

 pleted ; but at the present stage of our knowledge this is 

 far from accom[)lisliment. 



Though the remains of extinct birds are unfortunately 

 rare, such as have been brought to light have shown, in the 

 Hrst place, that many forms now confined to the Tropics, 

 in earlier times occurred in western Europe, when the 

 climatic conditions were doubtless widely different from 

 those now obtaining ; and, in the second, that some of 

 the most characteristic New World types have been derived 

 from the Old World. 



Thus, for example, remains of Uinturnis, an incipient 

 Woodpecker, and of Ctyptoniis, a primitive Hornbill, have 

 been found in the Eocene both of F'rance and Wyoming. 

 To-day the Picidse are almost cosmopolitan, being absent 

 only from Madagascar, Polynesia, and Australia; while 

 the Hornl)ilLs occur throughout Ethiopia and Indo-Malaya. 

 Remains of Limnator7iis, a Hoopoe, Necroinis, a Plantain- 

 eater, and of a Trogon have been found in the Oligocene, 

 and of Psittacus in the Lower Miocene of France. The 

 Trogons, indeed, are represented in the Eocene of France 

 (Phosphorites du Quercy) by three species of Arch(eotrogon. 



The Hoactzin [Opisthocomus) and the Cathaitidse are 

 commonly regarded as autochthonous New World types ; 

 but their remains have also been found in the Eocene of 

 France. 



Ornithologists hitherto, in discussing problems of dis- 

 tribution in space, have seldom taken into account that no 



