Io6 Allen, Origin and Distribution of N. A. Birds. X April 



sentatives in the rdle they fill in nature's economy. The Auks 

 number 13 genera and about 24 species, displaying considerable 

 diversity in size and form, and especially in the size and structure 

 of the bill, and in the character of the nuptial ornaments. Con- 

 sidering their high northern range, one is struck with the greatly 

 circumscribed distribution of many of the genera, only five out 

 of the 13 being circumpolar, three being confined to the shores 

 of the North Atlantic and Eastern Arctic Oceans, and five to the 

 shores of the North Pacific and Bering Sea. Their limited dis- 

 tribution and diversity of structure indicate a plastic group of 

 comparatively modern development. Being maritime species, 

 none of even the non-circumpolar species can be claimed as dis- 

 tinctively either North American or Eurasiatic. In favor of 

 their recent origin is the fact that, while almost arctic in habitat, 

 few of the genera have acquired a circumpolar distribution, as 

 they would in all probability have done had they existed in the 

 same diversity in preglacial times. The locally restricted forms, 

 moreover, occupy a region where food is exceptionally abundant. 



Of the three families of Longipennes, — Stercorariidaa, Laridaa 

 and Rynchopidte, — the Hrst is arctic, the second of world-wide 

 distribution, and the third essentially tropical. Even the genera 

 of the Longipennes are for the most part either circumpolar, cos- 

 mopolitan or tropicopolitan. Not a single genus is distinctively 

 North American, and many of the species are either circumpolar 

 or nearly cosmopolitan. 



The Tubinares are so largely pelagic, so wide-ranging, and 

 for the most part so little known as regards their breeding 

 stations, that they will be dismissed without further consider- 

 ation. 



Of the six families of Steganopodes four — Phaethontidae, 

 Sulidae, Anhingidae and Fregatidaa — are essentially tropical ; 

 another, Pelecanidaa, is semi-cosmopolitan, being found almost 

 everywhere outside of the arctic and subarctic regions. The 

 remaining family, the Cormorants (Phalacrocoracidae), is univer- 

 sally distributed, though the species are largely maritime rather 

 than inland, where they frequent only the larger rivers and 

 lakes. Not a single genus of this whole order is distinctively 

 North American. They are all birds of strong flight, and are 

 apparently old types which have long had a wide distribution, 

 the remains of Gannets, Cormorants and Pelicans occurring in 

 deposits of Miocene age in both North America and Europe. 



