AEEONAUTES. 367 



having four and the fourth toe five phalanges. This section is again divided into 

 ChaeturinsB and Malcopteryginae, the latter being restricted to the Indo-Malayan region 

 and New Guinea. 



We have therefore here only to do with the CypselinEe and ChEeturinse, which are 

 difierentiated by the structure of their toes. 



This curious feature has long been known, but its development has only recently 

 been examined by Herr L. Zehntner (' Zoologischer Anzeiger,' No. 319 (1889), and 

 'Ibis,' 1890, p. 196) in embryos of Cypselus melba. The result shows pretty conclusively 

 that in the intermediate stages of development the embryo of that species possesses 

 the normal number of phalanges, but that as growth advances one phalange in the 

 third toe and two in the fourth are lost by absorption into adjoining joints. 



The exceedingly rapid flight, often at a great height in the air, of the Cypselidee 

 generally, is a reason for their being seldom represented in collections of bird-skins, 

 few native collectors being able to shoot them. It is only by resorting to their 

 nesting- or roosting-places that any number of specimens can be obtained. 



Subfam. CYPSELINjE. 



To this subfamily belong the genera of Cypselidse which have an abnormal number 

 of phalanges to the middle and outer toes, the middle toe having only three phalanges 

 instead of four and the outer also three instead of five. The true Swifts of the Old 

 World all belong here, and two South- American species are comprised in the same 

 genus Cypselus. It includes A'eronautes and Panyptila, both peculiar to America, and 

 also one of the Palm-Swifts of the genus Tachornis and its ally Claudia. 



Of the twenty-four or twenty-five known species of Cypselinae only seven or eight 

 occur in the New World, and of these only one, Aeronautes melanoleucus, a bird of 

 our country, is found north of Mexico. Panyptila is represented within our limits by 

 all its species. Cypselus itself (in the New World) is confined to the Andes of South 

 America, neither Tachornis nor Claudia occurring at all. With Tachornis, a genus 

 represented in some of the larger Antilles by T. phoenicobia, Mr. Hartert associates 

 the Palm-Swifts of the East, and assigns a new generic name {Claudia} to Cypselus 

 squamatus of South America. 



AERONAUTES. 



Aeronautes, Hartert, Cat. Birds Brit. Mus. xvi. p. 459 (1892). 

 Panyptila (partim), Baird et auctt. 



This genus is very closely allied to Cypselus on the one hand and Panyptila on the 

 other, so much so that the single species it contains has been placed sometimes in one 



