AERONAUTES. 367 
having four and the fourth toe five phalanges. This section is again divided into 
Cheeturinee and Malcopterygine, the latter being restricted to the Indo-Malayan region 
and New Guinea. 
We have therefore here only to do with the Cypseline and Cheturine, which are 
differentiated 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. CYPSELINA. 
To this subfamily belong the genera of Cypselidee 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 Aéronautes 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 Cypseline only seven or eight 
occur in the New World, and of these only one, Aéronautes melanoleucus, a bird of 
our country, is found north cf 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 Zachornis nor Claudia occurring at all. With Yachornis, a genus 
represented in some of the larger Antilles by 7. phenicobia, Mr. Hartert associates 
the Palm-Swifts of the East, and assigns a new generic name (Claudia) to Cypselus 
squamatus of South America. 
AKRONAUTES. 
Aéronautes, 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 
