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U. S. P. R. R. EXP. AND SURVEYS-ZOOLOGY—GENERAL REPORT. 
Family CYPSELIDAE. The Swifts. 
Bill very small, without notch, triangular, much broader than high ; the culmen not one-sixth the gape. Anterior toes cleft 
to the base, each with three joints, (in the typical species,1 and covered with skin ; the middle claw without any serrations; the 
lateral toes nearly equal to the middle. Bill without bristles, but with minute feathersextending along the under margin of the 
nostrils. Nostrils elongated, superior, and very close together. Plumage compact. Primaries ten elongated, falcate. 
The Cypselidae , or Swifts, are swallow-like birds, generally of rather dull plumage and small 
size. They were formerly associated with the true swallows cn account of their small, deeply 
cleft bill, short feet, and long wings. They are, however, very different in all the essentials of 
structure, belonging indeed to a different order, or sub-order. The bill is much smaller and 
shorter ; the edges greatly inflected ; the nostrils superior, instead of lateral, and without 
bristles. The wing is more falcate, with ten primaries instead of nine. The tail has ten. 
feathers instead of twelve. The feet are weaker, without distinct scutellae ; the hind toe is 
more or less versatile, the anterior toes usually lack the normal number of joints, and there are 
other features which clearly justify the wide separation here given, especially the difference in 
the vocal organs. 
There are some forms of Cypselidae in which the usual proportional length of toes and number of 
their joints is as in other birds; nearly all the typical Old World genera, however, agree with the 
diagnosis above given. It is exceedingly probable, however, that the American genera have all 
the normal number of joints to the anterior toes, (3, 4, 5,) Panyptila, probably, not even form¬ 
ing an exception ; in this case they will he widely separated from the great majority at least, of 
the Old World species, which have 3, 3, 3. It may therefore he proper, on account of these 
and other differences, to divide the family into Cypselinae, confined to the Old World, and 
Chaeturinae, American and Asiatic. 
The American Cypselidae are readily distinguished by characters of the legs, and including 
the Old World Cypselus , which has no true representative in this country, convenient diagnoses 
of the genera will be as follows, without reference to other features : 
A. Legs very thick, more or less feathered. Tail forked. Second primary longest. Hind 
toe not posterior. 
Cypselus. —Hind toe directed entirely forward. Legs feathered to the base of the toes. 
Panyptila. —Hind toe directed laterally. Legs feathered to the base of the claws. 
B. Legs slender : naked. Hind toe directed backwards ; first primary longest. 
Nephocaeies. —Tail forked ; soft. 
Chaetura. —Tail even, the shafts stiffened and projecting as spinous points. 
PANYPTILA, Cab an is. 
Panyptila, Cabanis, Wiegm. Archiv, 1847, I, 345.— Burmeister, Thiere Bras. Vogel, I, 1856, 368. 
Pseudoprocne, Strecbel, Isis, 1848, 357. 
Tail half as long as the wings, moderately forked ; the feathers rather lanceolate, rounded at tip, the shafts stiffened but not 
projecting. First primary shorter than the second. Tarsi, toes, and claws very thick and stout; the former shorter than the 
middle toe and claw, which is rather longer than the lateral one ; middle claw longer than its digit. Hind toe very short ; half 
versatile, or inserted on the side of the tarsus. Tarsi and toes feathered to the claws, except on the under surfaces. 
The North American representative of this genus, with a general resemblance to Cypselus 
apus in form, is quite different in the structure of the feet These are stouter and shorter, 
feathered to the very claws, instead of to the toes only, and the posterior or inferior surface of 
