384 
DR. R. W. SHUPELDt’s MORPHOLOGICAL 
In the anatomy of its air-passages, its heart and vascular 
system, this Black Swift is likewise typically Cypseline. 
Coming to the skeleton, 1 fiud Cypseloides in its osteology 
agrees in the main with the group of birds to which it naturally 
belongs ; that is, it is essentially a Swift so far as this part of 
its organization seems to indicate; nevertheless, in several 
particulars it has a skeleton nearer the Swallows than has either 
Micropus or Chcetura. It has, for instance, the interorbital 
septum much as we find it in the Hirundinidcc generally, and a 
large sesamoid at the elbow, as in Swallows. But, what is still 
more significant, it has the vacuities, one on each side of the 
posterior mid-end of the premaxillary above, just beyond the 
frontal region, filled in by a thin continuous layer of bone — 
agreeing in this particular respect with the Barn-Swallow ( C . 
erythrog aster). Cypseloides, moreover, has its external narial 
apertures more circumscribed, or, in other words, more as we find 
them in certain Hirundines (see figures 22 and 23, Plate XXI.). 
Having compared the skeleton of Nyctidromus albicollis 
var. Merrilli with the skeletons of the other Caprimulgine 
birds of the U.S. avifauna which I have described on former 
occasions, I fiud that it agrees more nearly with the American 
Whip-poor-will ( Antrostomus vociferus ) than with any other. 
Osteologically, however, it may be found to agree still more 
closely with the “ Chuck- will’s- widow ” (A. caroiinensis ), but as 
yet I have not had the opportunit}^ of comparing it with that 
bird. 
The entire order of the Caprihulgi stands much in need of 
thorough revision, and extensive researches into structure will 
be required before we can know much of the true relation- 
ships and proper classification. Iam convinced that, so far as 
the United-States forms of this group of birds are concerned, there 
are certainly two very well-defined subfamilies of the Capri- 
mulgidce. From what we know of their external characters, and 
from what I have shown of their widely different internal 
structures, these might readily be characterized as the sub- 
families Antrostomince and Cliordeilince — the former to contain 
the genera Antrostomus, Phalcenoptilus, aud Nyctidromus-, the 
latter the genus Chordeiles. 
We have but to compare the skull of Xuttall’s Poor-will (P. 
Nuttalli, Plate XX.) with the skull of Chordeiles acutipennis 
var. texensis (P. Z. S. 1885, pi. lix.) to be convinced of the wide 
differences which exist in this part of the skeleton in these tv r o 
