384) 



DK. E. W. SHrrELDT'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 find CypseJoides 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 Chcetiira. It has, for instance, the interorbital 

 septum much as we find it in the Hirundinidce 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 premaxiilary 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. 

 erytlirog 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 alhicollis 

 var. Merrilli vvith the skeletons of the other Caprimulgine 

 birds of the U.S. avifauna which I have described on former 

 occasions, I find that it agrees more nearly with the American 

 Whip-poor-will (Antrostojmts vociferus) than with any other. 

 Osteologically, however, it may be found to agree still more 

 closely with the " Chuck- will's- widow " (A. carolinensis), but as 

 yet I have not had the opportunity of comparing it with that 

 bird. 



The entire order of the Capeimulgi 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. I am 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- 

 mulgidcB. 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 AntrostomincB and Chordeilince — the former to contain 

 the geuera Antrostomus, PJialcenoptilus, and Nyctidromus ; the 

 latter the genus Chordeiles. 



We have but to compare the skull of Nuttall's Poor-will (P. 

 Nuttalli, Plate XX.) with the skull of Chordeiles acutipennis 

 var. teccensis (P. Z. S. 1885, pi. lix.) to be convinced of the wide 

 differences which exist in this part of the skeleton in these two 



