This species has a close external resemblance to _P. subis_, for which
it has usually been mistaken. It is of nearly the same size, but the
feet are disproportionately smaller and weaker; while the wings are
shorter, the tail is as long and more deeply forked; the feathers
considerably narrower, and more attenuated (the outer .40 wide,
instead of .46). The colors above are more brilliant, and extend more
over the greater wing-coverts and lining of wings, while the quills
and tail-feathers have a richer gloss of purplish, changing to
greenish. An apparently good diagnostic feature is the concealed pure
white of the feathers about the anal regions, replaced in _subis_ by
grayish, rarely approximating to whitish.
A _Progne_ collected by Mr. Wright, at Monte Verde, is duller in color
than that from Remedios, but has still more concealed white below, in
the median portion, not only of the anal feathers, but of those of the
entire crissum and of the belly. A female bird, which I presume to be
the same species, can scarcely be distinguished from the female of
_dominicensis_, except in the brownish shafts of the longer crissal
feathers, and an almost imperceptible tinge of brownish in the webs of
the same feathers. It is almost exactly like the _P. leucogaster_ of
Mexico and Central America.
This species is included in the North American fauna in consequence of
the capture of a specimen (No. 10,368 ♂ _juv._, May 18, 1858) at Cape
Florida, which is with scarcely a doubt referable to it. This specimen
is a young male in its second year, so that it is difficult to
ascertain positively its relationship to the two allied species; but
as it agrees perfectly in its proportions with _cryptoleuca_, and its
plumage differs from the corresponding one of _subis_ in essential
respects, we have little hesitation in referring it to the former.
Nothing distinctive is recorded as to the habits of this bird.