546 
PROCEEDINGS OP THE ACADEMY OP 
shorter and weaker than that of the adult, and wanting its very acute tip, and 
sharply-defined ridges and angles ; brownish-black, fading into dull flesh-color 
at the base of the under mandible. Front white, but the crown and nape show 
considerable traces of the black that is to appear, which is now mixed with a 
good deal of light-brown. The pearl-blue of the back and wing coverts is 
everywhere interrupted by irregular patches of light grayish-brown, showing a 
tendency to become transverse bars ; this grayish-brown on the tertials deepens 
into brownish-black, and occupies nearly the whole extent of each feather. 
The primaries differ from those of the adult in having less of the silvery gloss, 
and the inner white spaces are more marked, being in fact much like those of 
the adult kirundo. The rump and under parts are pure white. The tail inten- 
sifies, so to speak, its adult characters as regards color ; and, independently of 
any other feature, will always serve to identify the species. It is deeply emar- 
ginate, but the lateral feather is not greatly produced, surpassing the second 
by scarcely more than the latter surpasses the third. Its inner web for an inch 
or so from the tip, and both webs of the other feathers, are quite decidedly 
grayish-black ; the intensity of this color, and also its extent, decreasing suc- 
cessively on each feather from without inwards, so that the central pair scarcely 
deepen their color at the tips. The outer web of the lateral feather generally 
stays pretty uninterruptedly white, but sometimes is just at the tip invaded by 
the darker color of its inner web. 
The preceding descriptions embrace all the well characterized stages of 
plumage of this species which are known to me, though there are, of course, 
intermediates in great variety between those' given. It is indeed a little 
remarkable, the number of specimens in immature or winter plumage which 
find their way into collections. Of the numerous examples before me, just one- 
half are in this state, all showing white fronts, and the usual deep black band 
through the eye. There would seem to be something peculiar in the habitat 
of this species, to cause it to differ so remarkably from its allies hirundo and 
macroura in this respect. I have purposely gone considerably into detail re- 
garding these immature stages, because of the great similarity which exists be- 
tween the species, and the same ages of “ S. Havelli ,” if, indeed, the latter be 
really distinct from it. The question of the relationship of the two has been fully 
discussed under the head of u S. Havelli .” 
Sterna Forsteri affords a good illustration of a species, bearing so intimate a 
general resemblance to another, as to be confounded with it at first glance, and 
yet when carefully examined proving to be totally distinct. It is perfectly easy 
to separate it from the hirundo by its characters of bill, wings, tail or feet, 
either of which taken alone would identify it. The following table will exhi- 
bit at a glance the distinctive features of our three most intimately allied spe- 
cies, between which, it will be observed, there is a complete and gradual 
transition in almost every respect. 
Differential Diagnoses of S. Forsteri , hirundo and macroura. 
S. Forsteri. — Bill (average) 1*60 along culmen ; depth at base *40; robust. 
Bill orange-yellow, nearly its terminal half black. White space between eye 
and cutting edge of upper mandible broad. Under parts white. Outer web 
of first primary silvery ; the inner webs also of the others strongly hoary, with- 
out well-defined white spaces. Tail bluish-pearl, like the back, its lateral 
feather greatly produced (average nearly 7 inches in length) ; its outer web 
white, inner the color of the rest of the tail. Legs long and stout; length of 
tarsus (average) rather over -90 of an inch ; orange-yellow, tinged with ver- 
milion. Lerigth of tarsus, middle toe and claw 2 inches. 
S. hirundo. — Bill (average) 1-45 along culmen ; depth at base *33; moderate. 
Bill vermilion-red ; its terminal third black. White space between eye and 
cutting edge of upper mandible narrower than in Forsteri. Under parts lightly 
washed with plumbeous, fading into white on the throat and abdomen. Outer 
