NATURAL SCIENCES OF PHILADELPHIA. 47 



to below the level of the jaw ; and a few more excessively delicate ones 

 reach from the posterior canthus of the eye some distance along the sides of 

 the occiput and nape. Entire upper parts, including the forehead, vertex, 

 occiput, and sides of head, (with the exception of the white feathers just 

 described) sides of neck, and wings and tail, glossy black. Inner webs of 

 the primaries dusky gray. Under wing coverts, (except the smallest row 

 just along the autibrachium and metacarpus,) white. Region about base of 

 under mandible blackish plumbeous, and a few feathers along the sides 

 under the wings and on the tlanks blackish ; all other under parts white, 

 motiled, especially on the breast and sides, with black, the throat alone re- 

 maining immaculate. Bill red, tubercle and base of upper mandible dark 

 bluish. Legs and feet an undefinable dusky in the dried state ; the anterior 

 border of ihe tarsus, and superior aspect of the toes dull greenish. 



Length about, 6-50 ; wing from carpus 3-75; tail 1-25; tarsus -70; middle 

 toe and claw 1-00; outer do. the same; inner do. -85; bill : chord of culmen, 

 (including width of knob) -40; along rictus -60; gonys -25; height at base 

 •30 ; width at base slightly less. 



The preceding is a description of the perfect plumage of this species, 

 which is of comparatively unfrequent occurrence. The usual state of plum- 

 age of the bird as met with in collections is much as follows : — Bill as de- 

 scribed above; filamentous feathers much as above described, but rather 

 shorter and more sparse, and scarcely appearing behind the eye and along 

 edge of side of lower jaw. Upper parts plumbeous black, sometimes slightly 

 interrupted in its continuity by a few whitish feathers about the scapulars ; 

 the primaries grayish black, paler on their inner webs ; secondaries grayish 

 white at their tips. Under parts white, as before, but very sparsely marbled 

 or waved with dusky; least so on the abdomen, most so on the sides and 

 breast, where the blackish so increases in amount as to appear more or less 

 continuous with that of the upper parts. Chin and s^des of jaw as above de- 

 scribed, but throat white, immaculate The dusky mottling varies greatly in 

 amount and in intensity with different specimens. Sometimes it is reduced 

 to a few isolated touches here and there, and again it is found to give the pre- 

 vailing color to the under parts. That specimens in this mottled condition 

 are not immature, is proven by the fact that the bill is fully grown and pro- 

 vided with a well developed tubercle; and that the forehead is thickly 

 covered with white setaceous feathers. The mottling, however, is confined 

 to the tips of the individual feathers, whose bases are pure white; aud is 

 thus apparently of a temporary and transient character, like that so frequently 

 met with in young or winter specimens of gulls and petrels. It may be a 

 seasonal feature, or one only found in birds of a certain age ; and yet nu- 

 merous facts tend to indicate it as a character of perfectly mature birds. 

 Were one to examine a specimen with the usual moderate amount of mottling 

 on the under parts, and notice the fact that the blackish occupies only the 

 tips of the feathers, he could not fail to be impressed with the analogy just 

 now hinted at, and to conclude that with advancing age the mottling would 

 grow less and less, and fina'ly disappear, leaving the under parts pure white, 

 as in pusilhts. Such, however, appears not to be the case. Specimens whose 

 age is attested by a fully developed bill and well formed tubercle, are those 

 most mottled below with blackish. And yet, no specimens have been found 

 with the breast or any other part of the under parts uninterruptedly black, 

 trenchantly divided from white areas. The peculiar kind of mottling exhib- 

 ited by this species is so unusual as a condition of perfect maturity, that the 

 suspicion arises that the very highest state of plumage is not yet known. 



Voting. — Entirely similar in plumage to the bird as just described ; but the 

 under parts white, scarcely relieved by mottling ; and the white extending 

 far around on the sides of the neck, leaving only a narrow median dorsal line 

 black ; the bill smaller than that of the adult, and the tubercle wholly vfant- 



1868.] 



