NATURAL SCIENCES OE PHILADELPHIA. 305 



slate. A broad transverse bar across the neck behind, the whole of the 

 lesser and median wing coverts, the bastard quills, the tertiaries, except at 

 their edges, and a terminal bar on the tail, black. The four outer primaries 

 with their outer webs, outer half of inner webs, and tips for some distance 

 black, the rest of the feather pearly white. Tips only of the fifth and sixth 

 black, their extreme apices with a white speck. Dimensions : Wing 12 - 25. 

 Bill above 1-40 to 1-50, height at base *59, at angle "40 ; tarsus 1'30 middle 

 toe, and claw 1-80. 



Habitat. Arctic regions of both hemispheres, coming south in winter. 



A specimen has the circumrostral space as far back as the eyes a light 

 brownish ashy, in marked contrast to the adjoining white. The bill is stouter 

 than usual, and of a bright chrome. 



A comparison of this species with the succeeding will be found under the 

 head of the latter. 



14. Rissa KoTZEr.ui Bon. 



?R. brachyrhyncha, Bruch, 1553, nee Larus brachyrh. Gould. R. nivea 

 Bruch, 1855, excl. synon. R. Kotzebui, Bp., 1856. R- brevirostris, 

 "Brandt," Lawrence, partim, sed nee Brandt, quae potius species 

 sequens. 



Sp. Char. Nearly adult. Bill rather long, and somewhat tapering towards 

 the tip, which is attenuated and decurved ; stout at the base, where it is much 

 deeper than at the angle ; culmen about straight to the nostrils, the con- 

 vexity beyond them to the tip very gradual and rather slight ; gonys doubly 

 slightly concave, the angle but little developed, so as to hardly touch a chord 

 drawn from the tip of the lower mandible to the base; but its apex acute. 

 Bill light yellow, slightly tinged with olivaceous, its tip somewhat clouded 

 with dusky. The specimen described, as being not fully mature, has a post- 

 ocular spot, and the nape plumbeous gray, which color on the back of the 

 neck fades into the pure white which intervenes between it and the mantle. 

 Mantle gray-blue, with a leaden tinge, b^t several shades lighter than in 

 brachyrhyttchus. This color extends nearly to the tips of the tertiaries, but 

 hardly at all invades the secondaries, which are pearly white for nearly the 

 whole length. Primaries : The shafts of all black, deepest on the outer ones ; 

 the first blackish-brown, its inner web dull white at the base, this white nar- 

 rowing as it ascends till it is lost an inch or two from the tip of the feather ; 

 there is no distinct line of demarcation between the two colors; second the 

 color of the first, but the white broader, better defined, and ending abruptly 

 one and a half inches from the tip ; third and fourth with the white still 

 wider defined, and running up rather further on the feather ; fifth bluish 

 white, with a. brownish black tip, half an inch long and a central field of 

 dusky along the shaft ; other primaries a lighter shade of the color of the 

 back, fading into white on the edges, without any black. An imperfect 

 subterminal bar on the tail, and dusky tips along the median wing coverts, 

 show the specimen to be immature. Tarsus shorter than the middle toe 

 without the claw ; the hind toe better formed than in R. tric/actyla. Legs and 

 feet dusky-olivaceus. (No. 21,287, S. I. Coll., from Semiavine Straits.) 



Another specimen (No. 15,693, from the N. W. coast of America) differs in 

 the following particulars : 



The bill, though stout at the base, is more tapering and attenuated at the 

 tip, which is more decurved ; and the convexity of the culmen is more gradual, 

 giving a somewhat different shape. The back is a rather darker shade of leaden. 

 gray, approximating to B. brachyrhyncha. The white of the inner vanes of 

 the outer primaries is broader, purer and more sharply defined. It agrees pre- 

 cisely in other particulars, the hind toe having the same developement. Dimen- 

 sions (of No. 21,287) : Bill along culmen 1-50 inches ; from apex of angle to. 



1862.] 21 



