The Zoologist — November, 1870. 2373 



occurrence. Both these conditions have been described and named 

 as characterizing distinct species. In the latter, the bird must not be 

 confounded with Uria Carbo, which is totally different. 



Dimensions.— Adult : Length (average), 13-00; extent (average), 

 22-50; wing 5-50 to 625; tail 200, a little more or less; bill along 

 culmeu 1-30; along rictus 1*75; along gonys "65; depth at base '45, 

 width -35; tarsus 1-25; middle toe and claw 1-75, outer do. slightly- 

 less, inner do. 1'40. 



It may be of advantage to look closely into the formation of the 

 white area upon the wing of this species, to the end that its composition 

 may be clearly understood, and recognized as different from that 

 which obtains in the allied species, U. Columba. The mirror upon 

 the upper coverts varies to a degree, and in a precisely similar way, 

 in each species; but when perfect constantly presents a radical 

 difference. 



When Uria grylle is observed flying, as is its wont, low over the 

 water with rapid beats of the wings, the eye receives the impression of 

 a black bird, with a large white circular spot on the wing. This spot 

 is constantly in view, and represents the retinal image resulting from 

 the white spaces upon both the upper and under surface of the wings 

 blended together by the rapid motion of the wings. Those who have 

 observed Uria grylle in its native haunts will appreciate the pertinence 

 of this remark. Uria Columba presents no such peculiarity of appear- 

 ance, there being no white upon the under surface of the wings ; and 

 the eye readily follows the movement of the small white space upon 

 the wings, as with the changing attitudes of the bird, it is now 

 apparent, now lost to view. 



In Uria grylle the row of great coverts upon the secondary quills 

 are basally black, terminally white. The outermost are white for 

 rather less than half their length, and the white occupies chiefly the 

 exterior webs. Nearer the body they are white for more than half 

 their length, and the white occupies both webs of the feathers. The 

 next row of coverts are wholly white in their entire length, except 

 perhaps for a very brief space just at their base; and they are 

 throughout long enough to cover entirely the dark portion of the first 

 row, reaching a little beyond and overlying the commencement of the 

 white upon the latter; so that the white is continuous and unbroken. 

 One or two more rows of coverts have precisely the same character 

 and continue the white space uninterrupted. The shorter coverts, for 

 about half an inch from the edge of the antibrachium are black ; the 



SECOND SERIES VOL. V. 3 I 



