54 NORTH AMERICAN BIRDS. 



f l . Bill cylindrical or compressed at base, where not broader 



than deep. 



g l . Partition between nostrils very thin (very much nar- 

 rower than width of a single nostril), entirely 

 within the nasal tubes. 



h l . Gonys very slightly or not at all concave, the tip 

 not distinctly decurved ; nasal tubes decidedly 

 longer than gonys... Fulmarus. (Page 57.) 

 h*. Gonys very strongly concave, the tip distinctly de- 

 curved ; nasal tubes not decidedly longer (usu- 

 ally shorter) than gonys (except in Bulweria). 

 i 1 . Depth of bill at shallowest part more than 

 one-fourth the length of the lower man- 

 dible, measured along the side. 

 /. Tail more or less graduated, and without 



white tip. 



A 1 . Tail less than half as long as wing, 

 and graduated for less than one- 

 third its length ; cutting-edge of 

 lower mandible decidedly con- 

 cave ; nail of lower mandible oc- 

 cupying at least one-third the 

 total length of the mandible, 

 measured along its side; plu- 

 mage and size very variable. 



-ffistrelata. (Page 63.) 

 A 2 . Tail more than half as long as wing, 

 and graduated for more than 

 one-third its length ; cutting- 

 edge of lower mandible straight, 

 or very slightly concave ; nail 

 of lower mandible occupying de- 

 cidedly less than one-third the 

 total length of the mandible, 

 measured along its side ; color 

 uniform dusky ; wing about 8.00. 

 Bulweria. (Page 69.) 

 f. Tail slightly rounded, and with a distinct 

 white tip. 



Cutting-edge of lower mandible 

 straight, and nail of lower man- 

 dible occupying less than one- 

 third its total length, as in Bul- 

 . weria; plumage bluish above, 

 and on sides of chest, the lower 



