20 NORTH AMERICAN BIRDS. 



Order LONGIPENNES.— The Long-winged 



Swimmers. (Pagei.) 



Families. 



a x . Bill with the lower mandible not longer than the upper, and not excessively 

 compressed. 

 b 1 . Covering of the upper mandible composed of three distinct pieces — a ter- 

 minal unguis, or hook, a lateral piece, and a cere-like piece saddled upon 

 the culmen, its edge overhanging the nostril. 



Stercorariidae. (Page 20.) 

 b 2 . Covering of upper mandible consisting of a single piece, through which the 



nostrils are pierced Laridae. (Page 23.) 



a 2 . Bill with lower mandible much longer than the upper, both mandibles excessively 

 compressed, like a thin knife-blade, for terminal portion. 



Rynchopidse. (Page 48.) 



Family STERCORARIIDjE.— The Skuas and Jaegers. (Page 20.) 



Genera. 



a 1 . Size large (in bulk equal to the largest gulls), and form robust ; depth of bill at 

 base equal to not less than half the length of the upper mandible, measured 

 along the side ; tarsus shorter than middle toe with claw ; tail short, nearly 

 even, the middle pair of feathers scarcely projecting beyond the rest ; color 

 dull brownish, sometimes streaked (never barred) with paler, the base of the 

 primaries with a whitish patch Megalestris. (Page 20.) 



a*. Size medium or rather small (not exceeding the medium-sized gulls), and form 

 more slender and graceful ; depth of bill at base less than half the length of 

 the upper mandible, measured along the side ; tarsus decidedly longer than 

 middle toe with claw ; middle rectrices in the adult projecting far beyond 

 the rest ; color plain slaty or dusky, often varied with white or yellowish, 

 in the adult, dusky barred with paler in young ; no white at base of primaries. 



Stercorarius. (Page 21.) 



Gentjs MEGALESTRIS Bonaparte. (Page 20, pi. VII., fig. 1.) 



Species. 



Common Characters. — General color nearly uniform grayish brown or sooty, 

 usually indistinctly streaked with light rusty, or cinnamon, especially around neck 

 and on back ; quills whitish at base. Eggs olive, spotted with brown. 



