562 BULLETIN 50, UNITED STATES NATIONAL MUSEUM. 



Bill moderately to strongly compressed, but exceedingly variable 

 as to relative depth and width, the culmen always more or less de- 

 cm'ved terminally, the tip of the maxilla overhanging or overreaching 

 that of the mandible to a greater or less extent; gonys shorter 

 (usually much shorter) than mandibular rami, the gonydeal angle 

 more or less prominent, sometimes conspicuously so; nostrils lateral, 

 near middle of maxiUa or posterior to the middle, narrow, longitudinal, 

 pervious, usually broader and rounded at anterior end, narrower and 

 acute posteriorly; frontal feathering always advancing farther on 

 sides of maxilla than at base of culmen, forming a prominent, usually 

 obtuse but sometimes acute, angle in nearly direct line behind nostril. 

 Primaries relatively shorter and broader and secondaries relatively 

 longer than in Sternidas. Tail usually truncate or very slightly 

 rounded, rarely forked, still more rarely cuneate or graduated; when 

 forked, the bifurcation only moderate, and tlie lateral rectrices in- 

 stead of being attenuated as in most Sternidie are broad and rounded 

 at tips, like the middle ones. Tarsus distinctly compressed, the 

 acrotarsium regularly transversely scutellate, the planta tarsi and 

 sides of tarsus with small roundish or hexagonal scales (reticulate) ; 

 upper surface of toes continuously transversely scutellate; anterior 

 toes fuUy webbed; hallux usually well-developed though small, 

 rarely (in one genus only) rudimentary or nearly obsolete. 



The Laridse are cosmopolitan in their range, though most numerous 

 in both species and genera in the Northern Hemisphere, America 

 possesses about thirty-five species, belonging to nine genera, of which 

 only eight species and one genus are extralimital to the present work. 



The birds of this family frequent the sea-coasts, estuaries, and 

 larger inlana waters. Their food consists of various marine animals 

 (including fishes), offal, insects, garbage from vessels, and, in fact, 

 anything eatable. They nest upon rocks, alo ag beaches (behind the 

 surf -line), and in marshes. Eggs several, variable as to ground-color, 

 but always spotted. 



KEY TO THE GENERA OF LARID^. 



a. Exposed culmen decidedly more than two-thirds as long as tarsus; tail truncate, 

 very slightly rounded, emarginate, or forked. 

 h. Hallux obsolete or rudimentary; tarsus shorter than middle toe without claw. 



Rissa (p. 564). 

 66. Ilallux well developed; tarsus longer than middle toe without claw. 

 c. Tail truncate or very slightly rounded. 

 d. Hallux joined to inner toe by a rugose or serrate membrane; tibia \vith less 

 than lower third unfeathered. 

 e. Depth of bill at gonydeal angle much less than distance from anterior end 

 of nostril to tip of maxilla and not greater than its depth at base; color 

 of plumage entirely white (sparsely spotted with dusky in young). 



PagopMla (p. 575). 



