NATURAL SCIENCES OP PHILADELPHIA. 293 



forked. Legs rather stout ; hind toe sometimes rudiuiental. Head never 

 with a hood ; in winter with the neck streaked with dusky. Under parts 

 white without a decided roseate tint. 



1. Larus. Size large or moderate. Bill stout, robust, obtuse, the tip not 

 attenuated, the angle usually very prominent. Convexity of culmen great 

 at the ends. Color white, nearly always with a darker mantle. Tail even. 



2. Blasipus. Size moderate. Bill rather slender, its tip somewhat attenu- 

 ated. General color dusky. Tail even, or very slightly emarginate. 



3. Rissa. Size rather small. Bill stout at base, but more attenuated and 

 decurved at the tip. Angle acute, but not very prominent. Hind toe rudi- 

 mental. Tail even ; somewhat emarginate in the young. 



4. Pagophila. Size rather small. Bill short, stout, obtuse. Tarsus v^ry 

 short, stout, arm rough. Tibire partially feathered. Webs excised. Color 

 entirely pure white. 



B. Xeme^;. 



Size moderate, small, or very small. Body more slender, general organiza- 

 tion more delicate. Bill generally slenderer and more acute, the angle not 

 very prominent, but acute, the tip decurved and attenuated. Tail variable, 

 even, forked, or cuneate. Legs rather slender. Hind toe always present. 

 Head usually with a hood, or with a black ring round the neck. Under parts 

 white, with a decided roseate tint. 



5. Chroicocephalus. Size moderate and very small. Bill slender, the tip 

 more or less decurved. Tail even. 



6. Rhodostethia. Size small. Bill short and very slender. Neck with a 

 black ring, but head without a hood. Tail cuneate. 



7. Xema. Size small. Bill short, rather slender, the angle acute. Head 

 with a hood and neck with a ring. Tail moderately forked. 



8. Creagrus. " Of medium size ; bill very strong and much curved ; mantle 

 grayish white ; tail deeply forked." Lawr. 



The above brief characters define the genera sufficiently for our present 

 purposes ; the aim being rather the determination of species than rigid syste- 

 matic classification. 



Genus 1. Larus, Linnaeus. 



Larus, Linn. 1744; nee 1735; (typus L. canus, fide Gray.) 

 Gavia, Moehring, 1752 ; nee auct. 

 Leucus, Kaup, 1829. 



Laroldes, Brehm, 1830; t. L. argentatus, Brunn. Bp. 1856; (typus idem.) 

 Planius, Reichenbach, 1853. 

 Glaucus, Bruch, 1853 ; (t. L. glaucus, Brunn.) 

 Dominicanus, Bruch, 1853 ; (t. L. marinus, Linn.) 

 Gaviiia, Bp. 1854, fide G. R. Gray ; nee Bp. 1856. 



Laroides, Bruch, 1855 ; (t. L. glaucus, Brunn. = Glaucus, Bruch, 1853.) 

 Leucus, Bp. 1856 ; (t. L. glaucus, Brunn. Emend. Leuc. Kaup, 1829 = Laroides 

 Bruch, 1855, vel Glaucus, Bruch, 1853.) 



The eleven species of the genus found in North America may be very na- 

 turally arranged under the following sections or subgenera : 



Section A. Leucus Bp. (Plantus, Reich. Glaucus, p. Bruch, 1853, La- 

 roides p. Bruch, 1855.) Large and powerful; primaries without any 

 black ; upper parts very light. 



a. Color above entirely white. 

 1862.] 



