. LXIII. 149 



dd. Head dark if dark below, head whitish (small or 



slender species, with a black hood in the breeding 



season, and the white under parts then pinkish or 



rosy-tinted.) . . . CHRCECOCEPHALUS, 5. 



6&. Tail forked; bill black, yellow-tipped. . XEMA, 6. 



** Bill paragnathous (mandibles even) ; tail forked (in our species) ; 



Terns. (STERNIN.E.) 



e. Toes full-webbed ; colors chiefly white, with a black cap at 

 most seasons and the quills silvery dusky, with a long 

 white stripe. 

 /. Feet black ; forehead without white crescent. 



g. Not crested ; bill stout, scarcely longer than tarsus. 



GELOCHELIDON, 7. 

 gg. Crested ; bill slender, much longer than tarsus. 



THALASSEUS, 8. 



ff. Feet not black ; back pale, no crest. . . STERNA, 9. 

 ee. Toes not full-webbed ; color quite dark. 



HYDROCHELIDON, 10. 



*** Bill hypognathous the lower mandible much the longer, 

 compressed like a knife-blade. Skimmers. (RHYNCHOPIN^:.) 



RHYNCHOPS, 11. 



/. STERCORARIUS, Brisson. J.EGEBS. 

 = Lestris, Authors. 



1. S. pomatorhinus, (Temm.) Lawr. POMAEINB 

 JJEGER. Chiefly blackish, colors varying with age; 

 middle tail feathers broad to the tip, projecting about 

 four inches; L. 20; W. 15. Northern, U. S. in winter. 



2. S. parasiticus, (Briinn.) Gray. PARASITIC J^EGEE. 

 General color dark brown ; middle tail feathers acuminate, 

 projecting 4 inches; L. 18; W. 13. Northern, U. S. in 

 winter. 



3. S. buffoni, (Boie) Coues. LONG TAILED JAEGER. 

 Similar, but still smaller; tail feathers filamentous, pro- 

 jecting 8 or 10 inches. Northern, U. S. in winter. 



