2 68 



WATER FOWL. 



KEY TO THE GENERA. 



A. Lores feathered. 



a. Serrations on the greater portion of the 

 cutting edge? of maxilla visible. 



a '. Plumage all white, or head and neck 



only entirely white. Primaries, black 



or blackish brown. 



a". Bill stout; depth at base more than ^ 

 half the length of the culmen; no ex- I 

 crescences on basal portion. Black j 

 space on commissure. Size large. 



b" . Bill weak; depth at base less than 

 half the length of the culmen; basal 

 portion covered with wart-like ex- 

 crescences. No black space on the 

 commissure. Size small. 



b'. Plumage never all white, nor with an 

 entirely white head or neck. 



b. Serrations of cutting edge of maxilla 

 visible only at angle of the mouth; com- 

 missure concave. 



c. Serrations of cutting edge of maxilla not 

 visible; commissure straight. 



SNOW GEESE. 



Chen. 



ROSS'S SNOW 

 GOOSE. 



Exanthemops. 



LAUGHING 

 GEESE. 



Anser. 



EMPEROR GOOSE. 



Philacte. 



CRAVAT GEESE. 



Branta. 



GENUS CHEN 

 (Greek xi)", chen, a goose). 



Chen, Boie. Isis, 1822, p. 563. Type Anser hyperboreus, 

 Pall. 



Bill as long as the head, powerful, higher than wide at base, 

 edges of maxilla and mandible greatly beveled, exposing the 

 prominent lamellae. Nostrils situated high on basal portion of 

 maxilla. Tarsus longer than middle toe and claw. Feet rather 

 small. 



Two species and one subspecies are retained in this genus, two 

 of which, the Greater and Lesser Snow Geese, possess nothing 

 to distinguish them apart save a difference in size. This, on an 

 average, is stated to be about nine inches in the total length, but 



