SUBFAMILY ANSERINE. 269 



as there is a great variation in the measurement of individuals, 

 it is not easy at times to determine as to which form an indi- 

 vidual belongs. These two Snow Geese are distributed in their 

 migrations over all North America, the imaginary dividing line 

 of the species and subspecies being the Mississippi Valley, which 

 is the winter locality of the less known Blue Wavey or Blue 

 Goose. 



KEY TO THE SPECIES. 



A. Feathering on lateral base of maxilla, 

 convex; blackish space at commissure. 



\ BLUE 



a. Plumage chiefly grayish brown and ( goose 

 bluish gray. \ c. ccsrule'scens. 



b. Plumage all white save primaries, which 

 are black. 



\ LESSER SNOW 



a'. Size small. Average total length said f goose 



to be 28 inches. \ ^ hyperboreus. 



\ GREATER SNOW 



b'. Size large. Average total length said ( goose 



to be 34 inches. J C.h. nivalis. 



GENUS EXANTHEMOPS 



(Greek ^ivBrnia, exanthema, eruption + i^a, opsis, 

 resemblance). 



Exanthemops, Elliot. B. of North America, 1868, vol. ii., 

 pi. xliv., text. Type Anser rossi, Cass. 



Base of bill thickly covered with wart-like excrescences; bill 

 weak, no gape at commissure and no blackish space present. 

 Feathering on lateral base of maxilla nearly straight. Size very 

 small. 



Only one species of this very distinct genus is known, the 

 diminutive Ross's Goose. It is no larger than many species of 

 Ducks, and can always be readily distinguished from all Geese, 

 in addition to its small size, by the conspicuous and unusual 

 excrescences at the base of the bill, which in some specimen^ 

 jover this part entirely. 



