256 NORTH AMERICAN BIRDS. 



Ear-opening immense, extending almost the entire height of the skull, 



the two ears conspicuously asymmetrical Asio. (Page 257.) 



& s . Length of cere along top less than chord of culmen, the upper outline not 



arched. 



c l . Ear-opening very large, with a distinct anterior operculum or " flap," 



the two ears conspicuously asymmetrical. (No ear-tufts.) 



d 1 . Smaller (wing 12.00-15.00, tail less than 10.00) ; bill larger, more 



exposed ; at least the terminal scutella of each toe exposed ; 



eyes larger, with irides dark brown or nearly black ; feet larger, 



and facial disk relatively smaller Syrnium. (Page 258.) 



d 2 . Larger (wing 16.00-18.00, tail 12.00 or more) ; bill relatively much 

 smaller, and nearly hidden by feathers ; toes entirely covered 

 with feathers ; eyes relatively much smaller, with irides yellow ; 

 feet relatively much smaller, and facial disk much broader. 



Scotiaptex. (Page 259.) 



c 2 . Ear-opening small, without anterior operculum, or " flap," the two ears 



not distinctly asymmetrical. 



d 1 . Ear-tufts very conspicuous ; tail reaching beyond tip of longest 



lower coverts ; two or three outer quills with inner webs emar- 



ginated ; toes covered with short but dense feathers, the claws 



wholly exposed ; bill exposed Bubo. (Page 262.) 



d?. Ear-tufts rudimentary ; tail not reaching beyond tips of longest 

 lower coverts ; four outer quills with inner webs emarginated ; 

 toes covered with long hair-like feathers, partly or wholly con- 

 cealing the claws ; bill nearly concealed by the loral feathers. 



(Very large; wing 17.00 to 19.00.) Nyctea. (Page 264.) 



a\ "Wing less than 10.00. 



ft 1 . Tarsus less than twice as long as middle toe, and much less than half as long 

 as tail. 

 c 1 . Tail more than two-thirds as long as wing, graduated. (No ear-tufts ; 



wing about 9.00.) Surnia. (Page 264.) 



<?. Tail less than two-thirds as long as wing, even, or slightly rounded. 

 d 1 . Ear-opening very large (nearly equal to height of skull), with ante- 

 rior operculum or flap, the two ears conspicuously asymmetrical. 



(No ear-tufts ; wing 5.25-7.20.) Nyctala. (Page 260.) 



d l . Ear-opening small, without anterior operculum, the two ears sym- 

 metrical. 

 e 1 . Nostril large, oval, opening in anterior edge of cere ; ear-tufts 

 conspicuous ; small (wing 5.40-7.80). 



Megascops. (Page 260.) 

 e 1 . Nostril small, circular, opening near the middle of the inflated 

 cere ; no ear-tufts ; very small (wing 3.50-4.40). 

 f 1 . Tarsus not longer than middle toe, densely feathered ; tail 

 more than half as long as wing, rounded. 



Glaucidium. (Page 266.) 



