256 XORTH AMERICAy BIRDS. 



Ear-opening immL-nse, extending almost the entire beightof the skull, 



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



I/. Length of cere along top less than chord of culmen, the upper outline not 



arched. 



C'. Ear-opening very largo, ivith a distinct anterior operculum or "flap," 



the two ears con.spicuously asj-mmetrical. (No ear-tufts.) 



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



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



c^-es larger, with iridos dark brown or nearly black ; feet larger, 



and facial disk relativelj- smaller Syrnium. (Page 258.) 



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

 smaller, and nearly- hidden by feathers: toes en tirelj- covered 

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

 feet relatively much smaller, and facial disk much broader. 



Scotiaptex. (Pago 259.) 



c^ Ear-opening small, without anterior operculum, or ■• flap," the two ears 



not distinctly asymmetrical. 



d}. 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.) 



(P. 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 whollj' con- 

 cealing the claws; bill nearly concealed bj- the loral feathers. 



(Very large; wing 15.50 to 19.00.) Nyctea. (Page 264.) 



rt'. Wing less than 10.00. 



//'. Tarsus less than twice as long as middle toe, and much less than half as long 

 as tail, 

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



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



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

 rf'. Ear-opening very large (nearlj- equal to height of skull), with ante- 

 rior operculum or flap, the two ears conspieuouslj- asymmetrical. 



(No car-tufts ; wing 5.25-7.40.) Nyctala. (Pago 260.) 



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

 metrical, 

 e". Nostril large, oval, 0]iening in anterior edge of core; ear-tufts 

 conspicuous ; small (wing 5.40-7.80). 



Megascops. (Page 260.) 

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

 cere ; no car-tufts ; very small (wing 3.50— i.40). 

 /'. Tarsus not longer than middle toe, densely feathered; tail 

 more than half as long as wing, rounded. 



Glaucidium. (Pago 266.) 



