EAGLES AND HAWKS. 



45 



The genus Haliaetus has the largest and highest bill ; 

 Aquila is that which has the bill next in length and 

 height. In Pandion it is shorter and broader. The 

 bill of Buteo resembles that of Aquila, but is propor- 

 tionally smaller, with its upper outline more sloping. 

 In Falco the bill resembles that of Pandion, but is 

 shorter, thicker, and furnished with an angular process 

 on the edge of the upper mandible, the nostrils round 

 with a central papilla. Accipiter has merely a promi- 

 nent festoon on the edge ; the nostrils are oblong, with- 

 out a central prominence ; the bill otherwise similar to 

 that of Falco, but smaller and more compressed. Per- 

 nis has the bill like Buteo, but the loral space is cover- 

 ed with small compact feathers. Milvus has a similar 

 bill, but the feet and tail are different. Lastly, Circus 

 has the bill more slender and tapering than that of any 

 of the above genera, and is further distinguished by the 

 ruff of feathers. 



Agreeably to these and other circumstances, the ge- 

 nera might be arranged thus : 



Circus. 



This arrangement may, of course, be converted into 

 the circular form. But another, with a central genus, 

 is quite as natural. Thus : 



