156 CHRYSOPTILUS. 



The lateral angle of the upper mandible, instead of 

 being close to the margin, as we have seen in Den- 

 drobates, is now either a little way removed from the 

 culminal ridge, or it is quite close. Now, the re- 

 lative powers of picking holes in trees, which all 

 these birds possess in different degrees, is always de- 

 termined by the position of this singular angle. In 

 those birds, which are proverbial for their superior 

 powers in this respect, the angle we are speaking of 

 is acute, and is nearer to the margin than to the top 

 of the bill, which thus as- 

 sumes the form of a sharply 

 angulated wedge (1), so that, 

 but for these angles, the bill 

 would be cylindrical ; every 



mechanist knows the superior power of a wedge 

 formed with acute angles over another where the 

 angles are obtuse (2). Hence it follows, that the 

 different sub -genera of Chrysoptilus are much in- 

 ferior in the power of breaking wood to those of 

 Picus. Some, in fact, frequently feed upon ants. 

 They are clearly, therefore, an inferior race, and 

 constitute the sub-typical genus of the family. 



And yet, although the characters of the Chry- 

 soptili, as a whole, will always prevent them from 

 being confounded with any other genus; the sub- 

 genera, or types of form, require much more study 

 than we have yet been able to give them. It is 

 very clear, however, that the group we shall now 

 enter upon is very distinct, not merely from Den- 

 drobates, but from the mere typical examples of 



