CRIMSON NUT-CRACKER. 159 



gradual developement and diminution of the strength 

 and form of the bill in this circular group will he 

 made intelligible by the following outlines of the 

 bills of the sub-genera which compose the circle. 



It is obvious that those bills are the strongest 

 whose mandibles are of equal thickness and of un- 

 usual shortness ; we consequently find that it is the 

 pre-eminent distinction of the two typical genera, 

 Pyrenestesy fig. l,and Coccolorus, fig. 2 ; all the others 

 having the bill either more lengthened, or the under 

 mandible much weaker than the upper. But this 

 change is nevertheless gradual. Pyrenestes^ fig. 1, 

 for instance, has the most conic bill of all, for it has 

 no notch at the tip. Then comes Dertroides, fig. 5, 

 putting on the appearance of a hornbill or a buceros, 

 not only on the knobbed front, but in the situation of 

 the nostrils ; its bill is something like the last, but it 

 is less conic and more lengthened. From this form 

 we pass to SpermopJiaga^ fig. 4, where the bill has 



