Swainson's Birds of Western Africa. 327 



Spermophaga, from which nature seems to return again to her first or most 

 pre-eminent type, by means of the haw-finches of temperate climates 

 (Coccothraustes) and the hard-bills of South America, Coccoborus. It is 

 among these latter buds, indeed, that we have the nearest approach to 

 that now before us. The gradual developement and diminution of the 

 strength and form of the bill in this circular group will be made intelligi- 

 ble by the following outlines of the bills of the subgenera which compose 

 the circle. 



" It is obvious that those bills are the strongest whose mandibles are of 

 equal thickness and of unusual shortness : we consequently find that it is 

 the pre-eminent distinction of the two typical genera, Pyrenestes, fig. 1, 

 and Coccoborus, fig. 2. ; all the others having the bill either more length- 

 ened, 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 Der- 

 troides, 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 Spermophaga, fig. 4., where the bill has less of 

 the conic form than any of those now represented ; its shape, in fact, is 

 intermediate between that of Dertroides and Coccothraustes to which it 

 leads. Coccothraustes, again, fig. 3., has a remarkably strong upper, but 

 comparatively a weak tender mandible, and the commissure is regularly and 

 gradually arched" from the base. Some of the species, however, of Cocco- 

 borus have the under mandible rather the smallest, so that by these birds a 

 passage is formed from one to the other. Coccoborus is nevertheless very 

 different ; for in the greater part of the species the two mandibles are per- 

 fectly equal, ^g. 2., and the margins, instead of being curved, are sinuated ; 

 the upper one, moreover, has a very small but obvious tooth, which none 

 of the other genera possess. Now, to unite this genus (which is strictly 

 confined to the warm parts of America) with that of Pyrenestes, there 

 should be a species with an unusually large bill, yet furnished with a 

 notch ; such a bird would obviously unite in itself the characters of both 

 genera, and such a bird we accordingly have in the Loxia Angotensis of 

 Linnaeus, erroneously supposed to inhabit Africa, but which we ourselves 

 shot in the forests of America. We have chosen to illustrate this pro- 

 gression by the form of the bill only, because this organ is the most 

 obvious to the generality of students, and will admit of more accurate 

 delineation ; but this chain of connexion is equally apparent in the varia- 

 tion of the wings and feet. We have thus presumptive evidence of a 

 circular group. Let us now see whether this group is natural ; that is, 

 whether it will bear the test of comparison with the orders of birds and 

 the tribes of the Insessores. The usual mode we have always adopted for 

 this purpose is to place the genera in a column which corresponds to those 

 which contain the groups represented, thus : — 



SUB-FAMILY COCCOTHRAUSTIN^. 

 1. Typical. 



Pyrenestes - The most perfectly conic bills. - - Conirostres. 



2. Sub-typical. 



Coccoborus - Bill notched at the tip. - Dentirostres. 



3. Aberrant. 



Coccothraustes - Wings long, tail forked, feet very short. Fissirostres. 



Spermophaga - Bill most lengthened - Teniurosires. 



-rt . ■ , f Wings short, feet lar<;e, very strong, ") <? 



Dertroides < ° ,-, ■ i r ° > - ocansores. 



(_ upper mandible curved above 



