160 
CRIMSON NUT-CRACKER. 
less of the conic form than, any of those now repre- 
sented ; its shape, in fact, is intermediate between 
that of Dertroides and Coccothraustes to which it 
leads. Coccot/imusiex, again, fig. 3, has a remark- 
ably strong upper, but comparatively a weak under 
mandible, and the commissure is regularly and gra- 
dually arched from the base. Some of the species, 
however, of Coccoborus 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 perfectly equal, 
fig. 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 Pprenestes, there should be a species with an un- 
usually 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 Angolensis of Linnaeus, erroneously 
supposed to inhabit Africa, but which we ourselves 
shot in the forests of America. We have chosen to 
illustrate this progression by the form of the bill 
only, because this organ is the most obvious to the 
generality of students, and will admit of more ac- 
curate delineation; hut this chain of connexion is 
equally apparent in the variation of the wings and 
feet. We have thus presumptive evidence of a 
circular group. Let us now see whether this group 
