Vol. XX 1 Snodckass, Gcos/>/:ii, Cocoruis, am} Crrthidia. 4- 1 I 



'9".i .1 ^ ~ 



and llic upiHM- aiiL^lc of ihc nostril is correspondingly farliuT hack. 

 The angulalion of the base of the culinen is slight, and the deliex- 

 ure of the upper toinimn is about 45°, being a little less than in G. 

 f. lUiiti rostris. 



As will be seen later, the skull of G. scandcus approaches most 

 closely to that of the genus Cocoriiis. 'I"he skull of G. f. aciilirostris 

 is nearest in size to the Cororiiis skull, but in structure the G. 

 scatuiens skull is almost intermediate between the two. 



A digression from tiie series will now be made to describe the 

 skull of the (]eos|oizan grouji having a strongly curved culmen. 



Gcospiza ciassirostris {{.\(mV\). (Plate XVII, T'igs. 14 and 15.) 

 — This species may be taken as a l\pical example of the Gcospiza 

 species foruu-rly included in a separate genus called C(V>uu/iyiic/tits, 

 a group characterized by having the culmen strongly curved. 



The skull of G. crassiroslris is in every way very similar to that 

 of G. foiiis. About the only difference is that the cuhncn is a lit- 

 tle more convex than in G.fortis,\\\\(\ the upper mandible is deeper 

 in front of the nostril. The crests of the two skulls ha\e about the 

 same develo[)ment, the interorbilal areas are the same, tlu' iipper 

 mandibles have the same deflexure, the nostrils are alike, the 

 descending processes of the nasals form the same angle with the 

 zygoma, and the post-froulal and scpuiinosal j)roccsses have the 

 same relative positions. 



A study of the Gcospiza skulls shows, then, that the various 

 species and varieties are related to one another mostly in a serial 

 manner. That is, evolution in the group has not been along lines 

 radiating fiom a common centre, but has consisted principall}' of 

 successive modillcatious along one line. This same thing is 

 evinced l)y a study of the color phases of the ])luniage. 



Cocor/iis (li^assizi 'I'ownsend (IM. XV 11, l*'igs. 10 and 11). — The 

 general characters of the skull are almost identical with those of 

 G.f. acntirostris or G. siciiukns. The upper mandible, however, is 

 relatively a little slenderer than in either of llusc, and the dcllex- 

 ure of the tomiuni is about |o". 'i"his is about 5" less than in G. 

 scaiulens. 



Cert hi ilia oliiutcca liilcDla ( K idgway ) . ( 1 '1 . X V II ," I-'igs. i 2 and 

 13.)^ 'I'hc skull of Ccii/iidiii is extremely similar to that of Cocor- 



