A.1A. Snodgrass, Gcospiza, Cocor/u's, and Certhidia. \o\ 



II. The Thoracic Skeleton. 



The sternum, shoulder girdle and ribs show no such modifica- 

 tions as does the skull. The drawings of the parts in Cocornis 

 agassizi (PI. XVIII, figs. 19. 20, 22) may be taken as typical for 

 all three genera. The sternum and shoulder girdle are of ordi- 

 nary Passerine form. The ribs are somewhat variable. There 

 are always seven that are well developed and generally there is 

 a small eighth rib. The latter is sometimes a mere bar lymg back 

 of the lower part of the neural arm of the seventh, but often it is 

 composed of distinct neural and haemal segments. The second 

 to fifth ribs inclusive always have large uncinate processes. On 

 the sixth rib there is sometimes present a well developed uncinate 

 process, but it is often rudimentary and is frequently absent. 



Such variations as these have no phylogenetic significance, for 

 they take place between closely related species and also in dif- 

 ferent individuals of the same species. 



III. The Tongue. 



Geospiza (PI. XX, Figs. 34-38, and 40). — The tongue of Geo- 

 spiza has a simple tapering shape, varying in length and thickness 

 according to the form of the bill. The thin terminal margin is 

 bifid and somewhat frayed. The upper surface is usually convex, 

 but it is often slightly and sometimes deeply grooved longitudinally. 

 This last character, however, varies between closely related species 

 and even in the same species (Figs. 34 and 37). Geospiza is 

 mostly granivorous but partly insectivorous. 



Certhidia (PI. XX, Fig. 41). — The tongue in this genus is the 

 same as in the slender-billed species of Geospiza^ except that it is 

 more constantly grooved above. It is slender, tapering and bifid 

 at the tip. Certhidia is insectivorous. 



Cocornis (PI. XX, Figs. 39 and 42).— In this genus the tongue 

 is very long and slender. It is deeply grooved above, and 

 expanded, bifid and greatly frayed out at the tip (Fig. 39) . It 

 differs considerably, as the figures will show, from the tongues of 

 both Certhidia and Geospiza. The food of Cocornis has not been 

 determined, but probably consists mostly of insects. 



