Systematic Positiun of Zeledonia coronata. 



17 



of use has not taken place by the shortening of all the 

 remiges, but only of the outer primaries. This method of 

 wing-reduction appears to be the invariable rule in the early 

 stages of flightlessness. 



Five ribs articulate with the sternum, and all are attached 

 to the anterior lateral process — as appears to be the rule 

 among the Passeres. These processes in Zeledonia are re- 

 latively short, as also is the bifurcate spina externa. 



The relative length of the anterior lateral processes and 

 the spina externa will possibly prove of some use in defining 



Text-fiff. 8. 



B. 



A. — Sternum and shoulder-girdle of Zeledonia coronata, skewing the 

 degenerate condition of the keel and the long and slender coracoids. 

 a.l.p. = anterior lateral process; «.c. = acrocoracoid ; s.e. = spina ex- 

 terna. 



B. — Sternum and shoulder-girdle of Sialia wilsoni. Note the deep keel, 

 the large hypocleideum, and strong coracoid. Additional letter : 

 h. = hypocleideum. 



the smaller groups of Passeres, though these proportions 

 must always be rigorously scrutinized, since they may vary 

 individually with the power of flight. But Turdus, Pratincola, 

 and Phylloscopus, for example, present so many distinct 

 generic types, though the differences are small. 



The coracoid in Zeledonia shews, like the keel of the 

 sternum, evidence of degeneration. Relatively to the corpus 

 sterni it is longer than in Sialia; this is due to the re- 

 duction of the sternum. Further, it has lost the strong 



SER. viii. — vol. v. c 



