1888.] PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 177 



other characters it becomes important, as it is by certain combinations 

 of characters, rather than by the presence or absence of any one or two, 

 that groups of birds must be divided one from another. 



In the Wrens the costal process is slender and so acuminate as to be 

 almost of needle-like sharpness, while in the Thrushes it is large, blunt, 

 and roughly rhomboidal in shape, although varying slightly in different 

 species. 



Tardus mustelinus has the largest costal process among the Thrushes, 

 not being equaled in this respect by T. swainsoni or T.fuscescens. ^The 

 Mimince are intermediate as regards the shape and size of the costal 

 process between the Thrushes and Wrens. 



The Wrens have the manubrium a little less deeply cleft than the mem- 

 bers of the two other groups under consideration, while the notches in 

 the posterior margin of the sternum are deeper. 



Sternum and pelvis of Campylorhynchus affirm. 



Sternum and pelvis of Harporhynchus currirostris. 



Sternum and pelvis of Merttla migrator ia. 



The sternum is viewed obliquely in order to better show the costal 

 process. 



Proc. K M. 88 12 Jl^e^L H-i'S* ? • 



