Vol. XVIII 



lyol 



Clark, The Classification of Birds. '\*1^ 



the bod)' uniformly covered with feathers. It would be possible, 

 therefore, to divide birds according to the pterylosis into ten 

 orders, nine of which belong in the subclass generally known as 

 Carinatae. The group Ratitai have so many characters in com- 

 mon which distinguish them from other birds, it is a conven- 

 ience to regard them as a subclass, of equal rank with the Cari- 

 natae. So far as the pterylosis is concerned, they comprise, how- 

 ever, only a single order. This type of pterylosis may well be 

 called 



Struthioniform. 



Adult without apteria or oil-gland ; plumage soft and lax, intermedi- 

 ate between down and contour-feathers. 



In the Carinatae, the adults all have contour feathers, the 

 pterylae are generally clearly defined, and the oil-gland is usually 

 present. If distinct apteria are wanting, the oil-gland is well 

 developed. The following are the patterns of the pteryloses of 

 the Carinate birds. 



Sphenisciform. 

 Adult without apteria, but with oil gland; plumage dense. 

 This style of pterylosis is characteristic of the Penguins. 



Colymbiform. 



Upper and lower cervical tracts not separate until near shoulder. 



Upper cervical tract deeply forked but branches not diverging. 



Dorsal tract broad, separate from cervical, and without any apterium. 



Humeral tract broad and distinct. 



Femoral tracts small, mostly separate from dorsal. 



Sternals broad, directly continuous with branches of the lower cervical, 

 which is quite deeply forked; and with no side branch. 



Ventrals t'e;'jK broad, directly continuous with sternals; ventral apter- 

 ium narrow but broadest behind. 



This style is characteristic of the Loons and Grebes. 



