that connect the Orders and Families of Birds. 503 



conspicuous here, but deficient in the family to which we now 

 proceed. 



We enter the family of Alcada by means of the genus Uria, 

 Briss., which, it may be remembered, was originally included 

 in the Colymbus of Linnaeus, and from which it has been sepa- 

 rated chiefly on account of the tridactyle conformation of its 

 foot. This character distinguishes the greater part of the pre- 

 sent group, which, in addition to Uria, contains the genera Alca 

 and Aytenodytes of Linnaeus. The latter genus apparently car- 

 ries to the extreme the typical character of those groups in 

 which the wings becoming gradually shorter, and less furnished 

 with feathers, lose at length all their powers of flight, and assume 

 the functions of fins instead of wings, to assist the bird in its 

 progress through the water. The whole of the family before us, 

 united by the form of the foot, is separated into generic groups 

 by the different shape of the bill. And here a beautifully pro- 

 gressive series of aflfinities is apparent throughout the whole 

 group. Beginning from the true Aptenodytes, we may observe 

 that the bill of that genus is long, rather slender, and somewhat 

 curved ; while that of Cafarrhactes, Briss., which succeeds, is 

 shorter and more elevated at the ridge ; thus leading the way to 

 Spheniscus, Briss., where the sides are compressed, and the cul- 

 men elevated into a sharp edge. This structure approaches the 

 form of the same member in the true Alca, in which the sides 

 are still more strongly compressed, and the culmen more ele- 

 vated. The Fratercuta, Briss., the well-known Puffin of our rocky 

 coasts, following Alca, exhibits the extreme of this singular con- 

 struction : and there cannot be a more interesting subject of 

 contemplation to him who may wish to witness the mode in 

 which Nature harmonizes her groups, than the gradual change 

 of form that unites the short and elevated bill of this last ge- 

 nus with the long and slender bill of Apienodytes. A similar 



gradation 



