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 Alcade by means of the genus Uria, 
Briss., which, it may be remembered, was originally included 
in the Colymbus of Linnzus, and from which it has been sepa- 
rated chiefly on account of the tridactyle conformation of its 
foot. 'lhis character distinguishes the greater part of the pre- 
sent group, which, in addition to Uria, contains the genera Alca 
and Aptenodytes of Linnæus. "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 hill. And here a beautifully pro- 
gressive series of affinities 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 Catarrhactes, 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 cu/- 
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 cu/men more ele- 
vated. The Fratercula, 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 Aptenodytes. A similar 
gradation 
