PYGOPODES, DIVING BIRDS. 333 
auks and penguins, lobate with basal webbing in the grebes; the hallux is present 
and well formed, with a membranous expansion, in loons and grebes, very minute 
and lateral in position in the penguins, wanting in the auks. The plumage is thick 
and completely water-proof; once observing some loons under peculiarly favorable 
circumstances in the limpid water of the Pacific, I saw that bubbles of air clung to 
the plumage whilst the birds were under water, giving them a beautiful spangled 
«appearance. The pterylosis shows both contour and down-feathers, both after- 
shafted ; in the penguins the feathers are implanted evenly over the whole skin; in 
the rest there are definite apteria; the auks have free outer branches of the inferior 
tract-bands, wanting in the loons and grebes. The oil-gland is large with several 
orifices. Among osteological characters should be particularly mentioned the long 
apophysis of the tibia found in the loons (fig. 8) and grebes, but not in the auks 
and penguins: in the latter, the patella is of great size, and it is stated to develop 
from two centres. In penguins and auks, the elbow has two sesamoids ; among the 
former, there is a free ossicle in the heel joint. The thoracic walls are very exten- 
sive ; the long jointed ribs grow all along the backbone from the neck to the pelvis, 
and form with the long broad sternum a bony box enclosing much of the abdominal 
viscera as well as those of the chest, perhaps to prevent their undue compression 
under water. The top of the skull has a pair of crescentic depressions for lodg- 
ment of a large gland; the palate is schizognathous. The sternum has a different 
shape in each of the families. There are two carotids, except among the grebes. 
The digestive system shows minor modifications, but accords in general with the 
piscivorous regimen of the whole order. The sexes are alike; the young different ; 
the seasonal changes often great. A part of the order are altricial, the rest 
preecocial. There are four families of Pygopodes, sharply distinguished by external 
characters ; three of them are represented in this country. The penguins (Sphen- 
iscide) are confined to the seashores of the southern hemisphere. This group is 
well marked by the solidity of the skeleton, and the flatness of most of the bones, 
with many peculiar osseous details; by a very special ptilosis, both in the lack of 
tracts, and the structure of the feathers themselves, many of which are curiously 
scale-like ; by the completely posterior set of the legs with extremely short tarsus, 
and especially, among external features, by the reduction of the wings to mere 
paddles, lacking specially formed remiges, unserviceable for flight, but highly 
efficient as fins to aid progress under water. There are twelve species of penguins, 
referable to three or four genera. One of the most singular facts in ornithology is, 
that some species of penguin do not lay their egg in a nest in the ordinary way, 
but carry it about with them in a pouch temporarily formed by a fold of the 
abdominal integument (Verreaux) ; thus affording a wonderful analogy to marsu- 
pial mammals. The author’s monograph of the Spheniscide will be found in the 
Proceedings of the Philadelphia Academy, of the present year. 
Family COLYMBID:. Loons. 
Bill stout, straight, compressed, tapering, acute, paragnathous, entirely horny. 
Nostrils narrowly linear, their upper edge lobed. Head completely feathered, the 
anti prominent, acute, reaching the nostrils; no crests nor rufis. Wings strong, 
with stiff primaries and short inner quills. Legs completely posterior, buried, 
feathered on to the heel-joint; tarsi entirely reticulate, extremely compressed, the 
back edge smooth; toes four, the anterior palmate, the posterior semilateral and 
having a lobe connecting it with the base of the inner. Tail short, but well formed, 
