192 SYSTEMATIC SYNOPSIS.— PYGOPODES. 
middle of the back. The marking a Me a small spot or stripe near the end of each 
feather, on the edge of each web; there is occasionally a second pair nearer the base of the 
feather. The amount of spotting is very variable with individuals; in the young the spots are 
always larger and more numerous than in the adults, and usually lengthened into oblique 
lines, producing a regular diamond-shaped reticulation. Northern Hemisphere at large; most 
of the U. S. in winter; breeds in high latitudes. Eggs 2-3, 3.00 X 1.75. 
62. Family PODICIPEDID:: Grebes. 
Bill of variable length, much longer or shorter than head; culmen usually about straight, 
sometimes a little concave, or quite convex, especially at the end. Commissure nearly straight, 
but more or less corresponding with the curve of the culmen, usually sinuate at base. Under 
outline of bill in general convex, with slight gonydeal angle or none. Sides of bill more or 
less striate. Nasal fossee well marked, the nostrils near their termination. Nostrils linear and 
pervious (broader in Podilymbus), upper edge straight, not lobed. Frontal extension of 
feathers considerable, and usually antiz run still further into the nasal fossa. A groove along 
the symphysis of the mandible extends often nearly to the tip. Eyes far forward, with a loral 
strip of bare skin running thence to base of upper mandible, very narrow in the typical forms, 
broader in Tachybaptes and Podilymbus. Head usually adorned in the breeding season with 
variously lengthened colored crests or ruffs ; when these are wanting the frontal feathers may 
be bristly. Neck usually long, slender, and sinuous. Plumage thick and compact, smoothly 
imbricated above, below of a peculiar smooth, satiny texture. Wings short but ample, very 
coneavo-convex ; primaries eleven, narrow, somewhat falcate, graduated, the three or four 
outer ones attenuate on one or both webs; secondaries short and broad ; tertials very long, 
hiding the rest of the quills when the wing is closed. Bastard quills unusually long, their tips 
reaching over half-way to the ends of the primaries. Greater coverts also very long. Tail 
rudimentary, represented by a tuft of downy feathers. Characters of the feet peculiar; for in 
other lobe-footed birds, as Phalaropes and Coots, the lobation is of a different character. Tarsi 
exceedingly compressed, with only a slightly thickened tract within which the tendons pass. 
Front edge a single smooth row of overlapping, the hinder ser- 
rate with a double row of pointed, scales; sides regularly trans- 
versely scutellate, as are the upper surfaces of the toes, the latter 
being inferiorly reticulate, with an edging of pectinated scales. 
Toes flattened out and further widened with broad lobes, espe- 
cially wide toward the end, and at base connected for a varying 
distance by interdigital webs. Hind toe highly elevated, broadly 
lobate, free. Claws short, broad, flat, obtuse, of squarish shape ; 
that of the hallux minute. 
The Grebes are strongly marked by the foregoing charac- 
ters, especially of the feet and tail, though they agree closely with 
the Loons in general structure and economy. Principal internal 
characters are the absence of one carotid, and of the ambiens, 
femoro-caudal and accessory semitendinosus muscles, the greater 
number of cervical vertebrae (19 instead of 13) and shortness of 
Fic. 530 bis. —F. fibula; T, the sternum, with lateral processes reaching beyond the transverse 
tibia, with a, its cnemial process, main part (the reverse of the case in Loons). There is a long 
and P, large patella, of a grebe; 
nat. size. 
cnemial process of the tibia, reaching high above the knee-joint, 
backed by a large patella of about equal altitude (fig. 530 bis.). 
The gizzard has a special pyloric sac; there are coeca and a tufted oil-gland. These birds are 
expert divers, and have the curious habit of sinking back quietly into the water when alarmed, 
like Anhingas. Owing to the virtual absence of the tail, the general aspect is singular, ren- 
