Birds of America
By John James Audubon, F. R. SS. L. & E.
GENUS V.--THALASSIDROMA, Vigors. PETREL.
Bill shorter than the head, slender, as high as broad at the base,
extremely compressed at the end; upper mandible with the nostrils dorsal forming
a tube on its ridge at the base, on which the dorsal line is concave and
ascending, then abrupt, afterwards, for a short space, straight, and lastly
decurved, the sides separated by a groove, convex, the edges sharp and
inflected, the tip decurved, slender, acute; lower mandible with the angle
rather long, narrow, and pointed, the dorsal line beyond it decurved, the sides
erect, the edges sharp, the tip decurved, acute. Head of moderate size, rounded
above; neck short; body rather slender. Feet rather long, slender; tibia bare
at its lower part; tarsus slender, reticulate; hind toe minute, with a conical
deflected claw; anterior toes of moderate length, slender, scutellate, webbed,
the third and fourth about equal. Claws slender, arched, compressed, acute.
Plumage very soft and blended, the feathers distinct only on the wings, which
are very long, with the primaries a little incurved toward the end, the second
longest, the first and fourth about equal; tail emarginate or even, of twelve
feathers. Tongue much flattened, tapering to a horny point; oesophagus wide,
within the thorax enormously distended, and with the proventriculus forming an
ovate sac, which is recurved; stomach very small; intestine short, of moderate
width; coeca small; cloaca globular.