Fourth toe shorter than third. Claws sharp and compressed. Tarsus covered in front with hexagonal scutes. Secondaries, thirteen. Keel of sternum entirely ossified.
The genus Procellaria. With tail rounded or nearly even. Two species— P. pelagica, 6 1/2", the Storm Petrel, legs and bill black, upper tail-coverts sooty black, rectrices sooty, white at base, shafts black, N. Atlantic southwards to W. Africa and Mediterranean ; and P. tethys, 6", similar to P. pelagica, but upper tail-coverts wholly white, tail slightly forked, Galapagos.
Also the genus Halocypteria. With tail cuneate. One species— H. microsoma, 5 1/2", legs, and bill black, sooty black, forehead and below brown, Lower California to Panama.
Also the genus Oceanodroma. With tail distinctly forked. Twelve species:—
O. leucorrhoa. 8". The Fork-tailed Storm Petrel. Legs and bill black. Head and throat grey. Upper tail-coverts more or less white. Bases of lateral rectrices black. Longest upper tail-coverts white, narrowly tipped sooty. Seas of northern hemisphere.
O. cryptoleucura. 7". The Madeira Storm Petrel. Similar to O. leucorrhoa, but longer upper tail-coverts, broadly tipped black. Hawaiian and Galapagos Islands. S. Atlantic, and as far north as Madeira.
O. macrodactyla. 8 1/2". Similar to O. leucorrhoa, but tail longer and more deeply forked, and upper tail-coverts tipped dusky. Lower California.
O. soccorroensis. 6 4/5". Similar to O. leucorrhoa, but upper tail-coverts chiefly greyish white (producing a distinct spot on each side of rump). Coast of Mexico.
Upper tail-coverts of same colour as lack, not white.
O. fuliginosa. 10". The Sooty Petrel. Legs and hill black. Under parts uniform sooty grey. Japanese seas.
O. melania. 9". Bill and legs black. Uniform sooty above, paler below. California. O. markhami. 9". Entire head tinged plumbeous. Peru.
O. tristrami. 9". Back, scapulars, and upper rump slate, each feather with one or two indistinct dark bars. Japan.
O. homochroa. 7 1/2". Legs and bill black. Under wing-coverts variegated with dirty white. California.
O. monorhis. 7 1/2". Similar to O. homochroa, but under wing-coverts uniform sooty. China and Japan.
O. hornbyi. 8 4/5", Legs and bill black. Under surface white. Breast with sooty collar. N.E. Pacific.
O. furcata. 8". The Fork-tailed Petrel. Plumage generally pale ashy. N. Pacific as far south as Oregon. (B.M. Cat., xxv. 343-357.)