BIRDS—PEOCELLAEINAE—THALASSIDROMA HORNBYI. 
829 
This genus is composed of the smallest members of the petrel family ; they are also the most 
diminutive of web-footed birds, hut yet they are able to contend with the strongest gales, and 
on such occasions appear to he particularly active and numerous. While hovering near the 
water, for the purpose of securing their food, they project their feet in such a manner as to give 
them the appearance of running on its surface. 
The species embraced in this genus may he arranged in the following manner : 
Plumage wholly bluish gray ; tail much forked ; legs and feet brown. Type of Oceano- 
droma , Bonap. T. furcata. 
Upper part of back gray, lower part ash gray ; collar around hind neck and under parts 
white ; tail forked. T. hornbyi. 
Plumage sooty brown ; rump white ; tail forked ; tarsi and feet black. T. leachii. 
Plumage dark sooty brown ; rump white ; tail slightly emarginate ; tarsi and feet black, 
with the basal two-thirds of the interdigital webs yellow. T. wilsoni. 
Plumage grayish black above, sooty brown below ; rump white ; tail a little rounded ; 
tarsi and feet black. T. pelagica. 
Upper plumage entirely black, below sooty black ; tail deeply forked ; legs and feet 
black. T. melania. 
^Oceanodroma, Reich. 
THALASSIDEOMA FURCATA, Gould. 
The Fork-tailed Petrel. 
Procellaria furcata, Gm. Syst. Nat. I, 1788, 561.— Lath. Ind. II, 825. 
Thalassidroma furcata, Gould, Voy. Sulph. Birds, 1844, 50; pi. xxxiii.— Cassin, Birds of Cal. & Tex. I, 1855, 
274 ; pi. xlvii. 
Oceanodroma furcata, Bon. Cons. Avium, II, 1855, 194. 
“ Thalassidroma cinerea, Gould.” Bon. 
Procellaria orientalis, Pallas, Zoog. Rosso-Asiat. II, 1811, 315. 
“ Thalassidroma orientalis, Gray.” Bon. 
Oceanodroma orientalis, Reich. 
Sp. Ch. —Entire plumage light bluish gray, paler on the forehead, the abdomen, and under tail coverts ; dusky around the 
eye ; greater wing coverts and secondaries with grayish white margins ; quills and tail brownish, the latter with the external 
web of the outer feather white ; bill black ; feet brown. 
Length, about 8 inches ; wing, G ; tail, 3| ; bill, | ; tarsus, -J. 
Hab. —Coasts of Oregon and Russian America. 
Specimens in Mus. Acad. Nat. Sc., Philadelphia. 
THALASSIDROMA HORNBYI, Gray. 
Hornby’s Petrel. 
Thalassidroma hornbyi, G. R. Gray, Pr. Zool. Soc. 1853, 62. 
Oceanodroma hornbyi, Bon. Cons. Avium, 1855, 195. 
Sp. Ch. —“Front, cheeks, throat, collar round the hind part of the neck, breast and abdomen, pure white; crown, lllnd 
head, a broad band in front of neck, bend of wing and lesser wing coverts, sooty grey; upper part of back gray ; lower part o f 
back and tail ashy gray ; greater wing coverts brownish gray ; tertiaries and quills deep black. 
“Total length, 8|" ; bill from gape, 10g", from front, 8|'" ; tail (outer feather,) 31" ; tarsus, 1" ; middle toe, 1".” 
Ilab .—Northwest coast of America. 
