BIRDS — PROCELLARINAE — THALASSIDROMA IIORNBYI. 829 



This genua is comjiosod of the smnlU'st nionihers of the jtetrcl family ; tliey are also the most 

 diminutive of web-footed birds, but yet tliey are able to contend with the strongest gales, and 

 on such occasions appear to be particularly active and numerous. Wliile hovering near the 

 water, for the purpose of securing their food, they project their feet in such a manner as to givo 

 them the appearance of running on its surface. 



The species embraced in this genus may be arranged in the following manner : 



Plumage wholly bluish gray ; tail mucli forked ; legs and feet brown. Type of Oceano- 



droma, Bonap T./urcata. 



Upper part of back gray, lower part ash gray ; collar around hind neck and under parts 



white ; tail forked T. homhyi. 



Plumage sooty brown ; rump white ; tail forked ; tarsi and feet black T. leachii. 



Pluma'je dark sooty brown ; rump white; tail slightly emarginate ; tarsi and feet black, 



with the basal two-thirds of the interdigital webs yellow T. tvilsoni. 



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. 



Oceanodi'oma, Reich. 

 THALASSIDROMA FURCATA, Gould. 



The Fork-tailcd Petrel. 



Procellaria furcata, Gm. Syst. Nat. I, 1788, 561.— Lath. Ind. II, 825. 



T haloisidroma furcata, Gould, Voy. Sulph. Birds, 1S44, 50 ; pi. xxxiii. — Cassin, Birds of Cal. & Tc.\. I, 1855, 



274; pi. xlvii. 

 Octanodroma furcata, BoN. Cons. Avium, II, 1855, 194. 

 " Thatassidroma cintrea, Godld." Bon. 



Procellaria orientalis, Pallas, Zoog. Rosso-Asiat. II, 1811, 315. 

 '^ Thalassidroma orientalis, Gray." Bon. 

 Oceaiiodroma orientalis, Reich. 

 Sp. Cn.— 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 wliite margins ; quills and tail brownisli, the latter with the external 

 web of the outer feather white ; bill black ; feet brown. 

 Length, about 8 inches ; wing, 6 ; tail, 3J ; bill, 2 ; tarsus, I. 

 Hab. — Coasts of Oregon and Russian America. 



Specimens in Mus. Acad. Nat. Sc, Philadelphia. 



THALASSIDROMA HORNBYI, Gray. 



Hornby's Petrel. 



TWajridromo Aorndsi, G. R. Gray, Pr. Zool. Soc. 1853, 62. 

 Octanodroma hombxji, BoN. Cons. Avium, 1855, 195. 

 Sp. Ch. — "Front, cheeks, throat, collar round the hind part of the neck, breast and abdomen, pure white; crown, hind 

 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 

 back and tail ashy gray ; greater wing coverts brownish gray ; tertiaries and quills deep black. 



"Total length, 8'" ; bill from gape, lOi'", from front, S't'" ; tail (outer feather,) 3J" ; tarsus, 1" ; middle toe, 1"." 

 Ilab. — Northwest coast of America. 



