506 MR. O. SALVIN ON THE AVIFAUNA 



(Rev. Zool. 1855', p. 14). Creagrus, as a genus, differs but slightly from Xema, both 

 having a deeply forked tail. The former, however, is a more robust form, and has the 

 nostril situated rather nearer the point of the bill. In coloration Creagrus wants the 

 black ring which encircles the hood of Xema. 1 doubt whether, in a well-considered 

 classification of the Laridae, the two genera could be maintained as distinct. 



Creagrus purcatus. 



Mouette a queue fourchue , Neboiix, Rev. Zool. 1840, p. 290. 



Larus furcatus (Neboux), Prev. et Des Murs, Voy. Venus, v. Ois. p. 277, Atlas, t. x. 



Xema fur catus, Brueb, J. f. Orn. 1853, p. 103. 



Creagrus furcatus, Bp. Eev. Zool. 1855, p. 14. 



Supra cinereus: capite toto et colli dimidio antico undique fuliginoso-nigris : plaga 

 frontali, scapularium margine externo, tectricibus alarum internis, cauda et corpore subtus 

 albis : remigum 1', 2', 3', 4' pogoniis externis cum pogoniorum internorum parte interiore 

 et apicibus nigris : rem. 3° et 4° ad basin griseis ; 5° et 6° extus griseis, parte apicali nigra ; 

 4°, 5°, 6° plaga apicali alba praeditis : rostro et pedibus rubris : long, tota 23'0, alae 16'0 ; 

 caudae rectr. med. 4-7, rectr. ext. 8'0 ; tarsi 1'9, digit, med. cum ung. 2-0. 



Hah. Dalrymple Rock, Chatham Island {Kellett & Wood). 



The above locality is assigned to a single adult specimen of this rare species in the 

 British Museum. It was obtained with other Galapagos birds during the voyage of 

 H.M.SS. 'Herald' and 'Pandora.' This locality is given with such precision that I 

 think there can be little doubt as to its correctness. The original example of this Gull, 

 the only other known, was obtained by Neboux, the surgeon of the French frigate 

 < Venus,' but is said to have been shot at Monterey, in California. Though it is 

 possible that the species may occur both in the Galapagos and on the mainland, it is 

 also possible an error has been made as regards one of the localities assigned to it. 

 Now as the species has never been seen by any of the many collectors of the United 

 States, and as several of the birds obtained during the voyage of the ' Venus ' have 

 wrong localities assigned to them, such as Calliste ruficervix from Guatemala instead of 

 Columbia, and, I believe, Zonotrichia coronata from the Galapagos (described under the 

 name Z. galapagoensis) instead of California, I am inclined to think the Californian 

 locality an erroneous one, and that this well-marked species must be added to the 

 peculiar fauna of the Galapagos archipelago. 



The British-Museum specimen has the division between the dark hood of the head 

 and neck more clearly defined from the white of the breast than is shown in the plate 

 above quoted, where the lower neck is suffused with a pale shade of grey. 1 have, 

 however, no doubt as to the identity of the specimen, and believe this difi'erence is to 



' Separate copies of this paper are dated 1854 ; but the paper itself was published, with different pagination, 

 in January 1855. Oray gives the former date for the introduction of the genus ; but the latter must be con- 

 sidered correct. 



