MONOGRAPH OF THE PETRELS. 



Koeding's Petrel is much darker, being sooty-brown over the whole body, while 

 the head is dark plumbeous. The rectrices are sooty throughout, or else but very 

 slightly paler at the base. The tip, however, of the inner web of the outer feather 

 is often paler, forming a noticeable spot in 83 per cent, of the specimens examined by 

 Mr. Emerson, who says that he also found this character in one example of 

 0. leucorrhoa in the United States National Museum, and then only on one outer tail- 

 feather. He states, moreover, that the tail in O. kcedingi is less deeply forked than 

 in the other Pacific Coast forms. 



Mr. Emerson gives the following measurements of 0. kcedingi from a series of 

 twenty-seven specimens from the vicinity of Guadalupe Island : — Wing, 5.45-5.80 

 inches ; tail, 2.45-2.84 ; forking of tail, 0.40-0.46 ; tarsus, 0.70-0.75. 



The Hon. Walter Rothschild has kindly lent me his specimens of O. kcedingi, a 

 species at present not represented in the British Museum, and I find that the wing 

 measures from 5.5-6.3 inches. 



O. leucorrhoa, according to my measurements of the series in the Tring Museum, 

 varies in length of wing from 5.9-6.3 inches, and Mr. Emerson records it as from 5.85- 

 6.35 inches. From the above summary it will be seen that the difference in length of 

 wing in the two species is not very pronounced. 



As in O. socorroensis (= O. monorhis) there is considerable variation in the 

 markings of the upper tail-coverts, certain specimens having the outer series 

 white, while some of the central ones are mottled with ashy-grey ; others have 

 narrow black tips and black shaft lines. Mr. Anthony has also noticed the variation 

 in the extent of the white on the upper tail-coverts. A few of the examples examined 

 by him had these coverts black, with whitish patches on the sides, while one specimen 

 had totally black coverts, but was otherwise similar to the white-rumped birds 

 (Auk, XV., p. 37). 



The difference between O. kcedingi and O. leucorrhoa has been given in the 

 above description of the species, and it has not been considered necessary to give a 

 coloured illustration of this Storm-Petrel. 



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