MONOGRAPH OF THE PETRELS. 



In a coloured sketch made by Dr. Pirrie, of the " Scotia," of a fresh specimen of 

 P. banksi, obtained about midway between the South Orkneys and Thule Island, the 

 bill is bluish-grey, but the nasal tubes and culmen to the tip of the unguis, are 

 depicted as black ; the bluish-grey colour being restricted to the lateral plate of the 

 upper, and the whole of the lower, mandible. A sketch of P. vittatus also made during 

 the Scottish Expedition, represents the bill of this bird as blackish, with the exception 

 of the lower plate of the under mandible, which alone is bluish-grey ; the tip and 

 upper margin of the under mandible are black. This difference in the colour of the 

 bills of the two species, if constant, may prove a better character for their separation 

 than any of those hitherto put forward. I can, however, detect no difference in the 

 colour of the bills of these birds in preserved specimens. 



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