Petrels from the North-East Pacific Ocean. 605 



to belong to CooJcilaria, though in tlie ' Monograph ' it was 

 associated with mollis and torquata, with which it was 

 compared when described many years previously." 



The characters of the forms are so slight that subspecific 

 value seeras most suitable, but upon close examination we 

 find the differences so peculiarly ranged that we are perhaps 

 dealing with species. Thus, while all are certainly very 

 closely allied and congeneric, the two forms most exactly 

 alike as to upper coloration, viz., nigripennis and defilippiana, 

 have very differently coloured primaries. This would be less 

 remarkable were it not that another couple almost exactly 

 agreeing in upper coloration, viz., leucoptera and hypoleiica, 

 differ in the same respect. The two pairs differ very de- 

 cidedly, the former being the palest, the latter the darkest 

 of the series. 



The two forms that have dark primaries, viz., hypoleuca 

 and nigripennis, are the darkest and lightest of the lot ; 

 while the two darkest, viz. leucoptera and hii]poleuca^ and the 

 two lightest, viz. defilippiana and nigripennis, differ most in 

 the coloration of the primaries. Species of Cookilaria have 

 different habits, flight, and notes from species of Pterodroma 

 or ^strelata, and can be recognised at sight ot in the dark. 

 Pterodroma and y^sfrelata are difficult to separate, as so 

 little is known about the species at present. • At the 

 Kermadec Islands three species of the genus Pterodroma 

 sensu lato breed together, viz. P. cervicalis Salvin, 

 P. neglecta Schlegel, and P. nigripennis Rothschild. If it 

 were true of this group that no two birds of the same genus 

 breed together, then we would know that P. cervicalis 

 Salvin and P. neglecta Schlegel should be referred to 

 different genera. As a matter of fact, though these two 

 birds differ very little in structure or coloration, so that 

 from skins it might seem impossible to allot them to 

 different genera, the birds are very different in nature, 

 having dissimilar habits (P. neglecta breeding above ground, 

 P. cervicalis in burrows) and very distinct notes. The 

 downy young of P. cervicalis is like a macromorph of that of 

 P. nigripennis, and differs in down colour-patter. i from the 



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