474 EIGHTH PACIFIC SCIENCE CONGRESS 



the north Pacific. It is possible that the four species are the result of 

 successive invasions from the south, the richness of forms in the Pacific 

 being possibly due to the greater availability of nesting islands as com- 

 pared with that in the Indian and Atlantic Oceans. 



Pterodroma rostrata 



Pterodroma neglecta 



I'hese two petrels, which are not closely related, occupy various 



islands in the south Pacific. It is impossible to say more about them at 



this stage, or to indicate their affinities. Like other members of the 



genus they appear to be derivatives of southern ancestors. 



Pterodroma solandri 

 A species confined, as a breeder, to the Tasman Sea. It may pos- 

 sibly be a derivative of Pt. macroptera. 



The sub-genus Cookilaria of Pterodroma 

 This difficult group, following its earlier clarification by Murphy 

 (1929), has been recently reinvestigated by Falla (1942, p. Ill), Flem- 

 ing (1941, p. 69), and Austin (1952, p. 392). As a result it appears 

 that four species are represented, each with a number of races differ- 

 entiated in isolated island groups: Pt. longirostris (with pycrofti), 

 Pt. leucoptera (with hrevipes), Pt. cookii (with defilippiana) and Pt. 

 hypoleuca (with nigripennis and axillaris). The group is entirely re- 

 stricted to the Pacific, which may mean that the Panama isthmus may 

 have already closed when the equatorial transgressions took place; thus 

 these invasions could have taken place during the periods of global 

 cooling in the Pleistocene Ice Ages. 



The interesting straggler of brevipes (breeding only in the South- 

 west Pacific) which was recorded in Great Britain in 1889 (Witherby, 

 1941, p. 66) can only be accounted for as a bird which had become 

 hopelessly lost. A similar record of Pterodroma neglecta (ibid., p. 62 

 must be explained likewise. Such birds which are found far from their 

 ordinary beats have probably become attached to wandering and mi- 

 gratory parties of other species (cf. Loomis, 1918, p. 138). 



STORM-PETRELS 



Nesofregetta albigularis 

 A sub-tropical species, confined to the Pacific Ocean, and which 

 has just crossed northward over the Equator to breed at Christmas 

 Island. 



4. NORTHERN ELEMENTS. 



Ekman (1953, p. 186) recognises for the northern hemisphere two 

 marine faunas, a tropical-subtropical and a northern. He points out 



