394 MR. H. SAUNDERS ON THE GEOGRAPniCAL 



Expedition from tlie edge of tbe pack-ice, now in the British 

 Museum, are wondei'fully bleached and weird-looking birds. 

 On reading the account given by Dr. Kidder respecting the habits 

 of this species at Kerguelen Island, where it seems to avoid 

 water and to prey principally upon the flesh of other birds, it is 

 rather remarkable that it should have varied so little ; but so far 

 as our present defective knowledge of distribution goes, the evi- 

 dence seems to point to the North Pacific as the district whence 

 the members of this group originally sprung. I am quite pre- 

 pared to learn that S. cMlensis goes as far as the Gralapagos, which 

 would considerably narrow the gap which separates it from S. ca- 

 tarrhactes. S. antarcticus is a still more specialized offshoot, 

 entirely absent from the great space which lies between New Zea- 

 land and the western shores of South America, and probably re- 

 stricted from ascending the eastern coast of that continent and 

 the coasts of Africa by the absence from those districts of the 

 gulls upon which it can directly or indirectly prey. 



In the North Pacific, again, where the Aleutian Islands form 

 a broken chain between Alaska and Kamtschatka, and enclose 

 Behring's Sea, is found a distinct and very local species of 

 Kittiwake Gull {Rissa Irevirostris, Brandt), having a short stout 

 bill, rudimentary hind toe, a grey mantle much darker than in the 

 Common Kittiwake, and orange legs and feet, but which calls 

 for no further remark. Over the same area is found the Common 

 Kittiwake, Bissa tridactyla, a species which ranges throughout 

 the whole Arctic and Subarctic regions, descending on the Atlantic 

 coasts somewhat further than on those of the Pacific. The vast 

 maijority of individuals throughout this area, are precisely identical ; 

 but some of the Alaskan examp)les have a minute but distinctly 

 formed hind toe, and even a nail, although this peculiarity is 

 not always equally developed on both feet of the same bird ! 

 Inasmuch as every other member of the family of the Laridse, 

 except Bissa, has a fully developed hind toe, it is tolerably evident 

 that in Bissa it has for some reason become obsolete ; and as the 

 survivors of the hind-toed Rissw are only found round Alaska, it 

 would appear probable that the North Pacific in this case also 

 is the point of dispersion and variation for this genus. 



Amongst the typical Gulls there are only two species. Lams 

 cjlaucus and L. leucopterus, which have white primaries devoid of 

 dark markings or " pattern " ; and these two range throughout 

 the whole Arctic and Subarctic region, including the North Pacific 



