DISTRIBUTION OF THE GULLS AXD TEKNS. 403 



ber of the same group, S. dougalli, has a very wide range, reach- 

 ing from temperate America and Europe to South Africa, Ceylon, 

 and the Andaman Islands, where it breeds, even to the northern 

 coasts of Australia. All these are typical species so far as shape and 

 the black crown to the head are concerned ; but from China and the 

 Andamans to Torres Straits and Eastern Polynesia we find S. me- 

 lanauclien, an oceanic species which has only a black band from 

 the lores to the nape, the crown being white ; this, again, is an iso- 

 lated form. In South America, from Brazil to Chili, there is ano- 

 ther species, S. triuleaui, which is singular in having no crest, but 

 only a dark streak from the eye to the ear and a party-coloured bill. 



Of the group of Little Terns, of which 8. minuta is the type, 

 there are several species, respecting which it need only be said 

 that the variations comprise the typically marked ;S^. lalcenarum 

 of South Africa, with a full black crown with white lores, B. minuta, 

 with only a partially black crown with black lores, and 8. nereis of 

 Australia, with uncoloured lores and a partially black crown. Their 

 distribution gives no clue to their point of dispersion. Neither are 

 the three species of Marsh-terns comprised in the genus SydroeTie- 

 lidon of much use ; they are probably Old- World forms, having a 

 wide range north and south. Only one, the Black Tern, S. nigra 

 (L.), is found in America as well as in the Palsearctic region, the 

 other two, S. hyhrida and H. leucoptera, ranging as far as Australia 

 and New Zealand. Sterna anglica, placed by some systematists in 

 the genus Geochelidon, and the River-terns, 8. seena of India and 

 *S. magnirostris of Tropical America, need no special remarks. 



Returning once more to the North Pacific, we find a remarkable 

 and very local form in Alaska, 8. aleutica, which has a white front- 

 let, black lores, a dark crown, and a dark grey mantle, the under- 

 parts being washed with grey. Looking at the head alone, it pre- 

 sents the markings of one of the group of Sooty Terns which have 

 been placed by "Wagler in three distinct genera, Onychoprion, 

 Haliplana, and Planetis, all based upon the same identical spe- 

 cies ! It differs, however, from all Sooty Terns in having the 

 rump and tail pure white, in which respect it resembles the bulk 

 of the Nearctic and Palsearctic species, whereas in the Sooty 

 Terns the rump and tail are dark like the mantle. At present it 

 is separated by an interval of upwards of 20° of latitude from any 

 of the Sooty Terns, of which there are three species, all wide- 

 ranging and intertropical ; but it is impossible to avoid consider- 

 ing it an important link in the chain of descent, the other com- 



