402 MR. H. SAUKDEBS ON THE GEOGRAPHICAL 



Africa to Australia and Polynesia we find a large Tern only differ- 

 ing from the usual style of coloration in having a white frontlet 

 band at the base of its bill, and which, in spite of local variations 

 in size and colour of mantle, seems to me to be but one species, 

 S. bergii, Licht. It would be tedious to enumerate all the typi- 

 cal species and to give their respective ranges ; but there is a point 

 in the distribution of some of those in the southern hemisphere 

 which must not be passed over. On the coasts of Chili, the 

 Straits of Magellan, and the Falkland Islands is found S. hirundi- 

 nacea, Less. {L. cassini, Sclater), rather larger than our Common 

 Tern, S. Jiuviatilis, and having a bright red bill. At Tristan 

 d'Acunha, and thence to St. Paul's and Amsterdam Islands, and 

 down to Kerguelen Island, we find a very similar Tern, S. vittata, 

 Grm., but smaller and with the underparts washed with grey, 

 closely resembling, in fact, our Arctic Tern, S. macrura, but 

 having a longer tarsus. The Tristan d'Acunha bird is undoubt- 

 edly ^S*. vittata ; but its connexion with S. liirundinacea is shown 

 by a visibly closer approach to that species than is the case in St. 

 Paul's or Kerguelen-Island examples. At Kergulen Island is also 

 found an aflined but quite separable species, 8. virgata, Cab., of 

 a more uniformly sooty hue, but still presentifig the characters 

 of an oceanic tern in its pointed red bill and elongated tail-fea- 

 thers ; this species is absolutely confined to that island. Passing 

 to New Zealand, we meet with very similar species, S. antarctica, 

 Wagler, in which the shape of the bill is somewhat modified, be- 

 coming short, stout, and considerably curved in the upper man- 

 dible, the webs of the feet are also more excised — peculiarities 

 which have led to its being placed by some systematists in the 

 genus Hydrochelidon, with which, however, it has no real afiinity. 

 Here the chain breaks abruptly, there being beyond this point no 

 connexion with South xlmerica to complete the circle. As the 

 northern representatives of these Antarctic species come down, 

 in winter at least, as far as South Africa, the point of union seems 

 in this case to be the South Atlantic ; but when and why the se- 

 paration took place in their breeding-range it is impossible to say. 

 New Zealand also possesses one isolated species, S. frontalis, a 

 rather larger Tern with a white frontlet, apparently more closely 

 connected with S. cantiaca than with any other. 



From the Eed Sea to the Laccadive Islands is found another of 

 these specialized forms, S.albigena, a slender species of the Common 

 Tern type, but washed all over with a sooty hue. Another mem- 



