NOMADIC MIGRATION. 167 



glaciers, they were ultimately isolated in several 

 colonies, some in the Nearctic region, some in the 

 Palaearctic region. What led to their ultimate 

 specific distinction we need not stay to inquire, 

 because that does not bear on our present object. 

 What I want to show is, that various species of 

 Shore Lark are left isolated along the line which 

 probably marked the small limits of their emigration 

 during this Glacial Epoch. Two species occur across 

 Central Asia from Palestine to China [Otocoris peni- 

 cillata} and Otocoris longirostris) ; one is an in- 

 habitant of North Africa and Arabia [Otocoris 

 biloplia) ; two inhabit the New World, one in the 

 Northern United States [Otocoris occidentalis), and 

 one in the Southern States, Mexico, and Central 

 America [Otocoris clinjsoUemci). The Common 

 Shore Lark [Otocoris alpestris) has succeeded in 

 becoming circum polar once more, as its common 

 ancestor was in Pr^-glacial times, and occupies the 

 belt of country above its more southern represent- 

 atives. If the limits of glaciation, as demonstrated 

 by actual geological evidence, are followed round 

 the Northern Hemisphere, we shall find these races 

 of Shore Lark left on its extreme margin, nomadic 

 migrants then as now I 



^ Four examples of this species have within the past year or 

 so been obtained in Bosnia. 



