236 Mr. H. Seebolim on the Aidic 



specific or suhspecific difference. T. sororius is more nearly- 

 allied to T. sieboldi, and can scarcely be regarded as more 

 than subspecifically distinct from it, if, indeed, a large series 

 of each would not prove them to be absolutely identical. 

 The nearly terminal black band across the outer tail-feathers 

 is very obscure in the Japanese form, and nearly obsolete in 

 the Formosan race. 



XXI. — On the Arctic Form of the Nutcracker, Nucifraga 

 caryocatactes. By Henry Seebohm. 



Many birds the range of which extends across the Palsearctic 

 Region vary in size, form, or colour in different parts of their 

 distribution, but the extreme forms being connected in the 

 intervening districts by intermediate examples, can only be 

 regarded as subspecifically distinct. The subspecific groups, 

 being only partially isolated, are consequently only partially 

 differentiated. The geographical distribution of these sub- 

 species varies in a rather curious manner, according to the 

 migratory habits of the birds. If the range of migration 

 extends beyond the Himalayas, the tendency is to form an 

 Eastern and a Western race, the individuals comprising the 

 former breeding in the East Palsearctic Region and wintering 

 in the Oriental or Australian Region ; whilst those of the 

 latter breed in the West Palsearctic Region and winter in 

 the Ethiopian Region or in the basin of the ^lediterranean. 

 The Eastern and Western races of the Curlew, Numenius 

 arquata and N. arquata lineata ; of the Whimbrel, Nu- 

 menius phceopus and iV. jjhceopus variegatns ; of the Bar-tailed 

 Godwitj Limosa I'vfa and L. rufa urojjygialis; and of the 

 Black-tailed Godwit, Limosa melanura and L. melanura mela- 

 nuroides, are excellent examples of this kind of subspecific 

 form. On the other hand, if the range of migration be very 

 local, extending longitudinally only to the adjoining valleys 

 and restricted latitudinally to the Palsearctic Region, a quite 

 different result is produced. Instead of an Eastern and a 

 Western form, we find a Northern and a Southern race. 



