250 ANNALS OF BIRD LIFE. 



characters for separating species into groups or 

 genera than many structural ones. Pattern of 

 colour is infinitely less liable to variation than 

 any structural character. Among the Passeres 

 especially, the systematic naturalist is often at 

 his wits' end to give a point of distinction which 

 will separate a number of obviously allied birds 

 into a group or genus. But when structural 

 characters fail, he is often helped out of his diffi- 

 culties in a very remarkable manner by the pattern 

 of colour on the plumage which extends through 

 an entire group of species. 



Some of the most curious instances of this 

 generic pattern of colour exist in the TURBINE, 

 which includes the Thrushes and their allied 

 forms. The Ground Thrushes, of which the 

 well-known White's Thrush is a typical species, 

 are separated from all other allied groups by the 

 pattern of colour on the under surface of the wing, 

 formed by the basal half of the outer web of the 

 secondaries and some of the primaries, which is 

 either pure white or light buff. This singular and 

 characteristic pattern extends through all the 

 forty species and races which comprise the genus 

 Geocichla. The typical Thrushes (numbering 

 some fifty species), of which the Missel-thrush is 

 a good example, are readily distinguished from 

 the Ousels or Blackbirds and the Ground 

 Thrushes by the streaked throat and the absence 

 of the wing pattern. In this group the sexes 

 are alike in colour. The Blackbirds are separated 



