viii DISTINGUISHING THE SPECIES 149 



some of its intensity and ultimately becomes shabby 

 brown. Such fading must be allowed for in naming 

 specimens from the descriptions given. Much 

 exposed specimens are generally weather-beaten, 

 and then they may be recognised by the lacerated 

 tips of their wings and their shaggy, partly-rubbed- 

 off coats. Occasionally, however, specimens are 

 met with in which the colours have failed to attain 

 their full brightness owing to their having been 

 chilled and starved before leaving the nest. 



Abnormal specimens having their coats tinged 

 with brown (due to prolonged chill in the pupal 

 stage), or showing irregular patches of white (due 

 to injury during the larval or pupal stages), or with 

 very short coats, are occasionally found. Dwarfed 

 specimens of each of the sexes are not rare, and giant 

 males of the Psithyri are now and then met with : 

 the collector must, therefore, not be surprised if he 

 occasionally takes a specimen that does not conform 

 to the dimensions given. 



Among the humble-bees there are several in- 

 stances of two forms so closely related to one 

 another that many entomologists have regarded 

 them merely as races of the same species. In the 

 British fauna there are four such couples, B. ter- 

 restris and lucorum, B. ruderatus and hortorum, 

 B. latreillellus and distinguendus, and Ps. vestalis 

 and distinctus. In each case the first -mentioned 

 form is more plentiful in the south and less so 

 in the north than its fellow. The southern form 

 has a shorter coat, is darker, lives in larger com- 



