POIs hiNGUISHING 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 Pszthyri 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, 2. Zev- 
vestyvts and lucorum, B. ruderatus and hortorum, 
B. latreillellus and distinguendus, and Ps. vestalrs 
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- 
