218 THE HUMBLE-BEE vil 
6. PSITHYRUS QUADRICOLOR, Lepeletier. 
Synonym :—barbutellus (Kirby), according to Smith. 
QUEEN.—Small; length 14-16 mm., expanse 32-35 
mm. ; sometimes smaller. 
Head black, the hairs on top sometimes tinged with 
yellow. Thorax black, with a yellow band in front; sometimes 
a few hairs on the back of the thorax are tinged with yellow. 
Abdomen black, with more or less yellow on the 1st segment, 
and with the 3rd and 4th segments white or yellowish-white, 
and the 5th segment dark reddish-brown. The base and 
middle of the 3rd segment are generally more or less 
blackened. 
The tip of the abdomen is more incurved than in any 
other species, so that the abdomen, viewed from above, is 
shorter and more rounded. 6th dorsal segment slightly 
and longitudinally raised in the middle towards the base, 
and slightly hollowed near the apex, where it is coarsely 
punctured. The 6th ventral segment is narrow and has its 
apex produced into a sharp hook-shaped point; the ridges on 
the sides of this segment are small and inconspicuous and do 
not nearly reach to the apex. 
MALE.—Length 13-15 mm., expanse 27-30 mm. 
Easily known from any other male humble-bee by 
the fact that the white (or yellow) tail changes at the tip, 
generally through more or less black, to reddish. 
Head black, with generally some yellow hairs on top. 
Thorax black, with a yellow band at the front and some- 
times a few yellow hairs or a faint yellow band behind. 
Abdomen black, with generally a faint yellow band on 
the Ist segment, and with the 3rd segment (except some- 
times at the base), the whole of the 4th segment, and 
often the sides, sometimes the entire area of the 5th 
segment white, sometimes yellow ; remainder of the 5th 
segment black, 6th segment reddish or black, 7th seg- 
ment reddish. 
