2J2 E. GABRITSCHEVSKY. 



combination of black and rufous, white and yellow, and black and 

 white stripes is more often found than black and yellow. This is 

 a characteristic feature of both insect genera in the European part 

 of the old world. 



An entirely different situation is found in the United States 

 of America. Even a superficial survey of the collections of 

 American (Syrphidae and Asilidae) flies and bumblebees shows 

 distinctly, that both insect genera have, strictly speaking, only 

 one pattern, namely, black and yellow striped individuals. 

 (Only two species, B. occidentalis and B. borealis, have parts of 

 their body covered with white hairs.) The combination of black 

 and rufous, yellow and white, black and white, is absolutely 

 absent or very rare on this continent. The overwhelming 

 numbers of black and yellow striped specimens among these flies 

 and bumblebees is a peculiar feature throughout the United 

 States. The phenomenon of color convergence has reached its 

 climax in North America. 



THE NORTH AMERICAN GROUP OF^Volucella Bombylans. 

 The systematic relationship of the American varieties of V. 

 Bombylans has been recently studied by Johnson ('16, '25) who 

 divides these flies into two large groups. To the first (the black- 

 faced group) belongs the eastern V. evecta, var. V. evecta americana 

 var. V. evecta sanguined, and the boreal V. evecta arctica. To the 

 second (the yellow-faced group) belongs the western V. facialis, 

 the Canadian V. facialis lateralis and the Vol. facialis var. 

 nifomaculata, which is found in Colorado and along the Rocky 

 Mountains. Excepting the coloration of the pleura, which may 

 be yellow or black in both groups, and excepting differences in the 

 color patterns of the thorax and abdomen, no other distinguishing 

 characters have been detected. It is very probable that all 

 European and American varieties might interbreed. 



CONVERGENCE OF COLORATION BETWEEN FLIES OF THE EASTERN 



STATES AND BUMBLEBEES OF THE SAME REGION. 



Volucella bombylans var. evecta-americana 



(PL. I., 15). 



The eastern Volucella bombylans var. evecta (PI. I., 15) americana 

 is entirely pale yellow except the last two to four posterior abdom- 



