AMERICAN PILOSE FLIES AND BUMBLEBEES. 275 



Volucella bombylans evecta (Walker) (PI. I., 14). 



The thorax, scutellum and the three first abdominal rings of 

 this fly correspond to V. B. evecta americana, (PI. I., 15), but the 

 posterior 4-6 segments may be either yellow or reddish. Evecta 

 is the upper austral form, extending through the transition zone. 

 This fly resembles closely the males of the eastern bumblebees. 

 Its coloration has altogether the aspect of these Hymenoptera, 

 but a strict parallelism in color patterns with any of the eastern 

 bumblebees is not traceable. Volucella evecta is a rare form when 

 compared with V. evecta americana. It is possible that a detailed 

 study of its distribution in the east might explain its color 

 patterns. 



Volucella bombylans evecta sanguined, (PI. I., 16). 



This variety is an extremely rare variation of V. B. evecta 

 americana. It has been recorded in the eastern states. This fly 

 has yellow hairs on thorax, scutellum and abdomen, except the 

 third abdominal ring, which is covered with fulvous pile. The 

 sides of this segment have some black hairs. This Volucella 

 represents, in a way, a parallel variation to that of V. rufomaculata 

 in the subspecies facialis, which is distributed along the more 

 elevated portions of the Rocky Mountains. V. sanguined is not 

 comparable to any bumblebee species of the eastern United 

 States. A third and analogous parallel variation is found in 

 Eristalis flavipes var. melanostoma (PI. I., 25) of the east, and a 

 fourth in Dasyllis fernaldi (PI. II., 18) an Asilid fly of the Rocky 

 Mountains. 



The sporadic reappearance of parallel variations in V. sanguinea 

 and Eristalis flavipes, which are analogous to the variety of V. 

 rufomaculata and Dasyllis fernaldi (PI. II., 18) of the west, 

 suggests that the genie mutations producing these color changes 

 in some individuals are probably of a related chemical structure, 

 in the sense of their end effect. It is also interesting that they 

 affect the same parts of the insect's body. The same argument 

 can be applied to the bumblebees. It would be more difficult to 

 explain, however, the way in which a new mutation could replace 

 the more abundant form for a given geographical zone. 



