AMERICAN PILOSE FLIES AND BUMBLEBEES. 2/7 



coloration of the segments is not so exact as in the first four 

 bumblebee species enumerated above, but the reappearance of 

 some segments with red pile must be regarded as a characteristic 

 feature in both insect genera of this region. It is strange that the 

 Caucasian mountain species of flies and bees are partly changing 

 their pile into a shining white color, whereas the American 

 mountain species tend to turn into a bright vermilion coloration. 

 Another group, consisting of bumblebees with a shining wax 

 yellow coloration is also present in the Colorado region. This 

 includes B. sonorus (PI. IV., 3), B. morissoni (PL IV., 4), B. 

 nevadensis (PI. IV., 5), B. terricola (PL III., 14). As regards the 

 distribution of black and yellow bands, the first three species are 

 like the first group of the eastern bumblebees, and the fourth one 

 is like the bumblebees of the second eastern group. The main 

 difference is observed in the tint of the yellow pile, which is 

 extremely bright in B. morissoni, nevadensis, sonorus and terricola. 

 It is apparently again a case of color convergence, but which is 

 present only in the hymenoptera group, as no flies of this kind 

 have been collected in this mountain zone. Occasionally it is 

 possible to find Volucella flies with the more brilliant wax yellow 

 pile, but it must be pointed out that the yellow hairs of the flies 

 vary in intensity of pattern from light ochre to swarthy brown, or 

 more exactly from maize yellow through wax yellow to deep 

 colonial buff. Many slight variations can also be noticed in the 

 red pile. The black color on the contrary is always constant. 

 Many Asilidae are like these bumblebees; an exact distribution of 

 the same colored bands can be observed in Dasyllis lata var. 

 a. D. champlaini, D. macquarti, D. grossa 9 (PL II., 7 8, 9, 12). 

 Mallota posticata (PL I., 19). 



CONVERGENCE OF COLORATION BETWEEN FLIES OF THE PACIFIC 



COAST AND THE Bombus SPECIES WHICH INHABIT 



THE SAME REGION. 



The Volucella bombylans facialis (PL I., 12). 



This fly is one of the darkest when compared with the other 



pilose species of this family. The pleura are black pilose; the 



dorsum of the thorax has a larger area covered with black hairs 



than in all other Volucella flies. The black hairs of the third 



