4/-^ 



Vol. 5, p 151-153. May 22, 1925. 



Occasional Papers 



OF THE 



Boston Society of Natural History. 



THE GENUS CHALCOMYIA (DIPTERA: SYRPHIDAE). 



BY RAYMOND C. SHANNON. 



The genus Chalcomyia Williston (Bull. Brooklyn Ent. Soc, 

 vol. 7, p. 133, 1885) appears to be peculiar to North America. It 

 was erected ifor Myiolepta aerea Loew and defined principally on 

 the basis of : antenna short, with dorsal arista ; marginal cell open ; 

 anterior (discal) cross-vein distinctly before the middle of the dis- 

 cal cell, usually rectangular; face black without tubercle; scutel- 

 lum unusually large, nearly square; males dichoptic. The two 

 last characters are peculiar to Chalcomyia, as hitherto known, and 

 easily suffice to define the genus. 



A second species, cyanea, was added by Smith, although the 

 scutellum in this species is not as well developed as in the geno- 

 type and the face of the male has a slight tubercle. Two addi- 

 tional species are now at hand which are still more aberrant. The 

 one, received from Mr. C. W. Johnson, is represented only by the 

 female and hence one of the generic characters found in the male 

 sex, i.e., dichoptic eyes, is not available. The scutellum is notice- 

 ably broader than long and the discal cross-vein is nearly at the 

 middle of the discal cell. The species is strikingly like the Xylotae 

 and one is at first inclined to locate it in the Xylotinae. However, 

 the discal cross-vein is rectangular as in the Chilosinae and the 

 abdomen is broadly oval and flat as in Chalcomyia aerea female 

 (rather elongate and parallel-sided in Xylota); the head is dis- 

 tinctly triangular and has a well-developed antennal prominence 

 as in Chalcomyia aerea and probably the male will be found to have 

 dichoptic eyes (holoptic in Xylota). 



The fourth species, both sexes, was standing in Dr. Aldrich's 

 collection labeled ''new species." The eyes of the male approach 

 each other very closely ; face concave and without tubercle in both 

 sexes; scutellum distinctly longer than broad; metasternum pilose; 

 body much more slender than in other species; petiole beyond 

 first posterior cell nearly as long as discal cross-vein. The inclu- 

 sion of these species in Chalcomyia necessitates a reconsideration 

 of the genus. 



The Chilosinae and Xylotinae are intergradant and their 

 separation is more or less arbitrarily fixed on the basis of certain 

 characters. A number of genera, three of which concern us here, 

 Myiolepta, Chalcomyia and Cynorhinella, occupy a rather inter- 

 mediate position between the two subfamilies. The latter two 



JUN -R 1925 



